Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2003
Publication Date: 8/7/2003
Citation: Keinath, A.P., Harrison Jr, H.F., Marino, P.C., Jackson, D.M., Pullaro, T.C. 2003. Increase in population of rhizoctonia solani and wirestem of collard with velvetbean cover crop mulch. Plant Disease. 86:719-725.
Interpretive Summary: Organic mulches made from cover crops that are killed and left on the soil surface are used extensively in organic and sustainable agricultural systems, particularly in developing regions. The tropical legume, velvetbean is used as a cover crop mulch in tropical regions of Africa, Asia and South America. Previous studies have indicated that the benefits of velvetbean mulch are that it provides nitrogen and other nutrients for rotational crops, suppresses weeds and nematodes, improves soil structure and reduces erosion. In this study, the effect of a velvetbean mulching system for fall transplanted collard in coastal South Carolina on the seedling disease, wirestem was determined. The occurrence of wirestem disease and its causal fungus, Rhizoctonia solani were higher in velvetbean mulched plots than fallow soil plots and plots where velvetbean was incorporated into the soil prior to transplanting collards. These results indicate that for collard, the benefits associated with the velvetbean mulch cropping system may be outweighed by the increased problem with wirestem disease. However, when velvetbean was incorporated into the soil, the disease was not increased. Thus, soil incorporation of a velvetbean cover crop may be necessary to prevent an unacceptable increase in wirestem disease.
Technical Abstract: Velvetbean has been used traditionally as a summer cover crop in the southeastern United States. We investigated the use of velvetbean as a killed cover crop mulch left on the soil surface before collard was transplanted in the fall. Control treatments were weed-free fallow and velvetbean that was killed and disked into the soil before transplanting. Incidence of wirestem caused by Rhizoctonia solani reached a maximum of 25% in 2000, but only 4% in 2001. Nevertheless, in both years, wirestem progression, area under the disease progress curve, and final incidence were significantly greater with cover crop mulch than in the fallow or disked treatments. Wirestem levels did not differ between the disked and fallow treatments in either year. Populations of R. solani in soil were greater with cover crop mulch than with fallow in both years and greater in the disked treatment than in fallow soil in 2000 but not in 2001. The higher level of wirestem and greater population of R. solani in the disced plot was attributed to greater velvetbean biomass in 2000 than in 2001. Velvetbean is not suitable as an organic mulch for collard production, but could be used as a summer cover crop if disked into the soil before transplanting collards.