There are a lot of reasons why certain patches of grass don’t grow very well, but one of the most common in Minnesota lawns is grubs (otherwise known as Japanese beetles). These harmful invaders lay their eggs in the dirt under your grass in the summer. Those eggs grow up and feed in the fall and spring. This cycle of feeding can be extremely harmful to the grass in your lawn. In this blog post, we’ll discuss the best time to treat for Japanese beetles/grubs in your lawn. If you don’t want to do the treatment yourself, let your local Minneapolis lawn care specialists (that’s us) help you by filling out a quote request .

To understand why this timing is best, we need to understand the life cycle of a Japanese beetle. As you can see in the handy chart below, a grub’s life cycle begins in the summer, when adult Japanese beetles lay eggs underneath the soil. After the grubs hatch from these eggs, they feed on grass roots through the fall and then dig down and go dormant during the winter. In the spring, they dig up and feed again before turning into adults and starting the process over.

The grubs are closest to the top of the soil in the spring and fall. Any other time of year would be difficult or impossible to reach them, and killing the adults doesn’t stop the process after they’ve laid the eggs. While it’s possible to treat the grubs in the springtime (April to June), that is not the ideal time to do it. In the spring, the grubs had an entire fall and winter to strengthen up and become larger so they are much more difficult to kill. In the late summer to fall, the grubs are just barely starting to grow and they are much closer to the soil surface so they are easier to kill. 

It’s important to note that just because you have adult Japanese beetles flying around doesn’t necessarily mean you have grubs in your grass. Adult beetles will fly far distances to munch on tasty bushes and leaves. If you take a small, flat shovel and dig just under and parallel to the grass (like in picture below), you should be able to see the grubs in the spring and fall. The grass in these areas will show bad growth and patchiness that won’t be apparent in other areas.

Example of grubs under grass

Here at KG Landscape, we think of the two weeks of the Minnesota State Fair as a great time to apply insecticides for grubs. By that time, the grubs have had enough time to start feeding on the roots and be very close to the soil surface but they are still small and easy to kill. The best treatment for these grubs is a chemical called “Imidacloprid” . It is safe for mammals and most fish so it has a small impact on the local ecosystem but does kill the grubs damaging the grass. We use a granular treatment that only requires one treatment per year until they are completely eradicated. It may or may not effect some honeybees, but if applied to only grass areas with possible grub damage, the impact on these important creatures will be minimal.

If you’re looking for lawn help in the Minneapolis/St. Paul area, look no further than KG Landscape. We have the experience and knowledge to help fix any lawn issues. Give us a call at our office 763-568-7251 or fill out a quote request and we’ll get in contact with you. Getting that golf course quality grass shouldn’t be impossible; we can help make it happen.

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