To Treat or Not to Treat

January 5, 2011 08:53 AM
 
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A soybean crop begins with placing seeds in soil—but how many seeds per acre and in what row width? After 15 years of replicated test plots, Farm Journal Field Agronomist Ken Ferrie thought he had the answers—and he did, for planting in the normal window.

Field value to protect. For soybean growers, getting young plants off to a fast, healthy start is a high priority. Seed treatments can help.

Choosing resistant or tolerant varieties is your first line of defense against pathogens—and an essential one. "But inbred disease resistance doesn’t really make a difference until plants reach the V1 or V2 stage," Ferrie says. "Seed treatments can help fill the gap, protecting seedlings until they reach that stage.

"With soybeans in the $12 range, every producer needs to seriously consider applying a seed treatment," he says. "Compared to $5 soybeans, you have a lot more value in your field to protect."

Still, Ferrie adds, there are no guarantees. Seed treatments don’t increase yields; they just help protect it. They provide a degree of insurance that you’ll get a healthy stand.

If there’s no threat, there will be no payoff. "Disease and insect issues revolve around the disease/insect triangle—you need a host crop, a pest and the right environment," Ferrie says. "If one element is missing, a seed treatment probably won’t earn its money back, or will return only a small portion of it. But with today’s soybean prices and the relatively low cost of seed treatments, most treatments probably will pay."

Seed treatments include fungicides, insecticides, inoculants and nematicides. "If you decide to apply one, you must select the right product for the issues you’re trying to manage," Ferrie says.

Here are some factors to consider as you make your seed treatment decisions.

Know your disease threats. Fungicide seed treatments help protect against pathogens that cause seed rot, seedling death and root rot. The infections they cause often are described as seedling blight or damping off. Pathogens that attack seedlings include Phytophthora, Pythium, Fusarium, Macrophomina and Rhizoctonia.

Phytophthora and pythium are also called water molds because they thrive in wet or saturated soils. "With these seedling blights, you will find rotted seed," Ferrie says. "It may rot even after it has already sprouted. To determine whether the problem is pythium or phytophthora, you’ll have to send the seed to a laboratory. But most seed treatment products that control pythium also control phytophthora, if they are used at the correct rates."

The other two most common seedling diseases, rhizoctonia and fusarium, occur across all moisture levels, not just in high-moisture field conditions.

"Rhizoctonia produces a distinctive brown or reddish-brown rot on the root," Ferrie continues. "The lesions will have a sunken appearance. They start at the soil line and extend below the surface."

Phytophthora, Pythium, Rhizoctonia and Fusarium pathogens reside in the soil. "Once you have them, there is no way to get rid of them," Ferrie says.

Evaluate disease risk. Launch your seed treatment strategy by analyzing the risk of disease.
"Look at the history of each field," Ferrie advises. "If certain fields, or parts of fields, have a history of root rots or seedling blights, they are prime candidates for treatment. The soil there probably tends to stay cool and wet."

Also consider planting conditions. "If you plant early, or in high-residue conditions, with a cool, wet environment, that’s a risk factor," Ferrie says. "Growers today are spread out—on a distant farm, they may want to plant both corn and soybeans before moving on. So seed sits in soil longer than it used to, in cool conditions."

Take drainage into account. "If drainage is moderate to poor, even if you plant in ideal conditions, it could rain a few days later," Ferrie says. "Then you will fight water molds."

Ohio State University plant pathologist Anne Dorrance puts it this way: "Has the field ever needed replanting? Is it poorly drained? Is it in no-till production? How many years out of the past five have soybeans been planted? If you answer yes to any question, or if soybeans have been planted at least three of the past five years, there’s a very good chance you’ll see a return on your seed treatment investment."

Seedborne disease. Seedborne disease that is caused by Phomopsis, which reduces germination percentage, is much less common today than when farmers planted mostly bin-run seed. "Farmers would know they had the disease when they harvested because it gives soybeans a chalky appearance," Ferrie says. "Today, if seed companies suspect Phomopsis is present, they usually treat the seed free of charge."

"Not all seed treatments are effective on Phomopsis," Dorrance says. "Seed lots with less than 70% germination should not be used."

Choose your weapon. Once you’ve identified disease threats, focus on the most serious ones and choose one or more products to control them.

"Choosing seed treatments is like selecting a herbicide combination to control weeds," Ferrie says. "With seed treatments, there are a number of active ingredients on the market, and companies blend them in order to make different products.

"Make sure you, or the seed company, apply the right product at the right rate for the pests and pathogens in your fields," Ferrie emphasizes.

Will treatment pay? While fungicides are a valuable tool for soybean growers, they are not a silver bullet.

"Fungicides help, but they can’t give complete control of soilborne fungi in extreme conditions," Ferrie says. "With wet soil and early planting, I’ve seen a soybean stand die even though the seed was treated. I once saw a grower replant three times, using treated seed, before he got a stand because the soil stayed cool and wet after planting."

That could happen if soils stay saturated for more than three or four days, Dorrance says. "There is only so much a seed treatment can do in extreme situations," she adds. "In any situation, seed treatments provide protection only while the seed coat is attached in the ground. Once that seed moves aboveground and the first unifoliates unfold, that plant is on its own."

"In test plots, when soil stayed wet and cool, we sometimes could see which seed was treated, but the stand was still so low we had to replant. If you have a soil like this, try to improve the drainage—or plant that field last, so the soil will at least be warm, even if it’s still wet," Ferrie says.

Remember, too, that soybeans can compensate for a poor stand. "Fungicide treatments allow for a healthier stand, more emergence and healthier plants," Ferrie says. "But, since 1992, with planting populations from 120,000 to 240,000, our studies have shown that population does not have a big effect on yield. Sometimes 120,000 plants outyield 200,000. Just because you end up with 10% to 20% more plants doesn’t mean you’ll get more yield."

On the flip side of that argument, "by treating seed, you may be able to plant a lower rate and reduce your seed cost," Ferrie says.

Insecticide treatments. Two products, Cruiser and Gaucho, give soybeans some systemic protection from bean leaf beetle and early soybean aphids.

"With Cruiser, protection can last from three to six weeks, with an average of four or five weeks, depending on environmental conditions," says Mark Jirak, crop manager for Syngenta Seed Care. "Factors influencing the length of control include soil moisture, temperature, rainfall and how fast the plants grow. Faster growth dilutes the insecticide in the plant.

"With aphids, you may see an impact on populations later in the season, because the insecticide killed earlier generations before they could reproduce," Jirak continues. "With bean leaf beetle, the second generation may not be as heavy, especially if most of your neighbors also treat their seed."

"With Gaucho, insect protection extends to the first trifoliate," says Marc Andrieux, product manager for Bayer CropScience.

"A seed treatment, by itself, may not ward off a heavy infestation of aphids," Ferrie says. "But it may slow them down and give you time to react. Following an insecticide seed treatment, you may need only one foliar spraying or Mother Nature may wipe out the aphids for you.

"Insecticide seed treatments can supplement scouting," Ferrie adds. "You may want to apply seed treatments on distant farms that are difficult to scout in timely fashion, or on fields near subdivisions where it’s difficult to spray."

Should you inoculate? "Inoculating with rhizobia bacteria, which produce nitrogen, may pay on fields that have been out of soybeans for a while," Ferrie says. "Many growers inoculate soybean seed after three years of corn, and that’s not a bad idea. I’ve seen fields where you could  document higher yield and fields where you couldn’t. But with high soybean prices, if you pick up a bushel or two in one field, or part of a field, it could pay for the inoculant."

Remember, inoculants contain live bacteria, so they must be handled more carefully than seed treatments for disease or insects.

In the past, there were several problems mixing inoculants with other seed treatments. "Today, manufacturers screen seed treatments for compatibility with inoculant products," Jirak explains. "Your dealer can tell you whether your seed treatment and inoculant can be mixed, either in a slurry or by applying them sequentially."

"Always be aware of how much time you have to plant the seed, from the time the inoculant is applied, in order to deliver the required number of live bacteria to each seed," Jirak adds.

"Our seed treatment products are always tested by inoculant companies, and the compatibility results usually are published on their websites," Andrieux says. "To our knowledge, there are no compatibility issues with any of our products."

Treat seed yourself? You can buy treated seed, treat it yourself or have it custom-treated.
"Just make sure the treatment is applied correctly and on time," Ferrie says. "With some products, you will get less buildup on the planter meter if you treat the seed ahead of time and let it dry."

Keep in mind seed quality and don’t pass seed through any more augers than necessary.

 

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