February 15, 2006 | By: Laura Skillman

All cases of Asian soybean rust on soybeans in the United States have occurred after soybeans have flowered. Being able to predict when flowering will occur can play a key role in scouting for the disease and ultimately reducing crop loss.

To determine if current predications are correct, the University of Kentucky College of Agriculture in conjunction with Wheat Tech Inc., a crop consulting firm in Russellville, Ky., conducted a study in 2005. The study included two varieties from each of four soybean maturity groups which were planted in three locations in the state – Lexington, Keysburg and Adairville, said Chad Lee, UK plant and soil scientist.

The current flowering predictions were established by UK last year using a crop simulation model to make predictions based on 29 years of weather data collected from UK’s Spindletop Farm near Lexington along with planting dates and soybean group maturity categories. 

Another goal of the project was to determine if flowering date was affected by location in the state.

“Our assumption going into the project was that with summer temperatures in western Kentucky slightly warmer than eastern Kentucky, soybeans planted in western Kentucky would reach the flowering stage sooner than those planted in eastern Kentucky,” Lee said.

Normal fertility and pest management practices were used in the study and the plots were scouted several times each week during the growing season to determine when the soybeans first began to flower.

Study results showed that the plots at Lexington and Keysburg followed the same general flowering date pattern, while the flowering dates at Adairville for the same varieties were a little sooner but only by a couple of days, Lee said.

Current flowering date predictions also proved satisfactory in the study.

Anyone planning field scouting based on the UK flowering prediction guide tables should begin checking 10 days prior to the predicted first flowering date. These dates will vary year-to-year due to temperature differences. The variation for first flowering date is greater for soybeans planted early than for soybeans planted later in the season.

The tables contain data on two-week planting intervals beginning May 1. UK does not recommend planting soybeans in Kentucky any earlier.

The publication, AGR-184, is a tool farmers can use in their soybean rust management program. It is available through county Extension offices or online at http://www.uky.edu/SoybeanRust.


Chad Lee, (859) 257-3203