Ask Us About Pests

December 11, 2007 - 11:23

Q Can’t I just trap out my fungus gnats with yellow sticky tape?

A Good question — and I get it a lot, as I’m sure my colleagues do, too. I think we are in agreement that if the population of gnats is low, yellow sticky tape can affect the population dynamics of the pest. Generally, however, it is not an effective method of control for fungus gnats, leafminers, thrips, etc. If the population is high, as is common in protected culture, it will have a minimal effect.

Are they attracted to the yellow tape (hopper tape) or yellow cards? Yes, they are. If you remember from high school physical science, specifically paper chromatography, plants are not all green. Yellow is a common color found in green plants, and that wavelength is, in many cases, even more attractive to many flying insects than the green. But female fungus gnats that need an oviposition site will ignore traps at some point and lay eggs in your pots or media.

There are a number of other cultural methods that are much more effective in keeping fungus gnat numbers down. Populations may be reduced by eliminating or minimizing breeding areas, or wet areas with high concentrations of organic matter. One common area that fits that description in protected culture is under benches where a lot of potting soil and other organic matter builds. It is also common to find breeding areas where potting media is prepared. The most obvious breeding site is on the benches where potted plants are often overwatered.

I have seen great population fluctuations because of inconsistent watering in woody ornamental propagation areas (the less water, the fewer the fungus gnats). Therefore, allow the surface of the potted plants to dry between watering cycles. If at all possible, sterilize mulches and compost before use. When all else fails, see some of the fine work that Dr. Ray Cloyd has done on cultural control of fungus gnats. He has often published his work here in GPN (visit our archives at www.gpnmag.com).

Q What can I use to kill the centipedes running around on the walls in our offices?

A I suspected that this was the common house centipede, as I’ve had many of them brought to me from classrooms by teachers and friends with office trailers. Once I have described the creature to them, they confirmed that that was their problem. It seems like my wife brings me one every year from her classroom, and she’s worried that it’s going to drag the second graders down the drain and have them for dinner.

The house centipede, Scutigera coleoptrata, is a yellowish to light-brown centipede with about 15 pairs of very delicate legs and three dark-colored dorsal stripes running down its length. The legs also have dark stripes. As a protective mechanism from predators, their legs can fall off if you look at them funny: They are very fragile! House centipedes are quite distinctive and very fast.

This creature probably originated in the Mediterranean region, but it can now be found nearly worldwide. It prefers indoor living, which is why it causes so much concern. Actually, it is quite harmless and can be a good creature to have around because it feeds on the bad bugs around the home and office, such as spiders, bedbugs, termites, cockroaches, silverfish and ants.

For an entertaining look at the house centipede from a layman’s view see the following website: www.math.umd.edu/~schris/scutigera.shtml. For a more scientific view, check out www.ipm.iastate.edu/ipm/iiin/housece.html.

The bottom line is that if you use pesticides on this creature, you are eliminating a beneficial organism as well as wasting pesticides and your own time. If you feel it is absolutely necessary, a common way to remove them is to trap them with sticky cards along their common travel routes.

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Do you have a question for our panel of experts? Send your disease, pest or growth-control questions to the appropriate person, and look for the answer in an upcoming issue of GPN.

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