High soybean prices might shift the economic threshold for treating pests to a lower level. If you spray more often, take steps to prevent resistance from developing.
Insect and disease control is a game you can win
One of the most rewarding—yet challenging—aspects of farming is that you’re always learning. In 2011, higher soybean prices put a twist on soybean insect and disease control.
"With $14 soybeans, versus $6, you have to look at things differently," advises Farm Journal Field Agronomist Ken Ferrie.
First, higher soybean prices lower the economic threshold for treatment, which makes scouting and quick response pay dividends. Second, more frequent treatment increases the need to manage pesticides to protect the environment and prevent resistance from developing. Third, scouting must continue late into the season.
"It will pay to treat for pests at a lower level of infestation," Ferrie says. "Soybean prices held at $4 to $6 for so long that some growers—who were trying to be responsible and avoid preventive applications—might not have taken the new economic thresholds into account the past couple seasons."
What makes the process challenging is that resistance is on the rise. "We must be stewards of the tools we have," Ferrie continues. "We can’t throw integrated pest management out the
window just because it requires fewer bushels to pay for treatment. Applying products when we don’t actually need them will speed up that process."
Preventive treatment backfires. This past year, Ferrie saw several poorly thought-out treatments backfire.
"Some growers made a preventive fungicide application for disease and included a pyrethroid insecticide for bean leaf beetles," he explains.
"As it turned out, the fungicide and insecticide, which might not have been needed in the first place, eliminated spider mite predators, so mite populations exploded and then they had to spray for mites," he says.
There are two concerns with increasing the number of pesticide applications, says Phil Sloderbeck, a Kansas State University (KSU) Extension entomologist before becoming KSU Southwest Area Extension director. "One is resistance—the more pesticide applications you make, the greater the chance of developing resistance in the target pest," he says. "The second is the impact on other organisms in the system. You might kill parasites and predators in the system. That can release other pests to become problems, or it can allow more rapid resurgence of the target pest, once the initial treatment wears off."
Appoint a pest boss. To effectively manage soybean pests in an environmentally sound fashion in 2012, start by appointing yourself, a family member or an employee as pest boss, Ferrie says. "Equip him with manuals and access to pest management websites, and let him make scouting a priority task. If you don’t have a pest boss available, hire a profess-ional," he advises.
Weather conditions and moisture influence pest problems and will help your pest boss determine if a particular pest is developing to economic levels.
Understand the current economic thresholds for treatment, Ferrie continues. Most land-grant universities publish economic thresholds for various pests, such as the bean leaf beetles table on page 62 from Iowa State University.
"To be responsible and economically efficient, base your treatment decision on the contracted price for your crop, not the price of the day at the local elevator," cautions Anne Dorrance, Ohio State University plant pathologist.
Late-season threats. Don’t ease up on scouting midway through the season. You could be blindsided by late-developing pests, such as bean leaf beetles, aphids and spider mites.
"A late flash of bean leaf beetles caught a number of growers in 2011," Ferrie says. "Some seed producers lost their premiums because of bean leaf beetles, which feed on the pods. In central Illinois, some populations were so heavy that insects fed on the stems of the pods and the pods fell off."
"Spider mites can sneak up on you because they are influenced by the weather," says Rod Wilson, who farms near Clinton, Ill. "In 2011, we treated spider mites in one field, but held off on treating two adjacent fields for 10 days. We saw a 5-bu. to 10-bu. per acre yield hit in the later-treated fields."
Even as a skilled pest manager, one who scouts intensively and bases treatment decisions on economic thresholds, Wilson needed to be reminded that thresholds are a moving target.
"Unfortunately, some pests, such as spider mites, don’t have precise threshold data that you can use to make your decision," Ferrie says. "It depends on the stage of the crop and the weather. If you get cool, rainy weather, it might solve the problem for you. But if it stays hot and dry, populations can increase rapidly."
Proactive approach. "If spider mites show up again next season, I’ll probably be a little more proactive," Wilson says. "I’ll probably treat at the front side of the economic threshold. But every treatment decision will be based on current economics and on scouting, scouting and more scouting—every field on a set schedule. If I find myself applying more treatments at higher soybean price levels, I’ll rotate active ingredients to help avoid resistance."
While using all best management practices, the bottom line is that damaging levels of late-season pests must be controlled, lest they skim the profit off a valuable soybean crop, Ferrie says. Watch for spider mites if the weather is dry, with temperatures above 90°F. They migrate from mowed yards and ditches into soybean fields.
Bean leaf beetles overwinter in crop residue or litter near bean fields. Early in the season, they feed on young soybean seedlings. They remain a problem all season long.
Soybean aphids can also blindside a grower later in the season, adds Farm Journal Associate Field Agronomist Missy Bauer.
"In our area of southern Michigan and northern Ohio, growers got used to soybean aphids becoming a problem every two years," she says. "That pattern has ended, however, so now it’s important to scout for aphids well into the season."
Understanding thresholds, appointing a pest boss, scouting for late-season threats and managing pesticides to prevent resistance (and wasted expenditures) will point you down the road to profit in 2012, Ferrie concludes.
- January 2012