Managing greenhouse insects

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.    

Starting clean

Do not carry-over insects from one crop to another. Keep thrips numbers down to less than 10 per card per week in the fall and winter on poinsettias and Dracaena. Avoid keeping houseplants or allowing weeds to grow in the greenhouse. When each batch of media arrives for a new crop, check it for fungus gnats by filling a one gallon zip-lock bag half-full with moist soil. If fungus gnat adults emerge within two weeks, consider applying a fungus gnat treatment at planting time. Check incoming plant material carefully. If insects are found, treat them with an appropriate product listed below to start with as clean a crop as possible.


Monitor thrips and whiteflies with yellow sticky cards. Change cards once per week. Use at least one card per house or one per 2,000 square feet. Check the first plants to flower for thrips. For spider mites and aphids, check susceptible plants like marigold (mites) and pepper (aphids), weekly. Potato wedges can be stuck in soil and checked 24 hours later for fungus gnat larvae. Systemic insecticides
Use Marathon, Tristar, Flagship, Safari, or Aria in poinsettia pots, lily pots, or in hanging baskets prone to problems with whiteflies, aphids, mealybugs or soft scales. Note: Aria does not work on silverleaf whitefly. Tristar and Safari also suppress thrips.

Preventing outbreaks

If yellow sticky cards or scouting indicates an increase in aphids, mites, thrips, fungus gnats or whiteflies, apply the following materials once per week until populations decrease to acceptable levels

Thrips: Avid, Mesurol, Orthene 97, Safari, Sanmite, Tristar, and Conserve. (Note: some thrips populations may be resistant to Conserve.)

Aphids: Aria, Azatin, BotaniGard, Celero, Decathlon, Discus, Distance, Endeavor, Enstar II, Flagship, Marathon, Ornazin, Orthene 97, Precision, Safari, Talstar, Tristar.

Whiteflies: Azatin, BotaniGard, Celero, Decathlon, Distance, Endeavor, Enstar, Flagship, Marathon, Ornazin, Orthene 97, Precision, Safari, Sanmite, Talus, Judo, Tame, Tristar (Note: many populations of silverleaf whitefly are resistant to Marathon, and some may also be resistant to Flagship, Tristar, Safari, Distance and Talus.)

Mites: Akari, Avid, Floramite, Hexygon, Judo, Ovation, ProMite, Pylon, Sanmite, Shuttle, Tetrasan.

Broad mites: Avid, Akari, Judo, Pylon, SanMite.

Fungus gnats: Azatin XL, Adept (not on poinsettias), Distance, Marathon, and (drenches) (perhaps other nicotinoids; not yet tested), Mesurol.

Mealybugs: Aria, Celero, Flagship, Orthene, Safari, Talus and Tristar.

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