“The rust prediction models say there was a fair to good chance rust spores were deposited in North Carolina this weekend. If so, we expect to detect rust in about three weeks in sentinel plots, which would be about Oct. 1. It will likely take another two weeks with optimal conditions for rust to increase to damaging levels, Dunphy says.

The soaring price for soybeans is likely to spur most growers to treat either late-planted, late-maturing soybeans or double-crop beans to prevent late-season yield loss to soybean rust. Choosing the right fungicide and applying it at the right time will be critical.

There are four primary choices for fungicide treatment of Asian soybean rust: chloronnitrites of which chlorothalonil is the only product labelled for use; strobilurins, which offer a number of fungicide options; or traizoles, again offering a number of options; or a fungicide with a combination of strobilurins and traizoles as the active ingredients.

Chlorothalonil can be effective, but weathers much quicker than other options, and as a result may need to be re-applied several times to get adequate protection from the disease.

Strobilurin fungicides are modeled after a natural anti-fungal compound produced by certain mushrooms. Strobilurins inhibit mitochondrial respiration in the pathogen. Strobilurins are typically absorbed by the cuticle, and act as protectant fungicides against Asian soybean rust.

Triazoles inhibit sterol production, which disrupts cell membrane function in the disease causing pathogen. Triazoles are absorbed and translocated upward in the plant. While they generally do not prevent infection, the triazoles can kill the fungus in the plant and prevent pustules and spores from forming.

Fungicide products containing both strobilurins and triazoles may be the safest bet for management of Asian soybean rust. These fungicides offer the grower the greatest flexibility of timing of application at a time when many growers are busy harvesting are getting ready to harvest other crops.

rroberson@farmpress.com