Forecasting outbreaks of Potato Blight in West Scotland

Abstract

The validity of forecasts of the first appearance of Potato Blight based on Beaumont's (1947) temperature-humidity rule has been investigated for the west of Scotland. Forecasts were all valid after the last days of June for the five years from 1944 to 1948, and were not valid before that time. This period is suggested as the ‘zero time’ of validity of forecasts in Ayrshire, and available evidence suggests that it varies for different districts. The effect of foliage Blight upon overall yield cannot yet be specified with accuracy. Forecasts would, nevertheless, be useful for protective sprays used to diminish the spread of Blight to the tubers. Such sprays should, nevertheless, always be used in conjunction with destructive sprays when possible. Reliable prophesies of the first appearance of Blight would also be valuable for timing the application of destructive sprays in the special case of seed crops of Epicure potatoes in the early districts of Ayrshire. The amount of Blight appearing naturally on the tubers is greatest when the disease develops slowly on the foliage. Such years may also bring a greater proportion of ware to seed, and there is a tendency for more Blight to appear on seed-size tubers than on the ware. Years of quick development of Phytophthora on the leaves have relatively little Blight on the tubers when no control of the disease is attempted.