It wasn’t too long ago that a soybean grower in the Southeast or Mid-South wouldn’t even have considered applying a seed treatment to his crop. What a difference a few years and a doubling of soybean prices  can make.
With nearby Chicago soybean futures trading for better than $12 a bushel for most of 2008, seed treatments for soybeans have moved from the category of a luxury to pretty close to being a necessity, according to Extension specialists.
“This was the first cool, wet spring we’ve had to deal with in five or six years,” says Trey Koger, soybean specialist with the Mississippi State University Extension Service . “It brought home the idea that if you’re not using a seed treatment on your soybeans, you need to be. It’s just a matter of time before you may get bit without one.”
Speaking at a Syngenta  Corn, Soybean and Cotton Field Day earlier this summer, Koger said university researchers have shown that seed treatments could pay off when soybean prices were much lower than they have been in recent months.
“Looking at a seed treatment containing Cruiser, researchers found that seed treatments produced a positive economic return more often than now when soybeans were selling for less than $7 a bushel,” he said. “Today the response is even greater.”
Researchers generally have been seeing the biggest responses in earlier plantings, but that doesn’t mean that soybeans planted after May 1 or even after wheat can’t use a seed treatment, Koger told field day participants.
“With wheat beans, we’re still developing a data set, but we think growers should use a seed treatment,” he noted. “For May 1 or earlier plantings, I would put it on every seed. I’ve never heard a grower say he wished he hadn’t used a seed treatment.”
He said he had received a number of calls from growers asking if they should apply a fungicide seed treatment on replanted soybeans.
“We use the same philosophy with replanted soybean seed that we use for the first planted seed. Do not plant soybean seed without a fungicide seed treatment. Our common seedling diseases such as Pythium are just as active in warm, moist soils, as they are in cool, moist soils.
Pythium, as well as other common seedling disease-causing agents can be just as devastating on replanted soybeans planted in late May as on early planted soybeans. Spending less than $3 an acre on a fungicide seed treatment is the cheapest and best return on investment of all the crop inputs. The last thing we want to do is have to replant soybeans because of losing a stand to seedling disease.”
There may be times, on the other hand, when diseases aren’t severe enough to kill the soybean plant and require replanting of soybean fields, Koger said. Several cases of what specialists are calling non-lethal Pythium occurred in Mississippi soybean fields in 2008.
“The organism that causes non-lethal Pythium is the identical pathogen as that which causes full-blown Pythium,” said Koger and Tom Allen, Extension plant pathologist with Mississippi State, in an article in the Mississippi Crop Situation report. “Non-lethal Pythium can result in infected plants that often do not grow normally or contribute to final yield.”
Non-lethal Pythium symptoms include thick cotyledons that often are twice as thick as normal cotyledons, they noted. Other symptoms can include aborted terminals and extremely small unifoliate leaves that may not be present.
“Infected plants are often characterized by the lack of unifoliate leaves and trifoliate leaves growing directly from the cotyledon region,” said Koger. “These trifoliate leaves often are the beginning of multiple stems typical of a plant that has lost its apical dominance; i.e., the same appearance as crazy cotton.”
Fortunately, the percentage of infected plants have been less than 20 percent of the population in fields containing non-lethal pythium. “Since infected plants typically do not develop pods and, thus, contribute very little to final yield, the final stand population should be estimated based on healthy plants only.”