Common Stalk Borer Activity Update: May 23, 2019

Originally Submitted: May 23, 2019

Not too much is new regarding common stalk borer activity when compared to last week. 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. 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 41o 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
503
 No scouting necessary.
Newell
553
 No scouting necessary.
Rapid City
543
 No scouting necessary.
Hot Springs
680
 No scouting necessary.
Lemmon
467
 No scouting necessary.
Faith
391
 No scouting necessary.
Cottonwood
523
 No scouting necessary.
Mission
521
 No scouting necessary.
Selby
408
 No scouting necessary.
Gettysburg
405
 No scouting necessary.
Pierre
524
 No scouting necessary.
Winner
668
 No scouting necessary.
Aberdeen
446
 No scouting necessary.
Huron
509
 No scouting necessary.
Mitchell
597
 No scouting necessary.
Tyndall
608
 No scouting necessary.
Sisseton
408
 No scouting necessary.
Brookings
435
 No scouting necessary.
Vermillion
722
 No scouting necessary.

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