By Adam Varenhorst
Another cool, wet week has led to a limited accumulation of degree days. Based on our calculations, common stalk borer activity still doesn’t warrant any scouting, but spraying field edges should be avoided around Hot Springs, Winner and Vermillion. We will continue to monitor the degree days and provide updates.
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.
| Location | Accumulated Degree Days
Since January 1, 2019 | Recommendation |
|---|
| Buffalo | 596 | No scouting necessary |
| Newell | 622 | No scouting necessary |
| Rapid City | 627 | No scouting necessary |
| Hot Springs | 767 | No scouting necessary.
Avoid spraying field edges. |
| Lemmon | 564 | No scouting necessary |
| Faith | 476 | No scouting necessary |
| Cottonwood | 601 | No scouting necessary |
| Mission | 622 | No scouting necessary |
| Selby | 515 | No scouting necessary |
| Gettysburg | 487 | No scouting necessary |
| Pierre | 639 | No scouting necessary |
| Winner | 789 | No scouting necessary.
Avoid spraying field edges. |
| Aberdeen | 564 | No scouting necessary |
| Huron | 638 | No scouting necessary |
| Mitchell | 734 | No scouting necessary |
| Tyndall | 749 | No scouting necessary |
| Sisseton | 515 | No scouting necessary |
| Brookings | 536 | No scouting necessary |
| Vermillion | 824 | No scouting necessary.
Avoid spraying field edges. |