Written by Dave Shetlar, Ph.D. (The BugDoc)
The Ohio State University
Everyone emphasizes white grubs in turf management, but the reality is that billbugs often cause more damage, on a per-acre basis, than white grubs! The problem is that most people fail to diagnose the damage done by these tiny beetles and their larvae. Billbug larvae burrow down seed-head stems in May and reach turf crowns in early June. At that time, the larvae drop out of the stems to dine on additional crowns nearby. By mid-June, if we get a spell of hot and dry weather, the turf will appear to enter summer dormancy, but if billbug larvae are present, the turf is actually being killed. This turf death won’t be discovered until September when summer-dormant turf should green up again.
Dr. Doug Richmond and his students surveyed lawns in Indiana and they determined that turf loss from billbug damage was more common than white grub damage. And, lower populations can cause other problems, especially weed establishment! Even if the infested turf is able to recover (new tillers can establish roots and survive), there is open space which is just what weed seeds need to germinate and establish.
The best approach to billbug control is to prevent their larvae from damaging the turf crowns. This can be accomplished by applying surface insecticides to kill the adult weevils (this should be done in the last week of April and the first two weeks of May, so we are too late for this season), or applying a systemic insecticide that will kill the larvae as they burrow down stems (right now!).
All the neonics are effective at killing the billbug larvae. Imidacloprid (Merit) and thiamethoxam (Meridian) are effective when applied in May, but both may run out of effective residual if you want to also kill the new crop of grubs in July. Clothianidin (Arena) seems to have a longer residual time, so a May application will take out the billbugs and the new crop of white grubs. We have also had very good success with chlorantraniliprole (Acelepryn), but this needs to be applied in April into mid-May for maximum activity. This same application will also remain until the grubs arrive.
Finally, billbug damage is rarely seen in irrigated turf and in those years when we have above normal rainfall through June! It appears that this extra water is what the new tillers need in order to establish a root system suitable to keep the plants alive through the rest of the summer. So, we are left with a dilemma! Let the turf go dormant in June and July to reduce grub populations or irrigate to mask the billbug damage, but increase white grubs!
For more information from The Ohio State University Department of Entomology, check out the following fact sheets:
Insects and Pests