Weeds Training for Master Gardeners


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Learn about kinds of weeds, their characteristics, what happens when they become invasive, and techniques for weed control

Weeds Training for Master Gardeners

  1. 1. WEEDSLinda R McMahanFaculty for Community HorticultureOregon State University ExtensionServiceYamhill Countylinda.mcmahan@oregonstate.eduPhotos by the author Identification and Control for Master Gardeners
  2. 2. Weeds Characteristics Identification Some Examples When just plain weeds become Invasive Control Strategies
  3. 3. So you have a weedWhat next. . . . In this case, our weed is really quite lovely, so what then?This particular ―weed‖ is Jimson weed, Datura stramonium, a toxic plantthat is considered to be an agricultural pest. However, some people growit for its ornamental value.
  4. 4. This one looks so pretty and it is growing in awetland along a nature trail in Beaverton, OregonIs it a weed or native plant? This is a good question to ask. The plant is purpleloosestrife, Lythrum salicaria, which is considered to be highly invasivethroughout most of the United States.
  5. 5. Removing some weeds can be very hardwork . .English ivy for example. How do we go about doing such a task? Can theremoved ivy be composted? What are the best methods of removal andcontrol?
  6. 6. First Let’s Look at WeedCharacteristicsA Weed is  Colonizerssometimesdefined as ―a  Reproduce successfully— someplant out ofplace,‖ but have numerous seeds, sometimesperhaps that genetically identical, for rapidis too simple establishment  Others quickly reproduce by vegetative reproduction  Have become successful hitchhikers in bird seed, garden seeds, plant pots, and on anything that moves including
  7. 7. First Let’s Look at WeedCharacteristicsWeeds can  May engage in chemical warfare byindeed be―crafty‖ and suppressing the growth ofit is surrounding plantssometimesquite difficult  Many survive in nutrient poor soil—to ―outsmart‖them some are even nitrogen fixers to gain a competitive advantage in poor soils  On the following few slides, I have referred to helpful web resources on the left panel of each page
  8. 8. http://www.nps.gov/plants/ALIEN/fact/alpemustard, visit this site maintained by theFor more information on garlicNational Park Service1.htm Now here’s a nasty weed known as garlicSome mustard, Alliaria petiolata. It is introduced from AsiaExamples and Europe. This weed is spreading rapidly throughout Oregon. It is a biennial and difficult to hand-pull. It helps maintain its weed status through chemical warfare by suppressing growth of other plants or interfering with their ability to form beneficial relationships with soil fungi.
  9. 9. For more photos and information about thishttp://www.missouriplants.com/Whitealt/Catiny weed, visit an information site at Therdamine_hirsuta_page.htmlMissouri Botanical GardenSome This plant, Cardamine hirsuta, is sometimes called snapweed orExamples shotweed for its habit of explosive release of its seeds when touched. As gardeners, you are perhaps more familiar with this plant. It is a winter annual, sometimes blooming and producing seeds before we emerge in late winter to check on our gardens.
  10. 10. http://plants.usda.gov/java/profile?symbol= profiles many plants, both native and not- To find out more, to to a USDA site that PLMA2 nativeSomeExamples Common plantain, Plantago major Here’s another familiar lawn weed. Each flower stalk reproduces over a long period of time, producing hundreds of seeds.
  11. 11. Visit this helpful website at The Universityhttp://www.ipm.ucdavis.edu/PMG/PESTNof California, Davis to learn more aboutannual bluegrass characteristics andOTES/pn7464.htmlcontrolSome Yet another familiar weed is annualExamples bluegrass, Poa annua, a common lawn pest. Annual bluegrass is extremely difficult to control because it seems to thrive with our common garden practices. Even though these plants have been sprayed with herbicide, they do not seem to be responding and even these small plants have already produced seeds.
  12. 12. Weed CategoriesDifferent  Winter Annuals – some of our mostgroupsrequire challenging garden pestsdifferentcontrol  Summer Annualsmethods  Biennial weeds  Perennials  Some have deep and persistent taproots  The ―nastiest‖ create underground runners or storage systems  Shrubs, Vines and Trees
  13. 13. Another DistinctionThese two  Some weeds aremajorgroups of Monocotyledons, including mostflowering notably weedy grasses and sedgesplants canrequire  Other weeds, often referred to asdifferentkinds of broadleaf, are Dicotyledonscontrol  If you are controlling broadleaf weeds such as dandelions in lawns using herbicides, be careful to choose appropriate products so as not to kill the grass as well
  14. 14. Native Plants as Weeds?  You may be confused to find native plants listed as weeds in some of the resources  Examples are yarrow (shown left), wild cucumber, poison oak, native irises, and horsetail  This is because some of these plants are considered to be agricultural pests, garden pests, or cause human or animal health issues-so control methods are available and may be appropriate in some cases
  15. 15. Weed Examples and Controls  The following slides show examples of various categories of weeds  In each case, control methods are mentioned  Please note that we will cover controls more thoroughly near the end of this presentation
  16. 16. Winter AnnualsBecause  Typically germinate in the fall andthey bloomand produce flower in the winter or early springseed in thewinter, these  Examples include snapweed, someweeds tend mustards, chickweed, and someto catch usby surprise if weedy geraniumswe are notwatching  They spread through seed production
  17. 17. Winter Herb Robert, Geranium robertianum, sometimes called ―stinkyAnnuals bob‖ is a newly listed invasive species in Oregon. The best control for this small winter annual is persistent hand weeding. It has a relatively short seed life of approximately 3 years so persistent control can effectively reduce and even eliminate the population. You have to be fast, however, this one can bloom in mid-winter! Pre-emergent treatments can also be effective.
  18. 18. Summer AnnualsAt  Seeds of summer annualsleast, summer annuals germinate in the spring, then bloomare more and set seed before fall frostsvisible, butthat does not  Examples includemean theyare always lambsquarters, pigweed, mallows, reasy to agweed, and spurgecontrol
  19. 19. SummerAnnuals Common mallow, Hibiscus trionum This weed often appears as a contaminant in bird seed. It has small but attractive flowers and a distinctive post-flower appearance shown here. it is a summer annual and can be controlled through hand weeding.
  20. 20. BiennialsSince they  Biennials typically have a 2-year lifeformrosettes the cycle. The first year, the seedfirst germinates and the plants produceyear, theymay escape a rosette, a round ―circle‖ of leavesour attentionuntil the that remains flat to the ground. Thesecond year following year, the stem ―bolts‖ tofloweringstem produce flowers and seedssuddenlybolts  Examples include bull thistle, foxglove, and common mullein
  21. 21. Biennial Bull thistle, Cirsium vulgare, is a biennial forming a pricklyWeed rosette the first year, than a tall blooming stalk One control for bull thistle is removal of all flowers before they set seed. Hoeing while plants are small is also effective. Seed are prolific. Repeated tilling or mowing and control with contact herbicides can also be effective.
  22. 22. BiennialWeed Mullein, Verbascum thapsus This biennial produces hairy felt-like leaves in a rosette (shown above) the first year. The second year, it sends up a tall stalk of attractive yellow flowers. A single plant can produce more than 100,000 seeds. Control is through competition with other plants (it likes bare ground), hand removal when the soil is loose, and deadheading to remove flowers and seeds before dispersal.
  23. 23. BiennialWeed Teasel, Dipsacus fullonum This common roadside weed seems to be increasing in Oregon. Recommendations for control include deadheading flowers or using herbicide at the rosette stage because some are not effective when the plant begins to bolt. Some say the ―hooks‖ on the seed stage of the flowering head may have been the inspiration for Velcro.
  24. 24. Biennial Wild carrot or Queen Anne’s lace, DaucusWeed carota Another ―pretty weed‖. This one has a tap root—it is a wild carrot after all. Its habit is usually biennial, but plants sometimes persist for additional years. This common roadside weed is resistant to many herbicides. When young, they often can be hand-pulled from soft or moist soil.
  25. 25. Perennial Weeds  Perennials are herbaceous plants that die back and regrow from underground roots or stems each year  Dandelions are simple perennials spreading by seed  Canada thistle, quackgrass, field bindweed, yellow nutsedge and others create underground networks as part of their reproductive strategy
  26. 26. Simple Ahh. Our old favorite the dandelion, TaraxacumPerennial officianale Each plant can produce hundreds of seeds which take off on the wind to infest the neighbor’s lawn as well as yours. Can be controlled through persistent hand-weeding with a weeding tool or selective broadleaf herbicide applications. Young leaves of dandelion are often available for use as salad greens.
  27. 27. Spreading Canada thistle, Cirsium arvense, is difficult toPerennial control –it is a perennial and spreads underground Unlike the biennial bull thistle, even persistent hand weeding or deadheading makes control difficult because underground pieces readily regenerate into new plants. Can sometimes be effectively controlled with weed barriers and with repeated 2-4 D or other contact herbicides beginning in September.
  28. 28. Spreading Wild morning glory aka field bindweed, ConvolvulusPerennial arvensis, is another perennial weed requiring persistence The PNW Weed Handbook recommends 2,4 D or glyphosate applied in the fall while plants are still actively growing. Most of the other chemicals listed are not available to homeowners. Persistent clipping and covering with landscape cloth are sometimes effective controls in smaller landscapes.
  29. 29. Weedy Woody Plants  Many woody plants can become pests, even invasive ones  Examples of invasive woody plants are Himalayan blackberry, honey locust, Norway maple, English ivy, and Scotch broom—all are problems in Oregon  Less invasive but common ones include the nightshades and poison oak
  30. 30. http://cru.cahe.wsu.edu/CEPublications/PNSee the following publication for moreinformation about nightshades in theW0588/PNW0588.pdfPacific Northwest Nightshades, Solanum nigrum and others These vine-like woody plants with poisonous black or red berries are of concern both as pests and for their toxicity. Seeds readily germinate throughout the year and they are tolerant to many herbicides, making control more difficult. Manual removal is often effective. If you choose herbicides, use during strong summer growth or early fall when plant resources are being sent
  31. 31. Scotch broom, Cytisus scopariusScot’s broom is a shrub first introduced into Astoria, Oregon as anornamental. Now it ―ornaments‖ our landscape, displacing native speciesand causing allergic reactions for many allergy sufferers. Biologicalcontrols have been introduced and are sometimes available. Othermethods of control include pulling with a ―weed wrench,‖ burning, and
  32. 32. The issue of weed control istough!Let’s  Identification is importantbegin to  ID helps us learn if the plant is afind weed or notsome  ID will tell us how important theanswer weed is to controls  ID will give us the information we need to recommend appropriate weed control
  33. 33. Weeds of the WestPublishe  A picture-basedd by OSU book, withPress entries groupedand by plantavailablein the familiesmaster  Most of thegardener common weedslibrary of Oregon are in this book  This is your first place to look!
  34. 34. Weeds of the Northern US andCanada Publishe  Includes many d by weeds and Lone relatives Pine Press –  Also arranged also by family available  Includes many in the master weeds of gardener wetlands and library waterways
  35. 35. Plant Identification ToolsTo find out  http://weeds.ippc.orst.edu/pnw/weehow itworks, go to ds?weeds/id/index.htmlthe site andlook at the  This is the picture part of the Pacificpicture of Northwest Weed Handbookbull thistle.Make sure  Unfortunately, it does not include ayou look atboth the key, but it can be used to help verifymature plant names and identities you findand seedlingto get idea of elsewherethis resource  This source includes photographs of seedlings which can be very useful
  36. 36. Oregon Small Farms Website The OSU Small Farms website offers another resource to learn about weeds It includes information on pasture weeds, management practices, weed toxicity, and guides to controlling some of the weeds (see field bindweed, for example) Remember that toxicity questions need the involvement of an OSU faculty member Pasture and commercial questions also need to involve an OSU faculty memberhttp://smallfarms.oregonstate.edu/weedsplants%2526pests
  37. 37. Some examples of commonweeds and recommendedtreatments Once you have an identification, solutions for control may be found in the PNW Weed Control Handbook, which is also available online This resource was developed primarily for commerical users and has limited information in available on weed control for home gardeners You may need to use approved web resources to find solutions The online version of the PNW Handbook is at http://weeds.ippc.orst.edu/pnw/weeds
  38. 38. When do ―Just Plain Weeds‖Become Invasive?  Some weeds are so aggressive that they have the ability to take over natural ecosystems, competing successfully with native plants  These have crossed the line into ―invasive plants‖ and are costing billions of dollars annually to control  Examples already considered are herb Robert (shown left), purple loosestrife, English ivy (shown left), and garlic mustard  More are shown in the next few slides, many were introduced intentionally to the US as herbs or
  39. 39. Shining geranium, Geranium lucidum, is a newly listed noxious weed inOregon. Usually grows as a winter annual.This species is spreading rapidly throughout the state. Oregon Department ofAgriculture notes that no biological control methods are availablehttp://www.oregon.gov/ODA/PLANT/WEEDS/profile_shinygeranium.shtml TheWestern Invasives Network recommends hand weeding, weeding with a flametorch, or selected broadleaf herbicide treatments.http://www.westerninvasivesnetwork.org/phpBB3/viewtopic.php?f=11&p=178
  40. 40. Himalayan or Armenian blackberry, RubusarmeniacusA vigorous grower introduced as a berry crop which subsequentlyescaped to the wild. Control is usually mechanical (mowing, cutting) orchemical (typical applications in the fall).
  41. 41. The evergreen blackberry, Rubus laciniatusThis introduced species is also considered to be invasive. Controlmethods are generally the same as for Himalayan blackberry
  42. 42. Yellow flag iris, Iris pseudacorusDespite the symbolism—this species was inspiration for the fleur-de-lissymbol, yellow flag iris is invasive in many parts of the world. It grows instreams and is spread through waterways. Control is difficult andexpensive.
  43. 43. Weed Control – checking the arsenalFast action  Mechanical and Cultural–preferredcan save a methodslot of effort. If  Deadheading or hand weedingyou can keep  Weed whackers, mowers, flamea weed from torchesflowering or  Mulching or covering – most weedsspreading, yo need sunlight to germinateu haveeliminated  Biological control if availableuntold hours  Tolerance of minor weedsof future  Chemical control if it is effective –control! the last choice – always read the label
  44. 44. Become Familiar with the HomeGarden Section of the PNW WeedHandbookhttp://uspest.org/pnw/weeds  Go to this site and look at the guidelines  Chemical tools are limited to only a?30W_INTG01.dat few – glyphosate, triclopyr, 2,4 D, and dichlobenil are the most common  Check the table on page 2 to see which practices and chemicals are effective on certain weeds and which are not
  45. 45. Pre-emergent Herbicides Check out this site made available through Washington State University Extension on the various kinds of herbicides available to the homeowner If using materials from other states, the most beneficial and relevant information can usually be found in neighboring states like Washington, Idaho, and Californiahttp://cru.cahe.wsu.edu/CEPublications/eb1214/eb1214.html
  46. 46. Corn Gluten Meal to control weeds? Some answers just seem too good to be true – Corn Gluten, unfortunately, fits into this category Corn gluten meal appears to work in other parts of the United States, but not in most of Oregon—instead it may make your weeds grow even more quickly. In our climates, it kind of acts like a fertilizer.
  47. 47. Vinegar as Weed Control  Acetic Acid was first introduced as an herbicide in Oregon around 2002  People began using it because ―concentrated vinegar‖ seemed like a good idea – Vinegar is 5% acetic acid  The 7% solutions generally found in these products are not concentrated enough to be effective  More concentrated products are possibly hazardous and may not be legal for use as herbicides in Oregon  See this factsheet for more information: http://oregonstate.edu/dept/nursery-
  48. 48. Thank You for Viewing thisPresentation  You may use this presentation and the photographs freely for educational purposes without express permission.  If you would like to use photographs for commercial purposes, please contact the author at linda.mcmahan@oregonstate.edu