We Have Color! and fungus gnats and whiteflies and aphids….


A few weeks ago, I reported on the poinsettias that the University of Rhode Island Master Gardeners are growing for sale in early December. Despite assaults from the above-mentioned (and common) greenhouse pests, the poinsettias are thriving. Many of the plants are showing bract color, and some are even boasting cyathia (the actual flowers).

The Master Gardeners employ integrated pest management (IPM) in the greenhouse, and for those of us who volunteer there, it’s always interesting and educational to see what’s being used each year. I like to imagine the ongoing war – on a very tiny scale – between the pests and the organisms we enlist to control them.

Here are the weapons in the IPM arsenal this season:

Gnatrol: this is a larvacide, added to water to control fungus gnats, which, like whiteflies, often occur whenever you water the plants from the top. The active ingredient in Gnatrol is Bacillus thuringiensis israelensis (Bti). To control adult gnats, we use sticky traps. A daily (and time-consuming!) fluffing of the soil in each pot also helps fight them.

fluffing, fluffing, always fluffing...

fluffing, fluffing, always fluffing...

Aphid Parasite Aphidius colemani: Aphidius colemani is a small parasitic wasp that lays its eggs in aphids. The eggs hatch inside and the larvae spin cocoons, which swell the aphid’s body. The adult wasps then exit the aphids’ bodies, leaving behind hard brown shells called “aphid mummies.”  Aphidius colemani is a very good flyer and is able to locate small colonies or even individual aphids! Gross, but effective.

Whitefly Parasite Encarsia Formosa: Encarsia formosa is a tiny wasp that attacks whiteflies. Adult female Encarsia kill whitefly scales in two ways: by puncturing and feeding on pupae, or laying their eggs in pupae (each female may produce 30-500 eggs during her lifespan). Encarsia eggs hatch into tiny larvae, which cause the whitefly pupae to turn black as the young wasps mature.

These wasps arrive on small cards, which are hung amid the plants throughout the greenhouse. The cards are replaced every couple of weeks. It’s cool to look at them through a magnifying glass, because you can see the wasps moving around.

Eretmocerus eremicus: another small wasp that parasitizes and host-feeds on silverleaf whitefly larvae. This is a valuable tool for controlling silverleaf whitefly, because it is more tolerant of higher temperatures and pesticide residues.

caution: parasitic wasps at work!

caution: parasitic wasps at work!

With less than two months to go before our big sale, the “points” are looking good, thanks to the efforts of Master Gardeners – and an army of tiny insects.


About dirtynailz

Writer for a daily newspaper, gardener, tree hugger, orchid-grower, photographer, animal lover, hiker, wilderness seeker. Proponent of clover in the lawn and a dog on the bed.
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3 Responses to We Have Color! and fungus gnats and whiteflies and aphids….

  1. shirley dobbins says:

    How would you recommend getting rid of fungus gnats..we you are their host? I seem to be hacthing them. Would the use of neem help?


    • dirtynailz says:

      I asked our poinsettia project manager about fungus gnats, and this is what she said:

      “Gnatrol is a drench we used this year but next year we will be using a better method called beneficial nematodes which is also a drench. Fungus gnats come from the moisture on top of the soil. A single application of beneficial nematodes is sufficient for preventing fungus gnat outbreaks or in the beginning phase of an outbreak. Adult fungus gnats will linger for several weeks after treatment as they gradually age and die off. The application should be repeated once if the first treatment was not effective. Larval numbers should decline rapidly over the week after treatment. Adult numbers will decline over a period of three weeks and are easily monitored on yellow sticky cards.

      The above is obviously being used in a greenhouse, not in a home environment, but I think a drench would be worth trying. Fluffing the soil around the plant is also helpful, and try not to allow the soil to become too wet. I have been told that watering your plants from the top can also encourage fungus gnats.

      I hope this is helpful. Good luck!


  2. Anisa Lene says:

    It’s hard to come by decent info on the web.


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