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Trap gnats with decaying vegetable pieces

Question: I recently transplanted two houseplants and now have gnats coming out of the soil and infecting my entire house. Is there any way to kill these little buggers or do I have to get rid of all the dirt and start over?

Answer: Fungus gnats can be a serious problem with houseplants as they can feed on plant roots as well as decomposing organic matter left in potting soils. The life cycle of fungus gnats (egg, larva, pupation and adult) is fairly short, perhaps two to three weeks.

The destructive stage is the larva or worm stage. The pesky stage is the adult, which can fly and be bothersome. These stages are overlapping so they will not all be flying at once; some will be in the egg stage, some in the larva stage, some pupating and some flying.

You can attract the larvae living and feeding in the soil to decaying vegetable pieces like small pieces of potato. You can lay pieces about the size of a french fry on the soil surface and the larvae will start feeding on them. You can collect these pieces and dispose of them and it will help get rid of a few of the buggers.

Let me point you in the direction of an organic product that may work for you. This is supposed to be available at hardware stores and home-improvement stores. With a homeowner trade name of Mosquito Bits, it was originally labeled for controlling mosquitoes but is approved for fungus gnats.

This organic product is made from Bt (a bacterium). There have been a few other homeowner products made from Bt for indoor plants, but they have disappeared from many marketplaces I assume because the homeowner didn’t know about them and how to use them.

A word of explanation. As I said, this is a Bt product. I have mentioned Bt in the past, with product names such as Dipel and Thuricide. This one is a different form of Bt. Using the Dipel or Thuricide form of Bt that you would use for grape leaf skeletonizer, tobacco hornworm, tomato fruitworm (insects that are in the order lepidoptera) will not work in this case.

This form of Bt is unique to certain types of insects in the order diptera, such as mosquitoes and fungus gnats. The commercial formulation of this product is called Gnatrol. Apply this product according to the label directions.

I put more information about different types of Bt formulations on my blog.

Question: I found this thing in the picture I sent to you under my Joshua tree this morning. It is about 6 inches long. Is it mold? I only water three times a week for five minutes.

Answer: I get a picture of this once a twice a year, usually in the spring when it is cooler, there has been rain and there is plenty of wood chips for it to feed on. This is called a slime mold and kind of resembles vomit.

No treatment is necessary. It is a good guy since it breaks down woody debris. it does not attack living plants.

If you want to be an industrialist, destroy it with the back of a rake and rake it into the mulch and soil. It will probably come back at some time but like a pest would. I will post pictures of some on my blog.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com.

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