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Strawberries: Organic Production

  1. 1. Strawberries: Organic ATTRA Production A Publication of ATTRA - National Sustainable Agriculture Information Service • 1-800-346-9140 • www.attra.ncat.orgBy Martin Guerena This publication provides an overview of organic strawberry production methods. It also covers inte-and Holly Born grated pest management and weed control techniques that can reduce pesticide use in strawberry pro-NCAT Agriculture duction. Included are discussions of weeds, pests, diseases, greenhouse production, plasticulture, fertil-Specialists ity, economics, and marketing. Lists are provided of further resources, both electronic and in print.©2007 NCATContentsIntroduction ..................... 1Planting Systems ............ 2Varieties ............................. 4Fertility ............................... 4Weed Control .................. 6Insect and MiteControl ............................... 9 Strawberries in hoophouse. Photos by Martin Plasticulture strawberries.Disease Control ............. 13 GuerenaGreenhouseProduction ...................... 16 Introduction Excel lent cu ltura l i nformat ion for SHarvest and conventional strawberry production—Postharvest ..................... 16 trawberries are a viable crop in most planting systems, pest control, cultivarEconomics ...................... 17 areas of the United States. Cultivars recommendations, etc.—can be obtainedMarketing ........................ 19 have been developed to suit most from the Cooperative Extension Service inReferences ...................... 19 agro-climatic conditions. In many loca- most states (also see Further ResourcesFurther Resources ........ 22 tions, demand for locally produced berries below). ATTRA’s Overview of Organic FruitAppendix A: Sources of far exceeds available supplies; small-scale Production provides general information onThermal Weeders ......... 25 organic weed control, organic fertilization, producers can thus get higher returns fromAppendix B: Recom- and some basic considerations for organicmended Strawberry strawberries than from most other crops.Varieties ........................... 26 disease and pest control. This publication Organically grown berries may command will cover problems specific to strawber- a price premium. Organic production ries and will offer organically acceptable excludes the use of synthetic fertilizers and solutions. We have not attempted to pesticides, and requires soil building and develop a one-size-fits-all prescription for organic (or other ecologically based) straw- biological pest control. Federal organic berry production. Rather we have intro-ATTRA—National Sustainable standards restrict claims of “organically duced the most common challenges andAgriculture Information Serviceis managed by the National Cen- grown” to those farms that are certified to offered some possible solutions and factorster for Appropriate Technology(NCAT) and is funded under a be organic by a USDA-accredited certifica- for consideration.grant from the United States tion agency. For more information, requestDepartment of Agriculture’s For many years, conventional strawberryRural Business-Cooperative Ser- the ATTRA publications Organic Farm Cer- growers have routinely used the soil fumi-vice. Visit the NCAT Web site( tification and the National Organic Program gant methyl bromide to control weeds, soil-html) for more informa-tion on our sustainable and Organic Orchard, Vineyard, and Berry borne diseases, nematodes, and soil-dwell-agriculture projects. ���� Crop Documentation Forms. ing insects. In October, 1998, the Congress
  2. 2. attached an amendment to the Clean Air Act which required EPA to make regulatory changes to the US phase-out of methyl bro- mide, resulting in a 100 percent reduction by 2005. (Anon., 2002) Currently, a criti- cal-use exception has been issued extending the phase out to 2007 for those who believe there are no technically and economically feasible alternatives to methyl bromide. There are feasible alternatives in straw- berry production, as many organic growers Strawberries in a basket. can attest. Photo courtesy of USDA/ARS rows of plants with one drip line running Planting Systems between them. The distance between beds Planting systems for strawberries vary, averages 40 inches. Drip tape is buried at a depth of about 2.5 inches. Wide beds depending on the environment and usually have four rows of plants and two production goals. The grower must decideRelated ATTRA drip lines, with 64 inches between beds. the relative priorities of yield, size, flavor, orPublications Spacing between plants in both types of other qualities of the fruit, and seek a sys- bed averages 12 to 14 inches.Organic Farm Cer- tem that balances these goals. Systems thattification and the focus primarily on yield are the least sus- Plastic mulch is used in both narrow andNational Organic Pro- tainable because of the enormous amount wide beds and can vary from a single stripgram of plastic laid between the plants to full bed of energy used for maintenance, plastic,Organic Orchard, Vine- and transportation. In many of these sys- coverage, where holes must be punched foryard, and Berry Crop tems, the plants are grown on raised beds the plant to develop. Some conventionalDocumentation Forms as annuals. This results in removal of the growers in California use clear plastic whichOverview of Organic plants, plastic mulch, and irrigation sys- warms the bed faster, stimulating early-Fruit Production tem at the end of every season. Regard- season growth; these growers use fumiga- less of the system used, conventional yields tion to control most weeds. Black plasticSeason ExtensionTechniques for Market are usually higher than organic yields. is used in organic production, primarily forGardeners However, studies have shown that organic weed control. Since the black plastic pre- producers can earn more profit per acre vents the sun’s rays from penetrating, theSources of Organic beds remain cool, resulting in slower initialFertilizers and Amend- than conventional producers. (Gliessmanments et al., 1996) growth of the plants and reduced irrigation frequency compared to clear plastic mulch.Alternative Soil Raised Bed Plasticulture. Organic and There is a plastic mulch on the market thatAmendments conventional growers in California and Flor- selectively permits soil-warming radiationWorms for Compost- ida, where most of the nation’s strawberries to penetrate while eliminating the light thating (Vermicompost- are produced, tend to favor this system. promotes weed growth. This type of plasticing) They grow plants as annuals, transplanting is preferred by growers in the southeast.Overview of Cover strawberry crowns in the late summer or early fall. Production starts in the late win- Raised beds provide good drainage. SinceCrops and Green ter and continues through the summer and they make the flowers and fruit easier to seeManures into late fall, depending on the area and and reach, raised beds also help growersBiointensive Inte- the varieties grown. Since methyl bromide to forecast yields, while making harvestinggrated Pest Manage- easier and faster. Some growers dig deepment is not allowed in organic production, crop rotation, green manure crops and compost furrows between the beds so that harvest-Farmscaping to ers do not have to stoop so low to search are critical to control soil-borne diseasesEnhance Biological for fruit. In cold climates, plants in raisedControl and pests. beds may be prone to freeze damage. Still, Two types of raised beds are used in these raised beds usually out-produce flat beds. intensive systems. Narrow beds have two Due to of increased aeration and protectionPage 2 ATTRA Strawberries: Organic Production
  3. 3. Plasticulture, Sustainability, and Organic Farming Plasticulture is not without its serious critics. The plastic has to come from somewhere, and it has to be discarded at the end of the one- to three-year production cycle. Clearly, critics say, this is not an environmentally sustainable system. And, says Cornell University fruit researcher Marvin Pritts, PhD, if you consider all the environmental costs to society, plasticulture is also not economically sustainable in the long run. Pritts also points out that even more plastic—in the form of row covers, tunnels, hoop houses, etc.—is needed to make the system work in cold climates. USDA researchers have shown that fields mulched with plastic cause four times more water runoff than fields mulched with organic materials. Due to this high rate of runoff, fields mulched with plastic suffer up to fifteen times more soil erosion than fields mulched with organic matter. (Anon., 1999c) Planting grasses or other types of vegetation alongside drainage ditches can reduce the rate of erosion and provide habitat for beneficial insects. Yet, even organic growers—especially those in California, where plasticulture has reigned the longest—are buying into the plasticulture production model. Why? The answer is weeds. Strawberries are notoriously prone to weed encroachment with resultant loss of productivity. Plasticulture provides good to excellent weed control without herbicides. The National Organic Program (NOP) states that plastic or other synthetic mulches are allowed in organic production, provided that they are removed from the field at the end of the growing or harvest season. Pritts admits that implementing some of these ideas requires well-informed and committed management. Moreover, produc- tion in each locale may require fine-tuning to get the right mix of groundcovers and timing for planting, mowing, and other manipulations. This is probably not going to be as easy as rolling out the plastic sheeting. Nevertheless, using small amounts of post-emergent herbicide, though not allowed in organic production, may be more sustainable than the continued use of tons upon tons of non-renewable, non-recyclable plastic mulch. Corn- and soybean-based biodegradable plastics are being developed, but it will be a while before a sturdy and durable biodegradable plastic capable of withstanding solar radiation, moisture, and equipment is available for strawberry production. Synthetic biodegradable polymers are being developed, but since they are synthetic, it seems unlikely they will be allowed in organic production any time soon.from splashing soil particles, plants in plas- for their area. Otherwise, a complimentarytic-mulched raised beds have less disease. copy of Nourse Farms Success with Plasti-Machinery is available to shape the bed, culture can be obtained by calling Nourselay out the irrigation line, and cover the Farms at 413-665-2658.bed with plastic mulch all in a single pass. Matted Row System. In this system theSources of bed-shapers and transplanters crowns are planted in early spring. As theare listed in the ATTRA publication Sea- plants produce flowers, the blossoms areson Extension Techniques for Market Gar-deners. Or check the following web pages: removed to encourage runner (or plant) production. The daughters root the bed and produce a crop the following spring. Weeds can be a problem in thisRecent research indicates that any variety system, and dead leaves and other debristhat normally does well in a specific region must be removed to reduce disease and pestwill do well when grown using plasticul-ture in that region. (Nourse, 1999) How- problems. However, once established, thisever, some of the cultivars that come from system can produce for three to four years,the California and Florida systems perform depending on pest pressure. The distancebest at a 12- to 14-inch spacing, while many between plants is 18 to 24 inches, and thenorthern cultivars do best at an 8- to 10- distance between the rows varies from 36inch spacing. to 50 inches, depending on the cultiva-By now, growers and researchers in many tion equipment used. According to Marvinstates have adapted and validated at least Pritts of Cornell University, the matted rowparts of the production model described system offers northern strawberry growersabove. Growers should check with their a low-risk system that requires less focusstate Extension Fruit Specialist to see if spe- and time than annual plasticulture systemscific plasticulture guidelines are available (Pritts, 2002) ATTRA Page 3
  4. 4. Researchers at the USDA Agricultural stimulate flower formation and to increase Research Service (ARS) in Maryland fruit size. At the end of the second sea- have developed a “modified or advanced” son the planting can be changed to the mat- matted row system to address weed and ted row system by letting the runners fill in pathogenic pests. This system uses matted empty spaces on the beds. row-type culture established on raised beds with subsurface drip irrigation and organic Varieties mulch. The mulch consists of a mixture of hairy vetch (45 kg/hectare [40.1 lb/acre]), Selection of appropriate varieties is impor- rye (78 kg/hectare [69.6 lb/a]), and crim- tant. Besides determining yields and qual- son clover (34 kg/hectare [30.3 lb/acre]) ity, the variety also determines production that fixes some nitrogen and provides an seasons and pest-control practices. Your economical, biodegradable mulch for sup- county extension agent can usually rec-Strawberry seeds. Photocourtesy of USDA/ARS pressing weeds and diseases, and reducing ommend varieties that have been shown to erosion. The organic mulch is cut or rolled respond well to the area’s climatic condi- down in April and two weeks later the bare tions. However, variety trials are usually root strawberry plants are planted through conducted utilizing conventional production the layer. systems. The variety’s performance may be different in an organic system. Therefore, Since 1996, the small-fruit breeding pro- organic growers are advised to plant more gram has conducted replicated performance than one of the recommended varieties and trials on both the advanced matted row sys- conduct their own variety trials. Other tem and a regional adaptation of annual hill organic growers in your area may also be plasticulture. Both of these systems were able to advise you. managed without methyl bromide fumiga- tion or fungicide application. Data from Strawberry varieties are classified as these trials were used to compare advanced either “June-bearing” or “Everbear- matted row and plasticulture for yield, fruit ing.” June-bearing or short-day variet- quality, and length of harvest season. Yield ies start forming flower buds as the day- for the two systems was variety-dependent, length gets shorter and temperatures get and the advanced matted row system had cooler. Everbearing or day-neutral variet- later production and slightly ies are insensitive to day length and pro- lower fruit quality. (Black duce fruit throughout the season as long as et al., 2002) night-time temperatures drop below 60° F. (Strand, 1993) Ribbon Row System. This system can employ high-den- Trials conducted in the northeast comparing sity or low-density planting on strawberry varieties under conventional and a single row. With low-density organic management systems demonstrated planting, the spacing is 12 to that the “Honeoye” variety was the most 36 inches between rows and 14 productive in terms of numbers and weight to 18 inches between plants. of harvested fruit and most profitable for With high-density planting, organic producers. (Rhainds et al., 2002) the distance between the rows is the same but the distance See Appendix B for a list of recommended between plants varies between strawberry varieties. 4 and 12 inches. The crowns are planted in the fall. Once Fertility they start blooming, the flow- ATTRA’s Overview of Organic Fruit Produc- ers are not removed, and fruit tion covers organic fertility management inStrawberries. Photo courtesy of USDA/ is produced in the first sea- a general way. However, there are at leastARS son. Runners are removed to two aspects of strawberry production thatPage 4 ATTRA Strawberries: Organic Production
  5. 5. are unique and distinct from other peren- weeds and will provide important long-nial fruits with respect to fertility. term improvements in soil fertility and soil organic matter. In areas such as coastalJune-bearing strawberries set buds for California, long growing seasons and highthe following year’s fruit in the fall. (Most land rents may make the extended use ofperennial fruit crops set their fruit buds in cover crops uneconomical. However, manythe spring or early summer.) To get a goodbud set, the plants must have adequate growers believe that the long-term benefitschilling and not be nutritionally stressed. of cover crops and rotations to soil fertilityTherefore, fertilizer applications are usu- and pest and disease suppression are worthally warranted in the late summer, giving the cost.the organic fertilizer material enough time Compost can be used as a supplement orto break down and provide nutrients for the alternative. Spreading and incorporat-plants during the crucial fall bud-set. ing the compost on the beds only, avoidingTiming is critical in supplying nitrogen to the furrows, will help concentrate fertilityberry crops and the nitrogen release rates and microorganisms where they are mostfor organic fertilizers may not match the needed. Compost application rates varynitrogen needs of the crop. A study on from 10 tons/acre to 3 tons/acre. Sup- plemental fertigation is necessary to carry Related ATTRAorganic fertilizers in California found great Publicationsvariability in the nitrogen availability of dif- the plants through the production season: Research from Ohio has shown that vermi- Bug Vacuums forferent sources of fertilizers. (Gaskell, 2004) Organic Crop Protec-These included guano, feather meal, liquid compost (compost made from earthworm tionfish emulsion, fish meal, pelleted chicken waste) applications increased strawberry growth and yields significantly. (Arancon et Sustainable Manage-manure, compost, and a green manure ment of Soil-Bornecrop. Initially, the soil nitrate nitrogen from al., 2004) These responses seemed not to Plant Diseasesthe green manure crop and compost kept be dose-dependent. Strawberries at one sitethe level of nitrogen at adequate amounts grew fastest and yielded most in response Notes on Compost to the 10 ton/hectare (4.05 ton/acre) ver- Teas(50 to 75 ppm) for three to four weeks andthen declined to background soil levels micompost application rate, whereas straw- Use of Baking Soda asbelow 10 ppm. berries responded positively and similarly a Fungicide to both the 5 ton/hectare (2.02 ton/acre) Direct MarketingSupplemental fertilizing is therefore neces- and 10 ton/hectare rates of application atsary to carry the crop through the season. another site. These responses could not Farmers’ MarketsStrawberry producers using the annual have been mediated by the availability of Communityplasticulture system must rely on soluble macronutrients, since all plots were supple- Supportedorganic fertilizers applied through drip mented with inorganic fertilizers to equal- Agricultureirrigation lines. Farmers using these sys- ize macronutrient inputs for all treatments. Selling to Restaurantstems must face solubility and the capac- Based on other research in the laboratory,ity of these products to be filtered through however, the responses could have been due Entertainment Farm-fine mesh without plugging drip emitters. ing and Agri-Tourism to production of plant growth regulators byProducts injected into the system may not microorganisms during vermicomposting. Organic Marketingemerge at the same concentration. In other Resourcessystems, foliar or side-dress applications The foliar application of aerobically-pre-will be warranted. pared compost tea increased yields in a British Columbia study. (Welke, 2004)While all perennial fruit crops will bene- Besides reducing incidences of Botrytis, thefit from the fertility provided by pre-plant compost tea treatment increased yields incover-cropping and green-manuring, straw- strawberries by 20 percent compared to theberries are so prone to weed problems that control and water sprays.pre-plant preparations to reduce weed pres-sure are practically mandatory in organic For more information on organic fertilizers,production. A thick cover crop of a grass/ vermicomposting, compost and cover crops,legume mix will help to smother out many request these ATTRA publications: ATTRA Page 5
  6. 6. of Organic Fertilizers and Amendments, rotations. That is, a bed may be allowed Alternative Soil Amendments, Worms for to fruit for two seasons before it is turned Composting (Vermicomposting), and Overview under and replanted to a cover crop. of Cover Crops and Green Manures. A weed competition study in a mature matted row planting was conducted over Weed Control a three-year period by Marvin Pritts and Weeds are one of the biggest problems Mary Jo Kelly of Cornell University (2004). that organic strawberry growers face. Pre- The impact of weeds on subsequent produc- plant site preparation is critical. Refer to tivity was determined. Plants in the weed- ATTRA’s Overview of Organic Fruit Produc- free plots had the highest yield, while sea- tion for site preparation strategies as well as son-long uncontrolled weed growth reduced for basic weed-control ideas. productivity by 51 percent. However, plants in several plots with a limited amount Cultural Methods of weed competition had higher yields than Organic growers will find that some hand those in the continuously weeded controls. weeding is necessary. Weeds in organic This indicates that plants from a well-estab-E uropean plasticulture systems can become trouble- lished matted row planting may be tolerant strawberry some even where black plastic mulch is to a limited amount of weed competition for used. In such situations, the weeds emerge at least two years. Growers should direct growers and from the planting holes made for the straw- a majority of their efforts and resourcesresearchers have led towards controlling weeds in the planting berry plants. The rows must be straight andthe way in innova- the plastic laid precisely to allow mechani- year. Once the planting is well established,tions and research cal cultivation of the furrows without dam- growers may limit the number of times theyinvolving mechani- aging the beds and plastic. hand weed to two or three per weed control in A variety of colored mulches have been Planters’ paper, a black paper mulch, wasstrawberries. studied in California to determine their con- used in matted rows for a biodegradable tribution to weed control and crop response. mulch study. (Weber, 2003) It reduced Black mulch provides the best weed con- weeds but degraded quickly along the edges trol but does not warm the soil as well as where it was covered by soil, allowing the clear plastic. Soil warming with clear plas- wind to tear and blow large pieces off the tic results in plants that grow and produce plots. The rate of degradation the first year earlier in the season, but weeds are not con- was quick but the paper still reduced weed trolled. Research determined that the effect population compared to clear mulch and of mulch color on transmittance of photo- the control. synthetically-active light (400 to 700 mm) through mulches was the key weed-con- Mechanical Methods trol factor. (Johnson and Fenimore, 2005) European strawberry growers and research- Green and brown plastic mulches provided ers have led the way in innovations and the best combination of soil warming and research involving mechanical weed con- weed control benefits at all trial locations. trol in strawberries. Recent research in the The matted row system (where plants from U.S. has confirmed the usefulness of the runners form a 6- to 30-inch-wide solid bed) flex-tine harrow, the brush hoe, and the fin- is commonly used by strawberry growers ger weeder for weeding strawberry plant- in many regions of the U.S. This method ings. (Pritts and Kelly, 1999) For instance, precludes mechanical cultivation for weed the brush hoe required only three passes control within the bed, though cultivation per season plus two hand weedings for com- is commonly used to renovate or narrow a plete weed control, compared to standard bed. Weed problems tend to increase with cultivation with a rototiller, which required the age of the planting. Many organic grow- three passes and four hand weedings. Visit ers have therefore chosen shorter fruiting the European Weed Research Society’sPage 6 ATTRA Strawberries: Organic Production
  7. 7. Physical Weed Control Web page www. habitat for spiders and has been known for more informa- reduce diseases. A study in Ohio showedtion on these and other mechanical cultiva- that straw mulch between strawberry rowstion tools. In plasticulture systems, harvest was equally or more effective than fungi-crews are sometimes used to weed when the cides for controlling leather rot (Phytoph-weed pressure is high or when the harvest thora cactorum). (Ellis et al., 1998)day is short. Research in West Virginia indicates that shredded or chopped newsprint makes anBiological Methods excellent and safe mulch. (Baniecki et al.,Before the widespread adoption of herbi- 1995) It can be applied over the top ofcides, geese were commonly used for weed the plants at the onset of winter, just likecontrol in commercial-scale strawberry pro- straw. It should be applied in a layer 4 toduction. In areas of concentrated crop pro- 5 inches thick (this will require about 500duction, farmers often had the benefit of to 600 pounds of chopped paper per 1,000weeder-geese services for hire. Weeder square feet), and will be subject to beinggeese can still be used to control grasses windblown until it is stabilized by rain or Sand a few broadleaf weeds, but close man- overhead irrigation. Only newspaper or trawberryagement of the geese is essential. Not every other recycled paper, without glossy or col- ored inks, may be used as mulch under the plants, espe-farmer will find the extra requirements National Organic Program standards. cially in thesuitable to his or her management regi-men. The extra work may be offset to some North, are com- Woolen landscaping fabric was the bestdegree by on-farm consumption of the geese alternative treatment in a study conducted monly mulched withor by sales of geese and their products. In in Minnesota. (Forcella et al., 2003) A straw over the win-any case, the geese must be removed before one-ply woolen fabric centered over the crop ter to minimize coldfruiting season, because they will eat straw- nearly eliminated weeds from rows, pro- damage.berries before going after grass. moted daughter plant rooting, and allowedUnder the National Organic Program (NOP), maximum fruit yield equivalent to thatraw animal manure must be composted obtained in plots that were hand weeded.unless it is incorporated into the soil not Cornell small-fruit researchers Marvin Prittsless than 120 days prior to harvest of a crop and Mary Jo Kelly have worked extensivelywhose edible portion has direct contact with with cover crops for weed suppression inthe soil surface or soil particles. Therefore, strawberries. They have tried several spe-geese would need to be removed from the cies—including tall fescue, marigold, buck-field and their manure incorporated at least wheat, and ryegrass—but sudangrass hasfour months prior to the beginning of straw- the most desirable characteristics: rapidberry harvest. ATTRA has more informa- establishment, low water use, low nutri-tion on the proper management of weeder ent use, and competitive displacement ofgeese available on request. weeds. Their research suggests that inter- seeding sudangrass between beds and mow-Organic Mulches ing it twice a year provides acceptable weedStrawberry plants, especially in the North, control without herbicides, especially whenare commonly mulched with straw over the used in conjunction with a winter strawwinter to minimize cold damage. In the mulch. However, a later study found that aspring, the straw is raked into the aisles sorghum-Sudan grass hybrid “killed” cover crop suppressed pathogens and weeds butwhere it provides some control of weeds and adversely affected strawberry growth andhelps to keep the berries clean. Caution yields. (LaMondia et al., 2002)must be taken with some organic mulchesin that they may harbor pests like snails, See the Matted Row System section aboveslugs, cutworms, earwigs, and sow bugs. for information on a USDA study using aOn the other hand, straw provides excellent killed cover crop mulch (hairy vetch, rye, ATTRA Page 7
  8. 8. crimson clover) to suppress weeds and of the acidic solution degrading the leaf’s reduce erosion. waxy cuticle layer, causing desiccation. The thicker the cuticle layer on the weeds, In USDA zones 6 and colder, another option the more frequent the applications or the is to plant spring oats in the fall. Freez- more concentrated the solution should be. ing weather will kill the oats, leaving a nice If preparing a homemade solution of vin- mulch. Yet another option is to plant sor- egar herbicide, include citrus oil or lemon ghum-Sudan grass in the late summer; it is juice along with a small amount of liquid not at all cold tolerant, and will be killed soap as a surfactant. Some commercial for- by the first frost. For information on the mulations are Alldown™ (SommerSet Prod- USDA’s hardiness zones, check the Web ucts, and Ground Force™ site html. (Abby Laboratories, The Organic Materials Review Institute Thermal Controls (OMRI) lists vinegar and clove oil herbicides Thermal technology, from flamers to infra- as restricted, meaning the need for and red burners, keeps evolving with new prod- use of these herbicides must be explainedT iming is ucts emerging onto the market. At present, in the Organic System Plan. Essential oil thermal control methods include handheld herbicides (clove, thyme, and mint oils) critical for contain phytotoxic compounds that have successful flamers, mounted row crop flamers, infrared weeders, steamers, hot water, and hot foam. been reported to kill grasses and broad-thermal control of Timing is critical for successful thermal leaf weeds. Commercial products includeweeds. The younger control of weeds. The younger the weed, Xpress™ (Bio HumaNetics, www.biohuma-the weed, the easier the easier it is to desiccate. Grasses can which is a formulation of thyme be burned back but the growing point usu- (10.4 percent) and clove (10.1 percent) oilsit is to desiccate. ally sends out new growth. Some of these and Matran 2™ which is 45.6 percent clove devices may not fit in a particular system oil. According to the manufacturer, the but others may be successful components of addition of the yucca extract ThermX 70 a weed control program. (0.3 fl. oz. /gallon) with fulvic acid (6 fl. oz./ gallon) to Matran 2™ significantly enhances For a list of thermal devices for weed con- its coverage and performance. Matran 2™ trol, see Appendix A. is also used in combination with vinegar. Be careful when spraying weeds and keep Vinegar and Essential the sprays off strawberry plants. Also care Oil Herbicides needs to be taken to avoid contact or inhala- tion, as the high acid content will burn skin The use of vinegar for weed control has and lung tissue. For more information on been the least-toxic choice of many home vinegar as an herbicide, check the USDA gardeners. Its effectiveness varies, depend- Web site ing on the type of weeds sprayed and the htm?docid=9666. concentration of acetic acid. Most vinegar available commercially is 5 percent acetic acid. Through distillation, the concentra- Woven Synthetic Fabric Mulches tion can increase to 15 percent and by other Synthetic fabric mulches (trade names: non-synthetic processes to 30 percent acetic Weed Lock, Weed Barrier, Weed Stopper, acid. Caution must be taken with formula- etc.) offer some of the same weed suppres- tions greater than 5 percent. Though there sion as regular plastic mulches, but have are more concentrated solutions of acetic the advantage of being water- and air-per- acid that are derived synthetically, these meable. Though initially more expensive types are not allowed in organic production than regular plastic, the higher-quality systems. Some commercial formulations grades of fabric mulch can be used year of vinegar herbicide include lemon juice after year. These woven mulches are used or citrus oil. The mode of action consists in essentially the same way as plastics in thePage 8 ATTRA Strawberries: Organic Production
  9. 9. systems described above. However, because White Grubsthey are water-permeable, it should not be Primarily a problem in the eastern U.S.,necessary to add irrigation lines under the white grubs can cause serious damage ifmulches in areas with adequate rainfall. strawberries are planted immediately after a sod crop. White grubs are the larvae ofInsect and Mite Control May and June beetles and other beetles inNumerous insects feed on strawberry plants Scarabaeidae. Late-summer or early-falland threaten yields. Extension Service spe- plowing destroys many larvae, pupae, andcialists are familiar with pests common to adults in the soil and also exposes thesespecific areas and can help with proper stages to predators. The milky-spore-dis-identification, which is the first step in pest ease bacteria, Bacillus popillae and Bacillusmanagement. A scouting program with reg- lentimorbus, are important natural enemiesular monitoring can help growers determine of Scarab beetles. Grubs ingest spores ofboth the pest pressure and presence of ben- these bacteria on the thatch or roots of theeficial insects. Once pest pressure reaches grasses they eat. The spores then germinatethe economic threshold, control actions and the bacteria multiply inside the grubs, Care necessary. If biological controls are which die and disintegrate, leaving many ommonto be used, they must be deployed before new, viable spores to spread the disease to succeeding generations. (Daar, 1988) strawberrythe pests reach critical levels. That is whymonitoring is so important. In large opera- pests include Beneficial nematodes are also effectivetions, where harvest crews are used regu- white grubs, straw- against soil-dwelling grubs. Steinernemalarly, training the crew foreman to identify carpocapsae will infect its host near the soil berry weevils, straw-insect pests and diseases can help in the surface while Heterorhabditus bacteriophora berry rootworms,monitoring process. actively searches for its host below the soil caterpillar worms,Beneficial-insect habitats planted along- surface. (Flint and Dreistadt, 1998) These lygus bugs, and spi-side strawberry fields provide shelter, pol- nematodes and milky-spore bacteria are der mites.len, and nectar sources to predators and widely available through mail-order gardenparasites of insect pests. Beneficial insects supply companies.are able to take refuge in the habitat whenfields are treated with a pesticide. When Strawberry Clipper (Strawberrypurchased beneficial insects are released, Bud Weevil)these habitats encourage the beneficials to The strawberry clipper or bud weevil,remain and continue their lifecycles, help- Anthonomus signatus, occurs only east of theing reduce pest populations. Some pests Rockies. Adult beetles emerge in the earlymay also inhabit the refuge along with spring, lay eggs in the buds, and then cutbeneficials, so it is important to monitor partly through the stem, causing strawberrythese habitats: For additional informa- buds to fall over or fall to the ground.tion, request ATTRA’s Biointensive Inte-grated Pest Management and Farmscaping Contrasting studies on strawberry clip-to Enhance Biological Control. per or bud weevil have been conducted. One study found that most of the 12 vari-Although pest problems vary with location, eties studied compensated for a significantcommon strawberry pests include white amount of flower bud loss, provided thatgrubs, strawberry weevils, strawberry root- the loss occurs early in the development ofworms, caterpillar worms, lygus bugs, and the inflorescence. (Pritts et al., 1999) Aspider mites. For more detailed information later study showed that liberal thresholdson the pests themselves, refer to the publi- developed from the previous studies werecations listed in the Further Resources exceeded in two of the three research sitessection below (see especially the publica- and damage levels were severe enough totions by Funt et al., 1997, Kovach et al., reduce yields significantly. (Handley et al.,1990, Maas, 1987, and Strand, 1993). 2002) The clipper moves at the very ATTRA Page 9
  10. 10. rate of 30 feet per season. In a new plant- attack from ground beetles and from par- ing, it is unlikely that the damage would asitic nematodes such as Steinernema or extend more than 30 feet from the perime- Heterorhabditus species. The root weevils ter into the plot. Damage may be somewhat are crawling insects that also have been more extensive in older plantings, but still excluded from fields by fences, trenches limited by the rate of movement of the clip- and barriers like sticky tape. (Bomford and pers (they will have moved approximately Vernon, 2005; Strand, 1993) 60 feet into a two-year planting and 90 feet into a three-year planting). Organic growers Lygus Bugs should destroy damaged buds, which con- tain eggs, eliminate trash and nearby foli- The tarnished plant bug or lygus bug (pri- age that provide hibernation sites for adult marily Lygus lineolaris in the East and L. weevils, and apply an organically approved hesperus in the West) can be troublesome, insecticide as a last resort. especially in plantings of day-neutral vari- eties which fruit throughout the growing season. Adults and nymphs (the nymphs Strawberry Rootworm cause the most damage) suck sap from the Strawberry rootworm (Paria fragariae) plant and inject a toxic saliva. This feed- adults feed mainly at night, making holes ing results in a characteristic deformation of in the leaves. The larvae feed on fine the fruits called cat-facing, which makes the roots and eat the crowns close to the berries unusable and unmarketable. ground. Cultural control consists of plowing infested fields after harvest and setting new plantings away from woods (favorable hibernation sites) and from older strawberry plantings. Apparently, IPM damage thresholds have not been established for the rootworm. If the grower feels that pesticide treatment is necessary based on scouting, nocturnal treatment should be aimed at the foliar- feeding adults, since there are no effective or registered insecticides available for con- trol of the larvae. Soil-dwelling predators such as ground beetles or insect-attacking nematodes like Steinernema species may Lygus bug. Photo courtesy of USDA/ARS provide some control. Keeping any groundcover well clipped for a distance of five to ten yards around a straw- Strawberry Root Weevil berry field, and otherwise destroying places The adults of these species feed mostly on favorable for hibernation, may help reduce leaves, causing minor damage. The larval lygus-bug populations. Adult lygus bugs stage is the problem, as the larvae feed on hibernate under leaves, stones, and bark. roots and crowns of the strawberry plants. They usually lay eggs in the stems of her- Root weevils have many alternate hosts baceous cultivated plants and broadleaf including other small fruits, cranberries, weeds. Legumes (vetches, clovers, alfalfa, grapes, mint, hops and many ornamental etc.) can harbor large populations of these plants. Rotation with nonhost crops like pests. This must be considered if beneficial corn, wheat, clover, and alfalfa can reduce habitats using these plants are established populations. (Berry, 1998) near strawberry plantings. Like other ground-dwelling pests, Straw- Trap crops are also useful in lygus bug berry Root Weevils are susceptible to management. In California, an annual trapPage 10 ATTRA Strawberries: Organic Production
  11. 11. crop mix of one dormant and one semi-dor- A fungus, Beauveria bassiana, has somemant alfalfa variety, two radish varieties efficacy against lygus bugs. In New York,(Daikon and Cherry Belle) and sweet alys- three years of tests concluded that the com-sum has been used with success. Lygus mercial formulation of B. bassiana, Myco-bugs move in from surrounding fields and trol™, reduced lygus damage about 50 per-settle on the trap crops, which can then cent compared to untreated controls, butbe treated with insecticides or vacuumed. was still considerably less effective than(Dufour, 2000) Bug vacs range from trac- synthetic insecticides such as malathion.tor-mounted machines to small hand-held (Kovach and English-Loeb, 1997) Myco-devices and are actually vacuum cleaners trol™ worked best when targeted at youngerfor pests. A trial by University of Califor- nymphs and when humidity levels werenia researchers concluded that three similar adequate. In combination with other cul-grower-designed vacuum machines reduced tural controls (choosing the right cultivarlygus bug damage compared to untreated and close mowing near the planting), use ofcontrols, but were not equal to chemical Mycotrol O™ (Laverlam Intl.), Botanagardcontrol with a pyrethroid insecticide. The (Laverlam Intl.) or Naturalis (Troy Biosci-damage, though reduced, was still consid- ences) could be of help to organic growers Sered economically unacceptable. (Pickel et in controlling lygus. ince lygusal., 1995) Research done in Watsonville, nymphs are While the lygus bug has several naturalCalifornia, demonstrated that lygus bugs most trouble- insect enemies, none of the native ones haswere more attracted to a field-edge alfalfa proved consistently effective in providing some, aim scoutingtrap crop than to a radish/mustard or straw- a commercial level of control in strawber- efforts at this lifeberry row. (Swezey, 2004a) Vacuuming ries. A small (1/8th-inch) wasp, Peristenus stage. Start check-the alfalfa trap crop with a tractor-mounted digoneutis, was introduced from Europe inbug vac reduced damage due to lygus bug ing for nymphs as 1984 and has exhibited excellent controlfeeding in associated strawberry rows when soon as flowers potential. However, this nymphal parasitoidcompared to vacuuming the whole field. appear. is difficult to rear, and is not commercially available. While it is spreading naturally in the northeastern U.S., it has not moved south of latitude 41°N (New York City). (Day et al., 1990) In California, Periste- nus digoneutis and P. stygicus were released in 1998. They have become established and annual increases in parasitism were noted in 2000-2002. (Fuester et al., 2004) Higher rates of parasitism by P. digoneutis were observed in New York on organic or casually sprayed farms than on intensivelyBug vacuum. Photo courtesy of USDA/ARS treated farms. (Tilmon and Hoffmann,This saved operating costs of the bug 2003) Anaphes ioles is a lygus egg parasit-vac and increased marketable fruit. For oid that has been used in California and inmore information on Bug Vacs, see the other states with some success. Research-ATTRA publication Bug Vacuums for ers who released 15,000 A. iole weekly onOrganic Crop Protection. one-acre strawberry plots observed a 64 percent suppression of Lygus hesperus com-Research conducted in New England found pared to a 44.7 percent reduction achievedvariation in susceptibility to the lygus bug with a pesticide application. (Udayagiriamong 20 strawberry cultivars. (Handley et al., 2000)et al., 1991) Honeoye, Sparkle, Veestar,and Canoga suffered the least from feeding, Since lygus nymphs are most troublesome,while Kent, MicMac, Scott, Blomidon, and aim scouting efforts at this life stage. StartRedchief suffered most. checking for nymphs as soon as ATTRA Page 11
  12. 12. appear. Tap 10 to 15 flower clusters over a two-spotted spider mite, Pacific spider mite, white plastic saucer so that the bright green and strawberry spider mite, among others. nymphs can be seen and counted. Deter- These plant-feeding mites consume juices mine the average number of nymphs per from strawberry leaves. Large populations cluster (total number of nymphs divided can reduce photosynthetic capacity, result- by total number of clusters). If sampling ing in weakened plants and reduced fruit is concentrated near weedy borders, the yields. Some growers who do not often action threshold is 1 nymph per cluster, but use botanical pesticides may see very few if done randomly throughout the planting, mites—if not reduced by pesticides, the nat- 0.5 nymphs per cluster should be consid- ural enemies of the mites will usually keep ered adequate to prompt a pesticide treat- them in check. These natural enemies ment. (Kovach et al., 1993) However, Cor- include other mites such as Phytoseiulus per- nell researchers caution that growers who similis, Metaseiulus occidentalis, and Neosei- intend to use the slow-acting biological ulus californicus, and insects like bigeyed insecticide B. bassiana may need to use a bugs, damsel bugs, minute pirate bugs, lower threshold. (Kovach and English-Loeb, lacewings, spider mite destroyers, and six- spotted thrips. Growers can buy some ofA 1997) If other natural enemies of lygus scouting are present—such as spiders, bigeyed bugs these predators from commercial insecta- method for (Geocoris species), assassin bugs (Zelus and ries to release on the farm. The predators two-spot- Sinea species), damsel bugs (Nabis species), can also be attracted and conserved natu- and lacewing larvae (Chrysoperla species)— rally through the use of insect habitats.ted spider mites hasbeen developed in you might want to consider adjusting the Insecticidal soaps, “narrow range” oils, threshold numbers accordingly. vegetable oils, neem-based products suchBritish Columbia as Trilogy®, and sulfur are acceptable miti-and successfully cides in organic production (check withimplemented both your certifier regarding specific products).there and in New Application instruments must thoroughlyYork. cover the leaves’ undersides, and products that are diluted must be applied in high volumes (more than 100 gallons of water per acre) to achieve complete coverage. Both oils and soaps can burn plants if over-applied or if high temperatures (greater than 80° F) occur during and after treatments. A scouting method for two-spotted spi- der mites has been developed in British Columbia and successfully implemented both there and in New York. (Kovach et al., 1993) To sample for these mites, walk diag- onally across the planting while randomly picking one mature, fully expanded leaflet from every other row, until 60 leaves are collected. If 25 percent are infested with mites (about 5 mites per leaflet), treatment Parasitic wasp Peristenus digoneutis. Photo courtesy of may be in order. Again, the number of USDA/ARS natural enemies should also be considered when determining a threshold for chemical Mites treatment. While this scouting method is The web-spinning spider mites are in the probably applicable to most areas, growers genus Tetranychus, which includes the outside the New York region should checkPage 12 ATTRA Strawberries: Organic Production
  13. 13. with their local Cooperative Extension Ser- If they become a problem, consult yourvice for scouting guidelines. local farm advisor, visit the numerous websites listed below under Further Contact Information for Beneficial Resources, or call ATTRA’s toll-free num- Organisms ber for information. Companies that sell mites and other beneficial organisms are listed in the California Environ- mental Protection Agency’s Department of Pes- Disease Control ticide Regulation booklet, Suppliers of Beneficial Diseases in plants occur when a pathogen Organisms in North America. (Hunter, 1997) An is present, the host is susceptible, and the online PDF booklet is free online and contains environment is favorable for the disease to contact information for 142 commercial suppli- develop. Altering any one of these three ers of the more than 130 beneficial organisms factors may prevent the disease from occur- that are currently used in biological pest control. ring. Organisms responsible for plant It not only indexes the suppliers by the natural enemies they sell, it also matches the beneficial diseases include fungi, bacteria, nematodes, organisms with their target pests. and viruses. If these organisms are pres- ent, then manipulation of the environment S and the host, to make it less susceptible, oil health andSome of the mites you see when scouting helps manage diseases on strawberries. managementmay be predator mites. You may need a Soil health and management are the keys are the keysmagnifying glass to distinguish between for successful control of plant disease. A for successful con-these beneficial mites and the pest mites. soil with adequate organic matter canOne key to telling them apart is that the trol of plant disease. house numerous organisms such as bac-beneficial predator mites are generally more teria, fungi, nematodes, protozoa, arthro-active than the two-spotted mites—they pods, and earthworms that may suppresstypically move quickly about the leaf sur- soil-borne pathogens. This disease sup-face looking for prey. Depending on your pression is caused by either antagonism,geographical area and the species involved, competition for nutrients, or competition forthe recommended ratio of beneficial mites space around the root (the rhizosphere) andto pest mites varies, but seems to aver- induced systemic resistance (ISR) or sys-age approximately 1:10. That is, if there temic acquired resistance (SAR) triggeredappears to be at least one beneficial mite in the plant. Increasing soil organic mat-for every 10 pest mites, control of the pest ter by incorporating cover crops or add-mites will probably be achieved naturally ing compost and organic fertilizers willwithout the intervention of miticidal sprays. help maintain these beneficial organisms.Dust that accumulates on the spider mite’s For more information, see the ATTRAwebbing creates an ideal shelter for the publication Sustainable Management of Soil-mites and their eggs. These little dust Borne Plant Diseases.“tents” discourage predators and pre- Rotating strawberries with other crops isvent the miticide from reaching the mites a critical factor in organic production andand their offspring. California growers many certifying agencies require it as acommonly water roads, post “slow” signs, component of the organic system plan.plant windbreaks and beneficial insect Crop rotation reduces insect, disease andhabitats, and use fencing to decrease dust in weed pests, improves soil fertility, improvesstrawberry fields. soil tilth and structure, reduces soil erosion and improves water management. CoverOther Pests crops, vegetable crops, legumes, and cerealsOther arthropods that will occasionally are recommended rotation choices. Avoidreach pest status include aphids, spittle- Solanaceous crops like tomatoes, potatoes,bugs, whiteflies, Cyclamen mite, various peppers, and eggplant that may harbor dis-caterpillars, earwigs, and leafhoppers. eases such as Verticillium. Research ATTRA Page 13
  14. 14. the Salinas Valley of California found that Elemental copper and sulfur have long been incorporating broccoli residues reduced Ver- used by conventional and organic growers ticillium dahliae in the soil and that rotation as pesticides for foliar bacterial diseases with broccoli may be a feasible approach to and powdery mildew, respectively. manage Verticillium diseases in susceptible crops. (Subbarao et al., 1999) Root Rot Complex Compost teas or extracts and other innova- Soil borne fungi such as Phytophthora, tive concoctions such as yeast-sugar solu- Pythium, Rhizoctonia species, and Verticil- tions, sodium bicarbonate (baking soda), lium dahliae are major pathogens that affect and milk have become popular as foliar strawberries worldwide. In organic produc- disease preventatives among many organic tion, the cultural methods described above growers. Compost teas and yeasts intro- —crop rotation, compost application, and duce non-plant-pathogenic microorganisms solarization—aid in the control of these dis- and biocontrol agents that compete with eases. Other cultural controls include using and antagonize disease spores as they try resistant varieties, planting strawberries in to establish themselves on the host. Baking a pathogen-free, well-drained soil, avoiding soda works at the chemical level, interfering over-watering, and planting only certified in spore germination. For more informa- disease-free plants. Some growers inocu- tion, request ATTRA’s publications Notes late the soil or the plants with a variety of on Compost Teas and Use of Baking Soda as commercially available biological products a Fungicide. such as Vesicular Arbuscular Mycorrhizae Soil Solarization Imagine harnessing the sun’s energy to destroy your enemies. Like Archimedes—the ancient Greek who used mirrors to con- centrate sunlight to burn the Roman fleet—farmers can destroy or disable insects, diseases, nematodes, and weeds in the field. The technique known as solarization consists of laying clear plastic mulch on moist soil. Heat is trapped under the plastic, raising the soil’s temperature, killing or debilitating pests. Most of the research worldwide has concentrated on hot and arid areas, but any place with hot summers is a potential site for this system. Usually this soil pasteurization process takes four to six weeks, but the amount of time depends on many factors such as rain, wind, day length, soil texture, and the quality of the polyethylene mulch. Ultraviolet-protected plastic is recommended so the mulch can be removed and re-used. Before solarization, certain types of organic matter, such as compost and residues from Brassica crops such as broccoli and the mustards, can be added to the soil for “bio-fumigation.” When heated in the solarization process, this organic matter releases volatile compounds that are toxic to many pests. Before solarization takes place, the land where the crop is to be seeded or transplanted must be prepared for planting. Beds must be shaped, drip tape installed, and fields leveled. This is to avoid stirring up the soil after solarization, which would bring fresh pest organisms to the soil surface. Depending on out- side temperature, intensity of sunlight, and types of pests, soil solarization can provide good pest control 8 to 10 inches deep, although the best control is generally obtained down to 6 inches. Special caution: During solarization, drip tape must be buried at least one inch deep to avoid damage from the sun’s rays. In experiments where the tape was placed on the surface of the bed and then covered with clear plastic, the drip tape was dam- aged by sunlight that was magnified by water droplets condensing on the underside of the plastic. Research conducted in southern California and Oregon has demonstrated that solarization has potential as a component in an integrated pest management program for root diseases in strawberry production. (Hartz et al., 1993; Pinkerton et al., 2002) Soil Solarization websites Soil Solarization Home: International Workgroup on Soil Solarization and Integrated Management of Soil-borne Pests: Soil Solarization: A Nonchemical Method for Controlling Diseases and Pests: les/filelibrary/40/942.pdfPage 14 ATTRA Strawberries: Organic Production
  15. 15. (VAM) or Arbuscular Mycorrhizae (AM), agents (a yeast and bacterium) resulted inTrichoderma species (Promot, SoilGard), better suppression of Botrytis and reducedStreptomyces griseovirdis (Mycostop), and the variability of disease control. (GuetskyStreptomyces lydicus (Actinovate). et al., 2001) Although there is not a high level of gray-Anthracnose mold resistance in any one strawberry cul-Anthracnose can be very serious, causing tivar, Earliglow is relatively resistant com-strawberry plants to die out in midsummer. pared to most cultivars. (Turns, 1990)The disease produces a rust color through-out the crown and eventually stops theplants from growing. Symptoms are most Leaf Spotnoticeable during summer dry spells. Leaf spot diseases—identified by the pres- ence of spots on strawberry leaves andSince high soil fertility favors anthracnose, stems—can be caused by the fungi Myco-little or no fertilizer should be applied sphaerella fragariae, Ramularia tulasnei,when disease pressure is strong. However, or Phomopis obscurans, or by the bacte-resistant cultivars can be grown success- S rium Xanthomomas fragaiae. These patho-fully at much higher fertility levels. (Maas, ome diseases gens are spread by splashing water and are1987) Anthracnose is more prevalent in of straw-the Southeast than elsewhere. Commer- harbored by dead leaves and other plant debris. Sanitation, as well as the recom- berries arecial growers in the Southeast should avoid mendations mentioned above on foliar dis- anthracnose, grayplanting on former strawberry sites and uselocally adapted resistant cultivars. ease preventatives, apply to leaf spot. mold, leaf spot, and powdery mildew.Botrytis (gray mold) Please NoteGray mold, caused by the fungus Botrytis Preventive treatments such as sulfur, copper, orcinerea, is one of the most common and compost teas applied prior to wet weather areserious fruit rot diseases. The fungus grows advisable for many diseases like leaf spot, graybest in cool damp weather, and gray mold mold, and powdery mildew. Also, studies havecan be devastating if rainy weather coin- shown that systems using organic mulches havecides with harvest, when strawberry fruit is a reduced incidence of soil-borne its ripest and most susceptible. Pickershandling infected berries can spread theinfection to healthy berries. Control of gray Powdery Mildewmold is aided by removing infected debris Powdery mildew is a fungal disease thatfrom the field and by providing good drain- affects strawberry foliage, flowers, andage. Infected fruit can be picked off the fruit. Caused by Sphaerotheca macularis,plants and placed in the furrow as long as its spores prefer intermittently moist condi-a cultivator can go through the field and tions and will not germinate in free-stand-bury this fruit. Clean mulch, which keeps ing water. In coastal California strawberryfruit off the ground, is also highly recom- fields, the practically year-round productionmended. Removing leaves from the field as season, foggy cool nights, and warm dayssoon as the harvest season ends can signifi- make the disease a major and very per-cantly reduce the incidence of gray mold on sistent problem. Sulfur is the most com-fruit in June of the following year. (Sutton mon control agent on both conventional andet al., 1988) organic farms. Milk has been used success-The following biorational products are fully against powdery mildew on cucurbitavailable commercially for Botrytis control: crops. (Bettiol, 1999) Sonata™ is an OMRI-Serenade (Agraquest), Mycostop (Verdera approved commercial formulation of Bacil-Oy), and Promot (JH Biotech). Research in lus pumilis that is used on strawberries forIsrael found that combining two biocontrol powdery mildew control. Seven-to ATTRA Page 15
  16. 16. day application intervals are recommended, Finally, prospective greenhouse growers depending on disease pressure. should spend some time exploring local markets (restaurants, groceries, etc.) Off- Greenhouse Production season greenhouse growers will be compet- ing with strawberries from California, Mex- Five factors—light, heat, pollination, pest ico, Chile, and Florida. Prices will have control, and economics—make winter straw- to offset the costs of production, so grow- berry production in a greenhouse very dif- ers will have to produce an outstanding ferent from field production. product. Cornell researcher Marvin Pritts Lighting is critical for winter production. found that the break-even price for green- The day-neutral cultivars (e.g., Tribute and house-grown strawberries was $3/pint. Tristar) or the short-day types (e.g., Jewel) He reports, however, that a small but sig- are much easier to grow during the short nificant number of consumers are willing days of winter than most of the traditional to pay that price for high-quality berries. June-bearing types. It is difficult and For more detailed information on green- expensive to get the June-bearing types to house strawberry production, go to www. fruit out of season. Even with the day-neu-S trawber- tral types, some supplementary lighting will BerryDoc/Berrydoc.htm. ries must be be necessary to get high-quality fruit. picked and Supplementary heat will have to be avail- Harvest and Postharvesthandled very care- able (in some cases the lighting will provide Strawberries must be picked and handledfully. enough heat). While some non-fruiting veg- very carefully. The fruit must be firm, well- etables (e.g., leafy greens, such as spinach) colored, and free from rot. When harvested can produce well in unheated greenhouses, at the right time and handled properly, strawberry plants need about a 68º F day strawberries will remain in good condition and 54º F night to produce good yields of for many days. Most California- or Florida- high-quality berries. grown strawberries found in supermarkets The grower will have to provide pollination. are picked three-quarters ripe to withstand Bumblebees are probably the best polli- shipping. The color of these strawberries nators in a greenhouse environment. Two is a full red but the taste is disappointing. commercial sources, GB Systems (P.O. Box Small-scale growers who pick ripe fruit 300, Locke, NY 13092; 315-497-3129) can easily compete with supermarket and The Green Spot (93 Priest Rd., Not- berries by offering a tastier, fresher berry tingham, NH 03290; 603-942-8925) sell to local consumers. bumblebees and bumblebee nesting boxes. Proper postharvest handling of strawberries Certain pests (usually the larger ones, is essential. Cooling the berries will remove e.g., tarnished plant bugs) can be effec- field heat and increase shelf life. Harvest- tively excluded from greenhouses, but oth- ing early in the day while temperatures ers, such as mites, aphids, whitefly, thrips, are cool and then pre-cooling the fruit and fungus gnats are likely to thrive and before shipping will extend the shelf proliferate. Due to the need for bumble- life significantly. bees for pollination, controlling these pests Forced-air cooling is the most common with conventional pesticides is not a good method used on strawberries. The flats idea. Fortunately, they can be effectively are stacked parallel to each other in a managed with biological controls, such as cold room with an open space between the beneficial mites and lacewing larvae. For flats. A tarp is then placed over the top the details of greenhouse pest management, and ends of the stacked cartons, with a fan contact ATTRA for our series of publica- located between stacks. The fan pulls cold tions on greenhouse IPM (or go directly to air between the gaps of the stacked flats, removing the field heat from the berries. ItPage 16 ATTRA Strawberries: Organic Production
  17. 17. is vital that the fruit be cooled as soon as the Tectrol® system go to the Transfreshpossible. The more the delay between har- web site at and cooling exceeds one hour, thegreater the losses to deterioration. (Kader, Economics1992) Water loss from strawberries can Strawberries are one of the most popularbe a problem, so it is critical to main- fruits in the U.S. The majority of commer-tain high humidity in the cooling facility. cial production is in California, Florida,Avoid wetting the fruit, which can cause Oregon, and Washington. Growers in thesedecay problems. states produce 95 percent of reported U.S.Fresh-market strawberries are usually sold output. Growers in the South, East, andin pint or quart baskets covered with plas- Midwest generally have small strawberrytic wrap. However, one-piece molded-plas- acreages located near population centers,tic containers called “clamshells” are rap- and rely on direct-market sales.idly replacing this packaging. The time Strawberries are a high-value crop, but theyand labor involved in packing the fruit in also have special production requirements,the traditional pint-size plastic baskets is a short shelf life, and a brief marketing sea- Sconsiderable, because shippers and buyers son. Initial investment in land preparation, trawberriesgrade fruit packed in this manner by the irrigation and other equipment can cost are one of thearrangement of the fruit in the flat. This about $2,000 per acre for a matted row most popularputs additional burden on the farm worker system (Ernst, 2003) to $10,000 per acre fruits in the pack the fruit correctly. The use of clam- for a plasticulture system. (Karcher, 2002).shells makes the strawberry pickers’ job a However, plasticulture systems produce ear-little easier; the wholesalers are not as con- lier and have higher yields—up to doublecerned with the appearance of the fruit the yield of matted row systems. Earlierpack since it looks uniform with the clear harvest may allow producers to receive thelid. Many of these clamshells are recycla- higher prices available at the beginning ofble. A drawback to the clamshells is the the season.greater difficulty of cooling the fruit. Theholes in the containers are not big enough to Organic strawberries are in high demandallow for rapid cooling, so extra time in the and this segment of the organic industryforced-air cooler is necessary. The clam- continues to grow at a rapid pace. Organicshell containers also hold less fruit than the strawberries now rank sixth among allpint baskets and are sometimes sold at a California organic fresh commodities,lower price. If you sell wholesale or directly with over 160 organic strawberry growersto stores, the buyers may require this type registered with the California Organic Pro- gram. (Swezey, 2004b).of packaging. Continuous cropping of strawberries is notWholesale strawberries that are shipped possible in an organic system that relieslong distances are placed on pallets and on crop rotations. The production cycle isare covered by bags that are injected with shorter (one to two fruiting years) and yieldscarbon dioxide after the fruit is thoroughly are both lower and more variable than incooled. This modified-atmosphere process conventional systems. Labor requirementsis patented by the Transfresh Corporation may be as much as twice those of a conven-of Salinas, California and is known as the tional system. (Pritts and Handley, 1999)Tectrol® Atmosphere Pallet System. The Since they face higher costs of productionprocess extends the shelf life of the fruit, (Table 1), organic growers must secure aallowing for transport and marketing. It premium price in order to make a also accepted in organic production. Itshould be noted that large volumes need to California research shows that at medianbe shipped to make this process economi- organic production levels, profitable organiccally feasible. For more information on production can begin at an average price ATTRA Page 17