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Copyright 2005, Board of Trustees, University
i \ Gulf Coast Research and Education Center
----.IFAS, University of Florida
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Bradenton, Florida 34203
Bradenton GCREC Research ReportBRA1985-3 January 1985
NEMATODE MANAGEMENT FOR STRAWBERRY
A. J. Overman
The well-drained, sandy soils desirable for .strawberry production favor the
survival and development of two nematode genera particularly damaging to
the crop: the sting nematode (Belonolaimus) and the root-knot nematode
(Meloidogyne). Soil fumigation is common practice for control of soil.pests
of strawberry in nurseries as well as in fruiting fields..
Control of soil-borne plant pests in the mulched beds of the .fruiting fields
does not lend itself to the concept of integrated pest management (IPM)
systems in which scouts monitor the crop for infestation levels and defer
the use of pesticides until the damage threshold is attained. Since consi-
derable costs of production have been encumbered before economic damage due
to soil-borne pests is generally apparent in either nursery or fruiting field,
growers must decide prior to planting whether a particular, selected field
will be fumigated and what level of control is economically necessary.
Ideally, the decision should be made during the previous crop on the land.
Scouting the previous crop (regardless of type) at maturity for nematode
associates, root diseases, and severity of.nutsedge and other weed infes-
tations will provide the information required for making an informed decision
on fumigating for the strawberry season. This is of particular importance
when nurseries or berry operations are being.rotated to areas with unknown
crop pest histories.
The high value of the crop and the relatively long growing season of both
nursery and fruiting field support the need for multipurpose soil fumigants
which control a broad spectrum of soil pests: nematodes, weeds, insects,
and soil-borne disease organisms. Nurseries require broadcast applications
which treat the entire surface of the field. Bed fumigation is adequate for
fruiting fields'using full-bed polyethylene mulch culture.
The entire industry benefits'when these chemicals are used responsibly.
Recently, several nematicides (ethylene dibromide, aldicarb, dichloropropene)
have been banned or restricted by the Environmental Protection Agency (EPA)
or removed from the market by the manufacturer because of concerns for ground
water pollution'in Florida. The broad spectrum fumigant methyl bromide,
popular in strawberry production, is presently receiving EPA attention and
researchers and growers must map new strategies in case the use of all soil
fumigants is limited in the future.
Therefore, in order to preserve access to fumigants, the proper dosage,
storage and disposal procedures should receive constant supervision in the
management system. 'Appropriate soil preparation prior to treatment, and
management following treatment, can also lead-to greater efficacy at rates
of application in the lower labeled range.
The following four factors can improve the efficacy of soil fumigants at
rates in the lower range by lowering the initial pest population, increasing
exposure time of the soil pests to the fumigant, and making pest populations
more vulnerable to the vapors:
1) Tillage: Post production strawberry plants should be incorporated
into the soil immediately after the last harvest or when daughter
plants are no longer required from the nursery. Procrastinating
only a few weeks permits disease organisms, nematodes and weed seed
to increase.' Soil preparation for the new planting :should begin -.,.
early'enough before fumigation to encourage decay of any plant ;
debris. The presence of live plant material in the soil profile
at the time of fumigant application reduces the efficacy of the..
chemical: gases are preferentially absorbed by the plant tissue. .-..
This reduces the concentration of gases encountering the soil
pests. Tillage over a period of weeks aerates the soil, exposes
different layers to sunlight, and disperses pest communities which ,,
have accumulated near concentrations of roots in the field.
2) Irrigation: Irrigation to provide moist soil during the tillage .
period is important not only to accelerate;the decay process, but :.
also to stimulate the germination of weed seed and fungal spores and.
to hatch nematode eggs. Actively developing soil pests are more .
vulnerable to the toxic vapors of the soil fumigant than dry,-
dormant life stages. If beds are constructed at the time of soil
treatment, it is imperative that the field surface be moist. Even
though the moist soil brought from below the surface is adequate
to maintain the integrity of the vertical sides of newly constructed
beds, soil from the surface buried in the beds will result in dry.
spots through which the fumigant will move too quickly to be effective.
Therefore, fields should be freshly tilled or irrigated before bedding.
3) -Temperature: Fumigants may be applied when the temperature of soils at
:the depth fumigants are placed lies between 50 and 800F. Ideally,
6-inch temperatures should range between 650 and 700F. However,-since
operations in the crop management system for strawberry, like many:
other commodities in Florida, are controlled by the calendar toa
large extent, growers must perform certain operations of the management
sequence within a short period of time, often when conditions are .
not ideal. Fumigation for the fruiting fields often occurs when so il
temperatures are excessively high, i.e., during July, August, and .
September temperatures at a 6-inch depth in moist, sandy soils of the
Gulf Coast range from 80 to 90 F. Nursery fields are often treated
at soil temperatures ranging between 60' and 700F. Adequate soil
moisture and friable tilth alleviate the problems of temperature
extremes, delaying premature vapor loss on the one hand and favoring.
vapor dispersion through the soil profile on the other.
4) Compaction: Soil should be compacted with a bed shaper or, for broad-
cast applications, a roller as the fumigant is applied. Uniform
compaction will retard the vapor loss and enhance optimum distribution
of the gases throughout the soil profile. Polyethylene film at
thicknesses generally used as cover or mulch does little to contain
the fumigant against premature loss to the atmosphere. The plastic
film is an advantage because it conserves the soil water in
which the gases are dissolved. Moisture which evaporates from
the soil surface of the plastic is not lost from the system.
Compaction contributes significantly to the water movement in
a film-covered soil; elimination of cracks and crevices and
maintenance of capillarity is important.
Soil fumigants available for strawberry production in peninsular Florida
are 1) Vorlex@ (dichloropropene/methylisothiocyanate mixture), 2) Vapanm
(metam-sodium), and 3) MBC (methyl bromide/chloropicrin mixtures). M C
containing 67% methyl bromide has been the popular product, but there is a
general increase in use of MBC containing 99% methyl bromide in both nursery
and the mulched beds of the fruiting field for more effective weed control.
Instructions on the labels for use on mineral soils should be followed.
The placement of the fumigant is of particular importance in multi-row/bed
crops such as strawberry. The number of chemical screams and the spacing of
the streams in the soil depends on the choice of chemical and the planting
pattern. One stream of Vorlex is calculated to treat an 8-inch band at the
6-inch depth of delivery; Vapam a 5 to 6 inch band; and MBC a 12-inch band.
Multiple streams may be used to fumigate wider swaths of.bed. It is'this
placement and not the width of the mulched bed which determines the portion of
the bed fumigated. For example, one stream of MBC in the middle of a 2 ft.-
wide mulched bed treats only the middle one foot band, nut the entire width
under plastic. Since plants in the fruiting field have traditionally been
spaced in two rows on a bed with the rows 12 inches apart, single streams
of MBC beneath each intended row have been adequate. With newly evolving ideas
for varying bed width and plant density, adjustments in stream spacing and
chemical calibration may be required. Weed control at the bed surface may be
incomplete mid-point between two streams and permit weeds to compete with
transplants set off-center of the fumigator chisels.
Because strawberry is vegetatively propagated, pests associated with the
crop in nurseries are moved with daughter plants into the fumigated soil.
In an environment of boilogical activity suppressed by the fumigant, the
transplanted pests may multiple rapidly. The grower should use clean plants
to protect his investment in furigart.
Alternatives to soil fumigation apply primarily for those growers who
control their land year-round. Certain cultural practices, when closely
followed, traditionally have reduced soil pest pressures. The procedures
are familiar, contributive, and relatively time-consuming compared to routine
soil fumigation. However, introducing procedures such as the following which
are compatible with specific crop management systems may defer the need for
or improve benefits derived from soil fumigants.
1) Clean fallow: Most economically important nematodes require roots
of living plants to thrive. Therefore, clean fallow deprives the
population of a food supply and over several months reduces numbers
.significantly. This is particularly true if fallowing is accom-.
plished by tilling the soil, exposing layers to sunlight and
dispersing nematode communities. Fallowing by use of herbicides
to deplete nematode populations is a much slower process because
the soil is not disturbed.
2) Cover crops: Two cover crops adaptable for fruiting field
management ar.e effective in discouraging sting and root-nezmato.e
populations: hairy indigo (Indigofena hirsvtan) and aeschynomene
(Aeschynomene americana). Although the popular sorghums provide
large masses of organic matter for soil conditioning, the plants
host the sting nematode and increase the need for effective'lematode
control in strawberry fields. Use of cover crops on fields which
will be fumigated increases cultivation operations because trashy.
soil leaves crevices and air spaces through which the fumigant can
escape into the atmosphere without first dispersing through the
soil mass.. Since the dosage rates of fumigants selected for
labeling are marginal for the sake of economy,-'the best soil.
preparation practices should be used to take full advantage of
the chemical; stubble of a heavy cover crop makes this more difficult
to achieve within the grower's timeframe.
In summary, some form of chemical assistance will be required on cultivated
sand land regardless of the care taken by growers to decrease pest pressures
through cultural practices because modern crop production demands maximum
yields to prosper. 'However, it behooves growers to manage fumigants
conservatively to obtain maximum performance.at minimal rates, in order 'to
preserve their availability. A combination of cultural practices, sanitation,
and chemical control is imperative to preserve the economic productivity ;of the.