Hello Tammie,

“Season long” grub protection is more of a marketing statement than a practical pesticide action. Since these preventative pesticides kill immature grubs before they can feed late summer through the following spring, they technically have provided a season’s protection. In reality, they are active and effective essentially in July. There are several active ingredients in these preventive pesticides with different optimal times of application. Quoting from the article:

“Preventive products containing imidacloprid, thiamethoxam or clothianidin will consistently reduce 75-100% of the grubs if they are applied in June or July and if they are watered-in with 0.5 inches of irrigation immediately after application. Lawn sprinklers can be used if you do not have an irrigation system.

There is another active ingredient in some insecticides called chlorantraniliprole that will also work 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. Chlorantraniliprole can be applied as early as April and up to mid-July.”

The active ingredient in Grub Ex is chlorantraniliprole. Since it is not very water soluble, it stays in the soil for a long time, so if there were baby grubs in the soil all season, it would be effective all season. However, since we only have baby grubs in July, it is practically only effective in July.

I would apply Grub Ex in May. Then, August through September pay attention to your grass and watch for any areas dying, or flip over a few square feet of lawn and if you find any grubs, you can apply a different pesticide, a curative type, that will actually kill feeding grubs.

”There are two chemicals, carbaryl and trichlorfon, that are considered curative treatments. They are short-lived compounds that kill all life stages of grubs. These two insecticides are the only options if high numbers of grubs are found in the fall and in spring before early May.”

Now to address your comment about moles. Having moles does not mean that you have grubs. You can have moles in your lawn without having a single grub. Quoting from the following MSU article: “First of all, let’s eliminate the one suburban legend that often comes forward when thinking of moles. Moles do not equal grubs and grubs do not equal moles. Just because you have moles doesn’t mean you have grubs and eliminating grubs will not eliminate moles! Moles are insectivores; they eat insects, worms, and other invertebrates. Notice they eat other delicacies besides just insects; grubs are just a portion of their diet. Now if you have grubs and they are slowly decimating your turf, you probably want to control them, but don’t go applying insecticides simply thinking you’ll get rid of the moles.” https://www.canr.msu.edu/news/moles_in_the_lawn

Finally, do not expect that treating your lawn for grubs will diminish the Japanese beetles on your grapes. Japanese beetles are prolific travelers. They can travel up to 15 miles from where they were grubs. If your grapes are a favorable buffet for the beetles, they will come from far to dine! https://extension.illinois.edu/blogs/ilriverhort/2015-06-29-japanese-beetle-myth-information-sandra-mason

Hope this helps.