Know Every Field's Weaknesses

Know Every Field's Weaknesses
Every field is different, with unique strengths and weaknesses. We don’t spend much time thinking about the strengths because they make farming easy. But the pest boss—the person on a farm responsible for all aspects of pest management—knows every one of those weaknesses. He or she must, in order to create and implement a pest control plan.

Pests take advantage of weaknesses, whether in varieties or in fields. “Some weaknesses affect an entire field, and some are found only in management zones,” says Farm Journal Field Agronomist Ken Ferrie. “As we plan pest management, we must go beyond field-scale, into individual management zones, to focus our scouting.”

Keeping track of every weakness in every field is a tall order. Here are some ways to focus your efforts:

Ferrie likes to divide pests into two categories—annuals and perennials. Annual pests, such as insects and rodents, might or might not show up in a field, while perennial pests are always present.

Annual pests often are affected by cultural practices, including crop rotation. For example, a field in continuous corn must be scouted carefully for disease. Fields coming back into production after years in a land-retirement program, and cover-cropped fields, might experience certain insect problems, and corn following pumpkins might suffer rootworm damage because rootworms are attracted to pumpkins.

Lodged corn might result in volunteer corn in the following soybean crop. If the corn was Roundup Ready or LibertyLink, the pest boss must take that into account when he plans his soybean weed control program.

“Some annual threats can be avoided just by keeping good records and using them to anticipate problems,” Ferrie says. “If a wheat crop is scheduled to follow a cereal rye cover crop, you might want to change the rotation in that field to avoid volunteer rye problems in the wheat. Consulting last year’s as-applied records will enable the pest boss to avoid violating label restrictions, which might lead to herbicide damage in a susceptible crop.”

The good thing about annual threats is they might not happen. “With annual threats, it’s usually not economical to use a preventive treatment if there is a reactive one available,” Ferrie says. “That’s why the pest boss needs to understand the threats in every field.”

Annual weed threats can be managed by scouting. “For example,” Ferrie says, “if a field of corn went down, the pest boss will plan to scout that field and see how much corn germinates in the fall or before planting in the spring. Then he can decide how to handle it in the following crop.”

Weed escapes, even if neutralized by walking or rescue-spraying, also target a field for special attention. “In that field, the pest boss will plan to use a herbicide with a different mode of action next season,” Ferrie says.

With reactive weed treatments, early recognition of the problem is essential. “Otherwise, weeds might get beyond the ideal size for treatment,” Ferrie says. “Weeds germinate at different temperatures; giant ragweed is early and foxtail and woolly cupgrass are late. By knowing which weeds are likely to be a threat in which fields, he can scout the right fields at the right time. His scouts must be trained to recognize weeds in the seedling stage.”  

Perennial weaknesses are always present in a field or management zone. They are problems the pest boss must manage around. Here are some examples:

  • Fields with poor drainage often experience water molds, which make it difficult to establish a stand. “If a field has a problem with water molds, you can manage it by waiting to plant until the soil is dry and the forecast says it will stay that way long enough to get the crop up,” Ferrie says. “This can work if the forecast is accurate and you have time to wait. But using treated seed to manage the water molds probably is a better solution. Treatment might not pay every single year, but because of the frequency of the problem, it will pay over the long term.”
  • If nematodes are present, they’ll be there for multiple crop years, whether the field is planted in corn or soybeans. Nematodes might increase the chance of sudden death syndrome in soybeans. “If the field has nematodes and you haven’t been able to manage the problem with variety selection, it should receive a preventive nematicide,” Ferrie says. “Here’s where it pays for the pest boss to be involved with the rest of the operation: If the farm has a multi-hybrid planter, they might be able to put the same variety in each seed tank, treat one tank of seed with a nematicide and plant the treated seed in the problem areas.”
  • Other pests that, once established in a field, are likely to stick around for years include true grubs, wireworms and insect-resistant corn rootworms. “In fields with insect resistance to a trait or insecticide, the pest boss must implement a multi-prong approach, changing both traits and insecticides,” Ferrie says. “Once he starts changing them, he must be aware of reactions between the insecticides and herbicides he is using.”
  • Once present, white mold remains in a field, although it shows up only when cool, wet conditions occur during the plants’ flowering period. Treatments include variety selection and planned fungicide applications.
  • If frogeye leaf spot develops resistance to a fungicide in a field of soybeans that becomes a long-term problem. Solutions include variety selection and changing to a fungicide with a different mode of action.
  • When herbicide-resistant weeds are present in a field, that’s a perennial weakness the pest boss must deal with every season.
  •  Some perennial threats are inherent with certain cultural practices. In fields where no-till, strip-till and cover crops are used, the pest boss can expect rodents such as voles and ground squirrels, every season. “Today, many farms use more than one system,” Ferrie notes. “They might adopt a system to manage the weakness in a certain field, such as no-till or strip-till on a field of highly erodible land. Pest management gets more complicated when different systems are in use.”
There are many reasons some fields have more weaknesses than others. Some have more pest issues because of the crop they are growing, so they require special attention. For example, seed corn tends to experience more pest problems than commercial corn.

Some fields have heavier weed pressure because, in previous years, a seed bank built up. For example, one study found velvetleaf seed was still viable after lying in the soil for 90 years.  

“We often experience heavy weed pressure in a newly acquired field,” Ferrie says. “Your practices might have kept your own weeds in check, but the previous operator of that new field didn’t do as good a job.”

Problems might migrate in from beyond the borders of your own fields. “Paying attention to fields upstream in your watershed might alert you to threats in your own fields before they become major problems,” Ferrie explains. “Flowing water carries weed seeds, as well as nematodes and disease organisms.”

Keeping a list of weed threats for each field, and maps of where they are located, is a necessity for scouts to focus their efforts. “Merely knowing which weeds are present is no longer enough,” Ferrie adds. “The pest boss must know what herbicides the weeds are resistant to. Using some preplant and postemergence herbicides to control resistant weeds might require changing genetic seed traits, which is why the pest boss should be included on the farm’s variety selection committee.

“The situation might be different in every field,” Ferrie continues. “Drawing upon good pest management records, such as aerial images, scouting reports and as-applied pesticide maps, the pest boss can lay out a plan to manage the weakness of each field.”

With good pest planning, modified as necessary each growing season, success builds upon success. “Sometimes a perennial threat can be turned into an annual threat or even eliminated,” Ferrie says. “For example, improving drainage in a field can reduce water molds. That leads to better stands, which improve weed control by closing the crop canopy.”

Preventive Versus Reactive Treatments

Knowing his fields might allow a pest boss to replace a preventive treatment with a reactive one, which is required only if a pest shows up in threshold numbers.
“With insects, some growers have moved away from planting traited seed, a preventive measure, to control corn borers,” says Farm Journal Field Agronomist Ken Ferrie. “As a result, they might see more borer pressure in their fields. But whether or not they do will depend on the insect survival rate and the environmental conditions.”

The previous year’s scouting reports will alert the pest boss to fields that might face a borer problem. To decide if treatment is needed, he or she will track heat units, monitor the borer population with insect pheromone and light traps and have the pest control team prepared to scout at the appropriate time. If they discover threshold levels of borers, the pest boss can control them with an insecticide.

“In contrast,” Ferrie says, “there’s no reactive treatment available for corn rootworm larvae [unlike the adult beetles, which can be controlled with an insecticide]. So in fields where rootworms are likely to be a problem, the pest boss will make a preventive application of an insecticide.”

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