By Lannie L. Lanier
County Extension Coordinator

Soybean rust continues to be a news worthy item this season. Here is an update on the situation.

Soybean rust is a new disease to the United States and our growers have never had to fight it before.

We in the Extension Service in Georgia are also learning much this season with regards to management. Because we do not know exactly how this disease will behave in the state in 2005, we are taking a very conservative approach to protecting the crop. We are basing our recommendation on the following items:

1. We have confirmed soybean rust in Seminole County and believe that it is also very likely present in Terrell County. This means that the disease has likely spread elsewhere in Georgia as well.

2. We now realize just how difficult it is to identify soybean rust in the field at its earliest stages. Growers will not be able to identify the earliest infection in the field without submitting a sample to the disease lab for analysis. Growers will be able to identify the disease once numerous pustules are present; however, this may be too late for optimum management.

3. Although the spread of rust in Georgia has been very, very slow, we recognize that the disease can move with explosive force when conditions are right.

4. We know that as soybeans move from vegetative growth to flowering, soybean rust often becomes a much more important problem and moves more quickly.

5. We believe that the first fungicide application made by the grower is the most important one.

Based on the points above, soybean growers in Georgia should be considering preparations to make their first fungicide application as their crop nears the bloom growth stage.

Advice on spraying fungicides:

1. When spraying soybeans for soybean rust, it is important to get complete coverage of the plant.

2. Growers should use a nozzle tip that will offer maximum canopy penetration and coverage.

3. Growers who apply fungicides with a ground rig should use at least a 15-20 gal/A spray volume. Applicators will likely need to use a spray pressure of 50 psi or better to maximize coverage.

4. Aerial applicators should use 5gal/A spray volume.

5. Applying the fungicide prior to infection, or when infection is very low, is critical to the success of the fungicide program.

6. Strobilurin fungicides, like Quadris and Headline, are protectants and offer little or no curative activity. If a grower chooses to use one of these materials without the addition of a triazole fungicide in the mix, he should only do so if confident that no rust is present in the field.

7. Growers are cautioned that use of a strobilurin fungicide without a triazole premix partner could be risky.

8. Triazole fungicides, like Folicur, Domark, Laredo, and Orius (tebuconazole) provide protective as well as some curative benefits. These fungicides are still best used prior to infection, or at least very early in the infection process to be most effective.

9. Not all triazole fungicides are created equal. Folicur, Orius, Laredo, and Domark are more effective than Tilt, Bumper, or PropiMax.

10. We estimate that the interval between applications of triazole fungicides will be about two weeks.

11. There are several products currently available (Headline SBR, Quilt, and Stratego) where a triazole fungicide is premixed with a strobilurin fungicide. The advantage that these premixes offer is that they have curative and protective qualities and the strobilurin fungicide in the mix extends efficacy from a two- week interval to three weeks.

12. Syngenta, maker of Quilt, recommends that 1% crop oil be tank mixed with Quilt to improve efficacy.

13. Growers should be prepared to make a second fungicide application 2-3 weeks after the first; however, they should consider weather conditions and the spread/lack of spread of the disease before making this second addition.

Benefits of making a fungicide application at bloom growth stage:

1. Rust may be on the move and will be difficult to detect in earliest stages.

2. Soybean rust is difficult to control once it becomes established in a field.

3. You will know that your crop is protected.

4. The first application may be the most critical.

5. Spraying at first bloom knowing that disease is in the state is good "insurance."

Risks to Georgia’s soybean growers who spray right now:

1. Although we have found that soybean rust has spread, it is spreading slowly and we really do not know how the epidemic will proceed.

2. Although our best understanding is that the disease will spread quickly at some point, we cannot be sure when that will occur.

3. Growers could spray now to be prepared for an epidemic that in reality is delayed for some time, or never even fully materializes.

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