Late foliar soybean fungicides

Rainy weather late in the season creates problems for soybean producers, but one researcher at the Delta Branch Research and Extension Center in Stoneville, Miss., is looking for ways to improve the seed quality of soybeans under adverse weather conditions.

“I am anticipating problems with seed decay in this year’s late Group 4 and 5 beans because of recent rains,” said Gabe Sciumbato, DREC plant pathologist. In 2008, the seed quality of most the early planted Group 4 beans in Mississippi was terrible.

Seed decay caused primarily by the fungus Phomophsis longicolla occurs when seed mature in warm weather and cannot be harvested at maturity. This fungus rots the seed on the plants and results in heavy dockage or refusal of the seed. Few management strategies provide complete protection. The producer cannot predict when a rainy period will occur.

Sciumbato is evaluating several foliar applied fungicides which are normally applied at the R3 to R5 growth stage. However, he is evaluating the effect of the fungicides when they are applied at the R5 to R6.5 growth stages.

Previous research has shown that these late fungicide applications result in little or no yield increase. Therefore, the only benefit of these treatments is to decrease disease and improve seed quality.

He is harvesting seed from each treatment to determine the fungi present in the seed. The seed will be graded for seed quality. Some trials are being conducted under a lateral move irrigation system where prolonged rainy periods can be simulated. Several different fungicides, fungicide timings and rates are being evaluated. Economic analyses are being conducted to determine which treatments are the most cost effective.

This research will provide a tool that a producer can use until soybeans varieties can be developed which are resistant to Phomophsis longicolla.

This research is funded in part by a grant from the Mississippi Soybean Promotion Board.

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