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Yield losses from foliar and soilborne peanut diseases

John Damicone: Oklahoma State University

<div>The foliar disease early leaf spot and the soilborne diseases stem rot and Sclerotinia blight are important disease of peanut in Oklahoma and worldwide. Quantifying yield loss is important for yield loss assessment on a regional scale and for evaluating the effectiveness of disease management programs in individual fields. Trials evaluating various fungicides and application timings were used to produce differential levels of disease and resulting yields. In evaluating associations between disease incidence and yield, critical point ratings near the end of the growing season generally were as effective as area under the disease progress curve. Relative yield was calculated as a percentage of the y intercept (disease=0) in regression analysis of disease incidence vs. yield. For early leaf spot on spanish-type cultivars, relationships of defoliation with relative yield were curvilinear with little decline in yield until defoliation reached ca. 60%. Thereafter, yield declined to reach ca. 50% yield loss at 100% defoliation. For Sclerotinia blight and stem rot, relationships between relative yield and incidence of blighted plants were linear. Yield loss declined about 1.5% for every percent increase in disease suggesting that disease was more extensive underground than was apparent aboveground. Cultivars with resistance to Sclerotinia blight had similar yield loss slopes as susceptible cultivars, but lower maximum levels of disease than susceptible cultivars.</div>