May 6, 2005 | By: Laura Skillman

Soybean flowering dates appear to play a critical role in managing soybean rust. As a result, specialists with the University of Kentucky Cooperative Extension Service have compiled a guide to help farmers and field scouts determine flowering dates.

Fungicides applications likely will not occur until soybeans first flower or sometime after first flowering, said Chad Lee, UK Extension agronomist. So, a crop simulation model was used to make flowering 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.

Lee noted that anyone planning field scouting based on the tables in the guide 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.

Flowering depends both on length of day and temperature, so flowering dates may occur slightly earlier in western Kentucky where temperatures generally are slightly warmer. Farmers in this area and the southern tier may want to adjust predictions up two to three days from the model.

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

The publication is a tool farmers can use in their soybean rust management program. It is available through county Extension offices or online at


Writer: Laura Skillman 270-365-7541 ext. 278

Contact: Chad Lee, 859-257-3203