Time for residents to deal with grubs

Now that lawns are beginning to green up, some Midlanders are finding patches of thin or dead grass in their yards. These patches may be the result of grubs eating the root system of the turf. Immediately after hatching in spring when soil temperatures rise, grubs start feeding on the roots of grass. In late May through June, grubs stop eating and begin the transformation into adult beetles. Grub damage may appear in home lawns from March to early May or from mid-September to November. Look for signs of skunks or raccoon digging into the patches or flocks of birds feeding around the dead patches, which can be easily pulled up or rolled back often exposing the grubs.

To confirm that the problem is caused by grubs, Michigan State University Horticulturalist Dave Smitley suggests you use a shovel to dig up several one square foot patches to a depth of about two inches around the bare spot and look for three-quarters-inch long, C-shaped grubs. If you find any, they are more than likely the larvae of European chafer, especially if they are found in lawns that do not receive sufficient nutrition to maximize root growth, sufficient irrigation or are routinely mowed too short.

A healthy lawn can support a grub population of five or more grubs per square foot with no visible turf damage and therefore no need to treat for grub infestation. The general damage threshold treatment to control European chafer beetle grubs is 10 to 12 grubs per square foot. However, if the turf is dense with a healthy, robust root system, it can withstand a bit more grub feeding.

The best way to prevent European chafer grub damage is to maintain a healthy lawn. To establish a grub-tolerant lawn, you should mow your lawn 3.5 to 4 inches in height, properly irrigate and fertilize it to maximize root growth. If the grub population is high (more than, say, 10 to a dozen per square foot) or if there is a history of damage in an area, it may be necessary to use an insecticide to control the grubs.

According to MSU, there are two types of insecticides to treat lawns infested with the European chafer grubs: preventive chemicals and curative chemicals. Preventative products work well on newly hatched grubs present in July. Curative products kill all life stages of the grubs in the spring if applied before early May. Carbaryl and trichlorfon are considered curative treatments and are the only options available if high numbers of grubs are found in the fall and spring before early May. Do not apply any curative compounds in the spring after May 15 because the grubs will have stopped feeding by then as they prepare to pupate. A target date of May 5 would be best for curative insecticidal products

Both carbaryl and trichlorfon are short-lived compounds that kill all life stages of the grubs. Should you choose to use a curative insecticide, water the affected areas immediately before and after the insecticide is applied with at least one-half inch of water. Grubs will move to the surface with the pre-watering and the product will migrate to the grub with the post watering.

MSU research suggests that while it will take 10 to 14 days for the grubs to begin to die after carbaryl is applied, it is a little more effective on European chafer grubs than trichlorfon. Trichlorfon should be expected to require at least five days after application to kill grubs, assuming it rains or irrigation was applied.

Preventative control can be accomplished with application of products that contain halfenozide, imidacloprid, thiamethoxam or clothianidin as active ingredients. Preventative insecticide products tend to be more environmentally friendly than curative products, but they will not control grubs in the spring, or for large grubs found from September to late May. They work very well, however, on newly hatched grubs present in July.

Properly applied, they will greatly reduce the possibility of subsequent damage to your lawn if you found lots of grubs during fall or if you want to prevent grub damage during fall of 2014 and spring 2015.

Preventive products containing the above active ingredients will consistently give 75 to 100 percent reduction of grubs if they are applied in June or July, and if they are watered-in with one-half to one inch of irrigation immediately after application. Watering immediately after application with at least a half-inch of irrigation is critical to obtaining good results. This also moves the chemical off the grass and will make the yard safe for children, pets and wildlife after the yard is dry.

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Time for residents to deal with grubs