Symphylans have invaded my garden, how can I get rid of them?


Bifenthrin is registered for vegetable gardens but is not currently registered to control symphylans. However, bifenthrin is a close relative of cyfluthrin which is registered to control symphylans, so it probably helped a little. In general, these pesticides are not as effective at controlling symphylans as some that were registered previously but are no longer available for home use. 

There is no "silver bullet" when it comes to symphylans. Tillage is one of the best tactics, and if you can till more than once between now and planting, the more the better... within reason. I realize you're trying to plant cool season crops, so even tilling once is better than not at all. Normally I recommend avoiding tillage when the soil is too wet (best to wait at least 2-3 days after rain), as that can damage soil structure, but in the case of symphylans, good soil structure actually favors their movement in the soil. As such, use your judgment regarding when to till. Also, high organic matter favors symphylans, so avoid tilling in compost or other organic matter. These are not necessarily permanent recommendations; rather, try to bring the symphylans under control first, then resort to more routine management practices and try to maintain a crop rotation that discourages them (see below). 

Here are two articles from the Pacific Northwest Insect Management Handbook that provide more details about symphylans:

The second article provides some information about crop rotations... a little late for your impending crop, but good info moving forward.

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