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

symphylans in soil
Photo credit: Ask an Expert
Q:

How do i get rid of symphylans? I have turned the dirt numerous times and treated with Bifenthrin as was directed by a soil expert at a local greenhouse ( 3 days ago) and they're still alive and well. Help!!! I am trying to get some of my cold crop starts in the ground, but want to get rid of these bugs first.

- Lane County, Oregon
A:

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 judgement regarding when to till. Also, high organic matter favors symphylans, so avoid tilling in compost or other organic matter. These are not necessarily permanent recommnedations; 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:

https://pnwhandbooks.org/insect/vegetable/vegetable-pests/common-vegetable/vegetable-crop-garden-sym...

https://pnwhandbooks.org/insect/ipm/garden-symphylan

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

Jeff Choate
Extension Horticulturist
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