Pythium and Fusarium love those cool soils below 60ÞF. Phytophthora and Rhizoctonia like the warm dirt. And without proper fungicide treatments before planting or in-season, these diseases can send soybean production almost to its grave.
Whether it's in the heart of the bean belt or in the South, many growers won't plant a single seed that isn't treated. That pleases Anne Dorrance, Ohio State University plant pathologist. “I highly recommend seed treatments in two-thirds of Ohio soil,” she says.
Alan Blaine, Mississippi State University agronomist, says soybean seed treatments “are an inexpensive insurance policy” that can often save growers from having to replant.
Kenneth Hood, Gunnison, MS, grows several different varieties of soybeans within a soybean, cotton and wheat rotation in the Mississippi River delta. His land borders the mighty Mississippi in many areas, so there are always opportunities for different types of soil to wash into his fields in wet years. To him, seed treatments are imperative.
“We buy our soybean seed in bulk and have it treated before it's delivered,” says Hood. Like many in the Midsouth, he plants soybeans early to take advantage of seasonal rains, getting them off to a good start. For Hood, early Group IVs go in the ground about April 1. They're followed shortly by late Group IVs and early Group Vs.
“It seems like we plant soybeans earlier than ever,” says Hood. “That makes the crop more susceptible to diseases. So it's more critical to have seed treatments to offset the threat of various diseases. All of our seed is treated with a combination of the fungicides Apron and Maxim.”
Blaine strongly advises growers to plant treated soybeans. “I believe in the Cadillac program of a full fungicide treatment before planting,” says Blaine, who deals heavily in Midsouth soybean production. “It's too risky to go to a field without it. It is an inexpensive insurance against a failed stand. Treatment costs run only about $2-3.50/acre, depending on your seeding rate.”
Blaine says that with the tech-fee-boosted costs of today's more popular soybean varieties, the cost of treated seed is minimal. “If a seed treatment will save me a stand in only one year out of 12, then I save on seed treatment costs over the entire period,” he says.
Given that a high percentage of Midsouth soybeans are planted prior to mid-to-late May, “all of these beans need to be considered for proper seed treatment,” says Blaine.
Due to the chance for early seedling problems, he recommends treatments geared toward control of Pythium. That disease and Fusarium can create instant problems when there is too much rain coupled with cool soil. Fusarium can create root rot problems, which causes seedlings to be stunted and weak. Apron, Maxim, SoyGard, Stiletto, Warden and other fungicides fit into this category.
Dorrance says many of the eastern Corn Belt sees soybeans planted in old lake beds that feature soils high in clay content that holds moisture. “These are high areas of replant,” she says, adding that Ohio has seen a soybean replant rate as high as 40% some years.
“Seed treatments will protect against a lot of that. And because of the increase in replants, we're finding that more growers are getting their seed treated,” says Dorrance.
If the germination rate is below 80%, it could be because seed is affected by Phomopsis/Diaporthe and other fungi, which generally means lower germination and vigor. Blaine says this can result in a greater chance of seed rot and a longer period between germination and seedling establishment. The longer this period, the greater the chance for disease loss.
A fungicide treatment will not improve seed quality, but it can help prevent seed decay for a short time in unfavorable weather conditions. And if there is an extended period of poor weather conditions after planting, even treated seed may not produce a uniform stand.
As soils warm up, late-planted seeds can experience damping-off problems from Pythium, Phytophthora and Rhizoctonia, which are most active when soils surpass the mid-60s in the north or in the 70Þ range further south. Stand reduction may occur. Dorrance says treated seed will help protect against those diseases early. “But treatments (seed coatings) only work until the plant is up and growing,” she says. “Then the plant has to rely on its resistance package.”
Phytophthora root rot can be controlled with resistant soybean varieties. “However, a number of different races occur, so previously resistant varieties may be susceptible to new races that develop within fields,” says Dorrance. “Varieties with a high level of partial resistance are also available. These varieties are susceptible to infection, but do not have the excessive yield loss associated with susceptible varieties.”
Hood says it's important to make sure in-season treatments are made to help control these diseases.
Additional diseases like Septoria brown spot or bud blight might even be thwarted if a good seed treatment program is used to promote a solid stand and vigorous growth.
Blaine, even though he recommends seed treatments for virtually all fields in the Midsouth, realizes that some growers will still look at their own conditions before spending the money.
If that's the case, he suggests fungicide treatments if seed germination is low, if growers have observed stand problems in the past, if soils will be wet during cool or warm conditions, or in no-till situations where soybeans will be planted into wheat stubble, residue or any other field high vegetation. Crop rotation is also important to help lower chances for diseases.
For further information on Midsouth area soybean disease control, visit the MSUCares Web site at msucares.com/crops/soybeans. For information on northern soybean production, visit the Ohio Field Crop Diseases Web site at www.oardc.ohio-state.edu/ohiofieldcropdisease/.