Damage
Distant: Turf thins in patches in lawns or golf course roughs. Dead patches may appear if a heavy grub infestation is combined with prolonged dry weather. Dead patches in the fall may become bare soil by April. Skunks and raccoons may turn over heavily infested turf in search of grubs to eat (Images D & E)
Up close: Turf heavily infested with grubs can be easily rolled back when most of the roots have been consumed. In the top 2 inch of soil under infested turf look for C-shaped white grubs 1/2 to 1 inch long
Time of year when damage appears: In southern Michigan European chafer grubs feed heavily in September, October and early November, then again in March and April, sometimes causing dead patches to appear and expand at that time. In the fall turf damage is more likely when grubs are feeding during a period of dry weather long enough to cause drought stress. In the spring turf damage may occur when grubs feed on turf roots in March or early April before the turf begins to grow.
Host: All grass types
Site: European chafer tends to prefer dry or well drained soils. Infestations may be heaviest in dry sunny areas, on slopes, or in sandy soil. European chafer grubs have caused turf damage on golf course roughs, home lawns, athletic fields and recreational turf. They are rarely a problem in turf irrigated daily with enough water to keep the soil moist.
Description of damaging stage: 0.5 to 1.0 inch long C-shaped white grubs. They have 6 legs, a brown head capsule, and visible chewing mouthparts. They can be identified to species by the pattern of hairs on the underside of the last abdominal segment, called the raster (Image F).
Management
Sampling: Between September 1 and November 1, dig a 1 ft2 area of turf down about 3 inches and sort through the roots and soil to look for grubs. Do this in several spots in the yard close to and around the dying patches of turf. If the removed turf is kept moist and watered immediately after being put back in place, it should re-establish. European chafer grubs are not usually found in daily-irrigated turf. However, European chafer, Japanese beetle, Oriental beetle, masked chafer and Oriental beetle larvae can be found in conjunction with each other. Since the control measures for all of these grubs species is similar, the same threshold applies for all four species. If an average of 5 grubs per square foot or more is found in non-irrigated turf or in a golf course fairway, or if 15 or more per square foot are found in an irrigated lawn, an insecticide application may be desirable.
Preventing Pest Injury to Turfgrass: Home lawns, recreational turf and golf course roughs can be managed to avoid insect injury without insecticides by using proper fertility, mowing at a height of 3.0 to 4.0 inch, and watering during dry periods. This will build a dense stand of turf and a diverse community of insects that will keep turf pests under control. All lawns in Michigan will typically start off lush and green in the spring and will go dormant and turn brown during periods of little rain. Information on the use of insecticides to treat turf pest problems is only meant to be used for the unusual cases where turf damage from pests becomes unacceptable. Even then, insecticides should only be used in areas of a lawn with severe turf damage, and only until a dense turf is re-established.
Using insecticides: Use insecticides judiciously, temporarily, and only in response to unacceptable turf injury. Many insecticides are poisonous if ingested, and therefore must be stored in places where they cannot be found by children. Use the rate recommended on the label for the pest you are attempting to control. Wear rubber gloves, safety glasses (or goggles), rubber boots, long pants and long sleeved shirts when mixing and applying insecticides. The most caution is needed when mixing a concentrated insecticide in water, because skin contact with the concentrated insecticide in the original container is more dangerous than contact with the diluted insecticide after mixing. Water the turf immediately after applying the insecticide to wash it to the base of the plants or into the soil and allow the turf to dry before allowing access by people and pets.
Chemical Control of Grubs: There are 2 types of chemicals that can be used for grub control: curative products (carbaryl and triclorfon) and preventive products (neonicotinoid insecticides such as imidacloprid, thiamethoxam, clothianidin and the anthranilic diamide insecticide, chlorantraniliprole). Read the ingredient section of the label of the insecticide package to determine which active ingredient is in it. The chemicals listed earlier are by common name. There are a myriad of trade names that these active ingredients are in.
The curative grub compounds work (or at least in the next 7-10 days). They need to be applied at the full rate recommended for grub control and should be watered in immediately after application with a minimum of 1/2 inch of water. See the specific sections for the species of grub you are treating for. They will give about 40-65% grub reduction. Don't use these too late in the fall as it will take one to two weeks to get to where the grubs are feeding. If it is getting cool, the grubs will not be feeding and will not pick up any of the insecticide. The grubs begin to pupate between mid-May and the beginning of June, depending on the grub species. They stop feeding and again, will not pick up any insecticide if it is applied too late. It is best to wait and apply a preventive compound for a spring grub problem unless there is a very high population.
The preventive grub compounds are systemic and are absorbed by the roots and moved throughout the grass plant. It takes a while for the materials to be absorbed by the plants and they work best on small grubs. It is important to get the material into the root zone so that it can be picked up by the plant. It is also important to apply it early enough to give the chemical a chance to be picked up by the grass before the grubs become large. When properly applied they will give 90+% control of grubs. They do not kill the grubs present at the time they are applied; they kill the ones that will be developing in 3-12 weeks. Ideally, the neonicotinoid applications should be made between June 1 and mid-July and should be watered-in with a minimum of 1/2 inch of water. Mow lawns before spraying an insecticide for grubs to avoid leaving spray residue on the open flowers of weeds which are visited by bees. They can be applied as late as mid-August, but it becomes more critical to supply irrigation the later you wait. The effectiveness falls off rapidly after about the 3rd week of August, even with irrigation. Chlorantraniliprole is a relatively new compound for grub control. It is much less water soluble than the neonicotinoids and therefore must be applied much earlier. April to mid-May is the optimum timing for chlorantraniliprole, followed with 1/2 inch of irrigation.
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