You can know if grubs are gone after treatment by digging up small soil samples and counting what you find. Wait 2 to 3 weeks after you apply the product before you check. This gives the active chemicals time to spread through your soil and kill the grubs feeding on your lawn roots.
I check my grub treatment verification results twice after each time I treat. At the two week mark, I dug up test spots and found grubs turning gray and soft. By week four, most of the grubs in those same areas were dead and shrunken. The change in color and texture told me my product was working.
The type of product you use affects how long you should wait to check grubs after treating. Systemic products take 1 to 3 weeks to kill grubs. They work as grubs feed on treated grass roots over time. Contact products kill faster within days when the active ingredient touches the grub. Know what type you used before you dig to check your results.
Penn State Extension teaches a simple method to count grubs in your lawn. Use a shovel to cut a 1 square foot (0.09 square meter) section of turf. Lift the grass and soil together like you are removing a piece of carpet. Check the dirt below for grubs and count how many you find. Do this in at least three spots across your lawn.
Good grub control results do not mean you find zero grubs in your test spots. Most products kill 75 to 100% of grubs, not all of them. If you started with 15 grubs per square foot and now find 2 or 3, your treatment worked well. Your lawn can handle a few grubs without damage. The goal is to get below 5 per square foot.
Signs of dead grubs tell you your treatment is working on the problem. Healthy grubs are white or cream colored with shiny skin that looks plump. Dead grubs turn gray, brown, or green and feel soft to the touch. Their bodies shrink and dry out over time. If you find mostly discolored grubs, your product did its job.
Watch your lawn surface for signs of success too. Healthy grass that was starting to yellow should begin to recover within 3 to 4 weeks after treatment. Brown patches should stop spreading once grubs die off. You may also notice fewer birds and skunks digging in your yard since they hunt for grubs as food.
If your test digs still show high grub counts after 4 weeks, you may need to retreat your lawn. This can happen if you missed the best application window or if rain washed product away before it soaked in. Apply a curative product and check again in another 2 to 3 weeks to see if grub numbers drop.
Mark your calendar to check grubs twice a year for ongoing peace of mind. Test in late August to see if new grubs have hatched. Test again in early October to confirm your fall numbers are low. This habit helps you catch problems early before they cause visible damage to your lawn.
Read the full article: Effective Lawn Grub Treatment Guide
