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Effects of Sprinkler Irrigation at Various Times of the Day on Development of Potato Late Blight. J. Rotem, The Volcani Institute of Agricultural Research, Bet Dagan; J. Palti(2), and J. Lomas(3). (2)(3)Ministry of Agriculture, Tel Aviv, and Meteorological Service, Bet Dagan, Israel. Phytopathology 60:839-843. Accepted for publication 11 December 1969. DOI: 10.1094/Phyto-60-839.

The effect of overhead sprinkling applied at various times of day on development of Phytophthora infestans on potatoes depended on seasonal weather conditions and density of stand. Under conditions highly favorable or submarginal for blight, the time of sprinkling had little effect. Under marginal conditions, overhead sprinkling encouraged blight, and morning irrigation had a greater effect than did midday or evening irrigation. The blight-promoting effects of morning sprinkling are related to the fact that, in Israel, the sporangia of P. infestans are dispersed in the morning and die under the usually adverse conditions occurring later in the day. An empirical and arbitrary macroclimatic value useful for indicating conditions governing potato blight has been found in the sum of the daily deficits of relative humidity and of the daily levels of total global radiation.