Tuesday, November 14, 2006 - 10:00 AM

Fungicide Trials for Control of Asian Soybean Rust in Florida.

D.L. Wright, J.J. Marois, P.J. Wiatrak, B. Leite, and T.W. Katsvairo. Univ. of Florida, 155 Research Rd., Quincy, FL 32351

Soybean rust (Phakopsora pachyrhizi) (SBR) can be a devastating disease and can reduce yields dramatically if left uncontrolled.  It can also be an expensive disease to control and could potentially result in soybean production being unprofitable if SBR becomes widespread.  Trials were conducted in Florida to evaluate the efficacy of fungicides and timing for control of SBR.  Fungicide applications were made 8, 14, 21, 28, or 35 days after bloom for the MG IV soybeans.  Both incidence (% leaves infected) and severity (amount of disease on each leaf according to the Bayer CropScience rating scale). Many of the best fungicide treatments showed no infection. On the other hand incidence was about 100% in the control plots. Severity was less than 1 (2.5% or less) of the leaf surface being infected.  Control plots averaged almost 4 (around 10%) of leaf surface impacted.  Folicur and Impact were the most effective of the fungicides applied after bloom in controlling both incidence and severity. Towards the end of the growing season, almost all treatments had higher LAI than the control. Control had the lowest 500 seed weight and was significantly lower than all fungicides.  Test weight was highest for QRD 288 and Quadris combinations and Laredo and Headline combinations and was significantly higher than the control. From these preliminary studies it appears that the control of SBR with present fungicide chemistry is feasible as several of the fungicides tested gave excellent disease control.