September 5, 2007 | By: Laura Skillman

Soybean rust spores likely blew into some areas of north and north central Kentucky from remnants of Tropical Storm Erin but in extremely low levels, and most of the state was not touched. As a result, while there is much rust activity in many nearby states, there’s little cause for concern in Kentucky, says a University of Kentucky College of Agriculture plant pathologist.

In most areas of the state that are still very hot and dry, drought and or charcoal rot are the greatest production risks to soybeans, said Don Hershman, UK plant pathologist. The fungus that causes charcoal rot is present in all agricultural soils in Kentucky where soybeans are commonly produced and favors hot, dry conditions.

“Charcoal rot and drought will be the biggest yield limiting factors in this year’s soybean crop,” Hershman said.

Most plants are infected with the fungus, but it remains largely dormant unless high temperatures and low soil moisture coincide with plants in the reproductive stages, he said. Charcoal rot is also exacerbated in weakened plants which can result from poor soil fertility and excessive seeding rates. The disease then increases as the stressed soybean plants approach maturity. Premature death of affected plants is a common outcome.

Yields can be severely compromised by charcoal rot. However, because the disease is most common during drought conditions, most producers attribute low yields in dry years to lack of sufficient soil moisture and do not usually realize that charcoal rot has also taken a toll. Under moderate drought conditions, affected plants usually occur in patches associated with compacted soils or on hills. In a severe drought, large percentages of fields may show evidence of disease.

Hershman said he expects soybean rust likely will be found in Kentucky sometime in September, a month earlier than last year but too late for any damage to occur to full season beans. Only double-cropped plantings could be at risk.

“People are hearing a lot about it because of the finds in other states, but the main thing is for Kentucky farmers not to get too concerned,” he said. “If it did drop spores in Kentucky, and I believe it did, we are still several weeks away from it developing enough for us to even find it, much less needing to spray for it.”

This is because the initial level of spores deposited is predicted to have been very low and some likely died due to UV radiation when the sun reemerged in areas that received rainfall. 

“In my opinion, the absolute earliest we may need to treat soybeans in potentially impacted parts of the state would be late September,” Hershman said. “By that time, most full-season crops will be far enough along that spraying will not be necessary. Double crop beans continue to be at greatest risk for possible damage by SBR where rains have occurred.”


Will Snell, 859-257-7288