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

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Weed Biology and Management

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weed biology and management

Weed Biology and Management

Curtis Rainbolt

Extension Weed Scientist

Everglades REC

weed biology and its impact on management
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
definition of a weed
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
weed impacts
Weed impacts
  • Weeds are costly
    • $24 billion in agricultural crop loss
    • $3 billion in control costs

Pimentel et al. 1999

weeds are costly
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
why do weeds always win
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

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
reproduction by seed
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
vegetative reproduction
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
weed identification goals
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
weed classification life cycles
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
differences between grasses and sedges
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.
fall panicum panicum dichotomiflorum
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
wild oats sorghum almum
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
broadleaf panicum
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
alexandergrass brachiaria plantaginea
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)
napiergrass pennisetum pupureum
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
paragrass brachiaria mutica
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
goosegrass elusine indica
Goosegrass (Elusine indica)
  • Found in many fields
  • Low growing
    • Very white, flattened stems
    • Looks like it has been stepped on
    • Probably not competitive
crabgrass digitaria spp
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
torpedograss panicum repens l
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.
spiny pigweed amaranthus spinosus
Spiny pigweed (Amaranthus spinosus)
  • Most common pigweed species
    • Stickerweed
  • Large, upright growth habit, entire leaves
  • Very evident spines located at nodes
alligatorweed alternanthera philoxeroides
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
common lambsquarters chenopodium album
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
common purslane portulaca oleracea
Common purslane(Portulaca oleracea)
  • Very common
    • Probably not competitive
    • Prostrate growing
    • Succulent
    • Leaves small, smooth, opposite or alternate
    • Small, yellow flowers
    • Red stems
common ragweed ambrosia artemisiifolia
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
ragweed parthenium parthenium hysterophorus
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
american black nightshade solanum americanum
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
sources of weed id information
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
secrets to successful weed control
Secrets to Successful Weed Control
  • Prevention
  • Prevention
  • Prevention
only you can prevent weed invasion
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
ecological weed management is based on how a plant is built
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
management timing relative to the seasons
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
management timing relative to the seasons42
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
manual removal hoeing pulling cultivation
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
biological control
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
  • 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