Gnats no big nuisance to outdoor plants

Question: Can you help me identify some insects on my grapes? They are quite small and devour the leaves of my grape vines, leaving them like skeletons. There are literally thousands of them in the summer. They stay until late fall and are very annoying. What can I do to get rid of them?

After several email exchanges, I finally determined that the reader assumed the insect she was seeing was the same one that caused damage in the summer.

The insects she is seeing now are fungus gnats. These are not particularly damaging to outside plants. They feed on decaying organic matter, such as mulches or other dead plants. They can be in the millions in wet mulch.

In houseplants, they can be somewhat damaging as they can feed on plant roots. When it gets hot, these critters will disappear from outside gardens. They are not related to holes in grape leaves or any other damage to grape plants. Do not treat with a pesticide.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. He can be reached at or 257-5555.