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Simulated rainfall to evaluate removal of pyraclostrobin applied for control of postbloom fruit drop of citrus.
F. P. GONCALVES (1), B. B. Forcelini (2), N. A. Peres (3), L. Amorim (1). (1) Escola Superior de Agricultura Luiz de Queiroz, Universidade Sao Paulo, Piracicaba, Brazil; (2) University of Florida, GCREC, Wimauma, FL, U.S.A.; (3) University of Florida, Wimauma, FL, U.S.A.

Postbloom fruit drop (PFD), caused by <i>Colletotrichum acutatum</i>, is one of the most serious diseases of citrus in southwestern São Paulo State, Brazil. In this area, the weather conditions are extremely favorable for PFD and fungicide applications are often made during rain events. Nevertheless, no studies have been conducted to determine the retention of fungicides applied to citrus flowers just before rain. An experiment was carried out in a randomized block design with 3-yr-old sweet orange trees. The following treatments were applied: four rainfall simulations - 0, 4.3, 13 and 50 mm/h each with or without pyraclostrobin application. Branches 20 to 60 cm long containing flower buds were used as replicates. Simulated rainfall was applied 30 min after pyraclostrobin (0.25g a.i./L) sprays. After the simulated rainfall, the flowers were inoculated with 5 mL suspension of 2.5x10<sup>5</sup> conidia mL<sup>-1</sup> and were kept in humid chambers for 16 h. The experiment was performed twice. Treatments from both experiments were compared using the area under disease progress curve (AUDPC) by Tukey’s test. Pyraclostrobin showed excellent PFD control in rainfall simulation with less than 13 mm/h. The reduction of incidence of symptomatic flowers ranged from 80 to 94% on sprayed trees. Fungicide wash-off was not observed on trees under rainfall simulation at 4.3 and 13 mm/h. However, with rainfall simulation of 50 mm/h, the amount of disease was similar on sprayed and non-sprayed trees. Our results indicate that wash-off of pyraclostrobin is influenced by rain intensity.<p><p>Keywords: Fungus, Fruits-Nuts, Citrus

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