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Weed Biology and Management

Weed Biology and Management

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Weed Biology and Management

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  1. Weed Biology and Management Curtis Rainbolt Extension Weed Scientist Everglades REC

  2. Weed Biology and its Impact on Management • What makes a plant a weed? • Cost of weeds • Why do weeds always win? Biology • Get to know the enemy • Anatomy of a weed • Common south Florida weeds • Strategies for weed management

  3. Definition of a weed: • A weed is an undesired plant out of place • Water hyacinth in a aquatic garden: not a weed • Water hyacinth clogging canals: a weed

  4. Weed impacts • Weeds are costly • $24 billion in agricultural crop loss • $3 billion in control costs Pimentel et al. 1999

  5. Weeds are costly • It is estimated that without control, sugarcane losses would be 50% from heavy infestations of fall panicum • In 2000, over $51 million was spent for weed control in US sugarcane

  6. Why do weeds always win? • Dormancy: broken when conditions favor survival • Rapid early growth and expansion • Early and fast root growth • Efficient uptake and processing of nutrients and water

  7. Why do weeds always win? • Ability to reproduce early in life cycle • Prolific seed production • Absorb resources in excess • Tolerate low levels of resources • Genetic and environmental adaptability • Ability to develop resistance to control measures

  8. Reproduction by seed • First infestation is dependant on seed • Estimates of the total number of weed seeds in the soil range from 4 million to 133 million per acre furrow slice

  9. Vegetative reproduction • Less longevity in soil than seeds • Very small structures can reproduce • Canada thistle: ¼” piece of root results in new plant • Torpedograss can reproduce from very small segments of rhizomes • Can be as prolific as seed production • Yellow nutsedge: 1,900 new plants and 18,000 tubers in one year from one plant

  10. Get to know the enemy: weed identification

  11. Weed identification goals • Impossible to learn the thousands of weeds found in Florida • Learn the primary weeds • Keep field notes • The goal is to learn how to identify a weed • Plant anatomy • Plant keys

  12. Weed classification: life cycles • Annuals- reproduce by seed only • Biennial: • Life cycle completed in two years • Flowering and fruiting in second year • Examples: wild carrot, cudweed • Perrenials: • Simple- reproduce by seed only • Creeping- reproduce by seed and vegetative propagules

  13. Differences between grasses and sedges: • Sedges have a solid, triangular in cross section, stem. Leaves are arranged in threes (extend in three directions). • Grass stems may be round or flattened.

  14. Purple vs Yellow Nutsedge

  15. Purple vs Yellow Nutsedge

  16. Common Sugarcane Weeds

  17. Fall panicum (Panicum dichotomiflorum) • Most common grass in the area • Relatively easy to identify • Stem can be hairy or smooth (hairy when young) • Ligule fringe of hairs • Round stem • Widely dispersed seedhead

  18. Wild oats (Sorghum almum) • Not really an oat • Closely related to johnsongrass • No rhizomes • Large, membranous ligule • Robust plant • Can look like sugarcane seedling when small

  19. Broadleaf panicum • Panicum adspersum (Urochloa adspersa) • Relatively prostrate growth • Wide leaves with wavy margins • Round stems • Usually dark green in color • Very similar to alexandergrass

  20. Alexandergrass (Brachiaria plantaginea) • Relatively prostrate growth • Somewhat wide leaves with straight margins • Round stems • Usually light green in color • Very similar to broadleaf panicum • leaves narrower (usually) • margins straight rather than wavy (usually)

  21. Alexandergrass vs Broadleaf panicum

  22. Napiergrass(Pennisetum pupureum) • Very robust plant • Forms dense clumps in fields • Long, wide leaves with finely toothed margin • Up to 12 feet tall • Seedhead has “bottle brush” appearance

  23. Paragrass (Brachiaria mutica) • Prostrate growing, medium size grass • Long stems covered with hairs • Short hairs on leaf surface • Swollen nodes • Grows in very wet areas • Often moves out of ditches • Pasture grass in Africa

  24. Paragrass (Brachiaria mutica)

  25. Goosegrass (Elusine indica) • Found in many fields • Low growing • Very white, flattened stems • Looks like it has been stepped on • Probably not competitive

  26. Crabgrass(Digitaria spp.) • Very wide first leaf • Initial clumping growth progressing to prostrate, tillering • Visible membranous ligule • Can be very hairy, or hairless, depending on species

  27. Torpedograss(Panicum repens L.) • Perennial with robust, creeping, sharply pointed rhizomes. • Leaf blade stiff and erect. • Hairs on upper and lower leaf surface. • Seedheads with stiff, ascending branches. • Occurs in wet areas.

  28. Spiny pigweed (Amaranthus spinosus) • Most common pigweed species • Stickerweed • Large, upright growth habit, entire leaves • Very evident spines located at nodes

  29. Alligatorweed (Alternanthera philoxeroides) • Common in many areas of the EAA • Prefers wet areas • Often spread by cultivation • Low growing • Hollow stems when growing in wet spots • Opposite leaves • Small white blooms

  30. Common lambsquarters (Chenopodium album) • Common some years • Usually during the cooler months (Dec, Jan) • Can be difficult to control • Waxy leaf surface • Small “dots” of wax are useful for ID • Gives leaves a white-gray color • Alternate leaves • Medium size lobes on leaves

  31. Common purslane(Portulaca oleracea) • Very common • Probably not competitive • Prostrate growing • Succulent • Leaves small, smooth, opposite or alternate • Small, yellow flowers • Red stems

  32. Common ragweed(Ambrosia artemisiifolia) • Often found on ditch banks and field edges • Deeply dissected leaves • Many hairs on upper and lower surfaces • Long seedhead at top of plant • Yellow flowers • Similar in appearance to ragweed parthenium • Different flower type

  33. Ragweed parthenium(Parthenium hysterophorus) • Primarily ditchbanks • Less common than common ragweed • Leaves less deeply dissected • Divisions don’t go all the way to the stem • White flowers • Single, not multiples

  34. American black nightshade(Solanum americanum) • Occasional weed in EAA • Problematic in vegetables (tomato, pepper) • Same family (Solanaceae) • Resistant to paraquat in some areas • Alternate leaves • Usually entire to somewhat lobed • Purple fruit • Seems quite competitive

  35. American black nightshade(Solanum americanum)

  36. Sources of Weed ID Information • Picture books: • Southern Weed Science Society ID Guide • Excellent resource • Very thorough (almost too many plants) • Web Picture/Taxonomic Sites • http://aquat1.ifas.ufl.edu/photos.html • http://www.griffin.peachnet.edu/cssci/TURF/turf.htm

  37. Weed management strategies

  38. Secrets to Successful Weed Control • Prevention • Prevention • Prevention

  39. Only you can prevent weed invasion! • Be careful what you plant • Consider all points of entry • Keep an eye out for new invaders elsewhere • Prevent reproduction of early invaders

  40. Ecological weed management is based on how a plant is built • Annual vs. biennial vs. perennial • Growth stage – perennials act like annuals for a short period • Timing relative to the seasons • Control prior to seed production

  41. Management timing relative to the seasons • Perennial weed growth schedule: • Spring: export carbohydrates from roots to new shoots • Summer: capture and assimilate new energy • Fall: “pack it in” for winter – carbohydrates transported to the roots • Winter: usually, minimal growth or activity

  42. Management timing relative to the seasons • Perennial weed management – general terms: • Spring: limit new growth – drain the roots • Summer: prevent energy capture • Fall: opportunity to attack the root storage system • Winter: eliminate new seedlings

  43. Manual removalHoeing, Pulling, Cultivation • Success determined by population and distribution – is it feasible? • Annual weeds easily removed • Perennial plants are often “subdivided” • Vegetative root pieces often produce new plants

  44. Biological control • Biological control of weeds in cropping systems is a difficult proposition • The control agent must be very host-specific and not injure non-target species • The life cycle of the control agent must match that of the target species • Surrounding habitat should support control agent survival and reproduction • In the future, possibility of bioherbicides

  45. Herbicides • Several good options for most crops grown in EAA • Applications should be timed to minimize competition with crop • Should be made prior to weed seed head formation

  46. Questions??