Consider evaluating every field this May. By evaluating, I mean walking fields using a set protocol, not the standard "windshield" survey. You can use a professional scout or evaluate fields yourself. However, make sure the evaluation is done competently.

Just because you have crop pests present doesn't mean that they need treating. In fact, I commonly recommend not treating based upon low number of pests observed.

When evaluating crop pests, two terms are used. They are economic injury level (EIL) and economic threshold (ET). The EIL is defined as: The lowest pest density at which economic damage occurs, or when the cost of pest control equals economic loss caused by the pest. The ET is defined as: The pest density at which some control should be exerted to prevent pests from reaching the EIL.

I use six field evaluation categories, which are related to EIL and ET. They are: 1) No evidence of pests present. When this occurs, I recommend returning to the field at the next planned visit. 2) Low pest pressure (below ET). In this situation, I may recommend returning to the field before the next planned visit. 3) When ET has been reached. Treatment or management practice response needs to be done soon. 4) When EIL has been reached. Immediate treatment or management is required to prevent further economic loss. 5) EIL has been exceeded. A rescue treatment is used to prevent further loss. 6) Crop damage is so severe that treatment is not necessary.

Economic loss is not just limited to crop yield. Pest control may be justified economically if there is the potential for yield loss, crop quality degradation, harvest difficulty, aesthetic issues or weed seed reduction. Economic loss can also occur with problems such as hail, drought, drowning, frost, poor germination, poor emergence, etc. These non-pest issues should be evaluated during field visits.

Pest type is critical. With weeds, we have a combination of perennials, annuals and biannuals; broadleaves, grasses and sedges; and cool-season, warm-season species. Even within categories there is difference in response to evaluation. For instance, we have developed competitive indexes for each weed species to be used in combination with weed population dynamics to estimate yield loss potential.

There are many reference materials that include crop scouting protocols for your region, including pest identification materials, pest life cycles and pest physiology. The two I use most often are the University of Missouri IPM series and the University of Illinois field crop scouting manual.

Before evaluating a field, know field history including location, cropping history, crop rotation, yield potential, pesticide application type, rate and history, variety/hybrid planted, planting date, planting rate, row width, tillage system, tillage timing, seed treatments, weather patterns, fertilizer and lime rates, previous pest problems, and other agronomic factors. These factors are critical when developing in-season agronomic management strategies.

A field scouting trip reveals which pests are present, what stage of growth each pest is in, what stage of growth the crop is in, health of pest and crop, and notes on whether the pest or problem is waxing or waning.

Crop problems are almost never uniformly spread throughout a field. Evaluation sampling areas within a field should represent no more than 5 acres. Rarely exceed a maximum of 50 acres to be treated as a single unit. It is more accurate to increase stops per field as compared to increasing samples per stop. When sampling, avoid field edges and non-typical field areas. However, these areas (especially grass/weed fencerows or waterways) often harbor pests and may be the first and/or targeted areas to be evaluated.

You should have a consistent routine and sampling plan. Do not make rash management decisions based upon initial observations. Information-based sampling protocol can be based upon crop type, calendar date, pests present, weather conditions, pest trapping programs and university or crop consultant alerts.

A magnifying lens, sweep net, camera (digital preferred for rapid image transfer), soil probe and sampling containers all are used when evaluating crop status. Be careful with photographs. I have been called to many field visits based upon misleading photographs. Many field problems have similar symptomologies. Make sure you have positively identified a problem before treatment or management.

Proper field evaluation requires many sampling methods. They are as varied as the number of field problems that occur. You may need to sample whole plants or individual plant parts. Be sure to look at roots, stems and leaves. Soil compaction, fertilizer injury, discoloration associated with diseases, insect feeding and herbicide injury all can injure crop roots. Do not overlook this underground environment. Early season stem injuries can be caused by soil crusting, insect feeding and herbicide injury. Look for several foliar problems including diseases, insect activity, herbicide injury, nutrient deficiencies, wildlife damage and frost injury.

Another key component of field evaluation is to know who knows. We cannot be experts in all phases of crop production. By evaluating fields properly in May and using all possible references, scouting techniques and people resources, you have a much better chance of success throughout the remaining field season.