White grubs about 1 inch long are being found in turf throughout Illinois by landscapers and turf professionals. These are not the larval stages of the annual white grub (masked chafer) or Japanese beetle that are still laying eggs. Instead, these are probably the progeny of the large number of May beetles that were present in much of Illinois earlier this spring. In most cases, the numbers per square foot are small, well below the 10 to 12 per square foot usually needed for turf dam-age. In some areas, however, turf damage is being seen in the form of browning, wilting turf.
If the number of larvae are small, one can probably wait to control them along with the masked chafer and Japanese beetle grubs in August. If numbers are large, then an application of trichlorfon (Dylox, Proxol), diazinon, or other labeled insecticide may be needed now to halt turf injury. Remember that diazinon is not labeled for use on golf courses and sod farms. Diaz-inon will also typically take about 3 weeks to kill the grubs, although the grubs apparently do not feed during that 3 weeks. One advantage of diazinon is that it should remain as an active residue for about 4 weeks. This is long enough to control the masked chafer and Japanese beetle grubs that will be hatching near the end of July. Trichlorfon will break down after about 5 days, so the same turf area may have to be treated again to control the masked chafer and Japanese beetle grubs. On the other hand, trichlorfon should kill the grubs within 3 days, helping calm those customers who pull up the turf to see if the grubs are dead.