Wanted for Yield Robbery: Sudden Death Syndrome

Photo credit: Iowa State University

Photo credit: Iowa State University

Catch this thief early by learning which environmental conditions the disease likes and which management practices it hates

Did you know that soybean sudden death syndrome (SDS) is now among the top yield-robbing diseases in the U.S.? If you have fields with a history of SDS, learn about how to manage the disease and prepare for if it hits your fields next year.

In years when weather conditions are conducive to the pathogen, such as 2010, yield losses can be devastating. That year, cool and wet conditions caused the disease to run rampant in the Midwest. Many farmers saw a repeat of those conditions early in the 2014 growing season.

Checkoff-funded studies show SDS cost U.S. farmers in excess of 25 million bushels in 2013 alone.

Photo credit: University of Illinois

Photo credit: University of Illinois

“We’ve had problems with SDS in our fields for close to 10 years,” says Rhonda Birchmier, soybean farmer from Maxwell, Iowa. “It is a problem for many people in our area, and our biggest concern is protecting our soybean yields. Over time, you can see a 20 to 50 percent reduction in yields—it can be very significant.”

Farmers in Iowa aren’t the only ones to struggle with the disease. SDS is a concern for farmers across the U.S. It was first reported in Arkansas in 1971, and it spread to the surrounding states of Tennessee and Mississippi. It then traveled up the Mississippi and Ohio rivers to Missouri, Ohio, Indiana and Illinois. Today, it stretches as far west as South Dakota, through the northernmost reaches of the U.S. soybean-producing region, all the way to the East Coast to Delaware and North Carolina.

How can farmers tell if they have SDS in a field?

SDS is a soybean disease caused by a fungal pathogen that lives in the soil and has three stages:

  1. Infection. Once a fungus infects a soybean plant, it colonizes in the roots of the plant.
  2. Root rot. After establishing itself in the roots, the fungus creates toxins that move from the roots up the stem and into the leaves.
  3. Foliar symptoms. Ultimately, the disease causes leaves to first turn yellow between veins and then die and fall off. This process can happen suddenly if environmental conditions are favorable for SDS.

Soybean yield loss depends on how early and at which growth stage the disease shows up.

Photo credit: Iowa State University

Photo credit: Iowa State University

What conditions are favorable for SDS?

SDS is caused by a fungus in the soil, but several factors can aggravate the disease, such as:

  • Cool and wet weather conditions
  • High moisture levels in the soil
  • Poor drainage
  • Soil compaction
  • Soybean cyst nematode (SCN) presence

Infection can happen very early, at the seedling stage, especially under cool and wet conditions. A dry summer can help to mitigate the effects of SDS, but heavy rainfall in June, July and August is very favorable for the disease.

Researchers have also found a connection between SDS and SCN.

“Research shows that when SCN is present, SDS is more severe,” says Leonor Leandro, Ph.D., associate professor in the Department of Plant Pathology and Microbiology at Iowa State University. “Plants with SCN tend to develop SDS earlier, and the infection is more severe than when the SCN is not there.”

How can farmers manage SDS?

Across the board, researchers recommend variety selection as the No. 1 way to manage SDS. At this time, however, there are no varieties with complete resistance.

“We know that some soybean varieties will have less SDS than other soybean varieties in the same field,” says Brian Diers, Ph.D., professor in the Department of Crop Sciences at the University of Illinois. “We do not have any varieties that have complete resistance to SDS, but we do see different levels of resistance.”

Work with your local seed suppliers and extension agents to identify the most resistant varieties available for your area, but remember that you’ll likely need to manage for both SDS and SCN at the same time.

“The problem is that in most of the soybean-producing regions of the U.S., we have SCN,” Leandro says. “If you can find a variety that is both SCN and SDS-resistant, that is your best shot.”

Leandro and Diers also recommend other practices to manage the disease, including:

  • Maintain optimum soil conditions to favor vigorous root growth. A good seed bed at planting, adequate air flow, good drainage and appropriate fertility levels all help to ensure root health.
  • Avoid planting during cool, wet springs. Plant the fields with a history of SDS last. That way, your planting can continue on schedule while potentially minimizing the effects of the disease.

“Since we’ve had problems with SDS for several years, we use the basic management controls, including planting in the warmest and driest conditions possible, implementing crop rotation and selecting varieties in our area that have the best resistance to SDS,” says Birchmier.

How is the soy checkoff helping?

The soy checkoff plays a critical role in directing research on important soybean-production issues. These projects aim to help U.S. soybean farmers increase yield, manage disease and other stresses and maximize profit opportunities.

Because SDS is so widespread across the U.S. soybean production area, the checkoff has made the disease an area of focus for soybean research.

“Creating resistant varieties for SDS is very challenging,” says Daren Mueller, Ph.D., assistant professor in the Department of Plant Pathology and Microbiology at Iowa State University. “When new varieties are developed, they are tested in a very controlled environment, like a greenhouse or a growth chamber. Unfortunately, these tests don’t correlate well with field results for SDS.”

Mueller is the project coordinator for a checkoff-funded regional study to find management techniques that can increase the effectiveness of soybean varieties with partial SDS resistance.

“Our proposal is to fine-tune what can be done to help give the resistant varieties a fighting chance,” he says. “We are specifically looking at the effects of early planting dates, seed treatments and foliar applications that may help farmers manage SDS better.”