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Field Perimeter

Wednesday, April 1, 1998
filed under: Insects

Byron Richard believes in being proactive, not reactive, when it comes to controlling grasshoppers in his southwestern North Dakota sunflower fields. Still, like any producer, he has no desire to spend any more money on insecticide applications than what’s necessary to achieve satisfactory control.

For the past two seasons, the Belfield, N.D. grower’s answer has consisted of a field-perimeter treatment program which has provided excellent ’hopper suppression — at a very low price. In 1997, the total cost of three perimeter sprayings — when extrapolated across his entire sunflower acreage — was just $2.80 per acre. And that investment included concurrent mid-season control of sunflower beetle populations.

Grasshopper infestations have been heavy in the Billings County vicinity the past few years. Typically, “where we especially run into trouble is when the cereal crops start to mature and the grasses dry up,” Richard notes. “Then the sunflower looks awfully green and attractive to the grasshoppers.”

But early season infestations of emerging sunflower can be equally troublesome. As a seed and herbicide dealer, Richard spends a lot of time in not only his own fields, but also those of customers. He advises fellow producers “to be on the ball and anticipate the grasshopper situation.” That first ’hopper flush is more difficult to scout for due to the insects’ smaller size, he notes, but close monitoring will locate them in grasslands bordering the sunflower fields.

Rather than waiting for populations to move into sunflower fields, Richard believes in treating hatching sites early with a residual insecticide. For that initial grasshopper flush, he uses the recommended rate of Asana and sprays a strip 60 to 100 feet wide. Part of that strip will overlap into the grassy areas bordering the field; the other part is within the ’flowers. “Don’t cut that rate,” he advises. “You’re doing only perimeter spraying, so it doesn’t cost much on a [whole-field] per-acre basis.”

That early treatment has provided excellent results for Richard the past couple years, suppressing the grasshopper problem until mid-summer when the small grains are maturing and approaching harvest. “Then we go with a different game,” he explains. Due to the sunflower’s height — and the fact that most ’flower acreage in his area is now solid seeded — “we’ve been hiring an airplane to spray two passes around the perimeter, covering basically the same area we did with the field sprayer in the spring,” Richard says. The insecticide of choice for this treatment is Warrior, a residual pyrethroid that’s “not quite as tough on the bees.”

Here’s where the insecticide performs double duty. “Usually, about the time we spray for that second flush of grasshoppers moving off the cereal crops, we’re also starting to notice sunflower beetles along field perimeters,” Richard reports. “So we’re ‘killing two birds with one stone.’ We nail those beetles that are defoliating the outsides of the fields, and we’re also setting up a barrier for the grasshoppers with the residual insecticide as they move out of the other ground.” Scout first to make sure the beetles haven’t already moved to the field interior, though, he adds.

In 1997, given the season’s particularly heavy grasshopper populations, “we ended up going back two weeks later and spraying that same perimeter again with Warrior,” he adds. Even with that third treatment, his total spray program cost, as previously indicated, less than $3.00 per acre on a field-wide basis. “It’s a very economical investment,” Richard emphasizes — probably about one-tenth the cost of a field-wide application.

Though the spring perimeter ’hopper treatment has been well-warranted in his area in recent years, Richard does not downplay the importance of field monitoring. “I wouldn’t encourage people to be lax about their scouting. You should always know what you’re spraying for,” he stresses. “But if the past couple years are any indication, most likely we’ll be treating for grasshoppers — especially that Asana program in the spring.

“In the summertime, when the grasshoppers are larger, it’s easier to scout, and you can pretty well tell if you’re going to have a problem.

“As a rule, I feel that one in the spring is most essential — and I’d probably do it regardless because it’s so economical.” When weighing mid-season threshold levels, “you know if you have grasshoppers, they’re going to become concentrated in the sunflower fields,” Richard observes. “You don’t need a very large population to justify the expenditure” of perimeter spraying.

“I’m not suggesting [area producers] will never have to spray the entire field, because there are other insect pests that can come into play,” Richard states. “But out here — especially in solid-seeded fields — the grasshopper has been our biggest program. And this perimeter-spraying program has been quite effective two years in a row.” The key, he concludes, is to treat early — before the insects move beyond field borders and spread out across the field. — Don Lilleboe
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