Earwigs on Nufar Basil
Answered by: Conrad Richter
Question from: Cathy Baumbauer
Posted on: July 14, 2000

I’m growing some of your Nufar sweet basil in my 2000 sq ft greenhouse for sale to local restaurants. It’s doing very well, but this is the second year I’ve had large earwig infestations on the Nufar. The insects live in the plants, around the growing terminal buds, and eat small holes all through the leaves. I’m losing a substantial portion of my crop to earwig damage. Do you have any advice on how to control them? Have you heard from anyone with a similar problem?

I only grow culinary herbs in my greenhouse. All my basil plants are in 1 gallon black plastic pots filled with Sunshine Mix, so I start with completely new potting media with each crop. In addition to those in the basil plants I’m finding a few insects on the top of the soil, and sometimes colonies are in the drainage holes of the pots later in the summer.

My floor is gravel, which may be where the earwigs are hiding. The greenhouse is empty and unheated from October through the first of March, which I hoped would eliminate some insect problems. (I’m in Bozeman, Montana.) I didn’t see any earwigs until about 2 weeks ago, but now they’re back!! I tried some earwig traps from Lee Valley Garden Supply--small covered containers with holes for access. You fill it half-way with water, cover with an oil slick and bait with tuna or fruit. So far I have captured zero earwigs--there’s no reason for them to leave their happy home in the basil plants. Last week I sprayed with soap and Rotenone pyrethrum, which seems to have knocked them back, but I’m looking for any help you may be able to offer.

Earwigs are omnivores, feeding on insects, vegetation and decayed organic matter. In the summer months they become most noticeable as the young adults emerge from the nests to forage. They hide in moist, dark locations during the day and come out to feed at night.

There are a number of chemical controls but from what you have tried so far it is clear that you prefer to use natural or non-chemical means of control.

You say you got some knock back with a rotenone and soap spray combination. We have not heard that earwigs are sensitive to rotenone, but they are sensitive to insecticidal soap which explains your results. They are also sensitive to pyrethroids, so you may want to try a combination soap-pyrethrum spray next. Safer’s makes one called "Trounce".

Earwigs are also sensitive to diatomaceous earth products. You can get some formulated with pyrethrum. The powder is dusted on the areas to be protected. The powder washes off readily so you may want to dust it on your plants each evening until the earwig problem abates. The presence of the diatomaceous dust make be unacceptable for your product -- you will have to experiment to see how well it washes off before harvest. Aside from the cosmetic detraction of using diatomaceous earth, it is otherwise very safe to use on edible plants.

An effective control program will benefit from a search and destroy strategy to eliminate nests. Earwigs like to nest in moist, dark areas, such as the undersides of pots as you have noted. Regular sweeps through your greenhouse looking for nests will help.

Traps are only part of the solution; they won’t give you effective control alone. But combined with the above measures they can help a lot. You can make your own traps with rolled up corrogated cartons or cardboard tubes filled with straws and sealed up at one end. Even if you do not trap any in the early part of the earwig season, don’t give up because the traps will pay off eventually.

You should remove potential sites outside the greenhouse where nesting can occur. Wet organic debris such as compost or grass clippings should be removed. Earwigs will migrate from outside. If practical, you can also seal up cracks through which earwigs could come in.

There are a few chemicals that can be applied to areas where nesting and foraging populations occur. Of course, such sprays should not be applied directly to the plants, but outside and around the greenhouse could be treated with chemical controls. Check with your local extension agent for advice on what to use in your area.

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