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Peanut pod rot, which can be caused by Pythium spp. and Rhizoctonia solani , is difficult to manage with fungicides. The objective of this study was to compare the effects of a calendar-based (CB) versus threshold-based (INC) fungicide application timings on pod rot incidence, yield, value of the crop, and returns minus fungicide cost. Large plot replicated trials were conducted in five fields with a history of pod rot. Pod rot was assessed weekly throughout the season following development of pods. Disease incidence was reduced by the preventative CB compared with INC or the non-fungicide treated control (NONE) in three of five sites. Disease was very low in the remaining two sites. Yield was not affected by treatment at individual sites, but in a combined analysis, INC at 1–2% incidence had higher yields than CB treated with mefenoxam or NONE. Occurrence of segregation 2 kernels, which results in a substantial reduction in price, was more frequent with INC and NONE than with CB at two sites. CB and INC had a higher value/ha than NONE, but there were no differences in return minus fungicide costs. CB had less pod rot during the season and a lower risk of segregation 2 kernels at harvest than INC. These results suggest that preventative CB applications made at early pegging should be used to manage pod rot. This recommendation is based on the reduction of risk to segregation 2 kernels, not because of a higher value/ha of the crop.

Peanut fields are monitored for pod rot, which is typically caused by Pythium spp. and Rhizoctonia solani, in order to determine need, and the type and timing of fungicide applications. Pod rot can lead to damaged peanut kernels and when damage exceeds 2.49%, substantial price reductions occur. Nine fields or tests were sampled weekly for pod rot during the 2009 through 2012 growing seasons. The sampling was conducted on fields treated uniformly with fungicides for pod rot or within large research plots with various fungicide treatments. Pythium myriotylum was the most frequently identified pathogen species, although Rhizoctonia spp. were also recovered from diseased pods at all sites. Pod rot incidence was related to percent damaged kernels at harvest in 3 of 5 sites. Collection of 304 samples (sample unit = 46 cm of row) in a field was required to estimate 1% pod rot accurately (CV = 20%). There was a linear relationship between average % pod rot in a field, and the percentage of sampling units (absence/presence) with pod rot at low disease incidences. Scouting for pod rot of peanuts to make in-season fungicide applications will be hampered by high sample number, destructive sampling of plants, frequent sampling (due to rapid increase of disease), and the poor relationship between disease during the season and kernel damage at harvest. Making one preventative application at 60–70 days after planting may be a better practice than timing the initial fungicide application based on sampling for disease.