Yermiyahu, U., Institute of Soil, Water and Environmental Sciences, Gilat Research Center, Agricultural Research Organization, Israel
Israeli, L., Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
David, D.R., Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel
Faingold, I., Institute of Soil, Water and Environmental Sciences, Gilat Research Center, Agricultural Research Organization, Israel
Elad, Y., Department of Plant Pathology and Weed Research, Agricultural Research Organization, Volcani Center, Bet Dagan, Israel

Nutritional elements can affect plant susceptibility to plant pathogens, including Botrytis cinerea. We tested the effect of potassium (K) fertilization on gray mold in sweet basil grown in pots, containers, and soil. Increased K in the irrigation water and in the sweet basil tissue resulted in an exponential decrease in gray mold severity. Potassium supplied to plants by foliar application resulted in a significant decrease in gray mold in plants grown with a low rate of K fertigation. Lower K fertigation resulted in a significant increase in B. cinerea infection under semicommercial conditions. Gray mold severity in harvested shoots was significantly negatively correlated with K concentration in the irrigation solution, revealing resistance to B. cinerea infection as a result of high K concentration in sweet basil tissue. Gray mold was reduced following K foliar application of the plants. In general, there was no synergy between the fertigation and foliar spray treatments. Proper K fertilization can replace some of the required chemical fungicide treatments and it may be integrated into gray mold management for improved disease suppression. © 2015 The American Phytopathological Society.