Is it too late to apply nematodes to the lawn to fight Japanese Beetles?

Asked October 12, 2018, 10:16 AM EDT

Hi! It already getting cold now by mid-October in the Twin Cities and I received a pacakage of nematodes this week to apply to my lawn for fighting Japanese beetles. I think there may have been a frost last night. Does it pay to apply them anymore? Should we wait until it warms up a few degrees closer to 50s next week? Also, should we wear gloves when using a sprayer for nematodes to protect our skin? Please advise. Thank you!

Hennepin County Minnesota nematodes

1 Response

The species of nematodes used against Japanese Beetle grubs is Heterorhabditis bacteriophora. It is commercially available. However, note that these nematodes are relatively expensive and must be applied several times as they do not live long in the environment. Nematodes need to be applied to soil at night and the soil must be irrigated daily to keep it moist so the nematodes stay alive.

These nematodes are microscopic parasitic roundworms that transport and feed on bacteria. When they find a grub, the nematodes penetrate the grub and inoculate it with bacteria, which quickly multiply within the grubs' bodies. This eventually kills the grubs.

The best time to apply nematodes depends on the weather and grub species. For Japanese Beetle grubs this is from mid-summer to late August. Because of this, it is now too late to apply the nematodes. For them to be effective, the soil temperature should be close to 60 degrees. It is doubtful that this is now true. Even a few warm days will not change the soil temperature.

Nevertheless, should you want more information about these nematodes, see:

Good Luck!!