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No soybean rust yet in south Louisiana

As of early June, Asian soybean rust is yet to be found in south Louisiana.

One of those searching, Blaine Viator, has “been to three or four of kudzu locations that are usually hit with a heavy, early infestation” and found no signs of the fungal disease.

“This far south, many of us plant soybean sentinel plots,” says the Plattenville, La.-based consultant. “One concern is planting them early enough. Here, I need to plant plots on March 25 in order to get them advanced enough before the commercial crop.”

However, due to an extreme spring drought, “the sentinel plots I planted – with only two exceptions – didn’t emerge. We just had no moisture for five weeks after planting.”

LSU plant pathologists “have some sentinel plots under irrigation. But it appears we’ll have fewer sentinel plots to rely on than we’re used to. That means more focus may be on kudzu. I don’t think that’s a huge problem because kudzu is a great early indicator for soybean rust.”

Has the drought tamped down the rust?

“I think there are a couple of things happening.

“Every year, we have quite a bit of volunteer soybean show up in our sugarcane. Farmers who use metribuzin (a pre-emergence herbicide) in newly-planted sugarcane know soybeans are fairly tolerant. In fact, that product is labeled at a very low rate in soybeans. That’s why we get a lot of volunteer soybeans in our cane.”

Producers don’t often spray to kill the volunteer soybeans. “Sugarcane can compete and usually with the first hard frost the soybeans die.

“Normally, I never find soybean rust on volunteer beans late in the fall. I don’t know if it’s due to growth stage, weather conditions or something else. But last fall, before the freezes, there were excessive amounts of rust in those volunteer beans. Just about every plant I picked up was affected.

“Unlike kudzu, soybeans can handle colder temperatures. That doesn’t mean they can take hard freezes – in fact, the 2009 freeze took almost all the volunteer beans out. But in light freezes like we usually get around here, soybeans are resilient and can sometimes survive.”

That was Viator’s “biggest concern” with rust in 2010. If not for the severe freeze, “I think we’d be in a bit of trouble with rust.

“The dry, cool spring we’ve had has probably also greatly reduced and slowed down the disease’s progression. There’s no doubt we’ll find it this season but, hopefully, by the time it builds up the crop will be past the susceptible stage.”

As for pests in south Louisiana’s soybeans “we have a situation occurring that tends to happen from time to time. Where we did get some stands of soybeans, the growers were delayed from getting herbicides out. They didn’t put out a residual and were tardy in getting glyphosate out of post-emergence control.”

That led to some fields developing weed problems, mostly annual grasses. “Prior to some of the recent rains, growers applied glyphosate. Since then, as the weeds desiccate and die, an onslaught of armyworms, corn earworms and other lepidopteran pests are moving in.”

Viator suspects the worms “probably hatched on the grasses and were feeding on it. Now, as the grasses die, they’re moving into the soybeans.

“Right now, that’s happening significantly in only a handful of fields. But that’s likely to change because there are more fields that need to be sprayed for grasses. Once those applications take place, we’re expecting more worm infestations.”


TAGS: Soybean
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