Pods at Risk of Bean Leaf Beetle Feeding

The first generation of BLB adults have been active in fields for some time now but are starting to set their sights on the pods. And the second generation will be starting soon which will definitely prefer feeding on the pods. So it is very important to scout fields at least once a week for the next month to make sure pod scars and holes in IP food grade and seed fields do not reach threshold. If adults are present and are starting to feed on the pods, scouting then should be every 3 or 4 days at least.

BLB feed on the surface of the pod, opening it up to pod diseases, especially in years with decent moisture and heavy dews. Some even have the habit of avoiding feeding on the pod but instead feed on the small stem holding the pod to the plant, clipping the pod and letting it drop to the ground. Not sure why but they do.

Regardless, to ensure seed quality, only a small percentage of the pods can have scars on them before you run the risk of quality being downgraded. The key is to act when thresholds are reached while making sure that adults are still present in the field and feeding or the spray will be unproductive since the critters that did the damage are long gone.

Scout at least 50 random plants in each field. Look at all of the pods along the plant. Look for any scars and holes on the pods. Also make note of any pods that have been clipped and dropped to the ground. Lastly carefully look at neighbouring plants to see if adults are present on the plants. Be very careful not to move around too much as the adults will drop to the ground at the slightest sense of your presence. it is a great tactic to escape predators.

If 5 of those 50 plants have feeding scars or holes on any of the pods and the adults are still visibly active in the field, a spray is necessary. There are no thresholds based on pod drop but if pods are being clipped off in several areas of the field along with some scars present on pods left on the plant, a spray may be necessary.

Figure 1. Feeding scars on the pods caused by bean leaf beetle.

Keep in mind that if you reach threshold early, there is still a risk of the second generation of adults emerging from the soil and feeding on the pods too so continue scouting fields that were sprayed. The days to harvest interval for Matador is 21 days and Lagon and Cygon is 30 days so taking a last look at each field prior to reaching the point of no return when spraying is no longer possible is recommended.|