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How to choose and when to apply grub control products for your lawn

Not all the grub control products on store shelves will be effective this spring. Here’s how to choose and use the right one for your lawn.

Grub damage to Central Michigan lawn. The dead patch in the front is directly caused by grub feeding. The flipped over turf is from raccoons and skunks feeding on the grubs. Photo credit: Terry Davis, MSU.

Grub damage to Central Michigan lawn. The dead patch in the front is directly caused by grub feeding. The flipped over turf is from raccoons and skunks feeding on the grubs. Photo credit: Terry Davis, MSU.

It has been a long winter in Michigan this year (2014-15), but lawns are now starting to turn green. Some people will find patches in their lawn where the turf is stunted or never becomes green and grows. Occasionally, a flock of birds may be observed feeding around the dead patches. These patches of thin or dead turf may be due to grubs.

Be sure the problem is grubs. Before doing anything, it is important to make sure that the problem is indeed grubs. If you see a dead patch, use a shovel to dig up a few Frisbee-size samples of turf around the bare spot to a depth of 2.0 inches and look for three-quarter inch-long, C-shaped white grubs. These are most likely the larvae of European chafer if they are found in lawns without an irrigation system. European chafer can devastate a lawn with little warning because the adult beetles fly at dusk when they emerge in June and early July, and can easily be overlooked because their evening flight to mate and lay eggs occurs after sunset. European chafer grubs can now be found in all locations in the Lower Peninsula, and in much of the Upper Peninsula of Michigan.

Japanese beetle grubs also feed on turf roots in home lawns, but they are not usually as much of a problem on home lawns as European chafer can be. Both Japanese beetle and European chafer lay most of their eggs in July, but Japanese beetles continue laying eggs into August. Japanese beetles are like to lay their eggs on irrigated turf like golf courses, athletic fields and highly maintained lawns. They can be abundant in in non-irrigated home lawns if we receive frequent rain in July, but are scarce in lawns that are very dry in July and early August.

The eggs of both species hatch about 10 days after they are laid. The grubs feed from the beginning of August until late October. By the end of October, they are fully grown. The larvae of both species look almost identical. They spend the winter as large grubs (3/4”-long) some 2 to 6 inches below the soil surface. When the ground warms up in the spring, they resume feeding and can cause damage from the time the grass turns green until they pupate in mid-May. They are big enough that they can cause damage any time after Labor Day if enough of them are present. Grub damage may appear in home lawns from mid-September to November, or from March to early May. However, for low-maintenance lawns, even if the turf is not killed from the grub feeding, the thinned and weakened turf may be prone to weeds and drought stress.

Grubs as they appear under the turf.

Grubs as they appear below the turf. Photo credit: Terry Davis, MSU

Healthy turf with a few grubs may not need an insecticide. It is important to realize that healthy turf, supported by frequent rain or irrigation, can support a grub population of 5 or more grubs per square foot with no visible turf damage. Despite the presence of a few grubs, if no damage is visible, no insecticide is required. A lawn should be mowed at 3.5 to 4.0 inches in height and properly fertilized to maximize root growth. However, if the grub population is high, or if there is a history of damage in an area, it may be necessary to consider using an insecticide for grub control.

Check for the active ingredient in a grub product. We sent Connor, an undergraduate technician working in our lab, to several of the local lawn and garden centers in the Lansing, Mich. area to see what kinds of products are available that specifically claim they will work to control grubs. He went to four different stores and found five to nine different products at each store. The profusion of different products can be rather mystifying. The critical issue with any grub control product is the active ingredient (more on those later in this article). There are many products available, some with the same active ingredients. The active ingredient(s) is usually shown on the bottom right or left of the front of the bag and is listed as a % of composition.

Water the lawn immediately after applying the insecticide. The second major concern is to make sure that the insecticide is thoroughly watered into the ground with at least a half inch of irrigation or rain immediately after the chemical is applied. Research tests over the last 25 years have clearly shown that watering immediately after application 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.

Use the right rate/amount of product. A third concern is the rate at which the insecticide is applied. The label lists the legal rate at which the product can be used. I found one insecticide that contains an appropriate active ingredient, but the labeled rate is about half of what is needed for reliable grub control. Information below will help you determine if rates are appropriate.

There are also products for sale that list grubs on the label - that do NOT work for grubs. Insecticides used for grubs can be separated into two groups based on how they work - preventive chemicals and curative chemicals.

1) PREVENTIVE Insecticides that will prevent grub damage this fall (2015) and the following spring (2016)

These products are used to prevent future grub problems, not to control the grubs present in the lawn in the spring. They will not work on grubs found in the lawn from the middle of October through the middle of May. However, when applied in June or July, they provide excellent protection against the next generation of grubs. So, if you need to apply the preventive insecticide BEFORE the grubs are there, how do you know if you need to use an insecticide or not? If you found lots of grubs or grub damage the previous fall or spring, then you may want to use a preventive insecticide for one or two years to build a more dense turf that will be tolerant of grubs. If you have treated for several years and you do not see evidence of grubs in your lawn or in the neighbor’s lawn, it may be time to stop treating. There is an erroneous philosophy being perpetuated that because we have European chafer and Japanese beetle in the area, it is necessary to treat every year or your lawn will be damaged by grubs. This is not true.

Preventive products are the most effective. However, products containing imidacloprid, thiamethoxam, clothianidin or chlorantraniloprole WILL NOT CONTROL GRUBS IN THE SPRING. They are preventive products that work very well on newly hatched grubs present in July, but do not work well for large grubs found from September to May. There are different recommended timings for application depending on the active ingredient. Although the bag often says apply anytime from May to Aug 15, it is highly recommended that products containing imidacloprid, thiamethoxam, clothianidin be applied and irrigated into the soil in June or July. If applied in early spring they may move through the soil or partially degrade by the time the grubs hatch in late July. If applied too late they may not be effective as they work best on small grubs. Preventive products containing imidacloprid, thiamethoxam or clothianidin 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 a half to one inch of irrigation immediately after application. Lawn sprinklers can be used if you do not have an irrigation system. Measure how much water you have applied by placing several cups on the lawn and running the sprinklers until they fill a half to one inch deep with water.

There is a new active ingredient in some insecticides called chlorantraniliprole that is also very effective in preventing grub problems, but it is less water soluble than the other preventive compounds mentioned above so it can be applied any time after the grass turns green in the spring until mid-July. Chlorantraniliprole,applied between April and the end of July will give very good grub control in the fall and in spring of the next year.

Some of these products come in a granular formulation that is applied with a fertilizer spreader or some products are designed to be mixed with water and sprayed. Also, in the last two years, several products have become available in an attach-to-hose bottle and are automatically mixed with water when applied.

Protecting bees and other pollinators. If you are applying a product containing clothianidin, thiamethoxam or imidacloprid, the lawn should be mowed prior to the application, so that no weed flowers are present when the insecticide is applied. These active ingredients can be toxic to bees if the bees visit flowers that were recently sprayed. Mowing prior to making the application will cut off any flowers and avoid this problem. Weeds that flower again after mowing are much safer for the bees. Bees won’t visit lawns unless there are flowers in it. In addition, grub control products that contain the active ingredient chlorantraniliprole are very safe for bees.

2) CURATIVE Insecticides

There are two chemicals, carbaryl and trichlorfon, that are considered curative treatments. They are short-lived compounds that kill all life stages of the grubs. These two insecticides are the only options available if high numbers of grubs are found in the fall and in the spring before early-May. Our research indicates they will kill 20 to 80 percent of the grubs when applied in September or 20 to 55 percent when applied in late October. They are not as effective as the preventive compounds in reducing grub numbers. Consider carefully whether it would be best to wait and apply a preventive later. If the need should arise to use a curative compound, make sure to keep the infested lawn watered and fertilized and treat the area again with a preventive application the next summer or the problem will likely reoccur in the fall or the following spring. Current research also shows that watering with a half inch of irrigation immediately after the application is essential to get effective results from these insecticides. Our research has indicated that carbaryl has been a little more effective on European chafer grubs than trichlorfon. Both compounds work equally well on Japanese beetle grubs.

It will take 10 to14 days for the grubs to begin to die after the insecticide is applied. One trichlorfon product has ‘24 Hour Grub Control’ in its name and would seem to indicate that it will kill grubs in 24 hours. However, even trichlorfon should not be evaluated for at least 5 days after application (assuming it rains or irrigation was applied), and carbaryl may need 3 to 4 weeks to be effective. Do not apply any curative compounds in the spring after May 15 as the grubs stop feeding in late May as they prepare to pupate. As with the preventive products, lawns should be mowed immediately before applying carbaryl or trichlorfon to protect bees.

3) Insecticides that DO NOT work on grubs

Do not use products containing ONLY lambda-cyhalothrin, gamma-cyhalothrin, bifenthrin, deltamethrin, cyfluthrin or permethrin for grub control. Products containing only these ingredients will not work for grub control because the active ingredient binds with organic material and will not move down to where the grubs are feeding. These products work well for above-ground feeding insects that live on the grass leaves or soil surface but not for insects that feed on the roots. At one garden center we were shown two products, one containing only permethrin and one containing only bifenthrin that the clerk led us to when we asked for products to control grubs. Neither of the products listed grubs on the label printed on the bag and neither of the products would have controlled grubs.

There is a widely sold trade name called Triazicide from Spectrum that lists grubs on the label and states that it will control insects above or below ground and has a picture of a grub on the front of the bag. It contains only lambda-cyhalothrin and/or gamma-cyhalothrin. Triazicide will not control grubs. However, Spectrum also has a product called Spectrum Grub Killer that is an attach-to-hose product containing imidacloprid. It will work well for grub control.

A summary for successful grub control

  • Check the bag to determine what active ingredient the product contains.
  • Do not use products containing ONLY lambda-cyhalothin, gamma-cyhalothrin, bifenthrin, deltamethrin, cyfluthrin or permethrin for any phase of grub control.
  • Do not use preventive compounds such as clothianidin, thiamethoxam or imidacloprid, now, in April-May. Use them in June or July to control grubs that would be damaging turf in the fall. Applying them now will allow some of the chemical to leach through the turf or to break-down to the point that not enough insecticide will be there in July to control grubs.
  • The preventive compound chlorantraniliprole should be applied between April 1 and July 15 to control grubs that would be damaging turf in the fall, as it will take longer for the material to move to where the grubs will be feeding in July.
  • To kill grubs in the spring (or fall) use carbaryl or trichlorfon.
  • Always wear rubber gloves and rubber boots when applying insecticides to turfgrass.
  • Make sure to irrigate the lawn with at least a half inch of water and allow the grass to dry before allowing anyone (people or pets) into the treated area. Irrigation is essential for the chemical to be most effective.*
  • Store insecticide products in a locked cabinet, inaccessible to children.
  • Proper fertilization is important to prevent and to allow the lawn to recover from grub damage.
  • Mow lawns immediately before applying an insecticide for grubs to remove weed flowers and protect bees.

*What is a half inch of irrigation? A half inch of irrigation is when lawn sprinklers are run until a coffee mug (or any container) fills to a level a half inch up from the bottom of the cup. You may want to place several cups around the area being irrigated.

Below is a short list of products being sold for grub control as of April 13, 2015 in four stores checked in the mid-Michigan area.

Available preventive products

  1. Scotts Grub-Ex - Granular
    chlorantraniliprole 0.08%
    Apply between April 1 and July 15 for best results.
  2. Bayer Advanced Season-Long Grub Control Liquid - attach-to-hose-bottle
    imidacloprid 1.47%
    Apply between June 1 and July 15 for best results.
  3. Bayer Advanced Season-Long Grub Control and Turf Revitalizer - Granular
    imidacloprid 0.25% and a low fertilizer rate (6-0-1)
    Apply between June 1 and July 15 for best results.
  4. (local distributors name) Premium Grub Control (Do not confuse with “Premium Insect Control”)
    imidacloprid 0.2% - Granular
    Apply between June 1 and July 15 for best results.
  5. Spectracide Grub Killer - attach-to-hose-bottle
    imidacloprid 1.47%
    Apply between June 1 and July 15 for best results.
  6. Bayer Advanced Complete Insect Killer Liquid attach-to-hose-bottle
    cyfluthrin 0.36% and imidacloprid 0.72%
    Apply between June 1 and July 15 for best results.
  7. Bayer Advanced Complete Insect Killer Granules - Granular
    cyfluthrin 0.05% and imidacloprid 0.15%
    Apply between June 1 and July 15 for best results.

Available curative products

  1. Gardentech Sevin Lawn Insect Granules - Granular
    carbaryl 2.0%
    Apply in spring or fall to active grubs.
  2. Bayer Advanced 24 hr Grub Killer Plus - Granular
    trichlorfon 9.3%
    Apply in spring or fall to active grubs.

 Products that will NOT kill grubs

  1. Spectracide Triazicide Insect Killer for Lawns - Granular
    gamma-cyhalothrin 0.05%
    This product will not kill grubs at any rate.

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