Issue 7, June 6, 2016

May Beetles

There are many species of the genus Phyllophaga, also known as true white grubs or May beetles that occur in Illinois. Their larval stage is one of the genera known as white grubs that feed on turfgrass roots, but unlike other white grubs in turf, true white grubs also feed on dead organic matter. For that reason, they are commonly found in flower beds, under dead logs, and in mulch causing no apparent damage.

True white grub adult.

Adult May beetles feed on oak, crabapple, ash, and other tree foliage at night in the spring, eating the leaf margin to the mid-vein. Damaged tree leaves with no apparent responsible insect during the day may be due to May beetle feeding. Verify the cause by scouting the foliage after dark with a flashlight; adults hide in turf during the day.

Most May beetles are about one-inch long stocky dark brown to reddish brown beetles. These typically have three-year life cycles, spent mostly as white grubs. This spring, we have been seeing a May beetle species that is a one-half inch long, tan adult beetle, similar in appearance to masked chafer adults.

Adult feeding on tree foliage is usually not heavy enough to warrant treatment. If needed, a single application of carbaryl (Sevin) or a pyrethroid will provide control. (Phil Nixon)

Phil Nixon

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