Distant: Yellow or thin patches of turf in golf course fairways in June or July. Sometimes the turf may die in small patches that may coalesce into larger patches (Images D & E).
Up close: Many (> 50 per square foot) small (1/8 to 3/8 inch long) white grubs in soil just under damaged fairway turf (Image F)
When damage would be found: June and July
Host: Usually bentgrass or annual bluegrass, although they can survive on the roots of all turf types.
Site: Golf course tees, greens and fairways.
Description of damaging stage: 1/4 inch long C-shaped white grubs. They will have 6 legs, a brown head capsule and chewing mouthparts.(Images C & G)
Sampling: Dig a 1 ft2 area of turf down about 1.5 inches and sort through the turf to look for grubs when damage is first observed. Do this in several places outside the edge of yellow or brown patches of turf. If an average of 40 grubs per square foot or more are found, a curative grub insecticide application may be helpful. Spot spray the affected area and water in with 1/2 inch of irrigation before the spray dries.
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 (product 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. These should be applied only after sampling and finding sufficient numbers to warrant an insecticide treatment and should only be applied to the areas exhibiting the population level and damage to warrant treatment. 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. The grubs begin to pupate between mid-May and the beginning of June, depending on the grub species. They stop feeding at that time and will not pick up any insecticide if it is applied too late.
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 2-12 weeks. Ideally, the neonicotinoid applications for Ataenius or Aphodius should be made between late April and June 1 for Aphodius, or between late April and July 1 for Ataenius grubs in Michigan. The insecticide should be watered in with a minimum of 1/2 inch of water. Chlorantraniliprole is a relatively new compound for grub control. It is much less water soluble than the neonicotinoids and therefore should be applied earlier. Early April is the optimum timing for chlorantraniliprole, followed with 1/2 inch of irrigation. Preventive compounds should only be used against Ataenius or Aphodius populations if there has been a multi-year history of damage in the same area.