Although the date of their arrival differs every year we can only assume the ever so painful Japanese beetle to arrive soon. While thinking ahead this year I wanted to take some time to explain their biology and control of this pest.
The Japanese beetle adults pupate from larvae in late spring and they begin to emerge from the ground this time of the year. Once emerging they begin to feed on what often seems to be only your favorite plants. Plants particularly at risk include those that have been recently transplanted or those that are stressed for one reason or another. Favorites for Japanese beetle include linden, crab apple, plum, and other fruit trees, rose bushes, grapes, and several garden variety vegetables. Watch out for the plants in your landscape that have red leafs. Though it’s impossible to protect all trees and ornamentals in any particular landscape, a few select plants can be protect by physical (netting or picking off the beetles each day) or chemical controls (Sevin, Orthene, Malathion, Azadirachtin or any of several pyrethroids). Repeat applications of these insecticides are required to provide protection for the two months or so during which these beetles are feeding.
During the next two months, these beetles will mate and the females will lay eggs in the turf. Females look for areas that can be easily burrowed into, and thus irrigated soils of golf courses, lawns, and athletic fields are often infested, especially in drier years. Adult females also prefer to lay eggs in lower cut turf. Aside from the physical damage to many plants, Japanese beetles can have a great deal of harm on our lawns as well. Although there are many grub species in Indiana today, the grubs from Japanese beetles can cause the dying of large spots in our lawns if untreated. As the new eggs hatch the larvae begin to feed on the turf grasses root system cutting off the water supply to parts of your lawn. Most of this damage can be seen in your lawn in early September so it is imperative to have a grub control on your lawn before the end of July. Two very effective grub control products include imidacloprid (Merit) and halofenozide (Mach 2). A more recent addition to the professional market is clothianidin (Arena) and results to date show that clothianidin is just as efficacious as imidacloprid and halofenozide. These products are long-lasting and are most effective if applied from late June through July. As with all insecticides, it is critical to follow the label directions exactly when making applications.
If grub insecticides fail or turf areas are unprotected, symptoms may begin to show up in September. Drought stress, loose turf that rolls up like a carpet, and in the worst case, skunk and raccoon damage are definite symptoms of grub damage. Dylox is the most commonly used insecticide at this time because it will attack the feeding larvae. Regardless, at this late stage, grub control products must be watered in thoroughly and may require 7-10 days to produce results, so don’t rush to a second application.
Grubs are too large to control by October, plus the returning rains will probably limit damage. As the temperatures cool, the grubs cease feeding and move down as much as 1 foot into the soil profile. Grubs contain a form of antifreeze so even the coldest of winters doesn’t affect survival. Thus, insecticides are no longer recommended at this time.
Although they can be a true pain for any homeowner, Japanese beetles are likely here to stay and there are controls that can limit their damage to our landscapes. Knowing the critical dates of control along with the correct pesticide is crucial in limiting their damage. If you have any other questions please reply at anytime or refer to Turf Tip 7/05/06 at Purdue Agronomy. Article written by Mike Van Horn.