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Common Stalk Borer Activity Estimate: May 12, 2022

Originally Submitted: May 12, 2022

Warmer weather during the last week resulted in fast accumulation of degree days throughout South Dakota. At this point in the season, no common stalk borer scouting is necessary, but many areas of the state are reaching the point where weeds along field edges should not be managed for the time being (Figure 1). Spraying weeds that are potentially infested will force any common stalk borer caterpillars to leave dying weeds and seek out alternative hosts.

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°F. 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 1300 degree days, 10% of the caterpillars will begin moving to corn. Corn should begin to be scouted at this point. At 1400 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

Map showing the current degree day accumulations of common stalk borers for several South Dakota locations. For assistance reading this graphic and data set, please call SDSU Extension at 605-688-4792.
Figure 1. Common stalk borer activity based on degree day accumulation for various South Dakota locations as of May 12, 2022.


Table 2. 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