The recent resurgence in soybean production in Alabama received a bit of setback this past year with a crop that was damaged by extreme drought and heat.

“We had about 350,000 acres of soybeans in 2010, and yields were down quite a bit to about 28 bushels per acre,” says Dennis Delaney, Auburn University Extension soybean specialist. “We got hit pretty hard by the drought. We made about 17 million bushels in Alabama in 2009 and only about 10 million this past year.”

The year 2009 was a very good one for Alabama soybean producers, with a record yield of 40 bushels per acre from approximately 430,000 acres.

“Agronomically, I think 350,000 acres is probably a better number for us. There are a lot of common diseases between soybeans and peanuts, so it’s better if we don’t have those two together in a common rotation. Sometimes you can get by with it, but other times, it’s a train wreck when you put one behind the other,” says Delaney.

This past year, in some areas where there might have been vegetation, producers just didn’t get pod set due to hot, dry conditions, he says. Even irrigated yields were down from where they should have been, he adds.

“We don’t have very much disease pressure in such a dry year,” says Delaney. “Early on, we had some non-lethal pythium, especially in heavier soils. When we used to plant without a seed treatment, we’d just lose a stand with wet weather early in the spring. But with fungicides on the seed, the plants hung around just long enough to barely survive.”

Asian soybean rust has been a hot topic in recent years, but in 2010, it didn’t show up at all until nearly harvest time. “One disease we did see a fair amount of last year was aerial web blight here and there across the state. The main control for it is fungicides, the strobilurin products, used as a preventative treatment.”

Reports of resistance

There has been a report in west Tennessee, says Delaney, of fungicide-resistant frogeye leafspot. The fungus Cercospora sojina causes the disease, however, it can be seedborne. Frogeye leaf spot is most likely to become a problem if infected seed is planted or if the disease occurred in the previous year’s soybean crop and the land is not rotated. Extended periods of wet weather during the growing season will favor disease development.

“They’ve picked up some resistance in west Tennessee, in some fields in river bottoms. This particular area had been in soybeans for at least three years. It had been sprayed at least three years with a strobilurin fungicide. The producer noticed that after the first spray, there was a lot of frogeye leafspot. He sprayed again, and it kept coming. True resistance was confirmed in that field. As with glyphosate resistance, the same chemistry was used year after year,” he says.

In this case, the chemistry was strobilurin, which is the most effective tool currently available for controlling a broad sprectrum of soybean diseases.

“Just like weed resistance, the best way to insure we don’t have this problem in Alabama is to rotate crops, plant resistant varieties, and spray only when needed. We also can rotate our fungicides. Some of the triazole fungicides like Domark have some pretty good activity on frogeye leafspot. Stratego and Quardris Xtra are pre-mixes of a triazole and strobilurin and also could be options,” says Delaney.

Herbicide resistance management strategies for cotton also hold true for soybeans, he says.

There are fast-changing lineups in soybean varieties from year to year, and it can be difficult to keep up, says Delaney. “A variety may last three years at the most, and then it is replaced by a new, hopefully better, variety.”

He advises growers to use multiple sources of information when selecting varieties, being careful to choose them for the nematode and disease resistance required by a particular field situation.

New varieties are in the pipeline, he says. “Dicamba or 2,4-D-resistant soybeans are probably several years off in the future, maybe 2013 or 2014, and they’ll be very early maturing varieties in the beginning. It’ll probably be 2015 before we see any of those varieties well-suited for the South.”

Delaney also notes that iron chlorosis has been a problem in Alabama in fields with  high-pH soils. “We looked at some in-furrow treatments last year of  iron chelates, and some of it looked pretty good.”

phollis@farmpress.com