The most effective window to apply beneficial nematodes for grub control in Pacific Northwest lawns is from late summer to early fall, typically August and September. A secondary, though less optimal, application can be made in the spring, from April to May.
The success of nematode treatment hinges on the lifecycle of the most common lawn grubs in the region—primarily the larvae of the Japanese beetle, European chafer, and Southern masked chafer—as well as specific soil temperature and moisture conditions.
Late Summer to Early Fall: The Primary Treatment Window
The late summer and early fall application targets newly hatched grubs when they are small and most vulnerable. During this period, from August through September, the soil temperature in the Pacific Northwest is generally within the ideal range for nematode activity, which is between 50°F and 86°F (10°C to 30°C).
