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2019 Common Stalk Borer Activity Estimate

Although most of South Dakota’s corn is still being planted or just emerging, it is important to remember some early season insect pests. In its early vegetative growth stages, corn is susceptible to feeding by the common stalk borer. For the most part, common stalk borer is considered to be only a minor or occasional pest. However, it is capable of reducing plant stands near the edges of fields or in any area of the field that borders a grassy or weedy area. Common stalk borers are an early season pest that initially feeds on corn leaves. As they grow, they move to the whorl of the plant and bore into the growing point. This activity can result in dead heart and subsequent plant death.

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. At this point corn should begin to be scouted. 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

In South Dakota, most of the state is still between conditions approaching egg hatch and egg hatch occurring. No scouting is necessary for common stalk borer at this time. We will continue to update this information.

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.

Table 2. Common stalk borer activity based on degree day accumulation for South Dakota.

Location
Accumulated Degree Days
Since January 1, 2019
Recommendation
Buffalo
448
No scouting necessary.
Newell
422
No scouting necessary.
Rapid City
491
No scouting necessary.
Hot Springs
603
No scouting necessary.
Lemmon
393
No scouting necessary.
Faith
338
No scouting necessary.
Cottonwood
448
No scouting necessary.
Mission
438
No scouting necessary.
Selby
340
No scouting necessary.
Gettysburg
319
No scouting necessary.
Pierre
440
No scouting necessary.
Winner
572
No scouting necessary.
Aberdeen
347
No scouting necessary.
Huron
401
No scouting necessary.
Mitchell
480
No scouting necessary.
Tyndall
515
No scouting necessary.
Sisseton
325
No scouting necessary.
Brookings
340
No scouting necessary.
Vermillion
610
No scouting necessary.

Related Terms

Corn, Crop Management