Chemotherapeutic treatment options to manage Xylella fastidiosa in shade trees

Xylella fastidiosa is a fastidious, xylem-limited, broad spectrum, bacterial plant pathogen native to the Americas, causing substantial economic losses to the viticulture, citrus, and shade tree industries. In shade trees the disease is manifested as a chronic late season leaf scorch largely confined to urban areas of southeastern North America. Proposed treatments include antibiotics and growth regulators. Recently paclobutrazol, a diastereomeric triazole with fungistatic and growth regulation properties has been associated with symptom remission. Investigation into direct interaction of paclobutrazol with X. fastidiosa show no significant reduction in growth at the manufacturers recommended dosage of 20 mug ml-1 however significant reductions in growth were observed at a dosage of 200 mug ml -1. Therefore high levels of paclobutrazol may have a direct effect on X. fastidiosa while other plant physiological effects induced by paclobutrazol merit investigation for association in symptom mitigation of X. fastidiosa.