{"id":2784,"date":"2019-05-22T00:05:12","date_gmt":"2019-05-22T07:05:12","guid":{"rendered":"https:\/\/depts.washington.edu\/hortlib\/pal\/pal-question-574\/"},"modified":"2023-08-04T10:01:12","modified_gmt":"2023-08-04T17:01:12","slug":"managing-fungus-gnats-indoors","status":"publish","type":"pal","link":"https:\/\/depts.washington.edu\/hortlib\/pal\/managing-fungus-gnats-indoors\/","title":{"rendered":"managing fungus gnats indoors"},"content":{"rendered":"

I need advice on how to rid my house of fungus gnats which were introduced in a bag of potting soil I used when repotting my houseplants. One plant is difficult to repot because it has long branches that cascade down the side of the pot in an intertwined mass.<\/strong><\/p>\n

I always let the soil dry out completely before potting, and also in between waterings. Recently I added a bunch of sand to the top of the soil. Would repotting again help? Is there a no-pest strip that is safe for use indoors for this insect? (I’m chemically sensitive and also concerned about the soil’s fungus).<\/strong><\/p>\n

 <\/p>\n

I’m sorry to hear of your struggle with fungus gnats. I consulted
\nUniversity of California, Davis Integrated Pest Management online, and
\nhere<\/a> is a link to their page on this insect and methods of controlling it. Here are excerpts which may be relevant to your situation:<\/p>\n

Purchase and use only pasteurized container mix or treat potting soil
\nwith heat or steam before using it; this will kill flies as well as the
\nalgae and microorganisms they feed on. Store pasteurized potting soil in
\nclosed containers to prevent it from becoming infested before use.<\/p>\n

Commercially available Steinernema nematodes, Hypoaspis mites, or the
\nbiological insecticide Bacillus thuringiensis subspecies israelensis
\n(Bti) can be applied to control fungus gnat larvae in container media.<\/p>\n

North Carolina State University Extension<\/a> also has suggestions on indoor control of this pest. Excerpt:<\/p>\n

Potted plants and other types of interiorscaping are often the culprits.
\nCheck plants to see if the soil is excessively wet. Drain any excess
\nwater from the dish below the pot. If the weather permits, move the
\nplants outdoors or allow the soil to dry down (not to the point where
\nplants wilt). You can also drench the soil as mentioned previously. Then,
\nincrease the interval between regular watering and the problem should
\nabate.<\/p>\n

If you can possibly repot the plant(s) which had the infested soil, and
\nuse sterile potting soil, that should help. If this doesn’t work, the
\nBacillus thuringiensis (Bt) or parasitic nematodes might be an option. I
\nthink the Bt might present problems for your chemical sensitivity, as you
\nwould need to avoid breathing it in, and prevent it from getting on your
\nskin and clothing. However, the Steinernema feltiae nematodes should not
\nbe a problem at all. One example of a source for these is Peaceful Valley Farm Supply.<\/a><\/p>\n

I don’t think adding sand on top of the potting soil will be effective.
\nIt might actually create a kind of crust over the top of the soil,
\ncausing a drainage problem. If you are concerned about fungus in the
\nsoil, using sterilized or pasteurized potting soil is a good idea. You
\ncan try using yellow sticky traps to catch the gnats; it can’t hurt,
\nalthough it won’t completely solve the problem unless you are willing to
\nrepot with new soil. Most garden centers sell these traps, or you can
\nmake your own as described by New Mexico State University Extension.<\/a><\/p>\n

You can also employ trapping techniques using yellow sticky traps. These
\nmay be purchased, or you can make them from yellow surveyors tape or
\nyellow plastic butter tubs, etc., coated with vegetable oil, Vaseline, or
\nother sticky material. Put these traps in a window or other well-lighted
\nlocation. The adult gnats are attracted to the yellow color and get stuck
\non the trap. This removes them from the home environment and reduces
\ntheir ability to reproduce. (They die on the trap.) After you catch a lot
\nof gnats, just discard the whole trap or wipe the insects off and reapply
\nthe sticky material mentioned above, and you are ready to catch more.<\/p>\n","protected":false},"excerpt":{"rendered":"

I need advice on how to rid my house of fungus gnats which were introduced in a bag of potting soil I used when repotting my houseplants. One plant is difficult to repot because it has long branches that cascade down the side of the pot in an intertwined mass. I always let the soil dry out completely before potting, and also in between waterings. Recently I added a bunch of sand to the top of the soil. Would repotting…<\/p>\n

Continue reading managing fungus gnats indoors<\/span><\/a><\/div>\n","protected":false},"author":4,"featured_media":0,"menu_order":0,"template":"","keyword":[89,132],"class_list":["post-2784","pal","type-pal","status-publish","hentry","keyword-insect-pests-control","keyword-potting-soils"],"acf":[],"_links":{"self":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/pal\/2784"}],"collection":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/pal"}],"about":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/types\/pal"}],"author":[{"embeddable":true,"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/users\/4"}],"wp:attachment":[{"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/media?parent=2784"}],"wp:term":[{"taxonomy":"keyword","embeddable":true,"href":"https:\/\/depts.washington.edu\/hortlib\/wp-json\/wp\/v2\/keyword?post=2784"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}