grubs

Asked March 4, 2014, 1:41 PM EST

Last August we had an infestation of grubs in the lawn. We put down grub control and had hundreds of dead ones. It seemed to work. What should we put down this spring to keep them from coming back? Thanks.

New Castle County Delaware lawns and turf grubs lawn grubs grub control grub lawn pests horticulture

1 Response

I am including here an excerpt from a Michigan State University Extension publication that addresses preventive and control treatment of grubs that you can see in its entirety at http://www.turf.msu.edu/home-lawn-grub-2013. The bottom line is that you will need to apply a grub control product this spring and then a grub preventive product this summer and subsequent summers if your infestation is extensive. There are two insecticidal chemicals, carbaryl and trichlorfon, that are considered control treatments. Products containing imidacloprid, thiamethoxam or chlorantraniloprole are used as preventive treatments.

1) PREVENTIVE Insecticide that will prevent grub damage in the Fall and the following Spring

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 had confirmed (meaning that you found lots of grubs) 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.

Products containing imidacloprid, thiamethoxam 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 or thiamethoxam 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. Preventive products containing imidacloprid or thiamethoxam will consistently give 75%-100% reduction of grubs if they are applied in June or July, and if they are watered-in with a ½" to 1.0" 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 coffee cups on the lawn, and running the sprinklers until they fill ½ to 1.0" 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 two preventive compounds mentioned above. Since it takes longer to move down to where the grubs will be, it is best to apply a product containing chorantraniliprole as early in the spring as is possible (no later than mid-May) for it to be most effective when the grubs hatch in July and August. Chorantraniliprole, when applied in April or early May, and irrigated into the ground, will also give very good grub reductions for the following fall and spring of the next year.

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 after the middle of September and in the spring before early-May. Our research indicates they will kill 20 to 80% of the grubs when applied in September or 20-55% 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 ½ 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 10-14 days for the grubs to begin to die after the insecticide is applied. One trichlorfon product called ‘Bayer Advanced 24 Hour Grub Control' seems to indicate by the name 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 - 4 weeks to be effective. Do not apply any curative compounds in the spring after May 15th as the grubs stop feeding in late May as they prepare to pupate.

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. There are a few combination products that include one of the above mentioned chemicals and one of the preventive compounds listed in section 1 above. These combination products will work to prevent grubs if applied in the early summer because they include a product that will move down to where the grubs are feeding. But I did find one product that contained only gamma-cyhalothrin that was being sold for grub control. It had a big picture of a grub on the bag. We tested this insecticide in 2006 and the results were the same as doing nothing at all.

Some insecticides are being sold as a hose-attachment product. They consist of a bottle of chemical that you attach to the end of your hose. One product containing imidacloprid will deliver enough of the chemical if it is applied to the area listed on the bottle to prevent grubs. However, there is another liquid product packaged the same way that contains 2 chemicals (one of them also being imidacloprid) that will not work for grub control if you follow the label instructions because not enough imidacloprid will be applied (see list at end of article).

IN SUMMARY

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 thiamethoxam or imidacloprid now. 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 in late April or Early May 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 and irrigate. Make sure the turf is watered with ½" of irrigation (see what is a ½" below) and fertilized.
Always wear rubber gloves and rubber boots when applying insecticides to turfgrass.
Make sure to irrigate the lawn with at least ½ inch of water and allow the grass to dry before allowing anyone (or pets) into the treated area. Irrigation is essential for the chemical to be most effective.
Store insecticide products in a locked cabinet not accessible to children.
What is a ½" of irrigation? A ½" of irrigation is when lawn sprinklers are run until a coffee mug (or several mugs) fills to a level ½" up from the bottom of the cup.

PRODUCTS AVAILABLE

A short list of products now being sold for grub control as of 4/23/2013 in the 4 stores checked in the mid-Michigan area.

Scotts Grub-Ex - Granular
chlorantraniliprole 0.08%
Apply between April 15 and May 15 for best results.
Bayer Advanced Season Long Grub Control and Turf Revitalizer - Granular
imidacloprid 0.25% and fertilizer
Apply between June 1 and July 15 for best results.
Bayer Advanced Complete Insect Killer Granules - Granular
cyfluthrin 0.05% and imidacloprid 0.15%
Apply between June 1 and July 15 for best results.
Bayer Advanced Season-Long Grub Control Liquid - attach-to-hose-bottle
imidacloprid 1.47%
Apply between June 1 and July 15 for best results.
(local distributors name) Premium Grub Control (Do not confuse with "Premium Insect Control")
imidacloprid 0.2%
Apply between June 1 and July 15 for best results.
Gardentech Sevin Lawn Insect Granules
carbaryl 2.0%
Apply in spring or fall to active grubs.
Bayer Advanced 24 hr Grub Killer Plus - Granular
trichlorfon 9.3%
Apply in spring or fall to active grubs.
Spectracide Triazicide Insect Killer Once and Done Granules
gamma-cyhalothrin 0.05%
Will not kill grubs at any rate.
Bayer Advanced Complete Insect Killer Liquid attach-to-hose-bottle
cyfluthrin 0.36% and imidacloprid 0.72%
This product will not deliver enough imidacloprid to work effectively - do not confuse this with the Bayer Advanced combination granular or the Bayer Advanced attach-to-hose-bottle product containing only imidacloprid (both of which do deliver enough chemical per area to be effective).