CHEMICAL CONTROL OF THE DOWNY MILDEW (Peronosclerospora sorghi) IN SORGHUM

• Main Authors: NICÉSIO FILADELFO JANSSEN DE ALMEIDA PINTO, CARLOS ROBERTO CASELA, ALEXANDRE DA SILVA FERREIRA
• Format: Article
• Language: English
• Published: Associação Brasileira de Milho e Sorgo 2006-04-01
• Series: Revista Brasileira de Milho e Sorgo
• Subjects: Sorghum bicolor; fungicides; seeds: downy mildew
• Online Access: http://rbms.cnpms.embrapa.br/index.php/ojs/article/view/171/169
• ISSN: 1676-689X; 1980-6477

Sorghum seeds of the cultivar SC 283, highly susceptible to Peronosclerospora sorghi were used in three experiments aiming the control of sorghum downy mildew. In the first experiment, seeds were previously treated with the following fungicides (g a. i. 100Kg-1 seeds): metalaxyl-M + mancozeb (5.6 + 89.6), metalaxyl-M + chlorothalonil (15.0 + 150.0), fosetyl-Al (240.0), propamocarb (722.0), metalaxyl-M (75.0), metalaxyl-M (37.5), fludioxonil + metalaxyl-M (12.5 + 5.0) and fludioxonil + metalaxyl-M (25.0 + 10.0). After these treatments, seeds were pregerminated, inoculated with conidia of P. sorghi and sowed in sterilized soil in the greenhouse. The experimental design was the one with randomized blocks, with 9 treatments in four replications. Fifteen days after sowing, the results evidenced that metalaxyl-M + mancozeb, metalaxyl- M + chlorothalonil, metalaxyl-M and fludioxonil + metalaxyl-M were highly efficient in the control sorghum of downy mildew (97.2 to 100.0%). In the second experiment, fungicides were evaluated for their efficiency in giving protection to seeds against oospores of P. sorghi present in the soil and in sorghum debris of systemically infected plants from the previous season. The following treatments were evaluated (g a. i.100kg-1 seeds): metalaxyl-M + mancozeb (5.6 + 89.6), metalaxyl- M + mancozeb (7.3 + 116.5), metalaxyl-M + chlorothalonil (15.0 + 150.0), metalaxyl-M + chlorothalonil (19.5 + 195.0), metalaxyl-M (37.5), metalaxyl-M (75.0), metalaxyl-M + fludioxonil (5.0 + 12.5) and metalaxyl-M + fludioxonil (9.0 + 22.5). Treatments were arranged in a randomized complete block design with 9 treatments in four replications. Plots were established in soil contaminated with oospores of P. sorghi derived from debris of systemically infected plants in the previous season. The plants were evaluated forty-five days after the sowing, and the fungicide metalaxyl-M (75.0 g i.a.100 kg-1) showed absolute protection against the systemic infection. The third experiment was performed to evaluate the efficiency of fungicides for the control of downy mildew through foliar application against systemic infection and local lesions of P. sorghi. Treatments were planted in four row-plots between two rows on a susceptible genotype, planted 40 days before, to act as spreader rows. The following fungicides were used in this experiment (g i.a.ha-1): metalaxyl-M + mancozeb (100.0 + 1600.0), metalaxyl-M + mancozeb (72.0 + 1152.0), metalaxyl-M + chlorothalonil (135.0 + 1350.0), metalaxyl-M + chlorothalonil (101.2 + 1012.5), fosetyl-Al (2000.0) and fosetyl- Al (1440.0). The experimental design was a randomized block with 7 treatments in four replications. Fungicide spraying, in number of four, was accomplished with a hand sprayer at a 14 day-interval, starting 21 days after planting. Evaluations were performed fourteen days after the last spraying and the results showed that the fungicide metalaxyl-M+ mancozeb and metalaxyl–M + chlorothalonil did not present systemically infected plants and local lesions which attends the field legislation of 0% downy mildew in seed production fields. The non-treated control had a 17.4% of systemically infected plants and local lesions.