Transcript Weed Biology and Management

Weed Biology and
Management
Curtis Rainbolt
Extension Weed Scientist
Everglades REC
Weed Biology and its Impact on
Management

What makes a plant a weed?



Get to know the enemy



Cost of weeds
Why do weeds always win? Biology
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 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
 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

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

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)

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)
Alexandergrass vs Broadleaf panicum
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



Swollen nodes
Grows in very wet areas


Short hairs on leaf surface
Often moves out of ditches
Pasture grass in Africa
Paragrass (Brachiaria mutica)
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.)




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.)





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)

Most common pigweed
species



Stickerweed
Large, upright growth
habit, entire leaves
Very evident spines
located at nodes
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 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)

Very common






Probably not competitive
Prostrate growing
Succulent
Leaves small, smooth, opposite or alternate
Small, yellow flowers
Red stems
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)

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)

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
American black nightshade
(Solanum americanum)
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.h
tm
Weed
management
strategies
Secrets to Successful Weed Control
1.
2.
3.
Prevention
Prevention
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
Questions??