Field effectiveness of fosetyl‐AI against citrus foot rot and brown rot1

The effectiveness of fosetyl‐A1 against citrus foot rot caused by Phytophthora citrophthora has been evaluated in a 25‐year‐old orchard of sweet orange cv. Tarocco, showing severe symptoms of the disease and in a 10‐year‐old orchard of the clementine‐type mandarin cv. Monreal, apparently healthy. All the trees were grafted on sour orange. In both orchards, three sprays at 200 g a.i. per 100 1 were applied in May, July and September for 3 years. The results were evaluated on the basis of yield and fruit quality. Trees of cv. Tarocco had yield increased by 25–44% whereas cv. Monreal yielded 3–16% higher than the unsprayed trees. Fruits of orange cv. Tarocco were collected from trees sprayed with fosetyl‐A1 and plunged in a water suspension of P. citrophthora. Fruits treated 11 days before inoculation showed an infection rate of 8.7%) whereas those unsprayed were 77% infected. Fruits inoculated 21 days after the treatment with fosetyl‐A1 were 32% infected whereas those unsprayed were 91%, infected. In other trials, trees of volkamer lemon were sprayed with a conidial and mycelial suspension of P. citrophthora at different times after application of fosetyl‐A1. The number of infected fruits and leaves in the unsprayed trees was very high (up to total leaf drop) and decreased sharply with the number of sprays (1 to 3).