With everything from sudden death syndrome to Asian soybean rust in soybeans, and gray leaf spot to charcoal rot in corn, weather is the single most important factor in determining what diseases will pack a punch in your fields this year. Don't get caught off guard.
These plant pathologists from across the Midwest review what growers dealt with in 2006 and predict what could be in store for you this growing season.
Terry Niblack, University of Illinois, says soybean cyst nematode (SCN) will most likely continue to be the biggest problem for soybeans in the state in 2007. Because so much is dependent on weather conditions, Niblack says she isn't sure what will be the biggest problem in corn, “but I expect to see significant increases in the number of acres affected by various corn nematode species.”
Last year, SCN troubled soybean growers across the state. “Our survey showed that 84% of the fields in Illinois are infested with SCN,” says Niblack. “More than two-thirds of the SCN populations have adapted at some level to resistant varieties carrying resistance from PI 88788.”
For corn, Niblack says corn nematode problems are increasing significantly, due to three factors: 1) Corn on corn allows them plenty of time to build up; 2) No-till, which also allows unchecked build-up; and 3) The use of new insect control approaches that don't impact nematodes.
In Indiana, Purdue University's Greg Shaner says, “A lot of pathogens on corn and soybeans are endemic — they survive in crop residue or in soil — so the major variables in year-to-year disease problems are hybrid or variety susceptibility and weather.”
Shaner doesn't believe the mild winter has particularly improved survival of pathogens, but also notes that it hasn't been warm enough for residue to decompose faster and cause numbers to decline.
In soybeans, Shaner will be monitoring Asian soybean rust. “Of greater concern to us is how early the rust is found in Mississippi, Louisiana and Texas.” These areas are the most likely source of spores for Indiana and Illinois.
In 2006, there were no major disease problems, according to Shaner. “Sudden death syndrome (SDS) and SCN probably caused the most damage, but weren't as great a problem as in some previous years,” he says. They did find rust late in the fall, but there was no loss.
In corn, he says stalk rot was more of a problem than usual and some leaf blight developed late in the summer on susceptible hybrids.
“The prevalence of SDS on soybeans continues to increase with each season,” says Alison Robertson, Iowa State University. For 2007, “the mild winter we've had thus far may favor bean leaf beetle survival, which would increase the risk of bean pod mottle virus (BPMV) in soybeans.”
Robertson says the possible increase in corn acreage and corn following corn could cause an increase in anthracnose and gray leaf spot. “Seedling blights, ear and stalk rots may also increase in prevalence,” she says.
SDS, BPMV, white mold and brown stem rot were the biggest soybean disease problems in 2006, Robertson says. In corn, “stalk rots were prevalent,” she says. “Anthracnose top dieback was also very common this year.” Foliar diseases occurred in both corn and soybeans.
Doug Jardine, Kansas State University, says he's concerned about gray leaf spot on corn since there will be more continuous corn planted in 2007. “Ear molds could also be a problem if we have a wet year, particularly around pollination time,” he says.
The outlook for soybean diseases is weather-dependent, says Jardine. “If it's dry, then expect charcoal rot. If it's wet, then SDS, Phytophthora root rot and stem canker become more of a problem.” He says cyst nematodes are always a threat, but “one benefit of more corn on corn is that it may help reduce cyst pressure in those fields for the next time beans are planted.”
Jardine says he's also concerned about soybean rust in 2007. “Given the large amount of inoculum currently surviving in the South, this could be the year it finally reaches Kansas,” he says.
Last year stalk rots in corn and charcoal rot in soybeans were the biggest problems for growers. SDS and SCN were also encountered in soybeans, and gray leaf spot and southern rust developed on corn late in the season in southwestern Kansas.
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In Minnesota, problems in 2007 are expected to be similar to those in 2006, says Dean Malvick, University of Minnesota. These include SDS, brown stem rot, SCN, drought and other root rots in soybeans.
For corn, he expects stalk rot, top dieback and drought to be problems again this year.
“This could change considerably depending on weather, when for example Phytophthora or white mold may increase substantially on soybeans,” Malvick says. “Likewise, a wet year could increase leaf diseases on corn, and a dry, hot year could increase ear rots on corn.
“It's difficult to get good estimates of the relative importance of different diseases, especially in a state like Minnesota where soybean production occurs over a distance of about 500 miles,” he says. The same goes for corn, so predicting diseases is a challenge.
“Looking toward 2007, SCN, Phytophthora root rot and SDS always have the potential to be serious problems for Missouri soybean growers,” says Laura Sweets, University of Missouri. “A cool wet spring could lead to seedling blight and root rot problems in both corn and soybean fields.”
Sweets says growers need to be aware of the soybean rust situation in the southern states and be prepared to take action if rust should develop. She also says the potential for corn stalk rots and ear and kernel rot problems shouldn't be overlooked.
In 2006, SCN, Septoria brown spot and SDS were all problems for soybean growers. Charcoal rot was also a problem due to hot, dry weather. For corn, “stalk rots, including charcoal rot, were the most widespread and severe corn diseases,” she says.
According to Tamra Jackson, University of Nebraska-Lincoln (UNL), the increase in continuous corn acreage will probably promote pathogen increase and survival. “Some corn in 2007 is at higher risk for the development of diseases caused by pathogens that overwinter in crop debris, such as gray leaf spot, Goss's wilt and blight and stalk rots.”
Loren Giesler, UNL, says, “soybean producers should consider managing seedling diseases if they've had problems in the past. Each year some part of the state has problems with stand establishment.” Giesler also encourages growers to sample their ground for SCN and stay on top of soybean rust developments.
Last year, Jackson says several diseases were unusually severe for corn in the state, including southern rust and gray leaf spot. “Fusarium and anthracnose stalk rots were the most frequently observed stalk rot diseases,” she says.
For soybeans, Giesler says Phytophthora root rot was a problem because of very wet conditions in some parts of Nebraska. He also says SCN continues to spread in the state, and growers should be aware of it.
“If 2007 brings a lot of moisture, then seedling diseases, Phytophthora root rot and Sclerotinia stem rot (white mold), will likely be problems in soybeans,” says Carl Bradley, formerly of North Dakota State University. If it's a hot and dry year, Bradley expects charcoal rot may be prevalent in the state. SCN will cause yield losses regardless of the weather, he says.
Bradley also says that growers need to be aware of the sentinel plot soybean rust monitoring program and track the spread of the disease.
SCN and charcoal rot had the biggest impact on soybean yields in 2006. “These diseases provided additional stresses to a soybean crop that was already stressed from the hot and dry growing season,” he says.
For corn, Bradley doesn't predict any major diseases for the upcoming growing season.
(Carl Bradley recently left North Dakota State University to become an Extension plant pathologist with the University of Illinois.)
Anne Dorrance, Ohio State University, says variety selection will be important for disease control in 2007. “As always, SCN and Phytophthora can sneak up on producers if they aren't careful about the variety they're planting,” she says.
Last year, “Frogeye leaf spot caused economic losses for the first time in Ohio since soybeans were produced here,” Dorrance says. “Approximately 350,000 acres were affected when frogeye encountered a highly susceptible variety.” She says frogeye leaf spot could be a problem again in 2007 if some of those susceptible lines are still planted.
Growers in Ohio should also keep an eye on the rust situation, as many other pathologists have recommended in their states.
“In normal to dry years, corn in South Dakota is generally not limited or even affected to any significant level by diseases,” says Thomas Chase, South Dakota State University. “My main concern for this year and the coming years is the shift to continuous corn,” he says. “We could start to see an increase in foliar diseases, although this may not become apparent for several years.”
In soybeans, “more and more fields in eastern South Dakota are showing up with damaging levels of SCN, and growers probably aren't even aware of the yield losses they may be experiencing,” Chase says. “A wet year will raise concerns for Phytophthora and the seedling/root disease complex, and would also make white mold and stem canker concerns.” He also says soybean rust is a major concern and will be closely monitored.
Last year, “there was an overwhelming drought effect on corn that eclipsed any disease problems.” Drought didn't affect soybeans as much, but some fields were damaged by charcoal rot. Phytophthora was not as severe as in most years.
In Wisconsin corn, “I suspect anthracnose will continue to be prevalent,” says Craig Grau, University of Wisconsin. “If the prediction of a warm and dry summer is correct, SCN and stem canker will be the most yield-limiting diseases of soybeans in 2007.”
Grau says anthracnose was also the most prevalent disease of corn in 2006. “There was a significant amount of premature death in areas with adequate rainfall, and anthracnose was the predominant cause.”
For soybeans, as in many other states, “SCN was likely the most yield-limiting soybean pathogen, followed by white mold, although spotty, in 2006.” Grau also says SDS was observed last year and appears to be increasing in Wisconsin.