Many worms, or more correctly, caterpillars, occur in alfalfa fields during summer. Their defoliating activity can sometimes devastate fields. There have been many questions related to Sampling for Summer Defoliators in Alfalfa.  

The following is a generalized sampling procedure for various larvae, such as the fall armyworm, corn earworm, beet armyworm, garden webworm, alfalfa webworm, alfalfa caterpillar, and green cloverworm, any or all of which may be in your field this summer.  

This sampling method is conducted by using a standard insect sweep net. Be aware that this method will not be satisfactory when sampling for the army cutworm and the variegated cutworm.  

Make 20 sweeps in each of 5 areas of the field. Count and record the average number of larvae per sweep. Next, measure or estimate the length of typical larvae of each species. To make the survey more meaningful, make a visual estimate of the percentage of defoliation in each area sampled and the percentage of plants showing feeding damage.  

It is also important to record any parasitized or diseased larvae of each species. If the number of healthy caterpillars exceed 5-6 larvae per sweep and defoliation is obvious then controls may be needed. If harvest time is near, haying will destroy most of the larvae and save the time and expense for chemical control.