Possible fungus gnats

kadasuki(z6 NW AR)March 9, 2010


I saw the thread on fungus gnats and wondered if that is what my buggy problem is. I know that if you put a banana peel into a bottle, cover it tightly with saran wrap, poke a tooth pick hole into the middle of the wrap and set out where you have fruit flies, that they will go into the jar and be trapped. I did this and none of my little flying bugs on my one brugmancia cutting went into the bottle.

I had no bugs until Valentine's Day when my husband brought me home potted blooming plants-tulips and orchids--from Walmart. Now WOW! By the way, I went to the Walmart garden shop and they have clouds of these little bugs flying around.

So I put 3 slices of potato on my plant's soil and now there are little tiny silvery bugs on them and my flying bugs have really multiplied.

So I guess it is fungus gnats. I can't find the mosquito dunks at Walmart like they used to have, now they just have some little poison pellets.

Sigh. Any other advice? Thanks.

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I bought a Hot Shot hanging bug collector and seems to be working. It's kind of like fly paper, but it is self contained. I am new to brugs so I might not be the right person to respond.
Good luck!

    Bookmark   March 9, 2010 at 6:37PM
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kadasuki, sorry about your problem with these pesky gnats. Here are a few things that can be done, but I am sure the experts will add to it. If you can't find the yellow sticky cards (don't recall name, but it's to trap flying insects), some have used yellow cards (poss. index cards) and smeared some Vaseline on them. Put next to your brugs where you see the gnats. Put a small dish with a bit of dish detergent and vinegar/cider vinegar and they will land and drown. I've done this myself and it does catch some. Replace some of the soil on the top of your plants with new soil to get rid of the gnats larvae, and don't keep the plants too wet, but let dry a bit between waterings.

    Bookmark   March 9, 2010 at 8:32PM
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I've tried vaseline on index cards and it was a freaking mess. lol You can get regular fly paper that comes in those little cylinders. The yellow sticky cards work better but the fly paper does an alright job. See if you can find anything containing Bt which is the active ingredient in Mosquito Dunks. Just remember that you can't use any pesticide when using Bt because it will kill it. You can try a layer of sand over the soil. It doesn't work well for me but some people swear by it.

    Bookmark   March 10, 2010 at 6:59AM
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I read that putting pieces of potato in the plants worked, to prevent gnats. I cut up a red potato and put a piece in each of my plants just in case. I don't know if it worked, since I never got gnats, but now I have potato plants, with great roots, does anyone know how to plant potatoes, I have no clue. Barbra,

    Bookmark   March 10, 2010 at 8:47AM
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haase(10 CA)

The potatos didn't work for me. The vinegar solution had a few gnats in it, but not enough to make a difference. The fly paper, however, worked, but not when I hung it up. The paper has to be closer to the soil. So I cut off 2 inch long pieces and stuck them around my brug pots. (- Well, of course, my brugs are all in pots.) I had noticed that the gnats walked around the edges of the pots a lot, before (or after) they were busy on top of the soil.

This worked. Gnats walked all over the sticky paper and it looked as if I had shaken the pepper shaker over the paper. Had to replace the paper after a few days, because there was no more room for more gnats. - And then they were gone.

A couple of weeks later, more gnats came and I did the same thing.

Good luck.


    Bookmark   March 10, 2010 at 10:59AM
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Barbra, thanks for the laugh! In first reading your post, I thought, WOW gnats get "red" potatoes instead of the regular potatoes (don't know about in TX, but here in CA red potatoes cost more). Then, when you wrote that they sprouted, what a kicker! Just plant your potatoes about 3" deep, and when the leaves come out of the soil about 3", add more soil. I read to do this about three or four times, which is called hilling. Good luck; it's also my first time planting potatoes.

    Bookmark   March 10, 2010 at 9:41PM
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Eloise, the cost of red vs white potatoes, run about the same here. I shop " Sun Harvest", Yesterday they were 2 Lbs for a $1, or a 5 lb bag for $2.99. My husband prefers the red, he said they are healthier for us, so that is what my plants got, I read . The article I read about the potatoes is attached:

by Dr. Richard Lindquist
Department of Entomology
The Ohio State University


Wondering what to do with those extra potatoes? Martha Stewart might have other suggestions, but we suggest using them to sample for fungus gnat larvae and other growing media-inhabiting creatures. This will help you know more about what is happening in your crops - which is what crop management is all about. Potato pieces pressed into the media are very useful for detecting fungus gnat larvae, and probably other potential pests such as bulb mites.

Fungus gnat larvae are especially harmful to plants in propagation beds, cuttings just after sticking, and seedlings - any plant with a limited root system. Fungus gnat adults are attracted to fresh potting media to lay their eggs. The larvae hatching from these eggs can be feeding on roots in a matter of days after potting plants. But that's not all. Recent research at Michigan State and Purdue Universities demonstrated the presence of fungus gnat larvae and bulb mites in some potting media before the presence of any plants. In other words, fungus gnat larvae could be waiting for plants to be added! Placing a cutting into media already infested with larvae is asking for trouble. Using the potato sampling method is useful as a kind of early warning system.

There are at least two ways to use this sampling method:

1. Cut potatoes into pieces about 1-inch thick (to prevent them from drying) and about 1-inch in diameter. Press the pieces slightly into the potting media surface and leave in place for 48-72 hours. Some cut the potato piece into a wedge, making it easier to push into the media. After the 48-72 hour period, lift the pieces and look for larvae, either on the potato piece or in the media where the potato was.

2. Cut the potato into "French fry" pieces and push them deeper into the media (1-2 inches), because fungus gnat larvae may be well below the surface.

The number of potato pieces to use in a sampling plan is a kind of educated guess at the moment. One suggested sampling plan is to use one potato piece per 100 square feet of bench area. You will need to use the number that can be examined within 48-72 hours of placing them in pots or flats. Much longer than that and the pieces either dry out or rot. It's not necessary to use potato pieces everywhere in the greenhouse, but only on those young plants on which fungus gnats are known to be problems. Should you give up the yellow traps for sampling adults? No. Yellow sticky traps should be used in addition to potatoes. The two methods together will give a pretty good picture of the fungus gnat situation.


    Bookmark   March 11, 2010 at 10:58AM
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I also read it in the Texas Agricu. article, they say about the same thing, I thought I was passing on good information, I tried it when I saw 2 fungua gnats in my greenhouse. I will also post their article(who knew it was so eazy to grow potatoes)



Bastiaan M. Drees
Professor and Extension Entomologist
The Texas Agricultural Extension Service
Texas A&M University System


The term, fungus gnat, applies to a number of species in the insect order Diptera, family Sciaridae (dark winged fungus gnat species Bradysia coprophila, impatiens and paupera). Fungus gnat adults are a nuisance to greenhouse operators, interiorscapers as well as consumers. The larval stages can damage healthy roots, stunting or killing young plants even where there is no fungal food source (Lindquist 1994). Prolonged infestations may cause stunted, off-colored plants or foliage (Cole 1985). Damage may actually be more severe to young plants when the potting media or soil has been sterilized. Fungus gnat larvae may also aid in the introduction and spread of plant diseases such as Pythium, Verticillium, Cylindrocladium, Scelerotinia and Theila-viopsis.

Description. Adult fungus gnats are small (1/8 inch long), fragile grayish to black flies with long, slender legs and thread-like antennae. Their wings are clear or smokey-colored with no pattern and few distinct veins. Larvae are clear to creamy-white and can grow to about 1/4 inch long. They have shiny black head capsules (Fig. 1).

Biology. Fungus gnats develop through complete metamorphosis: egg; larva; pupa; and adult. Development occurs in 2 to 4 weeks. Larvae feed primarily on fungi, decaying organic matter and plant roots, particularly in very moist enviro nments. Larval and pupal stages can also, however, survive periods of drought. Fungus gnats normally follow a predictable cycle of population development: The first two generations are the largest, followed by a leveling off or decline in numbers.

Continuous production (ie. adding new plants in fresh growing media) may keep fungus gnat numbers high, because the insects will keep moving to the potting mix containing the fresh media (Lindquist 1994).

Monitoring methods. Yellow sticky cards and potato pieces placed on potting media are good methods for monitoring adult and larval populations, respectively.

Yellow stick cards are most effective when place horizontally on the potting media surface, although vertically positioned cards hung over the crop canopy are also effective and trap more of other types of insect pests as well. Cards placed under the benches, close to intake vents, near doorways and outside the greenhouse can provide additional information to detect breeding areas. Continuous monitoring (weekly) can provide the following information: 1) first detection of low populations; 2) population density increases or decreases over time; 3) the level and length of suppression resulting from the implementation of suppression tactics.

Potato slices (roughly 1 by 1 by 1/4 to 1/2 inch pieces) placed on the surface of potting media are attractive to larval stages of fungus gnats. The potato slices should be left in place for about 4 hours before counting the number of larvae on and under the slices (Lindquist 1994). Results of this monitoring effort can be used to: 1) detect areas where larvae are developing; and 2) document the reduction of larval population densities after the implementation of suppression tactics by comparing results from before ant after treatment.

Management. There are no "economic threshold levels" established for managing this pest (Lindquist 1994). Thus, the decision to suppress populations is largely subjective, although regulatory or marketing forces may play an important role in the decision-making process.Fungus gnat control can be an important part of managing some plant diseases.

Integrated pest management of fungus gnats is best when a combination of non-chemical (cultural) methods are used with biological and/or chemical methods. Table 1 provides an inventory of considerations and options which can be incorporated into a fungus gnat management program. Cultural methods are largely preventive and must be maintained throughout the production cycle. Biological methods must be implemented early, when fungus gnat population levels are still low. Insect growth regulator products applied to the potting media are more compatible with biological control. However, once a severe problem has developed, an insecticide program using a combination of treatments for adult as well as larvae fungus gnat control may be necessary.

Literature cited

Cole, C. L. 1985. Fungus Gnats, L-2041. Texas Agricultural Extension Service, Texas A&M University System, College Station, Texas.

Drees, B. M. 1992. Pest Management Alternatives for Commercial Orna-mental Plants. Texas Association of Nurserymen. Austin, Texas. 140 pp.

Lindquist, R. K. 1994. Integrated man- agement of

    Bookmark   March 11, 2010 at 11:46AM
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