Seed and foliar: How to pick your soybean fungicides

What producers need to do with soybean seed treatments at this time of year — when it's early and some of the early varieties are just going in — is to assume that the weather will turn off cooler and wetter than you want, says Cliff Coker, Arkansas Extension plant pathologist.

“From that standpoint, we don't know what diseases will hit the soybeans. Will it be a water mold like Pythium? Will it be a warmer weather wet problem like Rhizoctonia?” To deal with either possibility, Coker says growers need to employ a broad-spectrum approach. That usually means the use of a product combination such as ApronMaxx.

“The choices for growers wanting seed treatments are ApronMaxx, Vitavax 200 (for Rhizoctonia) plus Allegiance (for Pythium), or Vitavax 200 plus ApronXL. Another combination that some use is Vitavax and Thiram plus Allegiance. Stiletto is also available for both Rhizoctonia and Pythium.”

In treating the seed, Coker likes to see a commercial seed treater or an on-farm seed treater that uses a slurry or mist to get good coverage. Way down the list is a “planter box” treatment. “It's very hard to get good coverage from dumping a product in the planter box and stirring it around,” he says.

From the foliar disease standpoint, options narrow. Producers should start looking for foliar diseases around the time soybeans begin flowering.

The diseases that cause most problems are aerial blight and Frogeye Leaf Spot. To deal with those two diseases, Coker says there's a product that — if used at the correct time — gives good control: Quadris.

“It must be used at the very earliest onset of disease if it's going to work well,” he says. “Another product is labeled for use, but we have a hard time finding it. It's an older product called Topsin M. It's fairly effective on Frogeye Leaf Spot, but isn't quite as effective as Quadris on aerial blight.

For aerial blight, the low-end rate of Quadris at 6 ounces does a really good job, according to Coker.

“I've never seen it not pay for itself. Most of the time, you get very good, positive returns from use of Quadris. But the timing must be proper. If you get in too late, you'll be lucky to break even with the cost.” (Syngenta recommends application between the R3-5 stage.)

Currently, some Arkansas soybean growers are trying some ultra-early stuff: maturity groups 0, 2 and 3. Those are normally associated with crops much further north of Arkansas.

“Anyone planting these groups had better have a seed treatment on them,” says Coker. “Soil conditions aren't going to be good for germination or emergence so you need that extra protection.

“Once you hit May and soil temperatures are nice and warm and plants emerge in three or four days, you might be able to do without a seed treatment. But if you're planting now, seed treatments are incredibly important. Cool, wet soils favor disease organisms not germination of seeds and emergence of plants.”

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