June 2005
Soybean Rust Fungicide Trials from
Brazil 2004The results for fungicide trials performed in Brazil have been recently posted on the Plant Management Network. Soybeans were planted in the late fall of 2003 and harvested in the late spring of 2004. Six varieties of soybean were planted in various areas of the country. Herbicide selection was the same for all trials, and the fungicides evaluated were myclobutanil, propiconazole, tetraconazole, azoxystrobin, tebuconazole, propiconazole + trifloxystrobin, pyraclostrobin, or mancozeb.
The results from the trials demonstrate some interesting trends. For three of the varieties, untreated disease (defoliation) occurrence ranged between 55 and 99 percent versus the untreated check by the end of the season, but yield was statistically unaffected at the 95 percent confidence level. However, for these three varieties, the mean yields for the plants receiving a fungicide (any fungicide) were always greater. For the other three varieties, a statistically significant increase in yield was observed for plants receiving a fungicide treatment (again, any fungicide treatment). These data illustrate the variability in disease signs versus yield, and why growers will have a hard time deciding whether it is economical to apply a fungicide or let the plant deal with the infection. (http://www.plantmanagementnetwork.org/pub/trial/fntests/)
