PLANT STRESS DUE to drought heat or insect damage during fungus growth usually increases aflatoxin levels in corn

PLANT STRESS DUE to drought, heat or insect damage during fungus growth usually increases aflatoxin levels in corn.

Aflatoxin still a concern for Southeastern corn growers

• You want the corn to mature before the temperature hits a sustained 95 degrees F. in the afternoon. • Temperatures must get really high for the fungus to produce toxins.

As the interest in corn production in the Southeast continues to grow, so does the need to reduce aflatoxin contamination and increase the value of the grain.

“We always stress planting early as a means of avoiding aflatoxin in corn, especially in dryland conditions,” says Austin Hagan, Auburn University Extension plant pathologist.

“You want the corn to mature before the temperature hits a sustained 95 degrees F. in the afternoon. Temperatures must get really high for the fungus to produce toxins.”

More corn varieties are coming onto the market that will have some drought tolerance, says Hagan.

“The ones we have now have been incrementally getting better as far as drought tolerance, but in a few years, that trait will be much stronger in the varieties coming down the line.”

Irrigation, however, is not 100-percent effective against aflatoxin, he warns.

“In the aflatoxin trials we conduct in the Wiregrass in southeast Alabama, we routinely see aflatoxin in our irrigated corn. Levels are not as high as they would be in dryland corn, so irrigation is not 100-percent effective, but it comes pretty close,” he says.

Harvesting early at high moisture and then drying the grain might be a strategy for reducing aflatoxin, especially in dryland fields where you’re more likely to have problems, says Hagan.

“Just blowing the lighter seed out of the back of the combine can help since that’s the seed that has been damaged by insects or rotted by the fungus.

“If it goes out the back, then a lot of your aflatoxin will go out the back,” he says.

The same concentration of aflatoxin will not be found in all of the kernels in a load, he says.

“Most of the kernels won’t have any aflatoxin or very little in them, but a few of them might have up to 14,000 to 15,000 parts per million in one kernel, and if it goes out the back of the combine, you can save yourself a lot of lot of trouble.”

In field trials, Hagan and other researchers have been looking at Afla-Guard and some of the advanced Bt traits.

One seed company is promoting its advanced Bt traits as a means of reducing aflatoxin in corn, he says.

Goes out at tasseling

“This is the second year we’ve looked at Afla-Guard. It’s applied over-the-top, and you’ll need a high-boy with a spreader on it or large spreader unit. It goes out as the corn goes into tasseling, hopefully right before a rain.

“It’s a grain product that basically is impregnated with spores of a non-toxic producing strain of aflavus.”

The idea behind the product, he explains, is that you put it out prior to the time the silks are infected by the fungus. The Afla-Guard fungus will sporulate on the ground and in the canopy, and those will be the first spores that get to the silks, he says.


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“So they will be the ones growing on the silks, and when the toxin-forming ones show up at about the same time, they’re excluded — it’s an exclusionary system.”

In a test conducted at the Wiregrass Substation in 2011, Hagan planted several different Bt-trait varieties.

“In that test, we didn’t see any effect from Afla-Guard on any of the variables we were looking at, and we also didn’t see a reduction in aflatoxin in the treatment.

“In the variety trial next to it, where we used Afla-Guard and a non-treated control, it looked like there was a reduction in several varieties in the trial. So it looked like we had a little less aflatoxin in the treated compared to the non-treated.

“One of the problems we run into in working with aflatoxin is that there’s a lot of variability from sample to sample that we pull out of these plots.

“It’s really difficult to show differences or suppression of aflatoxin with some of these treatments, and that has been an ongoing problem with some of our trials.”

The base genetics of a lot of corn varieties differ in their sensitivity to aflatoxin, says Hagan.

“That information hasn’t been generated to any degree for the varieties we grow down here. We simply don’t know which ones might have less toxin accumulation than others.

“In the statewide variety trials, we’re pulling kernel samples from most varieties in each of the trials, and we’re specifically looking for information as it relates to Bt traits.

“Some varieties seem to have more alfatoxin than others in the areas where the fungus occurred. But there’s still a lot we don’t know about these varieties.”

Hagan is also looking at the timing of Afla-Guard treatments. “Basically, when we pulled out the aflatoxin contamination levels, there were no differences among these treatments.

“On the Gulf Coast, we didn’t have much aflatoxin contamination on corn. The timing appeared to have an impact on insect damage from corn earworm in ears, but it really didn’t affect anything else, and it didn’t affect the yield.”

A test from Oklahoma showed that Afla-Guard does reduce aflatoxin, says Hagan. When they put it out early, there was no effect. But at V9 through VT, in three of the four timings, there was a substantial reduction in the amount of aflatoxin in corn. However, the numbers were still high, he says.

Less kernel damage

“At this point in time, from the different Bt II traits, we’re seeing less kernel and silk damage and some yield gains in some years, but that’s not resulting in a reduction in aflatoxin.

“So we’re not seeing an association between advanced Bt traits and less aflatoxin in corn, and there’s still a lot of work to be done on Afla-Guard to see how consistent it is in reducing the amount of aflatoxin on corn.”

Proline fungicide actually has a label for aflatoxin suppression in corn in the Midwest, and as far south as Arkansas, says Hagan.

“We should get the opportunity to add that label in Alabama. We don’t know if this treatment will work on aflatoxin, but we’ll be looking at it this year.”

Hagan says there have been a few concerns about Northern corn leaf blight on corn in Alabama.

“There are differences in sensitivity among corn varieties to the disease. On some varieties, the leaf spots will be about 2 or 3 inches long, while they will be about 18 inches long on another variety.”

Northern corn leaf blight doesn’t have the same effect on yields — particularly on early corn — that Southern corn rust can have, says Hagan.

“To really reduce yields in corn, Northern corn leaf blight has got to take out the ear leaf, and I haven’t seen many situations on early corn where that has occurred.

“If you plant double-crop corn, or corn after wheat, then all bets are off. It’s very active in double-cropped corn. The best defense is to plant early.

“Once we get into wet weather patterns in June, you could be in real trouble. Wet weather really drives foliar diseases in corn, and Northern corn leaf blight will be more severe in late-planted corn.”

Several new corn fungicides are on the market, including Evito T, TopGuard and Priaxor, says Hagan.

“In the trials we’ve done on early corn where disease pressure isn’t that great, there really isn’t a lot of difference between the generic products and the name-brand materials.

“But when you get into double-cropped corn or when you have severe rust, the name-brand products do a much better job of protecting corn, and we tend to see a higher yield gain with those products compared with generics.”

If you have reniform nematode, corn is great for rotating with cotton, says Hagan. It fits well, and it’ll knock down any reniform nematode problems.

“However, we run into problems when we have root-knot nematodes. If fields have root-knot nematodes with cotton, it’ll jump onto corn and will reduce yields substantially.

“You don’t get the stunting you sometimes see with other nematodes in corn, but in trials we’ve seen that corn dries down faster and yields are reduced.”

Materials like Mocap and Counter applied as a granular treatment in-furrow will not only suppress nematodes, but will have activity against insects, says Hagan.

“The other options are seed dressings that also are labeled for nematode suppression in corn.

If you’ve had a lot of root-knot nematodes in the field, and you’re in a corn/cotton rotation, it would help to put peanuts in the rotation to suppress nematodes and bring up yields on corn and cotton.”

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