Knowledgebase
Japanese beetle grubs? #840810
Asked July 15, 2023, 12:50 PM EDT
This spring i built a 5' x 11' raised garden which I filled with bagged soil (garden and potted) from COSTCO. I am now finding this huge numbers of grubs. Ace said to use Traizicide but that is a neurotoxin (safe of course????). Decided to pull out carrots and try with remaining tomatoes, peppers, and cucumbers. Other half of same garden is strawberries which I do not know if it is ok to use on. Will try and attach photos. Any assistance would be greatly appreciated. If I kill grubs will they be gone or return?
Thank you
Ken Noreyko
Jefferson County Colorado
Expert Response
Hi Ken,
There are several different grubs that can be found in a raised garden, many of which won't affect your vegetables. Before treating for them, it would be best to identify exactly what kind of grub you have in your garden. To do that, we would need a physical sample of the grubs, which you can bring over to CSU's State Plant Clinic (more information here: https://agsci.colostate.edu/agbio/plantclinic/).
Thank you!
Hania
The Jeffco Extension office is short staffed right now, so it may take longer to get your sample. In the meantime, I wanted to share more information with you.
The grubs in the soil are definitely NOT Japanese beetles grubs because they can only survive by feeding on turf grass. Many other species of grubs exclusively on turf grass, narrowing down the list of possibilities.
In my experience, the vast majority of grubs found in soil are usually the Bumble Flower Beetle grubs. They feed and thrive on soil with high organic matter. They are also often found in compost piles, container gardens, etc. These grubs feed on decaying matter and don't harm the plant. They are actually beneficial because they break down decaying matter. Here is more information: https://webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Bumble-Flower-Beetle1.pdf
And here: https://extension.usu.edu/pests/ipm/notes_ag/veg-bumble-flower-beetle
You can leave them in the garden, or since they are in high numbers, you could spread them out to other places in your landscape. Typically pesticides are not needed to control the grubs. If you choose to use the Traizicide, note that it is a broad spectrum insecticide so it will impact other beneficial insects/arthropods in the garden. Be sure to read the label and follow directions explicitly especially since you are growing vegetables/food for human consumption. The label should indicate if it is safe on strawberries.
Hope they can get you a confirmation on the identification soon. Happy to answer any more questions.
Thanks,
Lisa
Lisa Mason
Horticulture Specialist & Entomologist
Colorado State University Extension, Arapahoe County
