Management of Nematodes with Cowpea Cover Crops

 

K.-H. Wang and R. McSorley

University of Florida, Department of Entomology and Nematology, P. O. Box 110620, Gainesville, FL 32611-0620, U.S.A.

(Last updated on February 10, 2002)

 

Fig. 1. Cowpea planted as a cover crop (picture is courtesy of R. McSorley)

 

Advantages

Cowpea, Vigna unguiculata (L.) Walp., is well adapted to cultivation in the tropics and in the southern United States. One advantage of using cowpea as a cover crop is its ability to associate with nitrogen-fixing bacteria and thus benefit in Nitrogen (N) management. The effect of cowpea in nematode management is cultivar dependent. Some cowpea cultivars can be damaged by root-knot nematodes, the key nematode pest in many cropping systems in North Central Florida (McSorley and Gallaher, 1991), resulting in severe root galling.  Fortunately, some cultivars commonly cultivated have various degrees of resistance to one or more species and races of root-knot nematodes (Table 1, Gallaher and McSorley, 1993). This combination of nematode and N management could be especially useful in organic production systems where neither nematicides nor synthetic N fertilizers could be used.

Host status of Cultivars of cowpea to plant-parasitic nematodes

Host status of cowpea cultivars to various root-knot nematode species and races, and some other plant-parasitic nematodes are listed in Table 1. The host status is arbitrarily categorized the host status into 3 categories: poor, moderate and good hosts corresponding to their susceptibility to the nematodes. Growers should avoid using good or moderate hosts in their crop rotation if the specific nematode species or races are present in the field. Further information on the host status of cowpea cultivars to root-knot nematodes that might not be available in the market are listed in a publication by the International Meloidogyne Project (Sasser and Kirby, 1979). This information might be useful to plant breeders. Some cowpea breeding lines that had potential for use in development of new root-knot nematode resistant cowpea cultivars are reported from Arkansas (Kirkpatrick ad Morelock, 1987).

 

 

Table 1. Host status of cultivars of cowpea to plant-parasitic nematodes.

Cultivar

Target nematode

Host status

Reference

Colossus

Meloidogyne incognita

Poor host

Fassuliotis, 1976

California Blackeye #5

M. incognita

Poor host

McSorley and Gallaher, 1992; Fassuliotis, 1976

Iron Clay

M. incognita race 1

Poor host

McSorley et al., 1999

Iron Clay

M. javanica

Poor host

McSorley et al, 1999

Magnolia Blackeye

M. incognita

Poor host

Fassuliotis, 1976

Mississippi Purple

M. incognita

Poor host

Fassuliotis, 1976

Mississippi Silver

M. incognita race 1 and 3

Poor host

/nonhost

Gallaher and McSorley, 1993; McSorley et al., 1999; Kirkpatrick and Morelock, 1987; Fassuliotis, 1976

Mississippi Silver

M. arenaria

Poor host

Kirkpatrick ad Morelock, 1987

Mississippi Silver

Paratrichodorus minor

Poor host

McSorley and Dickson, 1995

Mississippi Silver

Belonolaimus longicaudatus

Good host

McSorley and Dickson, 1995

Tennessee Brown

M. incognita

Poor host

McSorley and Gallaher, 1992

Zippercream

M. incognita

Poor host

McSorley and Dickson, 1995; Fassuliotis, 1976

Purple Knuckle

M. incognita

Intermediate

 host

Gallaher and McSorley, 1993

Crimson

M. incognita race 3

Good host

Kirkpatrick ad Morelock, 1987

Elite

M. incognita race 3

Good host

Kirkpatrick ad Morelock, 1987

Elite

M. arenaria race 1

Intermediate host

Kirkpatrick ad Morelock, 1987

Whippoorwill

M. incognita

Good host

Gallaher and McSorley, 1993

Pinkeye Purplehull

M. incognita

Good host

Gallaher and McSorley, 1993

Texas Purplehull

M. incognita

Good host

Gallaher and McSorley, 1993

 

 

Fig. 1. Population densities of Meloidogyne incognita following seven cowpea cultivars in Alachuan County, Florida, 1991. Bars followed by the same letter are not different (P£0.05),  according to Duncan's multiple range test performed on log-transformed data (Gallaher and McSorley, 1993).

 



How to enhance cowpea effect

Initial beneficial effects of cowpea rotation on root-knot nematode populations were lost once a susceptible vegetable crop like tomato or pepper was grown. Combining solarization with a nematode resistant vegetable cultivar may provide the organic vegetable grower with a viable means for root-knot nematode management (McSorley et al., 1999).

Problems

Responses of a root-knot nematode species to cowpea depend on the local nematode isolates. For example, M. javanica from Florida might not behave the same way as that from Hawaii. Therefore, we cannot be certain that a cultivar reported to be a poor host for a particular root-knot nematode will behave in the same way in a field where the isolate has not been tested. For this reason, the resistance of a cowpea cultivar should be evaluated locally before it is widely planted.

Virulence of root-knot isolates within a local area might vary over time. Studies at University of California, Riverside showed that populations of M. incognita are heterogeneous groups of individuals varying in fitness. Some nematode isolates are virulent against the root-knot resistance gene, Rk, in cowpea (Petrillo and Roberts, 2000). Continuous culture of root-knot resistant cowpea will favor the resistant isolates of nematodes after generations. However, resistance breaking by root-knot will be less likely to occur if resistant cowpea varieties are rotated with commercial crops that are susceptible to root-knot.

Another dilemma in selecting a suitable cowpea cultivar for nematode management arises when mixtures of different plant-parasitic nematode species occur in a field. Cowpea cultivars may be chosen for resistance against several nematodes if possible. Otherwise, it is critical to focus management options on the key nematode pest.

It is important to note that cowpea is susceptible to some plant-parasitic nematodes, for example, the reniform nematode, Rotylenchulus reniformis (Robinson, et al., 1997). Fields infested with reniform nematode should not use cowpea for crop rotation.

 

References

Fassuliotis, G. 1976. Progress, problems and perspectives in breeding food crops for root-knot resistance, pp. 81-93, Proc. Res. Planning Conference on root-knot nematodes, Meloidogyne spp. January 12-16, North Carolina State University, Raleigh.

Gallaher, R. N., and R. McSorley. 1993. Population densities of Meloidogyne incognita and other nematodes following seven cultivars of cowpea. Nematropica 23: 21-26.

Kirkpatrick, T. L. and T. E. Morelock. 1987. Response of cowpea breeding lines and cultivars to Meloidogyne incognita and M. arenaria. Annals of Applied Nematology 1:46-49.

McSorley, R. 1999. Host suitability of potential cover crops for root-knot nematodes. Supplement to the Journal of Nematology 31: 619-623.

McSorley, R., and D. W. Dickson. 1995. Effect of tropical rotation crops on Meloidogyne incognita and other plant-parasitic nematodes. Supplement to the Journal of Nematology 27: 535-544.

McSorley, R., and R. N. Gallaher. 1991. Nematode population changes and forage yields of six corn and sorghum cultivars. Supplement to Journal of Nematology 23: 673-677.

McSorley, R., and R. N. Gallaher. 1992. Comparison of nematode population densities on six summer crops at seven sites in North Florida. Supplement to Journal of Nematology 24: 699-706.

McSorley, R., M. Ozores-Hampton, P. A. Stansly, and J. M. Conner. 1999. Nematode management, soil fertility, and yield in organic vegetable production. Nematropica 29: 205-213.

Petrillo, M. D., and P. A. Roberts. 2000. Influence of susceptible and resistant cowpea plants on life history traits of Meloidogyne incogita. Journal of Nematology 32:453 (Abstract).

Sasser, J. N., and M. F. Kirby. 1979. Crop cultivars resistant to root-knot nematodes, Meloidogyne species. Department of Plant Pathology, North Carolina State University, Raleigh, NC.