How to Test Whether Pesticides on a Field Growing Sunflowers Were Effective for Insects

Insect pests can destroy entire fields of sunflowers.

Sunflowers are grown commercially for various uses, the more common of these being as a food for birds and animals, as a food for humans, and for the oil. There are some pests that can damage or destroy all or a large part of a sunflower crop, and it is common to spray fields in order to control these pests. To determine if a pesticide spray was effective it is necessary to physically inspect the field.

Instructions

1. Go to five different random locations in the field of sunflowers. At each spot, check 20 different plants for the presence of the sunflower beetle, the main pest of the sunflower plant, or other insect pests. This is a repeat of the test that you should have done prior to spraying when you were making the determination of whether or not to spray for pests.

2. Count how many adults and larvae remain on each plant. The numbers of pests should be greatly reduced from the numbers you saw prior to spraying. Figure the average number of beetles on each plant by totaling all the adults together and dividing by the number of plants in the sample, then totaling all the larvae together and dividing by the number of plants in the sample.

3. Compare the number of adults and larvae per plant to the numbers that you recorded before spraying. If the numbers are significantly reduced consistently throughout the field, the spraying was effective. If the numbers are comparable to the beetle counts obtained before the application of pesticide, the application was not effective and may need to be repeated. Be sure you have waited an appropriate length of time for the bugs to die before entering the field in order to count.

Tips & Warnings

• If the number of pests have been reduced below the economic threshold, the spraying has done its job. This threshold varies by the age of the sunflowers. According to North Dakota State University, the plants can withstand up to two adults on each seedling or older plant and as many as 15 larvae per older plant. More insects than that can threaten the entire crop.

• An alternative to chemical sprays is the use of natural predators for biological control of sunflower pests. Various predators prey on the sunflower beetle during different life stages, including egg, pupa and adult. Such controls help to minimize crop damage without the use of harmful chemicals.

• When a field has been sprayed with pesticide, the chemicals will linger in the area. The length of time it remains hazardous depends on the specific chemical used and the weather conditions during and after the application. Observe all manufacturer's precautions regarding entering a sprayed area after treatment.

References

• North Dakota State University; Biology and Pest Management of the Sunflower Beetle in North Dakota; March 2000
• ND State University; Integrated Pest Management of Sunflower Insect Pests in the Northern Great Plains; Janet J. Knodel, et al.