EFFECTS OF ALTERNARIA-MACROSPORA ON THE YIELD COMPONENTS OF PIMA COTTON IN ISRAEL

Effects of Alternaria leaf spot (caused by Alternaria macrospora) on t he yield components of Pima cotton (Gossypium barbadense) were examine d in four field trials, for the lower (<30-50 cm), middle (30-50 to 70 -90 cm) and upper (>70-90 cm) layers of the canopy. The influence of t he disease on yield was determined by comparing measurements taken in fungicide-treated plots with those taken in untreated plots. Alternari a-induced defoliation was most severe in the lower canopy layer and gr adually decreased towards the upper canopy layers. Significantly fewer bolls (26.0%) were picked in untreated plots than in fungicide-treate d plots, but differences in average boll size (reduction of 1.07%) amo ng the treatments were non-significant. The relationship between disea se intensity and the loss of bolls was linear. Of the differences in y ield between fungicide-treated and untreated plots, 43.5% was observed in the lower canopy layer, 37.6% in the middle canopy layer and only 18.9% in the upper canopy layer.