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Threats to soybean crop reviewed at field meeting

Aug. 1, 2013 | 0 comments

Although much of Wisconsin's soybean crop had recently reached or was approaching its early reproductive growth stage heading into the last week of July, many fields were already facing a variety of threats that could affect their yields when they are harvested in a couple of months.

That was the message from University of Wisconsin Extension Service soybean and small grains specialist Shawn Conley at a field meeting of the Fond du Lac and Dodge County Corn Growers Association on the Ed Montsma farm.

His farm is a host site for corn and soybean plots overseen by the Extension Service, seed and supply companies, and local agricultural service providers. A field day will be held there on Tuesday, Aug. 27.

Soybean Diseases

In his observations at the plot here and other plots around the state, Conley has seen the greatest amount of septoria leaf brown spot ever during his years in Wisconsin.

He attributed this to the weak root development because of the sufficient or excessive moisture during the early part of the growing season.

The dying and dropping of leaves in the middle third of the canopy at this stage of growth indicates the septoria infection could spread to the top of the plant, Conley pointed out.

Although he didn't have any research references that are specific on the point, he surmised that a fungicide treatment to control the septoria outbreak has a good chance of providing a payoff this year.

Another relatively new soybean plant disease whose presence was detected in many areas in Wisconsin during 2012 is vein necrosis - the pre-mature bleaching and death of veins, Conley noted.

He credited the Wisconsin Soybean Marketing Board (WSMB) for funding support on tracking the thrips, which are the likely carriers and spreaders of the necrosis. He reported that the thrips have been seen in Iowa and Illinois already this summer.

Based on soil samples tested in 2012, Conley expects sudden death syndrome (SDS) to begin showing up in Wisconsin soybean fields by mid-August. He reminded growers and crop consultants to double check the symptoms for SDS and brown stem rot so they don't confuse the two.

Pest Patrol

Because the soybean aphid population topped the 250 per plant average, which is considered the threshold for economic losses, the Extension Service's soybean plot at Seymour in northern Outagamie County has been treated with an insecticide to control the pest, Conley stated.

He noted that the aphid populations have been relatively low at Arlington and in the plot here, where he found ladybugs that are natural predators of the aphids.

In the Extension Service's soybean plot near East Troy, plant defoliation by Japanese beetles was approaching the 20 percent economic threshold for which an insecticide treatment is advised, Conley continued. He was considering an aerial application of insecticide at that plot.

But not all of the threats to soybean plant health occur above the soil surface, Conley remarked. He cited the soil screenings conducted in 2012, which found that 5 percent of them were positive for the SDS pathogen.

Soil Sampling

Detecting the presence of the SDS pathogen is only one of the reasons to take part in the state's soil sampling program, which continues to receive strong support from the WSMB, Conley emphasized.

All growers are eligible to submit four kits of soil samples for free testing (request by e-mail to freescntest@mailplus.wisc.edu).

This program began as a screening for identifying the presence of the eggs of the soybean cyst nematode, which feeds on the plant roots and is believed to account for more than $1 billion in soybean yield losses annually in the United States.

The nematode has been found in a majority of Wisconsin's counties where soybeans are a significant crop.

Conley announced that the WSMB-funded testing of the soil samples, which can be collected and submitted at any time of the year, now also checks for corn pathogenic nematodes.

He reported that 20 percent of the soil samples submitted in 2012 tested in a moderate to high category of that corn nematode.

"I expect corn yield losses at Arlington this year" due to the corn pathogenic nematode, Conley predicted.

Other than getting a soil to verify if it is present, he said one way to cope with it is to treat corn seed with the Evicta or Poncho Votivo insecticide.

Variety Trials

Numerous product effectiveness, plant population, and other studies are being conducted in the test plots here and elsewhere this summer, Conley reported.

In one of the trials here, eight different combinations of seed treatments are being evaluated on three soybean varieties to determine the effect on plant population and whether the money spent on particular seed treatments is yielding a return, he explained.

Regarding those differing applications, Conley has already noticed differences in stand density and biomass.

He anticipates that those crop inputs are likely to produce good economic returns this year but added that another purpose of that study is to identify any differences between the products, including the net benefit based on what they cost.

A WSMB-funded project involves a comparison of how soybeans with differing traits fare with a variety of fungicide and insecticide inputs, Conley said.

One thing that is already evident is how an application of Cobra herbicide virtually "killed" soybean plants and set back their growth rate this year, he observed.

A study being conducted at the Montsma farm plot here is foliar feeding before the soybean plants begin to flower. At other plots, the research is looking at micronutrients, phosphorus, and potassium and some growth regulator treatments are being applied, Conley noted.

Multiple Studies

During the field plot meeting here, Conley pointed out the plots that are involved in the per acre population studies that started with plantings of 40,000-140,000 seeds per acre.

He said correlations with seed treatment fungicides are being monitored, replant decisions rest on the results, and the Cruiser seed treatment proved to be the most effective in 2012.

He also said that even per acre soybean populations of as little as 40,000 plants can achieve a closed canopy though relatively late in the growing season.

Some 40 different fungicide treatments are being monitored at the Extension Service plots this year, Conley indicated.

In one respect, the frequency of phythium, phytophthora, and other diseases in the plots this year is a good thing because of the data this will provide for sorting out the differences between soybean genetics and the multiple seed treatments, he explained.

At Arlington, misting is being conducted in order to induce white mold in some of the soybean plots, Conley reported.

Periodic updates for soybean management for the remainder of the growing season are available on the coolbean.info website.

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