Help! Why are there Fruit Flies on my  Herbs?

So, you’ve heard that herbs are pest free plants?

Some people think that herbs never have pest problems. Nope.

Not only do they get pests, sometimes they get mega infestations! The oils in many herbs keep them pest free, but many tender herbs can become pest ridden.

Herb plants grown in pots, and house grown herbs can be easily plagued by pests.  One common pest you may encounter with pot grown herbs are fungus gnats. To the naked eye, these little guys look like fruit flies.

You know, those annoying little bugs that hang around those old bananas in the fruit bowl? Yep, they look sort of like that. Just one eighth of an inch long this photo shows the greatly enlarged adult.

Adult Fungus Gnat on Sticky Trap

Entomologists can tell you all the differences between fungus gnats and fruit flies, but fungus gnats actually live in the top layer of soil of your plants. They feed off decaying material… and sometimes your plant roots. If you purchased an herb plant, you may be surprised to find after a few waterings that fungus gnats arrived in the soil!

A few things that can help

One way to keep ahead of these little critters is to put up yellow sticky traps. This method is fine for adults, but does nothing for the larval stages of the wee beasties.

Try to make sure that your soil dries out a bit between waterings, but not so much that you kill your plants. Fungus gnats like moist conditions and drying the top inch or two of your plants will help control them.

Repotting your herbs can help control fungus gnats. Look for a potting mix that does not contain lots of unpasteurized compost or peat. Both of these break down quickly and give fungus gnat youngsters lots of larvae-licious food.

For bigger infestations you can also purchase a Bt (Bacillus thuringiensis) product, which work beautifully.

You need to make sure you get the correct type of Bt, as several are available and each is species specific-meaning they only work on a particular type of pest. Make sure you purchase a type that is specifically intended for flies and mosquitoes-Bacillus thuringiensis israelensis.

Bt only controls the immature stages of a fungus gnat’s life. You will need to control the adults using the methods mentioned above, and may want to consider adding some insecticidal soap to your pest control arsenal. A light spritzing will help to knock down adult populations quickly.

Happy growing!

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