Project title: Development of cropping systems for nematode
management on agronomic and horticultural crops.
D.W.
Dickson and R. McSorley
Department of Entomology and Nematology
IFAS, University of Florida Gainesville, FL 32611
Field experiments were conducted in north Florida
(Suwannee County) from 1991-93 and in north-central Florida (Alachua County)
in 1993-94. The crop sequences at the Suwannee County site were: (i)
rotation crops during summer 1991; (ii) cover crop of rye during
winter 1991-92; (iii) 'Lemondrop L' squash during spring 1992; (iv)
rotation crops during summer 1992; (v) rye during winter 1992-93;
(vi) 'Classic' eggplant during spring 1993. The eight summer crop
rotation treatments were: 'Hale' castor, velvetbean, sesame, American jointvetch,
weed fallow, 'SX- 17' sorghum-sudangruss, 'Kirby' soybean, and 'Clemson
Spineless' okra as a control. Rotations with castor, velvetbean, American
jointvetch, and sorghum-sudangrass were most effective in maintaining the
lowest population densities of two root-knot nematode species (a mixture
of the Southern root-knot nematode and the peanut root-knot nematode),
but stubby root nematode built up in the sorghum-sudangrass rotation. Yield
of squash was significantly lower following sorghum-sudangrass than after
any of the other treatments except fallow. Yield of eggplant was significantly
greater following castor, sesame, or American jointvetch than following
okra or fallow. Several rotation crops evaluated here may be useful for
managing nematodes in the field and for improving yields of subsequent
vegetable crops.
In Alachua County in the 1993-94 seasons, rotation
crops of castor, velvetbean, 'Mississippi Silver' cowpea, 'Deltapine 51'
cotton, and 'SX-17' sorghum- sudangrass were effective in maintaining low
densities of the Southern root-knot nematode, whereas high population densities
(greater than 450 per one-half pint of soil) resulted after 'Clemson Spineless'
okra or 'Kirby' soybean. Similar patterns in densities of root-knot nematodes
were evident in a crop of eggplant planted in the 1994 season following
each of the rotation crops. The rotation crops planted during 1993 had
little effect on yield of eggplant in 1994. Eggplant yield was inversely
correlated with preplant densities of sting nematode, but not with the
initial density of root-knot nematode.
Microplots (small field plots) were used from 1991-94
trying to determine the effects of 12 summer crop rotation treatments on
population densities of the peanut and Southern root- knot nematodes and
on yields of subsequent spring vegetable crops. The crop sequence was:
(i) rotation crops during summer 1991; (ii) cover crop of rye during winter
1991-92; (iii) squash during spring 1992; (iv) rotation crops during summer
1992; (v) rye during winter 1992-93; (vi) eggplant during spring 1993.
The 12 rotation treatments were: castor, cotton, velvetbean, crotalaria,
fallow, hairy indigo, American jointvetch, sorghum- sudangrass, soybean,
horsebean, sesame, and peanut. Compared to peanut, the first eight rotation
treatments resulted in significantly lower numbers of the peanut root-knot
nematode juveniles on most sampling dates. Soybean, horsebean, and sesame
rotations were less effective in suppressing nematodes. Yield of squash
was significantly greater following castor, cotton, velvetbean, and crotalaria
than following peanut. Compared to the peanut rotation, yield of eggplant
was significantly enhanced following castor, crotalaria, hairy indigo,
American jointvetch, and sorghum-sudangrass. Several of these rotation
crops may provide a means for depressing the peanut root-knot nematode
population densities on a short-term basis to enhance yields in a subsequent
susceptible vegetable crop.
In 1993-94 the tests in microplots were designed
to determine the effect of several candidate rotation crops on the Southern
root-knot and stubby root nematodes. It is critical that rotation crops
intended for suppression of individual root-knot nematode species be evaluated
for their response to other nematode pests as wen.
The fourth set of experiments was conducted in the
greenhouse to determine the susceptibility of selected tropical rotation
crops to two races of the Southern root-knot nematode (races I and 3),
and the peanut and Javanese root-knot nematodes. The series of inoculation
tests included 'Rutgers' tomato and (or) 'Clemson Spineless' okra as hosts
susceptible to all of the nematode populations, and 'Florunner' peanut
and 'Deltapine 90' or 'Deltapine 51' cotton were included as hosts susceptible
only to the peanut root-knot nematode and race 3 of the Southern root-knot
nematode, respectively. Horsebean, 'Sesaco 16' sesame, and 'Kirby' soybean
exhibited intermediate levels of galling and egg mass production in response
to several root-knot nematode populations. No egg masses were observed
on crotalaria, 'Hale' castor, partridge pea, 'SX-17' sorghum-sudangrass,
or 'Mississippi Silver' cowpea in any of the tests. Velvetbean had only
a few galls and egg masses of the peanut and Japanese root-knot nematodes,
but none from either race of the Southern root-knot nematode. The response
of jointvetch was similar to that of cotton, with susceptibility only to
race 3 of the Southern root-knot nematode. Since several tropical rotation
crops showed resistance to several different root-knot nematodes, they
may have potential use in cropping systems in the southeastern United States
and other regions where these species and races of root-knot nematodes
predominate.