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.
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.
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.