Interactions of Tillage and Soil Fertility with Root Diseases in Snap Bean and Lima Bean in Irrigated Multiple-Cropping Systems

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Abstract
Snap bean or lima bean was planted each August following corn in a multiple-cropping system for 6 yr. Root and hypocotyl disease severity and postemergence damping-off (caused primarily by Rhizoctonia solani AG-4, Fusarium solani, a sterile white basidiomycete, and Pythium spp.) were greater in fall snap bean than in lima bean and in subsoiled or disked than in plowed treatments. In one year of three, postemergence damping-off was increased in snap bean by applying nitrogen broadcast preplant compared with applying it through overhead irrigation. Plowing reduced populations of R. solani AG-4 and Rhizoctonia-like fungi compared with disking but increased or had no effect on populations of Pythium spp. In spring snap bean, root disease severity was greater in single rows than in twin rows and with starter fertilizer than without. Subsoiling increased the number of plants with reddish brown sunken cankers on the hypocotyls compared with plowing. Numbers of Meloidogyne incognita juveniles in the soil and root-gall indices were greater in fall lima bean than in snap bean. In most tests, numbers of M. incognita juveniles and root-gall indices were not affected by tillage methods or fertilization treatments. Yield of snap bean was greater in the spring than in the fall.