Transcript Weed Biology and Management

Weed Biology
and Management
Everglades REC
Belle Glade, FL
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
• 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
 Weeds are costly
 $24 billion in
agricultural crop loss
 $3 billion in control
costs
Pimentel et al. 1999
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?
• 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
• First infestation is dependent 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
• 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
Get to know the enemy:
weed identification
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
• 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
• 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.
Purple vs Yellow Nutsedge
Purple vs Yellow Nutsedge
Common Sugarcane
Weeds
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
Fall panicum (Panicum dichotomiflorum)
Goosegrass (Eleusine indica)
• Found in many fields
• Low growing
– Very white, flattened
stems
– Looks like it has been
stepped on
– Probably not
competitive
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
Broadleaf panicum (Urochloa adspersa)
• Relatively prostrate
growth
– Wide leaves with wavy
margins
– Round stems
– Usually dark green in
color
– Very similar to
alexandergrass
Broadleaf panicum (Urochloa adspersa)
Crowfootgrass (Dactyloctenium aegyptium)
• Plants glabrous,
blade margins hairy
• Seed head like a crow
foot
• Bends and roots at
the lower nodes
Bermudagrass (Cynodon dactylon)
• Easy to identify
•
•
•
•
Small leaves
Rhizomes and stolons
Mat forming
Ligule fringe of short hairs (hard to see)
• Produces seed and spreads vegetatively
Bermudagrass (Cynodon dactylon)
Sorghum (Sorghum almum)
• ‘Wild oat’
• Closely related to
johnsongrass
– No rhizomes
– Large, membranous
ligule
– Robust plant
Sorghum (Sorghum almum)
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
Guineagrass (Panicum maximum)
• Some plants are
extremely hairy, while
others are hairless
• Small plants have
narrow leaves
• Becomes very large
• Highly branched
seedhead
• Round stem
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)
• 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
Spiny amaranth (Amaranthus spinosus)
• Most common
‒ Large, upright growth
habit, entire leaves
‒ Very evident spines
located at nodes
Livid amaranth (Amaranthus blitum)
• Can be prostrate or
erect
• Notched leaf tips
Alligatorweed (Alternanthera philoxeroides)
• Common in wet areas
of the EAA
‒ Often spread by
cultivation
‒ Low growing
• Hollow stems when
growing in wet spots
• Opposite leaves
• Small white blooms
Alligatorweed (Alternanthera philoxeroides)
Common lambsquarters (Chenopodium album)
• Common during the
cooler months
• Can be difficult to
control due to waxy
leaf surface that
leaves a white-gray
color
Common purslane (Portulaca oleracea)
• Prostrate, succulent
• Leaves small,
smooth, opposite or
alternate
• Red stems
• Small, yellow flowers
Common ragweed (Ambrosia artemisiifolia)
• Deeply dissected
leaves
• Many hairs on upper
and lower surfaces
• Long seedhead at top
of plant
• Yellow/white flowers
in multiples
Ragweed parthenium (Parthenium hysterophorus)
• Less common than
common ragweed
‒ Common along
canals, ditch-banks,
noncrop areas
• Leaves less deeply
dissected
‒ Divisions don’t go all
the way to the stem
• White flowers
‒ Single, not multiples
American black nightshade (Solanum americanum)
• Becoming more
common in EAA
‒ Alternate leaves
• Usually entire
to somewhat
lobed
‒ Purple fruit
Dayflower (Commelina spp.)
• Common in open
areas, field edges
– Small, probably not
competitive
– Prostrate growth habit
– Parallel veins on
leaves
– Actually a monocot
– Blue flowers
Weed management
strategies
Secrets to Successful Weed Control
1. Prevention
2. Prevention
3. Prevention
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
• 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
• 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
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
• 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 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
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
Contact information
Calvin Odero
Everglades Research & Education Center
3200 E Palm Beach Road
Belle Glade FL, 33430
561-993-1509
[email protected]