This research was an attempt to determine the most appropriate flower bud stages of sweet orange in which fungicide application is more effective to control postbloom fruit drop disease. The trials were carried out in a 'Natal' and 'Pera' sweet orange orchards (Citrus sinensis [L.] Osbeck). Flower branches of summer bloom (January, 1994) were randomly marked and the different stages of development of buds were characterized. In a first trial, the disease control was evaluated through manual spraying. The following treatments were applied (doses per 1 L): a) control; b) benomyl 0.5 g, when buds were marked (regular application); c) benomyl 0.5 g, 3-4 days after the treatment b (late application), and d) benomyl 0.5 g in 2 applications (regular application and 7 days later). In a second trial, the disease control was evaluated through regular spraying, using a tractor and speed sprayer. On 'Natal' orchard, the following treatments were applied (doses per 2,000 L): a) control; b) benomyl 1 kg on Jan 4th; c) benomyl 1 kg on Jan 4th and 11th; and d) benomyl 1 kg on Jan 8th. On 'Pera' the following treatments were applied (doses per 2,000 L): a) control; b) benomyl 1 kg, Jan, 4th; c) benomyl 1 kg, Jan, 4th and 10th; d) benomyl 1 kg + captan 3.5 kg, Jan, 4th); e) benomyl 0.75 kg + captan 2.5 kg, Jan, 4th; f) benomyl 1 kg + captan 2.5 kg, Jan, 4th; g) benomyl 1 kg + captan 2.5 kg, Jan, 4th + benomyl 1 kg, Jan, 10th; h) benomyl 1.5 kg, Jan, 4th; and i) benomyl 1.5 kg, Jan, 4th and 10th. Disease lesions on petals, fruit set and incidence of persistent calyx parameters were evaluated every other day. Through the results, it was possible to conclude that benomyl is efficient to control the disease in doses ranging from 0.5-0.75 g.L-1, and its response may be obtained in summer blooms when round to elongate bud stages are prevalent.
citrus; fruit set; Colletotrichum acutatum
