Weed Management
Weeds compete with vegetable crops for light, water, and nutrients.
This competition decreases plant vigor, yield, and crop quality. They also
interfere with hand harvest and can complicate or prevent machine harvest.
Weeds also serve as alternative hosts for diseases, viruses, and nematodes.
EDIS documents with lists of weed hosts for virus and nematodes
include “Common Weed Hosts of Insect-Transmitted Viruses of Florida
Vegetable Crops” (ENY-863) and “Weed Hosts of Root-Knot Nematodes
Common to Florida” (ENY-060). There are also a range of books and EDIS
documents that can help you identify weeds in Florida such as Weeds of
the South and Weeds of the Northeast.
Fields should be scouted frequently early in the production year when the
crop is more susceptible to competition. Keep in mind that weed popula-
as increased soil moisture or changes in soil type. Scouting should be
include locations with known differences that might lead to increased weed
incidence, such as low-lying areas and areas with a history of weeds. All
for selecting the correct method and timing of weed control. Weeds may be
annuals, biennials, or perennials. Annual weeds emerge from seed, grow,
grow through the heat of the summer months. Summer annuals include
pigweed, morningglory, crabgrass, pusley, and goosegrass. Winter annuals
emerge during the fall and grow during the winter months. Biennial weeds
seeds until after a dormancy period. Biennial weeds include wild carrot,
cutleaf evening primrose, and common mullen. Perennial weeds can grow
structures that generate new plants such as stolons, rhizomes, tubers,
or large roots. Perennial weeds include nutsedge, Bermuda grass, Brazil
pusley, and creeping beggarweed.
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ventive, cultural, mechanical, biological, and chemical. The most successful
weed management programs will incorporate more than one type of weed
control.
PREVENTATIVE CONTROL
and treat problem areas such as poor drainage prior to crop establishment.
prevent seed formation. Seeds can move on equipment, wind, animals, and
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ment, and other items. All equipment should be cleaned after completing a
populations. Purchase crop and cover crop seed from reputable sources
to limit the amount of weed seed contamination. Prevention of weed seed
production when possible will help reduce weed seedbanks over time and
reduce future problems. Keep in mind that seeds can mature on a weed in
some situations after it has been hand-pulled.
CULTURAL CONTROL
A healthy crop is a better competitor with weeds. Use healthy transplants
or seeds with excellent germination to insure quick canopy closure
when possible. Plants stressed by improper watering (too wet or too dry)
or diseases/nematodes are less competitive. Proper nutrition is important
weeds will. Select the proper row spacing that will allow for quicker canopy
closure.
Crop and variety selection has an impact on weed growth. Crops that
are tall or have large leaves shade the soil surface and prevent weed seed
germination. Crops such as cabbage, bean, and corn are very competitive
crops. Whereas onions and carrots allow more light to the soil surface and
are less competitive. The same principle of light penetration to the soil surface
can be applied to crop varieties – a variety that is compact or smaller in
growth will be less competitive compared to other varieties.
Multiple vegetable crops are grown with polyethylene mulch. The horti-
management, and increased fumigant retention. Plastic mulches also
prevent light penetration to the soil surface and inhibit weed seed germination.
Weeds can germinate under clear or white plastic mulches that allow
light to reach the soil surface. If white mulch is desired, select one that has
a black underside to prevent light penetration. When plastic mulches are
used, grass and broadleaf weed emergence is limited to the crop hole and
row middle. Minimizing the size of the planting hole can reduce the number
of weeds that emerge. Yellow and purple nutsedge are the only species that
pierce the plastic mulch and can rapidly spread within a mulched bed.
Crop rotation is an effective weed management tool. Growing the same
crop repeatedly with the same weed management practices can select
Properly designed rotations typically include a range of: (1) crop types,
preferably with a mix of row and agronomic crops, (2) planting dates, (3)
agrochemical inputs, and (4) weed management tools. Choose a rotation
based on crop competitiveness, use of mulch or cultivation, and different
herbicide modes of action. The inclusion of cover crops can be an effective
weed-management tool. Care must be taken to observe plant-back restrictions
for herbicides or injury may occur in subsequent crops.
Cover crops should be included in any crop rotation. Cover crops shade
the soil surface and prevent weed germination. Some cover crops such as
rye have allelopathic compounds, which are plant chemicals that prevent
seed germination. Additional information can be found in the EDIS “Annual
Cover Crops in Florida Vegetable Systems Part 1. Objectives: Why grow
cover crops?” (HS387).
MECHANICAL CONTROL
Mechanical weed control includes plows, cultivators, mowers, hoes, and
hand-weeding. Chisel and moldboard plows are used at the beginning of
controls small weeds by cutting the weeds and is shallow to prevent weed
seeds from being brought to the soil surface. A single cultivation provides
excellent control of annual weeds; however, cultivation may break apart
pieces of perennial weeds and cause the weed to spread. Repeated
cultivation is important for perennial weed control as it encourages repeated
growth and can reduce the carbohydrates in the storage structure of the
weed, which can reduce the population over time.
control small weeds by breaking roots or foliage. Basket cultivators will
provide control in the row middles; however, weed control in the crop row
control in the crop row.
Use mechanical weed control only when it will be most effective,
because mechanical weed control degrades soil structure, dries the soil
surface, and prunes crop roots.
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