Site-Specific Insect Management

Quantifying insect pest population and distribution across management zones has potential for site-specific insect management.

The variability observed in insect pest distributions across a field and over time has been one of the major challenges for insect pest managers. Because of this variability, the cost of getting an adequate picture of an infestation is often too high for use in production agriculture. Much effort has gone into developing more efficient sampling methods, such as sequential sampling and remote sensing, that allow accurate assessment of the infestation in a given field.

The next problem insect pest managers face is to determine the economic significance of the sampled infestation, which is done with the economic injury level (EIL) concept. The EIL relates pest abundance or damage to expected yield with the following formula:

EIL = economic injury level CC = control costs YL = yield loss per insect MV = market value of corn EY = expected yield (bushels/acre)

The calculation results in some measure of abundance (corn borers per stalk, mite-infested leaves) or damage (% damaged plants, tunnels per stalk) that is expected to result in a yield loss equal in value to the cost of treatment. Because it is economically undesirable to actually reach the EIL, treatments are generally made at a somewhat lower level of abundance or damage referred to as the economic threshold (ET).

Sampling costs have limited the compatibility of insect pest management and precision agriculture. Given that the cost of obtaining an adequate sample for an entire field is often prohibitive, the affordability of sampling smaller units as required by grid sampling approaches would be even lower. Sampling production management zones may offer a compromise. This involves grouping areas of the field with similar production potential together into management zones, and sampling each zone separately. This concept has two features that enhance compatibility with insect pest management. The first is reduced sample effort relative to the grid sampling approach, although more sampling still is required than for the whole field approach. However, our initial observations indicate that insect densities vary with management zone so it may be that sampling management zones may be more accurate than sampling the whole field because insect densities are more uniform within zones. The other feature is a better assessment of yield potential which improves the accuracy of EIL calculations. This, in turn, would lead to more efficient insecticide use.

For these reasons, our research is focusing on relating insect pests of corn to production potential management zones. If insect damage is proven to correspond to management zones, insect treatments could be targeted towards specific management zones instead of the whole field, thus reducing the amount of insecticides used and saving the grower money.

Objective 1:
Determine if insect pest (western corn rootworm, European corn borer, western bean cutworm, Banks grass mite) abundance differs among management zones.

Surveys of these pests were conducted in 2001 and 2002 within management zones in cooperator fields in Wiggins, Yuma, Brush, and Greeley, Colorado.

Study Findings

• Western corn rootworm larvae and adults were more common in high productivity management zones than in low productivity management zones.
• European corn borer larvae were more prevalent in the high productivity management zone at the most heavily infested field.
• Western bean cutworm egg masses were evenly distributed among management zones at one field, but at this same field larvae were most common in the high productivity management zone.

  Objective 2:
  Determine if production potential management zones influence insect damage.

This research is being conducted with the same corn pests at a field at ARDEC (Colorado State University Agricultural Research Development and Education Center) in Fort Collins. Because we are on university land we can infest plants with insects to determine if the observed differences in pest abundance among management zones is due to differential survival related to some management zone property rather than due to differential choice by adult pest insects. Also, our infestations assure that insects are present every season, which is not always the case in growers’ fields.

Study Findings:

In 2002, plots were infested with equal numbers of European corn borer larvae. When stalks were split, a differential rate of survival was observed among management zones.

In 2003 we are trying to relate abundance and damage of these pests to the following variables: Productivity level management zones (high, medium, low); moisture levels (irrigated, dryland); and nitrogen levels (irrigated 50,100, 200 lb N/ac and dryland 50,100,150 lb N/ac).

The research will give us a better understanding of how insect pest variability is related to production potential management zones. This, in turn, could lead to improved insect pest sampling as well as more efficient and economical insecticide
use.

Mr. Silas Davidson and
Dr. Frank Peairs
Department of Bioagricultural Sciences and Pest Management
Colorado State University