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Manage bugs to manage growth

Loretta Sorensen Published on 02 March 2010
Paul Gustad

Managing 2,000 acres of alfalfa and hay crops, corn fields, livestock and a multiple family farm operation make for busy days for Paul Gustad, his father Bud and brother Dean.

As they built their network of hay fields in southeast South Dakota over the past 15 years, the Gustad family found that drawing on the expertise of their local certified agronomists not only made their job easier, it resulted in higher-quality forage for their hay customers.

“We work in about 25 different fields,” Paul Gustad says. “Some of those we own, but much of what we do is custom work. We also market the hay we harvest, so we take advantage of anything we can do to make our work efficient and maintain the best quality hay.

Involving Greg Pirak at Valley Ag about eight years ago to monitor our fields and handle pest control was one of the best decisions we’ve made.”

Pirak, a certified agronomist who established his ag consulting business several years ago in Gayville, South Dakota, says controlling insect damage in alfalfa fields will quickly pay producers back with improved hay quality throughout the growing season.

“It’s incredibly important to control insect damage in order to harvest the best quality hay,” Pirak says. “Many times, re-growth is greatly affected by insects after the first cutting.

Alfalfa weevils can feed heavily enough after the first cutting that farmers think their alfalfa field is short of moisture because the stand is growing so slowly. What’s really happening is that the weevils are consuming every succulent little leaf that’s growing back.”

Pirak notes that second- and third-cutting alfalfa may produce more tonnage but actually contain fewer nutrients than the first cutting simply because weather conditions cause it to grow faster, which means fewer nutrients are drawn up into the plant. The overall result is a lowered relative feed value (RFV).

“On that second cutting, if you’re starting out with a lowered feed value of say 220 points because the alfalfa‘s growing faster now, that RFV can quickly fall to 170 or less depending on weather conditions and bug problems,“ Pirak says. “If the quality falls to 150 or less, dairy farmers are going to pass it up and you lose a significant profit.”

Gustad says relying on a professional to monitor insect infestations makes his family’s job much easier because insect problems and timing is never the same in any two consecutive years.

“The hay fields need to be checked all year round because a mild winter can mean insect problems could begin earlier than normal or a different kind of bug could infest the field at a different time than the previous year,” Gustad notes.

“Greg and his staff know what kind of weather gives which pest an advantage. They also know the appropriate time to spray and how many bugs per acre you need to find before you apply any spray.”

Pirak confirms that geography and weather are critical elements of insect control and says spring temperatures can vary greatly, which means the hatch of bugs like alfalfa weevils will occur at a different time every year.

“The weevils’ larvae look like little green worms with a white stripe on their back and a black head,” Pirak says. “The females lay a small oval lemon- yellow egg in dead stems or litter in the field.

Once the temperatures rise to 48 degrees or above, those eggs hatch. A lot of times you won’t see the larvae in the alfalfa till about the second week of May. That’s just when producers are debating about getting that first cutting.”

If weather conditions are just right, cutting the alfalfa can mean insects are at a disadvantage. A large amount of sunlight that floods a field coupled with dry weather conditions can mean the insects dry out, too.

“But if the weather’s against you and temperatures are cool, there’s more humidity in the air and that hay doesn’t dry out right away – it seems the insects survive that cutting pretty well,” Pirak says.

Other insects agronomists scout for in alfalfa fields are potato leafhoppers, grasshoppers and aphids. Leafhoppers can be difficult to see, aphids come in with wind currents and army worms can also wreak havoc on a field after traveling on air currents and dropping into an isolated section of a field.

“It’s hard to believe leafhoppers can cause so much damage to a field because they’re so small,” Pirak says. “Often, you’ll see the damage the leafhoppers do before you realize they’re in the field.

If you find less than one-half a bug per sweepnet, it’s time to spray. That’s the advantage producers have when we’re scouting their fields. We’ll usually find the bug before it has a chance to do real damage.”

Once insects are detected in a field, Pirak’s staff pinpoint the most effective treatment. Life cycles of the insect are considered in the process.

Some insects are susceptible to fumigants and others require a residual spray that will help control the bug over several weeks. The requirements for application prior to cutting and baling also need to be considered.

Gustad notes that the agronomists’ understanding of the insects, their life cycle and response to chemical control allows for more effective control in his family‘s fields, both in terms of cost and eradication.

“I know some producers just spray their fields every so often, but that takes out beneficial insects too,” Gustad says. “It seems like a waste of money to spray for bugs that aren‘t there.”

Pirak says it’s important for producers to recognize that spraying a field with a residual chemical too early in the life cycle of an insect could mean that much of the growth in the alfalfa field that occurs after the spray is applied remains unprotected.

“If you apply spray when the alfalfa is five inches high and then it grows to 18 inches, that 13-inch growth is susceptible to insect damage,” Pirak says. “The chemical only protects the foliage it was applied to. The new growth doesn’t benefit from that earlier application.”

Advancing technology in chemical application equipment makes modern insect control measures safer. Pirak says a well-managed control plan can result in the need for fewer applications over a period of time.

“In the last couple of years the weather conditions here have resulted in fewer insect problems so we’ve done less spraying,” Pirak says.

“We’re scouting fields all the time so we’re able to identify insect issues before they can become serious. It’s rare to see a stand of alfalfa killed because of heavy insect damage, but it can happen.”

Gustad says taking the guesswork out of insect management makes it possible for his family to produce better quality hay.

“We don’t worry about the insect side of things because we know Greg’s taking care of it,” Gustad says. “We know that they don’t need much time to develop a plan of attack if they do find insects. That leaves us that much more time to concentrate on getting our hay up.”  FG

Loretta Sorensen is a freelance author from Yankton, South Dakota.

Paul Gustad works with his family members to put up and market hay throughout the growing season. He and his family rely on a local agronomist to monitor insect problems in the network of hay fields so they can concentrate on producing the best quality hay for their customers. Photo courtesy of Loretta Sorensen.