Help! Why Are There Fruit Flies on My Herbs?

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Help! Why Are There Fruit Flies on My Herbs?

So have you heard the rumor that herbs are pest free plants?

Um, ‘fraid not. Not only do they get pests, sometimes they get major infestations! While it’s true that the oils in many herbs keep them pest free, many tender herbs can become pest ridden.

Plants grown in the house and in pots can be easily plagued by pests. One pest you may encounter with pot grown herbs are Fungus Gnats. If you have purchased herb plants, you may have been surprised to find that Fungus Gnat larvae hitched a ride home in the soil.

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 like that. Entomologists will be happy to tell you all the differences between the two, but the Fungus Gnat larvae actually live in the soil of your plants and feed off decaying material… and occasionally your plant roots.

One way to keep ahead of these little critters is to put up sticky yellow traps to catch the adults. This does not control larvae in the soil, but will prevent flying adults from laying more eggs.

You can also make sure that your soil dries out a bit between waterings. An easy way to check is to stick your finger into the soil. The top inch or so should feel fairly dry. Just don’t let your herbs dry out so much that you kill them. Monitoring the amount of watering helps, but it really doesn’t get to the root of the problem…which is where those annoying little larvae are happily munching away.

Repotting the offending plants can help, making sure you remove as much soil as possible. Try repotting with a mix that does not contain lots of peat, unpasteurized compost or leaf mold. All of these break down quickly and provide a smorgasbord of yummy organic matter for the Fungus Gnats to eat. Potting mixes containing cocoa fiber, charcoal, perlite, and vermiculite blends are all helpful since they do not decay as quickly as peat blends do.

You can also purchase a Bt (Bacillus thuringiensis) product for flies and mosquitoes which works beautifully for Fungus Gnat control. Make sure you get the correct type of Bt. Several are available and each is species specific. This simply means that they only work on a particular type of pest so if you purchase the wrong one, you won’t get the results you want. Bt is watered into the soil where the larvae ingest it. It is not effective for adult Fungus gnats, so a light misting of insecticidal soap and/or the sticky traps might be advised to knock down adult populations.

Okay, so you have the lowdown on those pesky little Fungus gnats now. I trust you are well armed with information and you’ll know what to do the next time you see them hovering around your plants.

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