By Adam Varenhorst
Not much has changed in terms of degree day accumulation for common stalk borers since last week. Cold low temperatures prevented most of the state from accumulating very many degree days. At this point in the season, no 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
Figure 1. Common stalk borer activity based on degree day accumulation for various South Dakota locations as of May 26, 2022.TABLE 2. 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. |
Source : sdstate.edu