Here's How to Keep Pests From Being an Unwelcome Surprise

October 20, 2017 12:16 PM
Here's How to Keep Pests From Being an Unwelcome Surprise

A pest boss—one member of a farm’s management team in charge of everything involving weeds, insects and diseases—earns his keep by preventing surprises. “That’s his job—to never be caught off guard,” says Farm Journal Field Agronomist Ken Ferrie. “A pest boss usually treats a problem while other farmers are still talking about it.”

That’s a tall order, considering how many insects and diseases can attack crops. But good pest bosses approach it systematically, Ferrie explains. They know what pests are likely to occur and when to expect them. They know how they will control them, where they will obtain pesticides and who will apply them. They target their scouting and know when to treat. Good records of every field make the task easier in successive years.

The job of a pest boss can be broken down into manageable chunks. Ferrie suggests starting by separating insects and diseases into “domestic” and “foreign” categories. “Just as soldiers, sailors and airmen defend our Constitution against all enemies foreign and domestic, a pest boss vows to protect crops against foreign and domestic pests,” he says. “Domestic pests spend their entire life cycle on the farm. Foreign pests winter elsewhere; they might or might not attack a farm in any given year.”

The first step is to know which pests overwinter in your area, making them a potential threat every season. “You can find that information through your land-grant university or in scouting manuals for your region,” Ferrie says.

After compiling a list of domestic pests, the pest boss studies their life cycles. “Some insects overwinter in soil and some in above-ground habitat, such as crop residue,” Ferrie says. “They overwinter in various forms, such as eggs or larvae.

“It’s the same with disease; some overwinter in the soil, some in residue. The pest boss understands how the environment influences pest outbreaks,” he adds.

The time of attack by domestic insects depends on heat units. “Insect heat units are different from growing degree days for crops,” Ferrie explains. “Growing degree days are calculated on a daily average; with insects, you collect heat units on the hour or even the half-hour.”

Every insect has a different threshold temperature at which development begins, and heat units are cumulative. “Say an insect begins to develop when soil temperature reaches 45°F,” Ferrie explains. If the temperature drops after a week, the insects might stop developing. Then when the soil temperature again rises above 45°F, development resumes.” Development thresholds for various insects can be found online and in scouting manuals.

Start keeping track of heat units on Jan. 1. Some land-grant universities monitor heat units at various locations around their state; then they estimate the development date for each locality based on long-term weather history.

“Domestic insects are fairly predictable,” Ferrie says. “Remember if an insect winters in soil, you must look at soil temperature. If it winters aboveground, like stalk borers, look at the air temperature. By comparing soil temperatures from previous years, you’ll know whether to expect an outbreak earlier or later than usual.”

You can also use your farm’s weather station. “Many weather stations today have the ability to add heat unit calculators,” Ferrie says.

It’s good to have multiple sources of heat unit data. “Some seed companies and retailers post heat unit data on the Internet,” Ferrie says. “I look at data from our weather station, farmers and land-grant universities from my own and neighboring states.”

Although heat units can’t predict domestic diseases, the pest boss still needs to use weather data. “Learn the life cycles of your most common diseases,” Ferrie advises. “Know what kind of weather holds the key to their development. For example, some soil-borne diseases thrive when it’s cold and wet; others like warm, wet conditions and still others prefer hot and dry. Among aboveground diseases, some like cool and humid conditions while others prefer warm and humid.”

Weather conditions alert the pest boss to disease outbreaks. “A pest boss knows that one day of cool, wet weather won’t trigger Northern Leaf Blight,” Ferrie says. “But if you have 10 days of cool, wet weather, be prepared to treat.”

Decades of weather data provide repeatable, chartable ways to avoid pest surprises, Ferrie summarizes. “Using weather history, we usually can predict within a week when a domestic pest infestation will occur,” he says. “That lets the pest boss assemble a calendar showing which insects and which generations as well as which diseases to watch for at any given time. Applying local weather data dials in the timing even tighter.”

For a few insects, such as spider mites, heat units are not a predictor. “Mites are present every year, but predators keep them in check,” Ferrie says. “In hot, dry conditions, the predators are gone, so mite populations build up and they become a problem.”

Foreign threats, insects and diseases that move through an area, are unpredictable. “Heat units are not effective in managing them,” Ferrie says. “One example is cutworm, which is carried by wind currents from Mexico or the Gulf states. While we can’t use heat units to predict cutworm infestations, we might be able to get some warning by monitoring websites to the north or south. If an Illinois pest boss checks websites in Tennessee or Oklahoma, he might discover the insects are moving up from the south.”

Sticky traps, attractant lures and black-light traps can alert a pest boss that insects are moving into the area. “Once you identify a threat, such as cutworm moths, in your traps, you can use insect heat units to calculate how soon their eggs will hatch,” Ferrie says. “With cutworms, we can predict the first shot hole feeding within three or four days.

“Some universities set traps throughout the state and report what they are catching,” Ferrie continues. “Neighboring pest bosses might team up, each setting traps for certain insects and sharing what they learn. Information can also be shared on social media.”

Some diseases travel as airborne spores. “Spores are difficult to detect,” Ferrie says. “You can trap soybean rust spores, but it requires training to identify them under a microscope. Your only other option is to send them to a lab for analysis. “So watch for weather conditions that allow disease spores to germinate.

Common rust in corn, for example, needs cool, moist weather. Southern rust spores germinate in warmer, moist conditions. Even if spores blow into your area, they won’t create a problem unless they have the right type of weather.”

Good records are crucial for planning and scouting. A farm’s records of past pest problems should be kept in the same file with the production records. “When there’s a pest threat, the pest boss needs to know which fields are most susceptible,” Ferrie says. “He must know which varieties and trait packages are planted in each field.

“For example, can a field handle rootworm and corn borers, or are the plants missing resistance to one or both insects? If the plants have genetic resistance, the pest boss can spend his time scouting other fields that might be at risk.” He also must know which fields are in continuous corn or soybeans because that increases risk.

“Knowing which disease and insect problems occurred, in which fields, helps you plan for the following year,” Ferrie says. “For example, once you have Goss’s Wilt, it remains present in crop residue until it is completely decomposed. So you’ll need to select hybrids to manage the disease. If you have a heavy infestation of Northern Corn Leaf Blight, choose hybrids with strong resistance scores the following year.”

Knowing environmental conditions in each field is important. “If some fields fight Pythium and Rhizoctonia, which are water molds, and Sudden Death Syndrome, which affects plants in wet conditions, advise the crop manager to avoid planting certain crops in those fields or consider applying seed treatments,” he adds.  

As scouting time approaches, the pest boss might use aerial imagery,

thermal imagery and drones. “Remote sensing shows which plants are under stress,” Ferrie says. “For example, spider mites move in from the edge of a field, but not from every edge. Now we can head straight to the problem area, rather than zigzagging across the field like we did years ago.”

Knowing what insects and diseases to look for, the pest boss is ready to scout fields. He carries a hand lens for a close look at tiny pests and a scouting manual or access to the internet to identify pests. “Some diseases, such as common rust and southern rust, are easily confused,” Ferrie points out. Scouting begins with fields most likely to harbor pest problems—a pest threat pecking order.

“The final thing the pest boss needs to know is the threshold for treatment of each pest,” Ferrie says. “Recommended treatment thresholds are available from land-grant universities, and the pest boss can also draw upon his own experience. Thresholds tell the pest boss when treatments will pay for themselves.”

A pest boss should be authorized to treat fields, without referring the question to a committee. That way he can treat before damage becomes serious (and before his neighbors do).

During the off-season, the pest boss studies products for various pests, and makes sure the farm has them on hand or knows where to get them. “The pest boss must understand products or consult someone who does,” Ferrie says. “If a product kills spider mites’ predators, but not the mites, it might make the problem worse.”

Once treatment is in order, the pest boss makes sure the proper fields get treated. “Some aerial applicators have an app that lets the pest boss outline a field and send it to the pilot to make sure he finds it,” Ferrie notes.

After treating, the pest boss ensures reentry deadlines are observed. Finally, he evaluates the effectiveness of each treatment. If one failed, he figures out why.

Failures can result from insect resistance or reinfestation. “Some soybean fields with Japanese beetles or spider mites had to be sprayed several times in 2017 because of reinfestations,” Ferrie says. “Make sure you know a product’s longevity. A product might be effective for 14 days, but the pest lasts for 21. Be ready to retreat.”

After the growing season, the pest boss reviews all the season’s pest problems. “If there was a surprise, figure out why,” Ferrie says. “That way, it won’t happen next year.”


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