Carrington Research Extension Center
North Dakota State University
NDSU Extension Service
North Dakota Agricultural Experiment Station

Ag Alert

July 22, 1999


Currently, the presence of European corn borer moths, eggs, and larvae generally appear to be low. However, don't discontinue your scouting efforts for this insect.

Corn becomes susceptible to European corn borer infestations after it exceeds an extended leaf height of 17 inches. Corn borer should be monitored weekly for at least five weeks once corn reaches the susceptible stage. Inspect plants for the presence of egg masses, whorl feeding, and active larvae. Whorl stage corn should be scouted by randomly pulling and inspecting the whorls from 10 plants at 5 locations in the field. Count and record the number of live larvae found and apply to a worksheet formula to determine if insecticide treatment is required. If your corn is tassel stage or older, examine the underside of the middle 7 leaves (3 leaves above and 3 leaves below the ear leaf) on 20 plants from 5 locations in the field. Multiply the number of egg masses found by the correction factor of 1.1. Complete worksheet to determine the need for treatment. If egg masses are detected on 20 to 25% of the plants scouted, significant larvae infestations may develop.

The management worksheet as well as scouting procedures and insecticide recommendations are available in the NDSU Extension Service circular E-1143 'ND Field Crop Insect Management Guide'.


The majority of canola fields in south-central North Dakota have completed flowering. Soon it will be time to start monitoring the crop to determine when to swath.

The following are two general guidelines to help indicate when intensive inspection is required in order to begin the swathing operation. The period between the end of flowering and maturity has averaged 21 days in 1994-98 canola cultivar trials at the Carrington RE Center. Keep in mind that this period may vary considerably depending on cultivars, growing season, location, etc. Another sign of canola being very near the swathing stage is the natural yellowing and senescence of leaves and leaf drop. When canola plants consist only of stems, stem branches and pods, the crop is probably very near the optimum time for swathing.

Canola swathing should be initiated when a minimum of 15-20 percent of seeds, contained in pods located on the main stem, have started to turn color. Seed color change is from green to light yellow, or reddish brown, brown, or black, depending on the cultivar. Seeds with only small patches of color should be counted as color changed. Seeds will begin maturing at the lower portion of the plant and will continue upward. Sampling should be performed throughout the field.

Details on timing the swathing operation may be obtained from the NDSU Extension Service circular A-1171 'Swathing and Harvesting Canola'.

Greg Endres, Area Extension Specialist/Cropping Systems, Email:
1999 Ag Alert Archive * Carrington R&E Center Home Page * NDSU Agriculture