Comportamento de cultivares de soja na presença da ferrugem asiática, em relação a programas de controle químico

Abstract

Soybean rust is caused by an obligatory parasite (Phakopsora pachyrhizi) which is being spread in Brazil at each new season since 2001 and, despite the efforts to control the disease, losses have occurred every year. It s control demands several tactics and chemical control with fungicides is the main method and still is indispensable. Control strategies such as the use of partial resistance cultivars are desirable, but still are not commercially available. The present study analyzed the existing differences among the reaction of short, medium and long cycle soybean cultivars to Asian rust and their response to fungicide sprays. The experiment was conducted at Uberlândia-MG, in field conditions from December of 2007 to May of 2008, on Syngenta Seeds Experimental Station. The studied variables were: visual severity (percentage of leaf area infected), number of pustules per cm2, percentage defoliation, productivity on kg per hectare and one thousand grains weight. The area under disease progress curve (AUDPC) was calculated from the variables visual severity and number of pustules per cm2. The variance analysis and the comparison of averages test Tukey (5% significance) were done for all variables studied. Significant differences were observed between the effects of cultivars and chemical control programs studied. Based on the studies of the present work, it was concluded that the cultivars M-Soy 8199RR and Emgopa 315RR were less susceptible to disease, and that the control program called monitoring (on which the appearance of new pustules of the pathogen were monitored to make the decision at each fungicide spray) was the most effective.