I. Nontechnical summary–Florida
Project coordinators: D. W. Dickson, Professor (Nematologist) and R. McSorley, Professor (Nematologist), University of Florida.
The following is a summary of four experiments conducted over the past 4 years to determine the effects of selected summer rotation crops on densities of root-knot nematodes and yields of subsequent spring vegetable crops.
Field experiments were conducted in north Florida (Suwannee County) from 1991-93 and in 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-sudangrass, ‘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 well.
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 1 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.
II. Nontechnical summary–Alabama
Principal investigator–R. Rodríguez-Kábana, Professor (Nematologist), Department of Plant Pathology, Auburn University, Auburn, AL.
The project was conducted to assess the value of selected rotation crops for control of root-knot nematodes and other soilborne disease problems in peanut, soybean, cotton, and vegetable fields in Alabama. Experiments were established in producer fields and in the experimental farms of the Alabama Agricultural Experiment Station. Peanut following castor bean, sesame, American jointvetch, partridge pea, velvetbean, bahiagrass, or cotton yielded an average of 25-60% higher than continuous peanut with or without nematicide application. The rotation crops were suppressive of root-knot nematodes and in most cases there was reduction in the incidence of southern blight in peanut. Sesame was planted in 1994 on 700 acres by two producers in Geneva county with satisfactory results. This producer experience demonstrated the feasibility of utilizing sesame in Alabama. In fields infested with root-knot nematodes and fusarium wilt cotton yields following bahiagrass were markedly improved over the yields obtained with continuous cotton. Cotton following bahiagrass was taller, had a larger root system with abundant mycorrhizae, than cotton following cotton. Similar improvements in yields were observed in experiments with soybean following bahiagrass or velvetbean. The soybean experiments were in producers’ fields in Baldwin county.
III. Technical report–Florida
I. HOST STATUS OF SELECTED TROPICAL ROTATION CROPS TO FOUR POPULATIONS OF ROOT-KNOT NEMATODES.
The susceptibility of selected tropical rotation crops to Meloidogyne incognita races 1 and 3, M. arenaria race 1, and M. javanica was evaluated in a series of inoculation tests. `Rutgers’ tomato (Lycopersicon esculentum) and (or) `Clemson Spineless’ okra (Hibiscus esculentus) were included as hosts susceptible to all of the nematode populations, and `Florunner’ peanut (Arachis hypogaea) and `Deltapine 90′ or `Deltapine 51′ cotton (Gossypium hirsutum) were included as hosts susceptible only to M. arenaria race 1 and M. incognita race 3, respectively. Horsebean (Canavalia ensiformis), `Sesaco 16′ sesame (Sesamum indicum), and `Kirby’ soybean (Glycine max) exhibited intermediate levels of galling and eggmass production in response to several of the root-knot nematode populations. No egg masses were observed on crotalaria (Crotalaria spectabilis), `Hale’ castor (Ricinus communis), partridge pea (Cassia fasiculata), `SX-17′ sorghum-sudangrass (Sorghum bicolor x S. sudanense), or `Mississippi Silver’ cowpea (Vigna unguiculata) in any of the tests. Velvetbean (Mucuna deeringiana) had only a few galls and egg masses of M. arenaria race 1 and M. javanica, but none from either race of M. incognita. The response of jointvetch (Aeschynomene americana) was similar to that of cotton, with susceptibility only to race 3 of M. incognita. Since several of the tropical rotation crops showed resistance to several different Meloidogyne spp., 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.
Our goal is to demonstrate the effectiveness and economic benefits of selected cropping systems for low-input, sustainable management of root-knot nematodes.
Specific objectives were to:
1. Develop and demonstrate the usefulness of selected tropical crops (short term) and forage crops (long term) in suppressing population densities of root-knot nematodes below damage levels
2. Provide information on crop yields, production costs, pesticide use, net returns, and financial risks due to adoption of these alternative crops
3. Determine the biomass added to the soil by each crop and the nitrogen mineralization following each crop
4. Demonstrate and test models of seasonal nematode multiplication on the alternative crops.