Predicting which diseases will impact corn or soybeans this coming growing season is far from an exact science. Diseases can blow in or blow up depending on wind, water and temperatures.
“It's unpredictable. Most of the pathogens that cause problems in corn and beans survive in the soil and on crop residue,” says Greg Shaner, plant pathologist, Purdue University. “Two other variables that determine disease problems are susceptibility of host plants and weather conditions.”
Plant pathologists add Asian soybean rust to their list of suspects. Its rusty dots haven't spotted U.S. fields yet, but scientists are geared up to sound the alarm if it hits.
We asked leading plant pathologists from across the Midwest what they expect the most dreaded corn and soybean diseases will be this year. Here's what they say.
“We always see some sudden death syndrome (SDS) in soybeans, but like most diseases the distribution and severity depends on weather. Soybean cyst nematode (SCN) and Phytophthora rot were problems last year and will cause some damage again this year.
Year in and year out, southern Illinois has charcoal rot problems, but this disease usually occurs in northern Illinois during dry conditions. In the northern part of the state both stem canker and brown stem rot are problems to scout for.”
Dean Malvick, University of Illinois
“SDS has been a problem recently in soybeans. We know the pathogen is pretty widespread. The key to SDS flourishing is heavy rain right around flowering and early pod fill. SCN is also widespread. The severity depends on the cropping history and the susceptibility of the cultivar.
“On corn, we're always concerned about gray leaf spot. We haven't had a big problem with it for several years because we haven't had a summer with lots of warm, muggy nights.”
Greg Shaner, Purdue University
“Charcoal rot in soybeans was epidemic in Iowa and Illinois in 2003. If we have a dry season like last year, it is likely to return. Virus diseases (bean pod mottle and others) are likely to cause problems if weather during the growing season is dry. If early season weather is cool and wet, damping-off, SDS and Phytophthora can be problems. White mold cannot be ruled out in a cool summer.”
X.B. Yang, Iowa State University
“If drought and high temperatures continue in Kansas, charcoal rot will remain a serious problem on both soybeans and corn. SCN will also continue to produce a small amount of yield loss statewide.
“If rains return to a normal pattern, we'll see an increase in gray leaf spot on corn and possibly Phytophthora root rot on soybeans. With current hybrids, we lose a small percentage of yield, about 5%, to Fusarium stalk rot on corn yearly.”
Doug Jardine, Kansas State University
“We could see seed killing from Pythium before emergence in southwestern Michigan if it's wet right after planting. We haven't seen white mold in a few years, but if we get lots of rain in late June and early July it could be a problem again. SCN will continue to be a major problem in Michigan for soybean growers.”
L. Patrick Hart, Michigan State University
“Cyst nematode is always a problem and continues to spread across the state. If we have a typical spring — slow warm-up, saturated soils and soggy fields — we'll see poor stands caused by root and seedling rots in the Red River Valley and south-central Minnesota where there are heavy soils and poor drainage.
“Soybean aphids have probably changed the picture for viruses. We don't have a good handle on that yet. We have seen unusual localized problems that are probably a result of aphid virus transmission. We're probably going to see more problems there if aphid infestations are as bad as in the last year or two.”
James Kurle, University of Minnesota
“We saw Pythium seed decay and seedling blight in corn last year because of a prolonged wet spring. The potential for those diseases is pretty high if we have a wet spring again.
“We always have trouble with SCN. The amount of Phytophthora depends on rainfall after planting. Weather is also going to have an impact on how much SDS we have.
“Look for Stewart's wilt on corn this spring. We've had some cold temps but not prolonged cold weather. I don't know what that's going to do to the flea beetle population.”
Laura Sweets, University of Missouri
“Early season moisture usually results in seedling disease problems. Soybean viruses (bean pod mottle virus and soybean mosaic virus) continue to be a problem as bean leaf beetles and soybean aphids plague production.
“Each year varies for foliar diseases on corn and their impact on production. Seasonal rains usually determine when gray leaf spot will develop to significant levels. Some years high temperatures slow the disease and reduce its impact.”
Loren J. Giesler, University of Nebraska
“Phytophthora root rot is usually our No. 1 soybean disease problem. If it's wet, then Phytophthora root rot as well as white mold will continue to be major soybean diseases. SCN was found for the first time in 2003 and was probably the worst disease problem for growers in the southern part of the state. It will continue to spread to more fields and affect more acreage.”
Carl Bradley, North Dakota State University
“In 2003, Phytophthora root rot was the big winner. The root rot complex (including Pythium and Fusarium) caused problems because we had wet soils for such a long time. We have a number of fields with SCN that aren't monitored and the spots are getting bigger.”
Anne Dorrance, Ohio State University
“In 2004, I expect SCN will continue to expand across the state. With the long-range outlook for continued dry conditions, I'm concerned that we may see more charcoal rot on soybean crops.
“Similarly, the risk of stalk rots will be high under dry, stressful conditions. At the end of 2003, gray leaf spot (GLS) was building on the corn crop in the southeastern part of the state. As such, the overwintering inoculum will be more plentiful and we may see more GLS if the dry weather breaks.”
Martin Draper, South Dakota State University
“SCN causes problems each year. White mold, brown stem rot and stem canker are expected to continue as important diseases, too. Phytophthora root rot remains a limited problem because the Rps1k gene has remained effective in Wisconsin. We will continue to monitor the frequency and types of viruses transmitted by the soybean aphid.”
Craig Grau, University of Wisconsin