Development of Cropping Systems for Nematode Management on Agronomic and Horticultural Crops
The project goal was to demonstrate the effectiveness and economic benefits of selected cropping systems for low-input, sustainable management of root-knot nematodes.
Specific objectives were:
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.
Approach and Results
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.
Field experiments in Alabama were established at the Wiregrass substation (peanut), at the E. V. Smith Center (cotton), and in two producer fields near Elberta, Baldwin county. In addition, three microplot experiments were conducted in the 'Old Agronomy Farm' on the Auburn University campus.
Each experiment consisted of 8-10 treatments with eight replications (plots) each, arranged in randomized complete block design. Field plots (experimental units) were each eight row swide by 33 feet long; microplots consisted of a 1 ft.2 area delimited with chimney flute as described in previous publications.
In each experiment data were collected on numbers of plant parasitic nematodes, disease incidence, and yield. All data were analyzed according to standard procedures for analysis of variance. Specific details varied according to the experiments but the methods followed are detailed in reprints included in the appendix to this report on file in the SARE office.
Castorbean and velvetbean were the most root-knot nematode suppressive and yield enhancing in rotations with peanut. Roots of both castorbean and velvetbean are known exude compounds that are nematicidal or nematostatic.
There is also evidence that the bacterial microflora of these plants is abundant in species antagonistic to root-knot nematodes. These results confirm findings in Brazil, Central America, and Mexico where the value of velvetbean to manage nematode and disease problems has been amply demonstrated. Velvetbean was once the premiere green manure crop in the South and was used in Alabama not only to improve fertility but also to manage soilborne pathogens and reduce weed problems.
Yield of peanut following sesame, hairy indigo, American jointvetch, or partridge pea were also significantly improved. Partridge pea was allelopathic to weeds so that plots with this legume were essentially free of this problem. Green manure production from hairy indigo and American jointvetch was outstanding, exceeding in most cases 10 MT dry matter/ha.
Sesame proved to be the most interesting rotation crop from an economical point of view. There is significant demand for the crop in the national and international markets. In 1994 two producers in Geneva County planted 700 acres of the crop with satisfactory results in spite of adverse weather conditions.
Results from soybean experiments in Baldwin County confirmed the value of velvetbean for the management of nematode problems. Yields of soybean following velvetbean were markedly improved. This was true for all cultivars tested in fields infested with a mixture of Meloidogyne spp. and the cyst nematode, Heterodera glycines. It is noteworthy that all cultivars tested in these experiments responded to the velvetbean rotation regardless of their level of resistance to the nematodes.
Bahiagrass pasture improved yields of cotton and soybean following it. This was true for all cotton and soybean cultivars tested. At the E. V. Smith center, the bahiagrass rotation improved the height and degree of mycorrhization of cotton plants and suppressed significantly fusarium wilt problems. These results corroborate earlier studies in Alabama and other southeastern states.
Microplot experiments at the Auburn campus demonstrated that castor, velvetbean and hairy indigo could be used advantageously to suppress root-knot problems and enhance yields of 'Black Beauty' eggplant following these crops.
In conclusion, our studies showed that:
1.) It is possible to increase crop yield and manage nematode and other soilborne disease problems by using crop rotations.
2.) Several "exotic" crops, e.g., sesame, velvetbean, can be used economically to improve yields in the southeastern United States.
3.) Rotation crops tested in our study can be incorporated into existing production system with minimal requirements in equipment or modification of cultural practices.
There remains need to determine the best cultivars and information on specific cultural requirements for optimal production of "exotic" crops under Alabama conditions.