Thursday, July 30, 2009

Floating row covers and vegetable insects

A previous post discussed germinating seeds with the fabric dual-marketed as seed germination fabric and floating row covers. The fabric covers placed over the top of plants can serve several useful functions including shading plants when transplanting, and shading to extend the life of cool season vegetables as hot weather approaches. They are also used to capture heat for fall frost protection.

Row covers are easy to use. Throw loosely over plants allowing slack for future plant growth. You can also use covers over hoops or wire tunnels such as in the photo above right. Anchor to the soil with U-pins bent from wire and punched through the fabric that touches the ground. Soil also can be mounded over fabric edges to hold it down. Covers allow light and water through and stop movement of insects.

Looking at what insects are trapped under covers with vegetable plants and which are barred access is worthwhile. Row covers can stop plant damage from troublesome insects such as spinach leafminer, aphids, leafhoppers, cabbageworm and cabbage looper. Summer pest protection is offered against squash bug, cucumber beetle, bean beetle, corn earworm, whitefly and grasshopper.

Before declaring victory and thinking covers will solve all vegetable insect problems, remember that several insects spend part of their lives in the garden soil. When they emerge to find their favorite plant food enclosed in a cover that protects them from predator insects, they readily multiply. Examples are cutworms and slugs that lurk in scattered soil locations.

Some insects concentrate on the soil immediately around their host plant and can be thwarted by crop rotation. These include onion and seedcorn maggot, flea beetle, Colorado potato beetle, corn rootworm (left photo larva in soil and right adult on corn silks) and tomato hornworm. Planting in the same location and using floating row covers can set up insect problems with these plants.

If a pest does multiply under a row cover, it may be best to remove it to allow natural enemies such as lacewings and ladybird beetles access to the pests. Also remember that squash and other vegetables depend on insect pollination so be sure not to screen out bees during flowering.

Photo credits:
* Row cover over growing tunnel, David Whiting
* Larva of the western corn rootworm, Frank Peairs, Colorado State University,
* Western corn rootworm adult on corn silks, Tom Hlavaty, USDA Agricultural Research Service,


  1. Hi. I love reading your blog and I'm wondering if maybe you might help me with a problem that we're having. My husband has built raised garden beds this year and we're using them for the first time. The soil and compost came from a local nursery. We planted some transplants: eggplants, tomatillos, tomatoes and cucumbers and all are doing fine. We also planted seeds for basil, thyme, cilantro, beets, lettuce, carrots and swiss chard. The seedlings begin to emerge and literally within a day or two they seem to have disappeared. Upon further inspection I have noticed that all of the starter leaves have been chewed off and all that remains is a very tiny bit of the original stem- if that. I've replanted three times this summer and the same thing happens. I'm becoming very discouraged as I was looking forward to a plentiful garden this year. I've inspected the area and these are the only suspects I can come up with: birds (finch, sparrows, flicker, jay, robins and grackles are in our backyard), squirrels (they usually go for the tomatoes and I haven't seen them in the boxes), or ants. Do you suspect any of these or is it something else all together? Any advice on how to nurture the seedlings along? (More mature plants are all fine).

    Thanks so much!

  2. In addition to birds clipping seedlings (floating row covers will shield them from this until they're large enough that birds won't trouble them), consider cutworms. Caterpillars that cut and kill tender seedling plants around the soil line are termed cutworms. The notorious "miller moth" that people in our area recognize in the adult flying form is Army cutworm in its larval caterpillar stage. There are others such as beet armyworm, Western bean cutworm, etc.

    Cutworms typically feed at night and hide in soil cracks, under dirt clods or seek other cover during the day. If you are going to find them, you have to go out after dark with a flashlight. Cutworms are preyed upon by ground beetles, rove beetles, spiders, tachinid flies, parasitic wasps and other garden insects as well as toads and snakes.

    Control weeds that attract egg-laying moths. Promote rapid seedling growth with good culture (water, loose soil, proper planting time, etc.) and use transplants as older plants aren't generally damaged. If transplants are tender, protect the stem at the soil line with cutworm collars (cardboard, foil) or milk carton rings. Insecticide baits are available for cutworms.

  3. Thanks so much for these comments. I think we've found our particular culprit- earwigs. It took a really long time to figure it out but I found a couple in some Swiss chard recently and did some research and have come to discover that our yard is infested. Unfortunately, now that you have posted about cutworms I think we may have caught one or two in our earwig "traps" so that might be our next gardening challenge. I really appreciate all of your posts and expertise. It's a great help to us newbies!

  4. Earwigs are generally a beneficial insect eating mainly aphids and other harmful garden insects. They will occasionally nibble on some soft plant parts but their reputation as a destructive plant pest is grossly overexagerated. See the CSU Extension fact sheet for more information on earwigs at Most gardens have many earwigs and they co-exist with plants quite well.

  5. Last year I had an intense earwig infestation. I went out at night to see who could be destroying our crop and found earwigs completely covering and devouring our plants. They took our beans, basil, kale and squash varieties. I even tried re-planting squash/zukes and they took them again. I am hoping with the soil improvements I tried this spring that I will have a better year. Have you ever heard of earwigs like this before?

  6. Thanks for the post and great tips..even I also think that hard work is the most important aspect of getting success..
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