Disease Note

First Observation of Potato Late Blight in Fall Potatoes Grown in Northeast Florida. D. P. Weingartner, University of Florida, IFAS, Agricultural Research and Education Center, Hastings, FL 32045.  Plant Disease 69:1101, 1985.  Accepted for publication 30 August 1985.  Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-1101d.

Potatoes (Solanum tuberosum L.) are grown during January–June as a spring crop in northeast Florida.  The feasibility of growing a fall crop during September–December is being investigated.  Although late blight occurs in the spring crop nearly every year, Phytophthora infestans (Mont.) de Bary has never been known to oversummer in northeast Florida, and observations in the past have documented that northern-grown seed potatoes are the source of primary inoculum for the disease.  An important change in this pattern was observed when an outbreak of late blight was observed 3 December 1984 in a farmer's field of cv. Sebago potatoes that had been planted in September.  Seed for the fall planting had been selected and saved from the farmer's spring 1984 crop of potatoes.  The outbreak of the disease was confined to the northeast corner of a 42.5-ha field.  A survey of adjacent ditches and fields near the infection focus revealed no potential oversummering solanaceous hosts of P. infestans.  The source of inoculum for this outbreak of late blight was therefore assumed to be the seed potatoes even though the disease was not detected in the seed crop or in northeast Florida during 1984.  The observation of late blight in fall potatoes in northeast Florida is of major importance because this is the first documentation that a fall crop of potatoes may enable P. infestans to oversummer in northeast Florida and thereby provide early season inoculum for the spring crop.