Common Stalk Borer Activity Estimate: June 5, 2024

Map showing the current degree day accumulations of common stalk borers for several South Dakota locations and the corresponding management recommendation. For a detailed description, please call SDSU Extension at 605-688-4792.
Figure 1. Common stalk borer activity based on degree day accumulation as of June 5, 2024 for South Dakota. Degree day data courtesy of the South Dakota Mesonet.

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

Originally Submitted: June 6, 2024

In southern South Dakota, enough degree days have accumulated for common stalk borer caterpillars to begin moving from alternative hosts into corn. Fields should be monitored for leaves with signs of defoliation.

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.
Accumulated
Degree Days		 Common Stalk Borer
Caterpillar Activity		 Recommendation
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

Related Content

Western bean cutworm caterpillar on corn.

Western Bean Cutworms Detected in South Dakota Corn

Western bean cutworm caterpillars have been reported in South Dakota corn. This pest can cause yield loss by feeding on the tassels, silks, and ears. In addition, ear feeding activities increase the likelihood of secondary diseases and mold growth on the ear.

Green plant with evidence of honeydew and an aphid colony.

Aphids Infesting Corn in South Dakota

Aphid populations are taking off in some southeastern South Dakota corn fields. The two aphid species that are commonly observed in corn include the corn leaf aphid and the bird cherry oat aphid.

Multiple grasshoppers feeding on a corn ear.

Grasshopper Populations Continue to Cause Issues in South Dakota

Recent reports of crop loss along field edges indicate that grasshopper populations in some areas of South Dakota are well above threshold. Unfortunately, crops are often the target of these moving populations.