Evaluation of chemical, biological, and cultural controls for the management of pod rot of lima bean caused by Phytophthora capsici
Date
2015
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Publisher
University of Delaware
Abstract
Lima bean (Phaseolus lunatus ) is an important crop for the Delmarva Peninsula, particularly Delaware, which plants more land area to lima bean than any other state. Yield loss due to diseases such as pod rot, caused by Phytophthora capsici, reduce profitability of the crop. Phytophthora capsici causes significant damage to lima beans during periods of high humidity and frequent rainfall. Symptoms include browning, drying, and abortion of the pod. Current management practices for pod rot are limited, and fungicide choices are few. Mefenoxam is the most widely used fungicide and it has been registered for use against P. capsici on lima bean since 2000, however, repeated applications have resulted in populations of P. capsici with resistance. Cyazofamid was approved for control of pod rot 2013, however use remains low because of the expense. The goal of this research was to identify new products and practices for managing pod rot of lima bean. These included identifying new fungicides with efficacy against P. capsici on lima bean, as well as evaluating biofumigation, biopesticides, and reduced tillage. All field experiments were conducted during the summer of 2013 and 2014 at the University of Delaware's Carvel Research and Education Center, Thurmond Adams Agricultural Research Farm located in Georgetown, Delaware. All 12 fungicides significantly reduced pod rot disease incidence compared to controls (P < 0.05), and mefenoxam, cyazofamid, fluazinam, oxathiapiprolin, and potassium phosphite achieved the best control. Detached pod assays conducted in the laboratory with the fungicides listed above support the results observed in the field, and indicate that flat pods are more susceptible to P. capsici infection than full pods within 72 hours post inoculation (P = 0.0378). Experiments conducted to evaluate the effect of biofumigant crops ( Brassica spp., Sinapis alba, and Sorghum bicolor ) and biopesticides (Actinovate, Double Nickel, Serenade Soil, Superzyme 1-0-4, RootShield, PlantShield, SoilGard, and Trichoderma aperellum ) were inconclusive. Infection was low in these trials yielding no significant differences between treatments. Low levels of disease also occurred in the reduced tillage experiment conducted in 2013, as the effect of various tillage and soil surface residue practices on managing pod rot were inconclusive.