New products for the control of soil borne Phytophthora species infecting citrus and ornamental plants

Control by chemical means is a widespread practice and a crucial aspect of integrated management of diseases caused by soil-borne Phytophthora in citrus groves and nurseries of ornamentals. In this study, systemic fungicides, including experimental active ingredients, were tested on citrus trees and rose plants stem-inoculated with P. citrophthora as well as on potted lantana and citrus plants transplanted in soil infested with P. cryptogea and P. citrophthora, respectively. Phosetyl-Al, mefenoxam and K-phosphonate were used as reference products. Among the new products, IR8465, IR8868 and IR8854 (Isagro, Italy) applied as preventive foliar spray, were as effective as phosetyl-Al in controlling citrus gummosis. Valiphenal, a mesosystemic dipeptide fungicide of the valinamide class of compounds recently registered against downy mildews of grapevine, potatoes and vegetables, was scarcely effective when applied as foliar spray on citrus due to its poor systemicity. Conversely, it was as effective as phosetyl-al in controlling both crown and stem rot of rose and root rot of lantana caused by P. citrophthora and P. cryptogea, respectively; thus indicating that the performance of systemic fungicides may vary with the host-pathogen combination because of the complex mode of action of these products. Soil drenches with both the fenilamide kylaraxyl, at a low dosage (120 g a.i./ha), and Remedier® (a biological product based on Trichoderma harzianum and T. viridae) were as effective as mefenoxam and kyralaxyl at a standard dose (476 g a.i./ha) in reducing root rot of citrus in soil infested with P. citrophthora.