Infected White Grub

People familiar with insect pathogenic beneficial nematodes know that Heterorhabditis bacteriophora (Heteromask) outperforms Steinernema feltiae (Scanmask) when it comes to controlling white grubs, but that doesn't mean that S. feltiae are ineffective. H. bacteriophora effectiveness drops off in colder temperatures, especially below 68°F, while the S. feltiae in Scanmask are active in soil temperatures down to 55°F.

Here are pictures of one of the white grubs we collected for our own lab test, exposed to 18,000 S. feltiae infective juveniles per square foot in a petri dish and then incubated at 15°C (59°F). The white grubs in the test were a mix of Japanese beetle (Popillia japonica) and Asiatic garden beetle (Maladera castanea). Below is the Asiatic garden beetle.

Closer investigation reveals the site of infection is on the underside below the anus (the black dot). For more on telling white grubs apart, see How to Identify (and Kill!) White Grubs.

When the soil is still cool (below about 68°F), kill your white grubs with Scanmask, at our recommended rate of about 25,000 nematodes per square foot; otherwise Heteromask is our first choice. Treat from March to June or August to September; late summer and early fall is best. See our white grubs page for more.

Happy gardening!