The effects of inter-crop cultivation between rows of citrus crop on spreading of Guignardia citricarpa ascospores and in the citrus black spot occurrence

Abstract

This study highlighted the effect of planting coast-cross grass and forage peanut cv. Amarilis between rows of Natal oranges on spreading of Guignardia citricarpa ascospores and consequent citrus black spot control. Treatments evaluated were: 1-conventional cultivation, free of fungicides; 2-conventional cultivation, using protective fungicides; 3-inter-crop cultivation of coast-cross grass between rows of citrus crops and; 4-inter-cropping cultivation of forage peanut between the rows of citrus crops. Quest Volumetric Spore System™ traps were set in order to determine the number of ascospores released. A total of 33 inspections were conducted weekly, from the end of August until early September the following year. A diagrammatic scale was used to determine the severity of the disease as well as the percentage of fruits having a commercial standard. The coast-cross grass was more effective in reducing the number of ascospores produced, whose average statistics were lower than in the conventional treatments, free-fungicides. The inter-crop and conventional cultivation method coupled with fungicide treatment was more effective in reducing the severity of citrus black spot symptoms, and differs statistically from the fungicide-free control method. These methods also resulted in a higher percentage of fruits of a commercial standard, ranging from the 89% through the 91% percentile, and the cultivation, free of fungicides, fell within the 73%.