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tage that all alternative fumigants have compared to methyl bromide is their
lower vapor pressure (volatility), which means that uniform soil distribution
often have not provided the same level of nematode control, and nematode
management in Florida agriculture has become more challenging. (For
more information on fumigation, see next section in this chapter, and EDIS
publications on this topic).
Increasing regulatory pressure on pesticides has not only impacted
fumigant use, but also other non-fumigant nematicides, such as many
organophosphate and carbamate nematicides (e.g. Temik, Nemacur). Due
to their generally high toxicity and environmental risk, chemical nematicides
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cently, some new products (Nimitz, Velum, Majestene) have become available.
These new nematicides have a much better human and environmental
not be considered fumigant replacements. Unlike fumigants, which will
control all or most soilborne pests and diseases, the new products will only
or mostly target nematodes, and additional measures need to be taken to
manage soilborne diseases and weeds.
Whereas fumigants need to applied several weeks before planting,
non-fumigant nematicides are typically applied shortly before or at planting
of the crop. Non-fumigant nematicide options are limited, and at the
moment include one older product Vydate (oxamyl), and the three newer
Majestene (Burkholderia, a biological). In crop (post-plant) applications
are only allowed for Vydate, Velum, and Majestene, and labels should be
consulted for each crop.
Crop destruction practices, using end-of season nematicides or fumigants,
can also help to reduce nematode levels. Plant-feeding nematode
populations in annual crops are always low at the start of the season, as
nematodes are dormant and often hiding in deeper soil layers, waiting
for new roots to feed on. Populations will gradually increase during the
cropping season, and tend to be at their highest at the end of the crop.
Applying a nematicide at that time would likely kill nematodes at the peak
of their population, and while they are still active and feeding, and are
season - especially in the middle of summer in Florida, when they tend to
move deeper into the soil waiting for the next crop to be planted. In such
cases, deep injection of fumigants (about 18” deep), can be done to target
nematodes hiding in deeper soil layers, and especially in heavily infested
OTHER NEMATODE MANAGEMENT OPTIONS
Ideally, nematode management should adopt a year-round approach,
the crop, to off-season nematode management. Nematodes usually are
plants. To prevent the spread of nematodes, avoid moving plants and soil
infested plants to run off, as this also spreads nematodes. Nematodes can
also be present in soil attached to farm equipment, tires, and boots.
Field preparation in Florida often includes soil fumigation. It can also
include compost, manure, or other organic amendment applications.
These may not directly kill nematodes, but will stimulate soil biology and
may increase nematode predators, parasites, and antagonists. Organic
amendments also will increase the water- and nutrient-holding capacity of
the soil, especially in sandy soils. As nematodes will cause more damage
to plants that are water-stressed, this can lessen the effects of nematode
injury, without actually reducing levels of damaging nematodes. During the
growing season, bio-stimulants, compost teas, and other organic materials
can be applied as well, and may help for the same reasons.
For certain crops, such as tomato, root-knot nematode-resistant cultivars
are available, and they have been shown to provide good protection against
most root-knot nematode species in Florida. Although even resistant tomato
varieties can still exhibit some root galling under high nematode levels,
variety is that the nematode levels in the soil decline rather than increase,
making it more feasible to grow a susceptible crop the following season,
e.g. a double crop.
Growing a crop on which the nematode cannot reproduce is a good way
to help manage some nematodes. Unfortunately, rotation is not as easy
for managing root-knot and sting nematodes, because so many vegetable
crops and weeds are hosts for these nematodes. However, if a rotation
schedule can be found, rotation in combination with fallowing and other
available practices can reduce root-knot nematode numbers. Annual crops
that are useful in a rotation plan for reducing root-knot nematode populations
include small grains, sudangrass, and resistant tomato varieties.
Fallowing is the practice of leaving the soil bare for a period of time, and
tends to be more effective when the soil is kept moist – which induces
nematode eggs to hatch, and emerging nematodes to starve as there is no
food source. It is also important to control weeds on which nematodes can
survive during the fallow period. During the off-season, frequent tillage can
also reduce nematode populations, by bringing nematodes to the surface
and exposing them to the sun. Solarization, covering the soil with clear plastic
for 4-6 weeks, is another method that can be used, although nematode
control tends to be limited to the upper soil layers.
Cover crops are always a good tool to include in a nematode-manage-
and weed suppression to disease and nematode control. Florida’s climate
allows for a wide range of cover crops to be planted. A common summer
cover crop in Florida is sunn hemp (Crotalaria juncea
nitrogen in the soil, but is also a poor host for many nematodes, including
root-knot nematodes (there are several EDIS publications on cover crops
and nematodes). Certain plants also have direct nematicidal properties,
such as marigolds (Tagetes spp.) and could also be used in rotations or as
intercrops.
Fumigation
Soil fumigation is a preplant chemical treatment of soil, using a pesticide
product (typically a liquid) that converts to form a volatile gas once released
into soil. The gas is able to diffuse through open pore space throughout the
soil to provide pest and disease control. All of the fumigants are phytotoxic
to plants and the fumigant gases must dissipate from soil, usually from a
few days to well over a month (depending on environmental conditions),
before seeding or transplanting can occur without risk of crop injury. They
are used globally on a wide range of annual and perennial crops, and
can be used alone or in combination to expand control of a wide range of
soil-inhabiting pest species including various insects, nematodes, fungi,
and weeds. Because of their wide range of pesticidal activity, they are often
called ‘multi-purpose’ or ‘broad-spectrum’ fumigants.
In Florida, soil fumigants are most commonly used in high-value cropping
systems to protect investment in crops where pest pressure is so high that
it would be economically unfeasible to grow a crop without the use of a
on production agriculture in Florida, and have catalyzed the development of
many high-value, raised bed and plasticulture cropping systems. Fumi
2019 Vegetable Production Handbook of Florida 25