Distribución temporal de síntomas del amarillamiento de la hoja en la ca？a de azúcar en Cuba

the objective of this study was to determine the temporal distribution of the physiological symptoms of leaf yellowing disease of sugarcane and its relationship with weather variables in the central region of cuba. field evaluations were conducted in three experiments in two locations, during the period from 2003 to 2007. monthly evaluations were carried out starting with the appearence of the first symptoms, using a hand refractometer to record values of refractometric brix of the basal third of the third leaf with visible dewlap (tvd). correlations of the values of observed brix were with climatic variables were obtained. the first symptoms of leaf yellowing appeared in plants of five months of age, independently of the time of sowing, at the beginning of the winter season, and then decreased with the beginning of the spring. the brix of the leaf increased from november and reached a maximum in april, after which the plants became asymptomatic. the decrease of the maximum, minimum and monthly average temperatures below 30, 21 and 25°c, respectively, as well as monthly precipitations lower than 50 mm, favored the expression of the symptoms, which were more related to climate than to crop age, in coincidence with the dry period of maturation and harvesting time of sugarcane.