Etiology of Peanut Pod Rot in Nicaragua: II. The Role of Pythium myriotylum as Defined by Applications of Gypsum and Fungicides

Peanut (Arachis hypogaea L.) is monocultured in western Nicaragua on loamysand soils, and a pod rot of unknown etiology can greatly reduce crop yield. Pythium myriotylum was frequently isolated from symptomatic pods in fields surveyed at Cosiguina, Leon, and Chinandega regions, although Rhizoctonia and Fusarium were also common. Applications of mefenoxam (0.57 kg a.i./ha), azoxystrobin (0.34 kg a.i./ha), and gypsum (670 kg/ha) at beginning pod and 28 to 35 days later were evaluated in field trials to determine their effects on pod rot and yield. Mefenoxam consistently decreased pod rot incidence and increased yield when disease was severe at Cosiguina. In Leon and Chinandega, azoxystrobin increased yield in fields with little pod rot, apparently by controlling stem rot (Sclerotium rolfsii), but did not decrease pod rot incidence. Application of gypsum had no effect on pod rot incidence or yield, but sometimes increased calcium levels in shells. Pod mycoflora isolations and response to mefenoxam suggest P. myriotylum is the primary cause of peanut pod rot in Nicaragua, especially in Cosiguina, where pod rot incidence was high. Accepted for publication 4 November 2009. Published 15 February 2010. The relationship between soil nutrient status and pod rot development in Nicaragua has not been explored, and there were questions of calcium availability in these volcanic soils exposed to frequent torrential rain. This study focused on the role of parasitic Pythium spp. and their interaction with calcium availability on pod rot incidence and peanut yield.