Scouting should begin as soon as crops begin to emerge. This is the time to evaluate plant population. Although plants are in early stages of growth, problems may arise now that eventually lead to decreased yields. You should make a general observation of fields once a week and look for trouble spots that show signs of abnormal growth or developing problems.
Regular scouting should take place during the first six to eight weeks of plant development. Weed control is especially important during this time because weeds compete with crops for nutrients, water and sunlight. This may be important if wet weather prevented timely herbicide applications.
Begin scouting for insects at plant emergence because economic injury will occur quickly on small seedling plants. Insect populations should be monitored on a regular basis throughout the growing season. Although the occurrence of some common insects is somewhat predictable from year to year, there is always a possibility that sporadic pests will emerge in localized areas.
One insect pest to watch for in corn fields is cutworms. Even though many corn hybrids offer some genetic resistance to cutworms, and some seed treatments provide some control, this may not be adequate with moderate to heavy infestations. Check 20 plants at five locations in a field. If an average of 1 plant in 20, or 5% of the plants, is showing cutworm feeding… it is time to apply a rescue treatment.
Another insect pest frequently seen this time of year in soybean fields is the bean leaf beetle. This pest overwinters in grassy areas… ditches, fence rows, terraces and waterways… and moves into fields from there. Fortunately, young soybean plants can outgrow much of this damage so control measures are rarely needed in the spring.
However, if you find an average of 2 to 3 beetles per plant when soybeans first emerge which is called the cotyledon stage or if you find 3 to 4 beetles per plant after the first true unifoliate leaf has emerged, then control measures may be warranted. Often treatments can be limited to those areas adjacent to grassy areas where they first start feeding. Once the plant has one or more trifoliate leaves emerged, the plant usually outgrows any feeding damage unless poor growing conditions prevent normal plant development.
One place to watch for bean leaf beetles is if you have a soybean field planted next to an alfalfa field. Often bean leaf beetles will first start feeding in alfalfa, then when the first cutting is taken, they migrate into the adjacent soybean field. Bean leaf beetle feeding can be extensive in the portion of the field next to the alfalfa and you may need to make one or two passes with a sprayer to control these beetles where they are concentrated.
Unfortunately, time restrictions prohibits inspecting every part of every field. In general, if the field is a regular shape, such as a rectangle or a square, walking the pattern of a “W” normally will give all areas of the field fair representation. In odd shaped fields, try to monitor areas throughout the field.
Keeping notes on past trends can help you determine what problems may occur and how to best manage different weeds and insects. You should refer to threshold levels, according to the plant growth stage and tolerance levels, to determine if a pesticide application or other control measures are needed. So as planting is winding down, take time to scout your fields. The time you spend now could pay big dividends at harvest.
For more information on crop pest control, contact your local Nebraska Extension office.