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Weeds 2009


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This lecture was given in September, 2009 as part of the California native plant gardening series ‘Out of the Wilds and Into Your Garden’

This lecture was given in September, 2009 as part of the California native plant gardening series ‘Out of the Wilds and Into Your Garden’

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  • 1. Out of the Wilds and Into Your Garden Gardening with Western L.A. County Native Plants Project SOUND - 2009 © Project SOUND
  • 2. Weeds & More WeedsC.M. Vadheim and T. Drake CSUDH & Madrona Marsh Preserve Madrona Marsh Preserve September 5th 2009 © Project SOUND
  • 3. Does this look like your garden? You’re not alone – weeds are a perennial concern in S. California gardens! © Project SOUND
  • 4. What is a weed? (definition)  Weed: any plant that is growing at a site where it is not wanted © Project SOUND
  • 5. Why control weeds? (it’s a war out there!)  Weeds compete with desirable plants for:  Light  Water  Nutrients  Space  Weeds also provide hiding places for insects and serve as a source of plant diseases.  Weeds can kill a gardener’s enthusiasm, which can cause them to abandon the garden; Game ends – weeds winprojectprofiles/art26290.html © Project SOUND
  • 6. Weeds are particularly challenging in W. L.A. County  No killing frosts or smothering snow; weeds that are annuals in many climates are perennial in ours  No killing high temperatures  People water a lot (up to now)  Lots of weedy plants to spread their seeds/invade via roots  Use of ‘mow & blow’ gardeners – weeds hitch-hike betweenCastor Bean ( Ricinus communis) gardens © Project SOUND
  • 7. Where do alien weeds come from?  Many of California’s noxious and invasive weeds came from regions with comparable climates in the Mediterranean region, Australia, S. Africa  Others, including many garden Mediterranean Climate Zones weeds come from nearly all parts of the globe, including particularly western and central Asia, Russia & Europe  They were introduced through human activity, both accidentally and intentionally, including by gardeners. Percentage of invasive plants accidentally or intentionally introduced to California. © Project SOUND
  • 8. Weeds tell a story….  Type of soil – some prefer certain soil characteristics  Available light  Soil nutrient levels (low or high)  Watering practices  Cultivation practices – how much the soil is disturbedTo know a weed is tolearn about your garden –  And many other thingsand to understand how tocombat it! © Project SOUND
  • 9. The more you know about your garden’s own weeds, the better youwill be able to deal with them © Project SOUND
  • 10. In the garden (and in the operating room), first do no harmYour plan to combat weeds should be reasonable andenvironmentally friendly © Project SOUND
  • 11. Integrated Pest Management (IPM) "Optimum combination of control methods including biological, cultural, mechanical, physical and/or chemical controls to reduce pest populations to an economical acceptable level with as few harmful effects as possible on the environment and nontarget organisms." R.L. Hix,CA Agric. Magazine, 55:4 (2001) © Project SOUND
  • 12. The IPM Pyramid – ‘first do no harm’  Use the least invasive – and often most effective - means first:  Prevention – cultural practices  Mechanical Controls  Naturally occurring biological controls (native)  Consider using non-native biological controls (herbivores; diseases)  Use chemical controls sparingly, as a last resort: Non-native and chemical controls may  Naturally occurring elements have the important drawback of non-  Biologics – chemicals made specificity – they kill the good species by plants that are toxic to weeds along with the bad.  Non-biologic herbicides © Project SOUND
  • 13. An IPM system is designed around six basic components1. Set Action Thresholds  Before taking any pest control action, IPM first sets an action threshold, a point at which pest populations or environmental conditions indicate that pest control action must be taken. The level at which pests will either become an economic threat is critical to guide future pest control decisions.2. Monitor and Identify Pests  Not all insects, weeds, and other living organisms require control. IPM programs work to monitor for pests and identify them accurately, so that appropriate control decisions can be made in conjunction with action thresholds. This monitoring and identification removes the possibility that pesticides will be used when they are not really needed or that the wrong kind of pesticide will be used.3. Preventive Cultural Practices  As a first line of pest control, IPM programs work to manage the crop, lawn, or indoor space to prevent pests from becoming a threat. These control methods can be very effective and cost- efficient and present little to no risk to people or the environment. © Project SOUND
  • 14. An IPM system is designed around six basic components4. Mechanical controls: Should a pest reach an unacceptable level, mechanical methods are the first options to consider. They include simple hand-weeding, erecting weed barriers, and tillage to disrupt breeding.5. Biological controls: Natural biological processes and materials can provide control, with minimal environmental impact, and often at low cost. The main focus here is on promoting beneficial herbivores that eat target pests. Use of plant pathogens – ones specific to the weeds of interest - also fits in this category.6. Chemical controls: Synthetic pesticides are generally only used as required and often only at specific times in a pests life cycle. Many of the newer pesticide groups are derived from plants or naturally occurring substances (e.g.: allelopathic analogues), and further biology-based or ecological techniques are under evaluation (particularly for agriculture, forestry applications). © Project SOUND
  • 15. Integrated Pest Management (IPM) applies to weeds as well as other pests  Set Action Thresholds  Does your entire yard need to be weed free? Choose an area and focus on it.  Prioritize weeds by invasiveness  When to take action against specific weeds  In general, a smaller weed is easier to remove than a larger one  In general, you want to remove a weed before it flowers & sets seed © Project SOUND
  • 16. If you can, do a little bit – but do it consistently Weeding just 15-30 minutes a day is often all that’s needed © Project SOUND
  • 17. Integrated Pest Management (IPM) Monitor and Identify Weeds  Get to know the ‘weed seasons’ of your yard:  Cool-season weeds sprout any time from fall through spring. They flower in late spring/early summer. The plant may disappear during the hot dry summer, but you’ll see even more of germinating seedlings the following fall. Cool season weed  Examples: Annual Bluegrass, BermudaAnnual Bluegrass – Poa annua Buttercup; Mustards; Clovers; Cheeseweed  Warm-season weeds tend to start growing in the spring and hang around all through the growing season.  Examples: Crabgrass; Bermuda Grass; Kikuyu Grass; Fountain Grass; Spotted Spurge; Bindweed; Nutsedge;  Any season – some species grow all year long in our climate Warm season weed  Examples: Creeping Woodsorrel (Oxalis) ; Crabgrass – Digitaria species © Project SOUND
  • 18. Climate change: long periods of hot weather during winter rainsFavors growth of many weeds: jump-start on growth seasonExample: Panic Veldt Grass - Ehrharta erecta © Project SOUND
  • 19. Integrated Pest Management (IPM) Monitor and Identify Weeds  Get to know the geography of your garden’s weeds  Areas prone to weeds require special monitoring & early intervention  Discovering geographic patterns may suggest changes in gardening practices – decreasing water to the area; increased hand-weeding frequency; etc.  Know that wildlife (birds, etc) will bring seed into your yard. Be extra vigilant in areas where they eat, perch etc.Oxalis/ Creeping WoodsorrelOxalis corniculata © Project SOUND
  • 20. Each garden is unique: garden weeds in context  Soil (including previous amendments)  Light & water  Gardening practices: tilling, raking, mulches, ‘top soil’, hired gardener’s practices  The age of the garden (or part of the garden)  Previous (and current) plants  Weeds that hitch-hike in with purchased plants  Invasive garden plants [ivy; bamboo; dichondra; etc] Dichondra  What’s growing nearby:Dichondra micrantha  Birds bring seeds; seeds blow(Dichondra repens)  Weeds grow into the yardWe will introduce you to some general principles, strategies and toolsthat you can apply to your own situation © Project SOUND
  • 21. Garden weeds may vary widely from year to year…  Example: Shepherd’s Purse (Capsella bursa-pastoris)  Why?  Conditions are right for germination of dormant seeds; temperature; rainfall  Seeds survive up to 35 years in undisturbed soils  When conditions are right – they are ready  New seeds may have been brought in by gardening practices  New seeds may have come in through natural means; wind, birds, etc. © Project SOUND
  • 22. The Weed IPM plan for your garden – a work in progress  Requires observation & knowledge – specific for your garden  Will vary somewhat with:  Yearly weather conditions  Maturity of plants  New plants, and other changes to the garden  Will be modified based on your previous experiences  Suggestion: keep a garden notebook/journal © Project SOUND
  • 23. Identifying weeds  Proper weed identification may be your hardest task.  Flowering and growing patterns are of great importance as most weeds are classified as either annual, biennial, or perennial.  The color, shape, and placement of the flower on the weed will also aid you in identifying the weed.  Take pictures of the weeds – or collect and Kikuyu grass press them - as you find them; makes Pennisetum clandestinum identifying and recognizing weeds much easier.  Try to find them on-line, in books or have them identified by an expert (County agriculture extension; local weed control district).  If “new” or unfamiliar weeds appear, have them identified quickly and take appropriate control measures if necessary © Project SOUND
  • 24. Great resources on-line & in books © Project SOUND
  • 25. Identifying weeds is key to your weed strategy  Knowing the ID of a weed will tell you:  Growth pattern – annual or perennial weed  Cool/warm season weed – when to look for it  How it likely enters your garden – suggests ways to prevent this  Useful mechanical/physical controls  Chemical controls (if needed)Kikuyu grass is used for lawns © Project SOUND
  • 26. Integrated Pest Management (IPM) Preventive Cultural Practices The first line of defense against all weeds is good prevention General goals:  Prevent the introduction of weeds into the garden  Prevent the spread of weeds in the garden  Promote the health & vigor of desired species ‘An once of prevention is worth a pound of cure’ – simple preventive practices can save you serious gardening headaches © Project SOUND
  • 27. Common Purslane - Portulaca oleracea  Characteristics:  Succulent foliage (healthy edible; probably should be grown as a garden vegetable)  Grows in moist areas (usually)  Summer (warm season); origin - Asia  Growth form: herbaceous annual  How it spreads: seeds (> 50,000 per plant; stem pieces  Control Methods:  Solarization for pre-planting removal.  Mulch & dry conditions usually prevent it from establishing  Easy to pull or hoe, but pieces of stem can re-root readily, so be sure to remove them from the garden. © Project SOUND
  • 28. Prevention/Cultural Practices – avoidance/ prevention is key  Avoid introducing new weeds into the garden:  Use only weed-free mulch, topsoil, other amendments (if any); beware of ‘free’ material unless you know it will not contain weeds/weed seeds  Check new plants to be sure that weeds are not ‘hitchhiking’ in the pots  Be sure to not bring weed seeds into garden on your clothes, shoes, etc. © Project SOUND
  • 29. Cultural practices: just good old garden management practices  Sanitation  Clean equipment (including lawnmowers) to prevent spread of weed seeds/cuttings  Weed Disposal:  Annual weeds can be composted if they are not in seed.  Place perennial weeds in a garbage bag, solarize (leave bag in sun) & dispose of them in green waste.Note: a ‘hot’ compost bin will killsome – but not all – weed seeds,  If any weed is a big problem in yourso be cautious garden, think twice before putting it in the compost pile. © Project SOUND
  • 30. Cultural practices: good garden management  Keep garden plants healthy; help them to out-compete the weeds  Plant native plants densely enough to crowd out weeds  Choose native plants that:  Are vigorous growers – will out- compete the weeds  Will prevent weeds from growing by:  Providing too much shade  Producing allelopathic chemicals that either inhibit weed seed germination or weed growth: examples: Salvias?, Chamise, Manzanitas, CA Walnut,Purple Sage – Salvia leucophylla probably other CSS species © Project SOUND
  • 31. Integrated Pest Management (IPM) Physical Prevention – 2nd line of prevention  Weeds have growth requirements - like any other plant:  Water  Correct amount of light  Correct temperature  Appropriate nutrients  Prevent seed germination & seedling growth by limiting the weed’s access to ‘growth requirements’  Remember: limit any one of these and you’ll significantly decrease the ability of a weed to take over your gardenBlack Nightshade - Solanum nigrum © Project SOUND
  • 32. Fortunately, weeds need water to germinate and grow  Water-wise gardening methods will limit some weeds, simply by decreasing available water  Particularly helpful for shallow- rooted weeds  Also useful for ‘weeds of wet places’ – will not survive in dry soil  Use target watering methods – water only the plants you want (drip; hose)  Be patient – first couple of years, when you need to water shrubs more, are the worstBroadleaf Plantain - Plantago major © Project SOUND
  • 33. Broadleaf Plantain – Plantago major  Characteristics:  Large leaves from basal rosette; originally brought from Europe as medicinal plant  Usually in damp area of garden  Growth form: herbaceous perennial  How it spreads: seed  Control Methods:  Crowd out; needs bare soil to germinate, grow  Decrease water; aerating the lawn will also help.http://www.wildflowers-and-  Dig out before they set seed. Be sure to remove as much of the roots as possible - regrow from any pieces of the fibrousYou can use your knowledge of rootstalk that remain in the soil.a weed’s growth requirementsto save time and effort  Chemical control -spot-treat with glyphosate (Roundup), taking care not to get the chemical on desirable plants. © Project SOUND
  • 34. Before planting a new area…prevention almost always better than control  Kill weed plants & seeds  Solarization  Chemical methods  Turn the soil as little as possible – avoid bringing up buried weed seeds  Control weeds before installation – always less work in the long run  Be patient – the more weeds/seeds are removed before installation, the fewer you’ll have to pull later Bermuda Grass Cynodon dactylon © Project SOUND
  • 35. Understanding seeds: what seeds need to germinate  Water – need to ‘re-hydrate’ before seedling can start to grow  Light (small seeds, including many weeds) or dark (larger seeds) Virgin’s Bower - Clematis ligusticifolia  Correct temperature; may be warm Native plant – requires cold treatment or cool – and may be a rather narrow range. In general, weeds tend to have larger ranges, but many are ‘warm season’ or ‘cool season’ weeds  Other factors (heat; smoke; cold pre-treatment, etc): in general, Oxalis/ Creeping Woodsorrel weed seeds have few of these – it’s Oxalis corniculata one of the reasons they are so Weed – no special requirements successful © Project SOUND
  • 36. Key preventive method: blocking sunlight so light-requiring seeds can’t germinate  Mulches  Organic  Inorganic  ‘Weed block’ methods  Planting natives that will create shade © Project SOUND
  • 37. Why barrier methods work: several effects  Block light, preventing seed germination  Physically prevent seedling growth  Reduce soil temperature – particularly in spring – delay emergence  Increase soil moisture below the barrier – too much for some species (seeds & seedlings rot)  Decrease moisture above the barrier – too dry for germination  Chemical compounds released from barriers/ mulch may inhibit germination and/or kill seedlings © Project SOUND
  • 38. Plastic weed barrier cloth (weed block) – is it good for native plant gardens? Arguments for Arguments against  Doesn’t stop all weeds from growing Stop some weeds seeds  Weeds grow through the holes cut for from germinating; blocks planting light & forms physical  Weeds grow through/on top of the barrier barrier cloth Relatively easy to install  Cloth gets clogged over time – becomes a water barrier  Can promote stem & root fungal disease in trees & shrubs; interferes with proper drainage  Doesn’t allow groundcover plants to root – or for successful re-seeding  Hard to keep from looking unsightly- even under mulch  Can’t be used well on slopes or other uneven terrain © Project SOUND
  • 39. Physical barriers have their place  Weedblock (plastic or other)  Under pathways  Under patios, sitting areas (hardscaped areas)  Other areas where planting is not an option  Other physical barriers (e.g., mowing strip, heavy metal or wood strip set on edge) at shrub bed/turf interface to prevent turf and turf weeds from encroaching into planted beds You may also choose more eco-friendly barriers © Project SOUND
  • 40. Eco-friendly ‘weed block’ choices  Newspaper (use a good thickness to block light)  Cardboard  Degradable weed block materials – most are paper-based ‘Garden Trail’ weed block © Project SOUND
  • 41. What kinds of seeds are susceptible to ‘dark inhibition’?  annual species that are small- seeded and have a light requirement for germination such as common lambsquarters‘Garden Trail’ weed block and pigweeds are sensitive to surface barriers  large-seeded annuals and perennial weeds are relatively insensitive to the darkness; however barriers/mulches still provide mechanical barriers to seedling growth. © Project SOUND
  • 42. Mulch – the best surface physical barrier for native plant gardens  Kind of mulch  Should be appropriate for the native plants you’ve planted  Organic (bark, etc) for most local shrubs/trees  Inorganic for Coastal Prairie (wildflowers) and desert plants  Must be course enough texture to allow the mulch surface to dry out  Depth of mulch layer  Must be deep enough to preventLesson: geography of weeds light from reaching the seedssuggests that mulch layer may be beneath it.too thin at the edge © Project SOUND
  • 43. IPM plan changes through the life of a garden/bedPre-planting: Prevention/removal Years 1-2: Monitoring & Removal © Project SOUNDPre-planting: Prevention/practices
  • 44. Knowing the life cycle of weeds is key to your plan  Knowing the ID of a weed will tell you:  Growth pattern/life cycle – annual, biennial or perennial weed  Cool/warm season weed – when to look for itAnnual weed – Gnaphaleum sp.  How it likely enters your garden – suggests ways to prevent this  How it spreads  Useful mechanical/physical controls  Chemical controls (if needed) Perennial weed - Oxalis pes-caprae © Project SOUND
  • 45. Annual, Biennial & Perennial Weeds Short-lived (fixed) Spreading Character Annuals perennials or perennials biennials Vegetative < 1 year 2 to a few years Long, indefinite lifespan Vegetative No Accidental Yes reproduction Seed longevity Years to decades Years to decades A few years Energy allocated to seed High Medium high Low production Establishment Seeds Seeds Mainly vegetative Usual means of In soil, manure, Soil, wind, feces, In soil dispersal equipment, wind crop seed Lambsquarters, Quackgrass, Examples Dandelion Annual Bluegrass bindweed © Project SOUND
  • 46. Annual weeds  Spread by seed. They may self-seed or they may be brought into the garden by wind, water, birds, animals or people.  The most important way combat annual weeds to prevent more seeds from developing. Annual weeds are phenomenally prodigious seed producers.  A single crabgrass plant, for example, can produce 100,000 seeds  If you dont get rid of these intruders before they develop viable seeds, the number of weed plants will increase every year,  Examples of annual weeds include: bindweed, chickweed, crab grass, knotweed, lambs-quarters, mallow, pigweed, purslane, speedwell, spurge and yellow oxalis  Your strategy: kill before they flower Annual Sowthistle & set seed Sonchus oleraceus © Project SOUND
  • 47. Annual weeds, ancient wisdom  Getting weeds out of the garden at the start of the season, when theyre most vulnerable, is a smart strategy: it is easiest then & it keeps annual weeds from forming seed heads © Project SOUND
  • 48. Puncture vine - Tribulus terrestris  Characteristics:  Sharp, thorny burs  Grows in dry areas of garden  Growth form: herbaceous annual  How it spreads: seed  Control Methods:  Prevent introduction: sanitation  Hoe or dig plants before they can set seed; cut below the crown to prevent regrowth.  Chemical control: pre-emergence herbicides containing trifluralin or pendimethalin may be used on some lawn grasses and ornamentals. For post-emergence control in lawns, use a selective herbicide containing MCPA, MCPP, and dicamba. © Project SOUND
  • 49. Vigilance is the key  The only way to control annual weeds is to get rid of them before they go to seed. Luckily annual weeds are very often shallow rooted and can be easily hand pulled or cut off with a hoe.  Hopefully you will see less and less annual weeds as the season goes along, but new seeds will always find their way in and some seeds remain dormant in the soil until ideal conditions present themselves and they germinate, so weeding is an ongoing process.If you get in the habit of doing a little weeding each time youwork in your garden – or even every day - it won’t become anoverwhelming task (this is known as the ‘Bradley Method’. © Project SOUND
  • 50. Crabgrass - Digitaria species  Characteristics:  Thrives in hot moist areas – lawns, flower gardens  Shallow-rooted  Growth form: annual grass  How it spreads: seed  Control Methods:  Pull before it sets seed.  Water deeply, but infrequently; this tactic will dry out crabgrass roots, killing the weeds or at least diminishing their vigor.  Solarization can control crabgrass if high temperatures are achieved. © Project SOUND
  • 51. Crabgrass - Digitaria species  Control Methods:  For chemical control in lawns and around ornamentals, use a pre- emergence herbicide such as trifluralin; apply it in late winter to early spring, depending on when crabgrass germinates in your zone (a local nursery or your Cooperative Extension Office can provide this information). For post-emergence control around ornamentals, apply fluazifop-butyl or sethoxydim. © Project SOUND
  • 52. Control methods: mechanical  Hoeing is by far the easiest  Draw Hoe - the familiar flat- bladed hoe works best when pulled. With a sharp blade, you can make quick work of the long rows between vegetable crops.  Warren Hoe - has a pointed bladerics_3.htm heart-shaped blade that is usually used for creating furrows but also works well for small weeds and weeding between rows.  Scuffle, Stirrup, Hoola or Dutch Hoe - Cuts weeds at the surface in a push/pull motion. Easy to use and nice for covering a larger area. © Project SOUND
  • 53. Control methods: mechanical © Project SOUND
  • 54. Control methods: mechanical  Hand pulling/digging  Good for small numbers of weeds  Allows you to get the roots out (important for some perennial weeds)  The easiest and most convenient weeder is your hand.  It becomes second nature to yank a weed or two every time you walk outdoors.  Hand pulling is also the best method for a densely planted garden bed that has been neglected.  Wide variety of hand tools – try them out to see what works best for you © Project SOUND
  • 55.  The Heart Hoe with its singleClassical weeding tools edge thin blade is for ridding your garden of unwanted weeds and roots. It also is handy for weeding the cracks in the sidewalk and driveway.  The Claw is excellent for cultivating flower beds and vegetable gardens.  The Cape Cod Weeder has an angled blade that removes weeds below the surface of the soil. This tool will also handle those weeds in the cracks of sidewalks and driveways.The Weed Slicer (Dutch Hoe) cuts off weeds at the roots with little soil disturbanceThe Diamond Hoe has an unique diamond-shaped blade for cultivating soil, dislodgingweeds and roots, or breaking up clumps of dirt.The Trowel is for digging; The Transplanting Trowel has a narrower blade for precisedigging in any garden. It is very good for tight spaces, planting bulbs or fittingtransplants into a full bed.The Dandelion Weeder is for getting under weeds with tap roots, like dandelions, andprying them out. © Project SOUND
  • 56. Spotted Spurge - Chamaesyce (Euphorbia) maculata  Characteristics:  prostrate, often forming dense mats  Broken stems emit a milky sap  Growth form: herbaceous annual (summer)  How it spreads: seed  Control Methods:  Prevent it’s entry into the garden – good prevention methods  Solarization prior to planting to kill seeds  Mulching to prevent germination  Hand pulling  Only if these fail do you resort to chemical methods © Project SOUND
  • 57. Annual Bluegrass - Poa annua  Characteristics:  Bunching grass  Great seeder  Growth form: annual grass (cool-season)  How it spreads: seeds  Control Methods:  Avoid bringing into garden – particularly in nursery pots, on equipment, clothing  Mulch - coarse, thick to block light  Limit water; Zone 2 or 1-2 – has shallow roots  Mechanical weeding – before it seeds  Chemical methods – often not needed © Project SOUND
  • 58. Integrated Pest Management (IPM) Mechanical/Physical Controls – other  Flaming  Done with a high flame temp. torch;  Plants are not burned but ‘boiled’  Not very effective with grasses  Be careful to not ignite mulch  Foaming –  Hot-foam and steaming is mainly done by professionals; cool foams are available (Weed B Gon & others)  Good selectivity – can ‘spot kill’  No fire danger  Can’t use near water; kills fish  Boiling water – good for weeds in pavement © Project SOUND
  • 59. Integrated Pest Management (IPM)Mechanical/Physical Controls, cont.  Mowing/cutting (e.g., ‘weed-whacking’)  Good in large areas; better than nothing  Ok for annuals prior to seeding; not so helpful for perennials  Tilling  Keep to a minimum – brings up new seeds in our climate  Newer technologies  Lasers – now being tested in agriculture © Project SOUND
  • 60. Consider buying some good tools  If you do a lot of weeding you’ll grow to appreciate a good tool – works well & easier on the body Radius Garden Weeder © Project SOUND
  • 61. What the pro’s like….  Asparagus knife  Hori-hori knife  Fiskars ‘Big Grip Knife’ (~$10) © Project SOUND
  • 62. Perennial Weeds  Live more than a single season.  Usually reproduce both by seeds and vegetative reproduction (underground root systems (rhizomes) and/or sending out runners (stollons) aboveground.  Are the most difficult to get rid of in the garden.  Examples include: bindweed, nutsedges, dandelion, dock, ground ivy, horsetail, Japanese knotweed, plantain, poison ivy, Bermuda grass, etc.  some weeds that are annuals in other climates are short-lived perennials in ours (Ex: Cheeseweed) © Project SOUND
  • 63. Cheese Weed - Malva neglecta  Characteristics:  long, tough taproot  Growth form: herbaceous short-lived perennial (in our climate)  How it spreads: seed  Control Methods:  Hoe or pull these weeds when theyre young.  Chemical control:  pre-emergence herbicide containing isoxaben to prevent seedlings from becoming established in lawns and around ornamentals.  post-emergence control in lawns, use a product containing MCPA, MCPP, and dicamba.  Spot-treat young weeds with an herbicide containing glufosinate-ammonium or lyphosate, avoiding contact with desirable plants. © Project SOUND
  • 64. Some weedy invasive perennial grasses spread viaseed alone Pampas Grass - Cortaderia selloana Fountain Grass – Pennisetum setaceum Mexican Feather Grass – Nassella (Stipa) tenuisima © Project SOUND
  • 65. But most have modified roots & stems that help them to thrive Runners (stolons): A well known example of that would be crabgrass. It spreads with creeping stems that grow along the ground. Buds along the runners produce plantlets that root and spread very quickly Roots or Rhizomes: Quackgrass would fall into this category. It has tough, white rhizomes that look like roots and are very sharp. Weeds that spread by roots or rhizomes can regrow after being cut back. Even chopped up pieces of root or rhizome may regrow. Bulbs and bulbils: An example of this is a spiky grass called nutsedge. It has tubers or little bulbs that break off when you pull the grass therefore never eliminating the plant. They can pop up over night (again and again and again...!). © Project SOUND
  • 66. Weeding Perennial Weeds If you catch them young, perennial weeds can usually be pulled out of the ground easily. Once established, they can be next to impossible to get rid of, as anyone who has battled Bermuda grass or yellow nutsedge in flower beds will attest. With perennials, it is essential to get all of the plant out of the ground. When perennial weeds are tender seedlings, they can usually be pulled up by hand with ease, especially when the soil is moist. But the more time you allow these weeds to take hold, the harder they are to eradicate. The least bit of Bermuda grass rhizome left behind can sprout into a new plant. The best time to weed is shortly after a rain or an irrigation cycle. Hand-pulling is the quickest method. If the weeds dont yield easily or if they detach from the roots when you pull, switch to a trowel or dandelion weeder and dig or pry them out. © Project SOUND
  • 67.‘Weed Twister vs. Tree of Heaven © Project SOUND
  • 68. Special management strategies for perennials  Exhaust the roots by continual cutting/hoeing  Remove roots/rhizomes or other reproductive organs from the soil © Project SOUND
  • 69. Burmuda Buttercup : Oxalis pes-caprae Hoeing and tilling are not good choices for removing perennial weeds. Hand weeding will work if you are very thorough about getting the whole plant and root system. Sometimes herbicides are the only solution for eradicating tough perennial weeds like poison ivy, ground ivy and brambles. © Project SOUND
  • 70. Yellow (Creeping) Woodsorrel - Oxalis corniculata  Characteristics:  Very aggressive invader  Sun or shade  Growth form: herbaceous perennial with fleshy taproot  How it spreads: seed (propelled to 6 ft); shallow, spreading root system  Control Methods:  Dig out small plants before they set seed.  Water deeply but infrequently © Project SOUND
  • 71. Yellow (Creeping) Woodsorrel - Oxalis corniculata  Control Methods:  For chemical control, use a pre- emergence herbicide containing oryzalin or pendimethalin to prevent seeds from germinating and becoming established. Spot- treat oxalis in garden areas with glyphosate, taking care to avoid contact with desirable plants © Project SOUND
  • 72. Integrated Pest Management (IPM) Biological controls The use of plant-feeding insects, pathogens, or diseases that are host- specific to a noxious or invasive weed species, with the intention of suppressing the weed’s population to an acceptable level. Biological control does not intend to eradicate the target weed species, but instead is used to bring the plant into balance with the rest of the landscape. It is important to note that successful biological control agents are specific to the plant they are intended to control. In other words, the biological control agent feeds and develops only on the intended weed species. Therefore, the risk to other plants and organisms in the ecosystem is minimal. Examples:  Large herbivores: sheep, goats  Weed-specific pests (insects)  Example: releasing weevils that eat the seed of musk thistle; Releasing an insect whose larvae eat the roots of the weed. -Releasing a round worm (nematode) or a mite that causes a gall (swelling) on the plant. -Infecting the weeds with specific fungi that damage that weed.  Potential problems: loss of specificity; toxicity of other control methods to the insects  Weed-specific diseases  Example: Puccinia rust can be used to control nutsedge Lots of interest/research but not much application to garden yet © Project SOUND
  • 73. Integrated Pest Management (IPM) Chemical controls  Non-biologics  Vinegar mixed with a little dish soap  Non-selective – don’t get it on things you want  Works best on young weeds  Salt – best for weeds in pavement  Biologics  Example: AAL-Toxin (isolated from the pathogenic fungi, Alternaria a lternata f. sp. lycopersici ) - Highly susceptible species include such important agricultural weeds as black nightshade © Project SOUND
  • 74. Control methods: ‘Safe Organic’ pre- emergents with corn gluten meal  ‘Safer ‘Concern’ - Contains corn gluten meal (84%) and sulfate (16%)  Application Recommendations:Apply 10-20 lbs. per 1000 square feet in the Spring & Fall for pre-emergent protection. Weed Prevention Plus is granulated and easy to apply with a spreader or you can apply with the 5 lb. shaker bag to small garden areas. Homogenous pellet provides uniform nutrient and herbicide distribution. This product can also be applied as a regular nitrogen fertilizer in the Summer.  Recommended for the control of curlydock, purslane, clover, dandelions, crabgrass and many other common weeds. Proper application provides up to 90% effective weed control in the first year for dandelions and crabgrass. Safe for children, pets and wildlife immediately after application. Can be applied at any time without burning. Water thoroughly after application then allow to dry for 2-3 days. © Project SOUND
  • 75. Some pesticide definitions Preemergence Herbicides  Preemergence herbicides affect germinating seeds.  To be effective, the herbicide should be applied two to three weeks before weed seeds germinate.  Consequently, preemergence herbicides are most effective against annual weeds. Postemergence Herbicides  Postemergence herbicides are used to kill weeds after the weed plants are up and growing.  To be effective, most postemergence herbicides must be absorbed through the leaves; consequently, liquid sprays generally work better than dry, granular materials.  Postemergence herbicides are most effectively applied when weeds are young and growing vigorously.  For some weeds, repeated application at 20–30 day intervals may be required for control. © Project SOUND
  • 76. Some pesticide definitions  Selective postemergence herbicides  are usually used to control annual, biennial, and perennial broad-leaved weeds because they will kill many broadleaf plants without damaging grass plants.  There are also selective herbicides that kill only grasses  Nonselective postemergence herbicides  kill all plants, both desirable and undesirable.  These herbicides can be used to spot treat perennial grassy weeds that are not affected by selective herbicides.  To spot treat an area, thoroughly wet the weed foliage with herbicide solution. © Project SOUND
  • 77. How do herbicides work Pre-emergent Post-emergent  Block key chemical pathways in the plant: plant hormones; chemicals needed for photosynthesis  Inhibit basic cell functions: cell division; production of key chemicals © Project SOUND
  • 78. Herbicides: pre-emergent  Last 6-12 months © Project SOUND
  • 79. Herbicides – post-emergent © Project SOUND
  • 80. Yellow nutsedge - Cyperus esculentus  Characteristics:  Looks like a sedge  Grows in moist areas  Growth form: perennial sedge (summer)  How it spreads: seed; tubers (nutlets) from roots  Control Methods:  Remove when young ― < 6 inches tall. Older, taller plants are mature enough to produce tubers; when you dig or pull the plant, the tubers remain in the soil to sprout.  For chemical control, try glyphosate, being careful not to get the chemical on desirable plants. It is most effective when the plants are young; it will not kill tubers that have become detached from the treated plant © Project SOUND
  • 81. Bindweed - Convolvulus arvensis  Characteristics:  Also called wild morning glory, bindweed grows in open areas usually in loam to clay soils  Growth form: perennial vine from deep root  How it spreads:  Bindweed is deep rooted, so pulling usually doesnt eradicate it ― the stems break off, but the weed returns from the roots.  Control Methods:  Dig the roots out repeatedly (persistence is required).  Prevent seeding: hard-coated seeds can sprout even after lying dormant in the soil for 50 years! © Project SOUND
  • 82. Bindweed - Convolvulus arvensis  Control Methods:  For chemical control, you can use a pre- emergence herbicide containing trifluralin around ornamentals. In midsummer, when bindweed is at the height of its growth season but has not yet set seed, spot-treat isolated patches with glyphosate, taking care to avoid contact with desirable plants. If the weed is twined around desirable plants, detach it before treating. Repeated applications are usually needed to destroy the root system. © Project SOUND
  • 83. Bermuda Grass - Cynodon dactylon  Characteristics:  A fine-textured and fast-growing perennial, frequently planted as a lawn  Growth form: perennial grass (summer)  How it spreads: spreads by underground stems (rhizomes), above ground runners (stolons), and seed.  Control Methods:  If you have a Bermuda grass lawn, use deep barriers or edging to prevent it from advancing into other parts of the garden. © Project SOUND
  • 84. Bermuda Grass - Cynodon dactylon  Control Methods:  Dig up stray clumps before they form sod, being sure to remove all the underground stems; any left behind can start new shoots. Repeated pulling and digging are generally necessary to stop this weed; mulches will slow it down, but it eventually grows through most of them.  For chemical control, you can use a selective herbicide containing fluazifop- butyl or sethoxydim, which can be sprayed over some ornamentals. Spot- treat actively growing Bermuda grass with glyphosate, taking care not to get the chemical on desirable plants. © Project SOUND
  • 85. Other weedy grasses that spread via seed and rhizomesQuack grass - Elytrigia repens Panic Veldt Grass - Ehrharta erecta Kikuyugrass - Pennisetum clandestinum © Project SOUND
  • 86. Safety precautions when using herbicides Read and follow all package instructions Provide adequate ventilation and wear a respirator, rubber gloves, goggles, and protective clothing when handling. Remove contaminated clothing and launder prior to reuse. Shower after completing the job. Wash hands with soap and water before eating, smoking, or using the toilet. Store in a secure, dry, well-ventilated, separate room, building or covered area © Project SOUND
  • 87.  Most herbicides become less effective when a plant is under stress. Along with crops, most weeds are also experiencing water stress under current conditions. Therefore, you may have to wait until the soil is fairly moist before applying any systemic herbicides (e.g., Roundup) to manage weeds. Most systemic herbicides perform better under conditions that are ideal for weed growth. When the plants are free of stress, herbicides are absorbed faster and move better within the plant system, providing more efficient kill. © Project SOUND
  • 88.  Fall is a good time to apply systemic herbicides to manage perennial weeds. These weeds have perennating organs like rhizomes and stolons that help them persist year after year. Development of these organs usually occurs during the early fall. During a drought, it is possible that drought tolerant perennial weeds are more prevalent in fields than annual weeds. Therefore, fall may be a good time to apply a systemic herbicide (an herbicide that is absorbed and moved within the plant tissues). A non-selective systemic herbicide like glyphosate could be applied as a spot application. Grass killers (graminicides) like sethoxydim, clethodim or fluazifop may also be applied during fall to manage perennial grasses. The main key to control of perennial weeds is application of glyphosate, dicamba (Banvel), and/or 2,4-D when they are are in the bud to bloom stage, or as late in the fall as possible before the weeds senesce or growth ceases due to frost or freeze. At this growth stage, the weeds will move herbicide throughout the plant and into the roots, resulting in maximum kill of the entire plant. The best opportunity for making this type of application is during the late-summer through fall after wheat harvest when plants have grown undisturbed for several months. © Project SOUND
  • 89. Potential problems with use of herbicides Cost Herbicide-resistant weeds. The evolution of "superweeds" capable of resisting herbicides © Project SOUND
  • 90. Summary: Identifying a weed will allow you to choose the best strategy to prevent its spread Annual weeds – reproductive strategy: seeds  Key – prevent seed production Biennial/non-spreading weeds – reproductive strategy: seeds  Removal (mechanical best) – hopefully when young (year 1)  Prevent seed production – year 2 Perennial weeds – reproductive strategy: seeds, vegetative  Removal – hopefully when young (year 1)  Prevent seed production and/or other primary means of reproduction  May need to use chemical controls – but only after other means are exhausted  Use UC IPC website for up-to-date management recommendations © Project SOUND
  • 91. Advice from pros: The ABC’s of Weeding  Learn how the weeds spread (root system or seed dispersal) to understand when and how to handle them.  Keep cultivation/tilling to a minimum  Get the weeds early before they flower and go to seed.  Get ‘em while they’re small.  Frequent, short weeding sessions are the best way to stay on top ofRepetition is the key to weeds. Not only does this eliminate acombating persistent weeds. long, tiring weeding session, it alsoEven tough weeds such as lets you dispatch weeds while they’rebindweed and kikuyu grass can still small and easy to brought under control with  Weed wet. Weeding goes faster andcareful and fastidious weeding easier when the soil is moist thanpractices. when the soil is dry © Project SOUND
  • 92. What is a noxious weed?  Invasive alien plant: an invasive unwanted non-native plant  According to The Flora of North America, the most comprehensive reference on this continents plants, one-fifth to one-third of all species growing north of Mexico have come from other continents.  Noxious weed: any species of plant which is, or is likely to be, detrimental or destructive and difficult to control or eradicate  We are located in the Los Angeles Weed Management area – report noxious weed infestations to them © Project SOUND
  • 93. Comparison of common weedy plants and invasive plants. Agricultural or garden weeds Invasive plantsIntroduction Usually accidental by people, Can be accidental, but more often animals, equipment, or seed the original intention was for contamination. ornamental or aquarium use, or for forage, food, fiber, medicinal, or soil stabilization purposes.Disturbance Require human disturbance to Benefit from human disturbance, but establish and persist. disturbance not required.Persistence Will not persist without human Once introduced, plants survive and disturbance, usually soil tillage or spread on their own without further irrigation. human assistance.Life form Primarily terrestrial annuals or All growth forms, including aquatic, herbaceous perennial species. climbing vines, parasitic, herbaceous, or woody plants. Can have annual, biennial, or perennial life cycles. © Project SOUND
  • 94. In natural areas (and in your garden ecosystem), noxious weeds impact native ecosystems by:  Reducing biodiversity  Altering hydrologic (water) & soil conditions  Altering fire intensity and frequency  Modifying successional pathways  Competing for pollinators  Displacing rare plant species  Replacing complex communities with simple communities Grass – Bromus tectorum © Project SOUND
  • 95. Characteristics of invasive plants: general  Fast, aggressive growth that robs soil, water and nutrients from desirable plants nearby.  Quick adaptation to the existing environment.  Ability to thrive in disturbed areas (wet or dry) and poor soil.  Resistance to heat and drought.  Deep, strong roots making them difficult to eradicate.  Lack of natural pest or predator. Invasive species seldom show signs of disease or pest damage.Coast Acacia – Acacia cyclops  Some invasive species are able to produce toxins that inhibit competitors growth. © Project SOUND
  • 96. What you can do about invasive weedy plants in S. CA 1. Know what species are a problem in your area 2. Get rid of these plants in your yard 3. ‘Don’t Plant a Pest’ 4. Report infestations 5. Lobby to get weedy pest plants out of the horticultural trade © Project SOUND
  • 97. Where to learn more about invasive plants… © Project SOUND
  • 98. Don’t Plant a Pest  Iceplant/hottentot fig (Carpobrotus edulis)  Ivy (Hedera spp.)  Periwinkle (Vinca major)  Pampas grass (Cortaderia selloana)  Fountain grass (Pennisetum setaceum)  Scotch, French, Portugese, bridal, and Spanish brooms  Acacia/western coastal wattle (Acacia cyclops) Acacia  Myoporum (Myoporum laetum)  Mexican fan palm (Washingtonia robusta)  Canary island date palm (Phoenix canariensis)  Brazilian pepper tree (Schinus terebinthifolius)  Blue-gum and red-gum eucalyptus (Eucalyptus globulus, E. camuldulensis)  Tree of Heaven - Ailanthus altissima © Project SOUND Myoporum
  • 99. I thought that was a native plant…  Some native plants can ‘take over’ and become weedy or invasive:  ‘groundcover’ natives that spread via rhizomes [Woodmints] or stolons [native strawberries]  Clonal species [Narrow-leaf Willow; some of the shrubby native mallows]  Plants that grow very fast [Calystegia]  Plants that reseed very well in your yard [grasses; some wildflowers]  Know the characteristics; plant where you take advantage of these characteristics – e.g., where you want them to take over © Project SOUND
  • 100. Climate change & invasive plants Gardeners may also have to cope with a new cast of characters. Some researchers are trying to identify exotic species with weed potential before they jump the garden fence - plants with windblown or bird-dispersed seeds, species that reproduce vegetatively through runners, generalists that thrive in a variety of habitats - and working with growers and nursery folk to make sure new invasives dont get into the horticultural trade. Climate change is a moving target, and some effects could turn out to be stronger than the models account for. Theres also no foolproof way to identify which plants will become invasives. But with weeds moving both in from wildlands and out into them, its safe to say that weed control will still be on every thoughtful gardeners agenda. © Project SOUND
  • 101. “When you want to shift your ch’i (energy), go to your garden and start pulling weeds.” © Project SOUND