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Don’t Sweat Ilevo-Induced Singed Soybeans

If you think your Ilevo-treated soybeans look a bit rougher than normal after you’ve sprayed them with a residual preemergence or postemergence herbicide, they likely are.

Still, your short-term worries should shortly wilt. So far, industry and university research shows this “halo effect” of soybeans with brown-tinged cotyledons will soon dissipate.

“Under cool and wet conditions, it is common to see that side effect,” says Kiersten Wise, Purdue University Extension plant pathologist. “If you are using preemergence herbicides, it can be a bit worse. Your beans might look beat up for a few days as they emerge.”

However, they quickly grow out of this ugly duckling phase, she says. This also shows Ilevo is working, adds Mike McCarville, Bayer CropScience technical service representative.

“When you see that halo effect, it is a good indication that it (Ilevo) is being taken up by the plant,” he says. “That way, you get early-season protection by SCN (soybean cyst nematode) and SDS.” (Ilevo also has activity against SCN in the root zone.)

What Ilevo Does

Ilevo (fluopyram), a Bayer CropScience seed treatment, debuted this year to manage sudden death syndrome (SDS) in soybeans. SDS symptoms seemingly come out of nowhere in soybean reproductive phases later in the summer -- hence the sudden death name. Early symptoms include upper leaves that yellow and defoliate in small areas. Affected areas may enlarge and other field areas may exhibit symptoms. Later on, in severe cases, leaflets drop off, and leave the petioles (leaf stalks) attached.

Although symptoms appear suddenly, infection starts earlier, with roots being infected as early as one week after crop emergence. Ilevo helps manage SDS by protecting young soybean seedlings on the roots and crowns of young soybean seedlings. These infections that then result in Fusarium root rot can produce the toxins that cause the later-season symptoms of SDS. However, dry weather during reproductive stages can nix infections that occurred during cool and wet early-season conditions.

Early on, though, Ilevo can discolor soybean cotyledons in a manner that mimics disease or an abiotic stress like herbicide injury. “When the fungicide is in the plant, it moves to the cotyledons,” says Wise.

The fungicide accumulation results in the phytotoxicity that causes cotyledon tips to turn a yellow-brown color. This necrosis is typically uniform and present on every seedling grown from Ilevo-treated seed, say university scientists. However, environmental conditions may impact the frequency, uniformity, and severity of the phytotoxicity observed.

The good news is the halo effect goes no further than the plant’s cotyledons. Typically, the plant’s cotyledons fall off within the first 30 days of emergence. Meanwhile, this Ilevo-induced phytotoxicity goes no further than the cotyledons.

“When the active ingredient in Ilevo is taken up by the plant, it is a light-sensitive reaction that occurs on the edge of the cotyledons,” says McCarville. “There is no sign that the phytotoxicity goes anywhere else. We have never seen the halo effect in vegetative tissue, such as in the trifoliate leaves. With four years of our testing, there is no negative impact on the halo effect on yield.”

This also coincides with a 2014 university trial near Wanatah in northwestern Indiana funded by the North Central Soybean Research Program and supported by Bayer Crop Science. It’s important to note this was just one location and one year, so the results should be interpreted accordingly.  “But in that trial we had in Indiana, there was no yield loss,” says Wise.

By themselves, preemergence herbicides can also cause soybean seedling damage, particularly when cool temperatures team up with rain soon after seedling emergence. Most often, preemergence herbicides are PPO-inhibitors (flumioxazin, sulfentrazone, saflufenacil; group 14) or photosynthetic inhibitors (metribuzin; group 5) that can injure plants grown in cold, wet soils.

The 2014 study did show increased phytotoxicity in seedlings from Ilevo-treated seed. More severe phytotoxicity occurred in Ilevo-treated seed than non-Ilevo treated seed with several herbicide treatments. However, this phytotoxicity did not impact stand by growth stage V4.

Meanwhile, SDS was reduced in treatments that had Ilevo-treated seed. Treatments with Ilevo resulted in an average gain of 5 bushels per acre compared to the base seed treatment across all treatments.

So Should You Use Ilevo?

It’s important to note that conditions that favor the halo effect and preemergence herbicide injury also favor infection by Fusarium virguliforme, the fungus that causes SDS. If a field has an SDS history and is likely to be planted under less-than-ideal conditions, paying for Ilevo benefits to curtail SDS may outweigh any short-term injury to seedlings in the cotyledon stage.

“If you plant into less-than-idea conditions, into cool and wet soils, it is it is very conducive for the fungus that causes fungus,” says Wise. “This is where the treatment has the most effect. So even though you might see the phytotoxicity, it prevents (SDS) damage in the long run.”

If you’re using preplant or preemergence residual PPO-inhibiting herbicides to diversify your weed-control management plan, continue to do so whether or not you use Ilevo. “Those herbicides are critical for battling herbicide-resistant weeds,” says McCarville.

Midwestern university scientists in Indiana and Iowa are currently conducting interaction research between preemergence herbicides and Ilevo seed treatment in 2015. Early observations from Iowa and Indiana in 2015 are similar to the 2014 study in Indiana, the university scientists report. Although Ilevo causes temporary phytotoxicity and preemergence herbicide applications slightly increase it, preliminary data in Iowa indicates preemergence herbicide applications did not increase seedling damage from Ilevo-treated seed when compared to treatments with no herbicide application.

Wise adds, though, that other early-season maladies mimic the halo effect. “You can also see things like seedling blights, like Pythium (root rot) and Fusarium, in soybeans planted under these conditions,” she says.

One way to detect Ilevo damage is to snap several cotyledons and look for green on the inside to distinguish from other injuries or diseases. If you are still unsure of the cause of the damage observed, send a sample to a local diagnostic laboratory. Obtaining an accurate diagnosis will allow you to determine the best management strategies for your soybean field, say the Midwestern plant pathologists.

Editor’s Note: Portions of this article were taken from
http://www.extension.iastate.edu/CropNews/2015/0522Mueller.htm. Authors
include Kiersten Wise, Purdue University; Daren Mueller, Iowa State
University; Yuba Kandel, Iowa State University; Bryan Young, Purdue
University; Bill Johnson, Purdue University; and Travis Legleiter,
Purdue University.

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