BIOLOGICAL CONTROL
Biological control relies on the use of one or more biological agents to
damage a weed species. This method uses plant pathogens, insects, or
weed species (e.g. tropical soda apple leaf beetle and tropical soda apple,
Pakistani hydrilla tuber weevil and hydrilla). Because these organisms
have narrow feeding habits, this method is typically used in natural and
aquatic areas for a single invasive species. Biological control is not used in
research is being conducted and new techniques may emerge in the future.
CHEMICAL CONTROL
Proper herbicide selection can be an effective weed control tool. Herbi-
growth. Herbicides are separated by application placement, selectivity, and
translocation.
Application placement includes foliar-applied or soil-applied herbicides.
Foliar-applied herbicides control the weeds after emergence above the soil
surface (post-emergence). Proper coverage of the foliage is important for
foliar-applied herbicides and a surfactant is often required for proper absorption
of the herbicide. Soil-applied herbicides control the weeds before
emergence above the soil surface (preemergence). Soil-applied herbicides
are applied to the soil surface or require incorporation into the soil surface.
Incorporation reduces vaporization of certain herbicides or places the herbicide
closer to the weed seed. Incorporation tactics include irrigation, rainfall,
broadleaf or grass weeds only. Auxin herbicides (2,4-D, clopyralid) control
broadleaf weeds only and thus are commonly used in grass crops or
turfgrass. Carfentrazone and certain sulfonylureas have excellent control of
broadleaf weeds and low-to-no injury to grass crops. Grass-only herbicides
can be applied over the top of broadleaf weeds.
Herbicides can be grouped as translocating or contact herbicides. Translocating
herbicides (glyphosate, halosulfuron) move from the contact point
to another part of the plant. This is important when controlling perennial
weeds, which require root death for complete control. Contact herbicides
(carfentrazone, paraquat) kill the area around the contact point; complete
coverage is important for these herbicides.
Herbicide-resistant weed species have become more problematic. Paraquat
resistant American black nightshade, paraquat-resistant goosegrass,
and glyphosate-resistant Palmer amaranth have been documented or
observed in Florida vegetable crops. To prevent resistance, growers should
incorporate nonchemical methods, rotate modes of action, use products
with multiple modes of action, use correct rates, and constant monitoring.
Other EDIS documents that provide information about herbicides in
vegetables and fruits include “Calibration of Chemical Applicators Used in
Vegetables” (HS1220) and “Factors Affecting Herbicide Use in Fruits and
Vegetables” (HS1219).
Nematode Management
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gens that growers in Florida are facing. They are hard to recognize, often
confused with other biotic or abiotic problems, and can cause total crop loss
in many fruits and vegetables. This is especially true in Florida’s warm and
sandy soils, where nematodes, such as root-knot (Meloidogyne spp.) and
sting (Belonolaimus longicaudatus), can build up rapidly to high and damaging
levels. In Florida, much more than anywhere else, managing nematodes
is not an option, but a must.
LIFE CYCLE
Plant-feeding nematodes go through 6 stages—an egg stage, 4 immature
stages, and an adult stage. Many species can develop from egg to egg-laying
adult in as little as 21 to 28 days during warm summer months. Immature
stages and adult males are long, slender worms. Mature adult females of
some species such as the root-knot nematode change to a swollen, pearlike
shape, whereas females of other species such as the sting nematode
remain slender worms. Nematodes are too small to be seen without a microscope.
It is believed the root-knot nematode survives from season to season
primarily as eggs in the soil. After the eggs hatch, the second-stage juveniles
invade roots, usually at root tips, causing some of the root cells to enlarge
where the nematodes feed and develop. The male nematodes eventually
leave the roots, but the females remain embedded, laying their eggs into a
jellylike mass that extends through the root surface and into the soil.
DAMAGE
Root-knot nematodes usually cause distinctive swellings, called galls, on
the roots of infected plants. Infestations of these nematodes are fairly easy
to identify: dig up a few plants with symptoms, wash or gently tap the soil
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cantly, and depends on the crop and nematode species. On cucurbits and
tomato, they can grow as large as 1 inch in diameter; on pepper, eggplant
and strawberry, they are always much smaller. On the roots of grasses
and certain legumes, root-knot nematodes can reproduce without causing
galling. The formation of these root galls reduces uptake of water and
nutrients. Also, galls can crack and facilitate the entry of soilborne pathogens.
Root-knot nematode galls are true swellings and can’t be rubbed
of legumes. Aboveground symptoms of a root-knot nematode infestation
include stunted plants, wilting during the hottest part of the day (even when
soil is moist), loss of vigor, yellowing leaves, and other symptoms similar to
those associated with a lack of water or nutrients. Infested vegetable plants
grow more slowly than neighboring, healthy plants, beginning in early to
midseason. Plants produce fewer and smaller leaves and fruits, and ones
heavily infested early in the season can die. Damage is most serious in
warm, irrigated, sandy soils. Symptoms are often wrongly attributed to lack
of fertilizer or water, soil insect or disease damage, or plugged drip tapes. In
the fumigant rig was pulled up too early, or inserted too late.
Root injury from other nematode species can produce aboveground
symptoms similar to those from root-knot nematodes. However, the actual
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by-looking and have slightly swollen root tips, as can be the case with sting
nematodes, or show dark spots or necrosis, which can be caused by lesion
nematodes (as well as certain soil pathogens). In all such cases, nematode
NEMATICIDES
For over 50 years, soil fumigation with methyl bromide was the preferred
method to manage soilborne pests and diseases, including plant-parasitic
nematodes, in a wide range of horticultural crops. Because methyl
bromide was categorized as a Class I ozone-depleting substance in the
1990’s, production and use of methyl bromide was phased out gradually,
and currently methyl bromide in the US is practically gone. Since the
alternative fumigants to methyl bromide. Much of this research was focused
on evaluating existing fumigants that had limited usage as long as methyl
bromide was available, such as 1,3-D (Telone), metam (Vapam/Kpam)
and chloropicrin (Pic), as well as some new fumigants, such as dimethyl
24 2019 Vegetable Production Handbook of Florida