When to apply Scotts GrubEx

Asked April 29, 2016, 3:16 PM EDT

I would like to know when the right time is to apply Scotts GrubEx? Thank you for your assistance.

Dakota County Minnesota

1 Response

The active ingredient in Scotts Grubex is chlorantraniliprole. The following excerpt from a Michigan State University bulletin explains when it and other grub killing pesticides should be applied.

"1) PREVENTIVE insecticides that will prevent grub damage next fall (2016) and following spring (2017)

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 confirmed grub damage the previous fall or spring, meaning you found lots of grubs, 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 chafers and Japanese beetles 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, 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, the pesticide may move through the soil or partially degrade by the time the grubs hatch in late July. If applied too late, preventative products may not be effective as they work best on small grubs.

Preventive products containing imidacloprid, thiamethoxam or clothianidin will consistently reduce 75-100 percent of the grubs if they are applied in June or July and if they are watered-in with 0.5-1 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 coffee cups on the lawn and running the sprinklers until they fill a half to 1 inch deep with water.

There is another 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 can be applied as early as April and up to mid-July. This chemical will give very good control of grubs."

In summary, Scotts Grubex can be applied now. Follow label directions. Go here to read the complete Michigan State University bulletin: