Ag News

Threat of Asian soybean rust heightened in 2019

In the Georgia Soybean Commission’s spring newsletter, UGA Extension Plant Pathologist Dr. Bob Kemerait warned soybean growers that the risk for Asian soybean rust is worrisome in 2019 in part because of the mild winter weather. Kemerait said soybean rus twas found on April 7 on kudzu that survived the winter in Tattnall County. Early detection is an indication the disease could be a problem for soybean growers this year and they should plan accordingly.

From Kemerait’s article:

Asian soybean rust is potentially one of the most damaging diseases to affect soybean production in Georgia and elsewhere in the southeastern United States. When environmental conditions are favorable and when the disease occurs by early-to-mid reproductive growth stages, significant damage can occur that will result in yield loss unless the crop is protected with fungicides. Though significant effort in breeding soybeans for resistance to this disease continues, our commercial varieties planted now are susceptible to rust.

Unlike other diseases and nematodes affecting the soybean crop, the spores of the soybean rust pathogen often do not survive the winter months between cropping seasons. The fungus that causes soybean rust is an “obligate parasite” which means that the fungus must survive on a living host (plant). During most winters in Georgia, temperatures dip low enough, long enough, to kill the plants where the rust disease would survive, most typically kudzu and volunteer soybeans. Because of this, soybean rust will not be present in Georgia until A) kudzu or another susceptible host re-emerges after the winter months and B) spores of the rust pathogen are reintroduced into Georgia, perhaps from southern Florida or the Caribbean. Through the UGA Soybean Rust Sentinel Plot Monitoring Program, funded by the Georgia’s soybean producers and the Georgia Commodity Commission for Soybeans, it has been found that soybean rust is typically not detected in the state until June and even into July in some years. Later introduction of soybean rust back into Georgia reduces the risk that growers face to this disease.

Temperatures during the winter of 2018-2019 were fairly mild and there were no prolonged periods of freezing weather or “hard freezes”. Primarily, mild conditions last winter allowed kudzu to survive where normally it would have been killed back. As early as February, soybean rust had been detected on kudzu growing in Gainesville, Florida, and Mobile, Alabama. By April 7, soybean rust was found on kudzu that survived the winter in Tattnall County. This was earliest post-frost period detection of soybean rust in Georgia since 2004.

Early detection of soybean rust in Georgia does not guarantee that the disease will be a significant problem in the coming season. However, it is a strong indication that it could be a problem and that soybean producers should plan accordingly. The most significant yield loss and damage occurs when infection of the crop occurs earlier, rather than later in the season. Given that the disease is already known in the state, growers should carefully follow further reports from the UGA Sentinel Plot program of the development and spread of the disease in the state.

Depending on weather during the season (wetter or drier), rust may develop quickly or very slowly. As a minimum, growers should be prepared to make a fungicide application to their crop as early as the R1 (bloom stage). The crop remains susceptible until the R6 (full seed size) stage. Your local UGA Extension agent can provide information both on the spread of the disease and on fungicides programs that can best protect your soybean crop.