Wallaces Farmer

Soybean SDS and the 2020 derecho

Will more corn residue left in fields affect soybean diseases in 2021?

November 12, 2020

4 Min Read
Leaves of soybean plants infected with sudden death syndrome
SYMPTOMS: Leaves of soybean plants infected with sudden death syndrome initially show scattered yellow spots between leaf veins. Daren Mueller

The derecho left large amounts of downed corn in fields as it swept across Iowa in August. Farmers faced the challenge of determining the best way to deal with this corn, which in some cases is being left in the field. Most of these fields will be planted to soybeans in 2021. But how will all the corn residue, including corn kernels, affect soybean diseases next season?

If there is increased corn residue in the field, the typical concerns about cooler, wetter soils should be considered, say Iowa State University Extension plant pathologists Daren Mueller and Alison Robertson. ISU soybean disease researcher Leonor Leandro agrees.

Cooler, wetter soils in the spring can lead to root and seedling diseases of soybeans, such as fusarium root rot and pythium root rot. As a side note, a lot of corn residue in a field may increase the risk of certain corn diseases if planting corn on corn.

SDS survives on crop residue

Another soybean disease that may be affected is sudden death syndrome. Corn has been shown to be an asymptomatic host, which means it can be infected by the fungus that causes SDS but doesn’t show symptoms. But more concerning, say Mueller and Robinson, is research from 2016 that showed the pathogen that causes SDS, Fusarium virguliforme (Fv), can actually grow on corn residue, especially the kernels.

With soybean checkoff funds, the role of corn residue on SDS development was investigated in Iowa, Indiana, Michigan, Wisconsin and Ontario, from 2016 to 2018. In these studies, plant pathologists explored the timing of Fv colonization of corn and soybean roots under different tillage and residue management systems. In all years, Fv levels were detected in corn roots from most fields when sampled at multiple times, with greater levels of Fv being detected in 2017.

Tillage practices showed inconsistent effects on Fv root colonization and SDS foliar symptoms. Residue management did not alter root colonization of corn or soybean plants by Fv. In general, plots with corn residue did not differ in SDS development across site-years, although plots with corn residue did have more SDS in one location. This study did not include corn kernels, which in most years are generally not present in corn residue in large amounts as they are this year.

What does this mean for 2021?

What does this mean for derecho-affected fields in 2021? “To begin with the good news, we generally did not observe corn residue affecting SDS development in our research,” Mueller says. “However, if fields have a history of SDS, the extra corn residue, especially with kernels present, may increase the risk of SDS a few ways.”

It may increase the chance of getting the root rot phase of the disease (cooler, wetter soils early in the season) and may increase the amount of disease-causing inoculum in a field if the corn kernels are indeed colonized by Fv.

“To put this into perspective, however, the role of corn residue on SDS risk is minor compared to the field history,” he says. “Did you have SDS in a field before? Or just with the weather conditions during the 2021 season?”

Seed treatment for SDS

Should farmers treat soybean seed for SDS control for 2021 planting if there is more corn residue in these fields? Probably not, say the ISU plant pathologists. The possible greater risk of SDS caused by increased corn residue should not change your previous plans regarding SDS. “In other words, if you were already going to treat with an SDS seed treatment, then do so,” Mueller says. “If you are on the fence, perhaps this may push you to use an SDS seed treatment.”

Keep in mind, not all the SDS seed treatments are created equally. Check out the seed treatment efficacy chart for last year’s SDS ratings and a recent Crop Protection Network article on efficacy of seed treatments for SDS. “We will be updating the efficacy chart for seed treatments in early 2021 as we evaluate the 2020 data,” Mueller says. “Stay tuned.”

 

SDS is a formidable foe

The fungus that causes sudden death syndrome in soybeans survives on infested crop residue or in soil for several years, says Iowa State University Extension plant pathologist Daren Mueller. Crop rotation with corn is not effective in controlling SDS because the fungus can increase on corn residue. Root infection in soybeans can occur within days of planting and is favored by high soil moisture. Significant rainfall during reproductive stages favors foliar symptom development. Soil compaction and infection by soybean cyst nematode (SCN) can increase SDS severity.

Several soybean varieties have partial resistance (resistance made up of more than one gene) to SDS. Check with your seed dealer to identify an appropriate variety. Effective seed treatments also can help reduce SDS. Reducing soil compaction and soybean cyst nematode population densities can decrease the risk of SDS. For more information, see the Crop Protection Network Sudden Death Syndrome publication.

Source: ISU, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

 

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