Control of Citrus Variegated Chlorosis by Pruning

Abstract

Approximately 20% of the citrus groves in S5o Paulo State are affected by citrus variegated chlorosis (CVC). The disease is caused by the bacterium Xylella fastidiosa which is readily transmitted by various sharpshooters. Trees are infected when they are fed on by infec- tious sharpshooter or when trees are produced using infected budwood; the bacterium subse- quently spreads throughout the trees and the results in a non-productive tree. When trees over about 5 yrs of age become infected by sharpshooters, some individual branches of the trees will show symptoms, but most of the branches will show no symptoms for several years. The observa- tion that the bacterium appears to spread slowly was confirmed by dot-immunobinding assays. The bacterium was readily detected in symptomatic leaves but was not detected 50 cm below the last leaf with symptoms on a given branch. Based on these observations, CVC was virtually elimi- nated from 552 hectares of sweet orange on Cleopatra mandarin rootstock by pruning 50 to 100 cm below any symptomatic leaves. Before pruning, approximately 15% of the tress had symptoms of CVC. After initial pruning, the trees were examined and pruned every other month for 6 months. The trees are now being examined and pruned annually. Very little CVC has been detected in the last 3 yrs and the trees are very productive. In contrast, significant losses due to CVC are occurring in groves on adjacent farms that have not been monitored or pruned.