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Common Stalk Borer Activity Estimate: May 25, 2023

Map showing the current degree day accumulations of common stalk borers for several South Dakota locations. For a detailed description of this graphic and data set, please call SDSU Extension at 605-688-6729.
Figure 1. Common stalk borer activity based on degree day accumulation for various South Dakota locations as of May 25, 2023.

Written collaboratively by Adam Varenhorst, Philip Rozeboom, Patrick Wagner, and Brad McManus.

Originally Submitted: May 26, 2023

No scouting is necessary for common stalk borer as of this week. Across South Dakota, the young common stalk borer caterpillars are active in alternative weed and grass hosts.

When 1,300 accumulated degree days are surpassed, the caterpillars will begin moving from these hosts in search of corn. We recommend that weed management on field margins is not done at this time, as it can cause the caterpillars to move into the corn field early.

Predicting Common Stalk Borer Migration Into Corn Fields With Degree Days

The hatching and movement of common stalk borer caterpillars can be estimated by using degree days with a developmental threshold of 41 degrees Fahrenheit. Common stalk borer eggs typically begin to hatch at 575 degree days. The caterpillars finish hatching and begin development on weeds and grasses at 750 degree days. At 1,300 degree days, 10% of the caterpillars will begin moving to corn. Corn should begin to be scouted at this point. At 1,400 degree days, 50% of the caterpillars will or have moved into corn.

As a reminder, the equation for degree days is:

(Maximum Daily Temperature + Minimum Daily Temperature) ÷ 2 - The Developmental Threshold

Table 1. Common stalk borer caterpillar activity based on accumulated degree days.

Degree Days
Common Stalk Borer
Caterpillar Activity
0-574 Conditions favorable for egg hatch. No scouting necessary.
575-749 Eggs begin to hatch. No scouting necessary.
750-1299 Young caterpillars begin boring into grass and weeds. No scouting necessary. Avoid spraying grass and weeds along field edges.
1300-1399 10% of caterpillars begin moving into adjacent corn. Begin scouting field edges for defoliation.
1400-1700 50% of caterpillars moving into adjacent corn. Continue scouting for defoliation along field edges. Spray if necessary.

Related Topics

Corn Insects