Control of Brown Stripe Downy Mildew of Maize by Metalaxyl

LAL, S., S. C. SAXENA, and R. N. UPADHYAY. 1980. Control of brown stripe downy mildew of maize by metalaxyl. Plant Disease 64:874-876. Seed treatment with metalaxyl at 4 g/ kg controlled brown stripe downy mildew (Sclerophthora rayssiae var. zeae) of maize up to 30 days after planting. When combined with seed treatment, one foliar application of metalaxyl (225 ppm) on the 30th day after planting resulted in excellent disease control and increased grain yield and 1,000 kernel weight. MATERIALS AND METHODS Four field experiments were done with metalaxyl (25 WP) to control BSDM at Pantnagar during 1977 and 1978. In the first experiment 2, 4, 6, 8, 10, and 12 g of metalaxyl slurry was used per kilogram of seed of susceptible hybrid VL-54. Based on the results of the first experiment, in the second experiment, seeds of hybrids VL-54 and Ganga 5 were slurry treated with 4g/ kg (Table 1). In the third experiment, one or two foliar sprays were applied 30 and 40 days after planting hybrid VL-54, with or without seed treatment (Table 2). In the fourth experiment, maize cultivars Ganga 5, Ganga 2, J 603, and VL-54 were planted Brown stripe downy mildew (BSDM) (Sclerophthora rayssiae var. zeae Payak and Renfro) on maize occurs in India, Nepal, Thailand, Pakistan, and Bangladesh (3). In India, it has been most severe in Uttar Pradesh, Himachal Pradesh, southern Rajasthan, Punjab, and hilly parts of West Bengal, especially in areas that receive 100-200 cm of precipitation (6,10). It has caused 63% loss in the Tarai area of Uttar Pradesh (9). Although extensive studies have been done on chemical control of maize downy mildews incited by Sclerospora, little information is available on BSDM (1,2,6-8,11,13). Its severity has been reduced by six sprays of mancozeb (0.3%) or by three sprays of either triphenyltin chloride or triphenyltin acetate (6,8,9). Because maize is predominantly a Journal series publication 1810, The Experiment Station. 0191-2917/80/09087403/$03.00/0 © 1980 American Phytopathological Society 874 Plant DiseaseNol. 64 No. 9 rainy season crop in India and neighboring countries, fungicides are washed off the foliage, rendering the sprays less effective. The present investigation reports for the first time effective control of BSDM by seed treatment and one foliar spray with metalaxyl. Table 1. Effect of metalaxyl seed treatment (4 g/ kg) on the incidence of brown stripe downy mildew (BSDM) BSDM incidence'1,000 Days after planting grain wt Yield Cultivar 30 40 50 60 (g) (kg/ha)