Greenhouse - Insect Management

Insects can easily build up in greenhouses due to the perfect growth environment. The following are some thoughts on managing insects in greenhouse production.

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 1 gallon ziplock bag half full with moist soil. If fungus gnat adults emerge within 2 weeks, consider applying a fungus gnat treatment at planting time. Check incoming plant material carefully for insects.

Scouting

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 sq ft. Check the first plants that flower for thrips. For spider mites and aphids, check susceptible plants like marigolds (mites) and peppers (aphids), weekly. Potato wedges can be stuck in soil and checked 24 hours later for fungus gnat larvae. Systemic insecticidesUse 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.

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, Conserve, Mesurol, Orthene 97, Safari, Sanmite, Tristar.
Aphids - Aria, BotaniGard, Decathlon, Discus, Endeavor, Flagship, Marathon, Orthene 97, Precision, Safari, Talstar, Tristar.
Whiteflies - Azatin, BotaniGard, Decathlon, Distance, Endeavor, Enstar, Flagship, Marathon, Ornazin, Orthene 97, Precision, Safari, Sanmite, Talus, Judo, Tame, Tristar (Note: Q biotype may be resistant to Marathon, Flagship, Tristar, Safari, Distance and Talus).
Mites - Akari, Avid, Floramite, Hexygon, Judo, Ovation, Pylon, Sanmite, Shuttle, Tetrasan, Ultiflora.
Broad mites - Avid, Akari, Judo, Pylon, SanMite.
Fungus gnat (drenches) - Azatin XL, Adept (not on poinsettias), Distance, Marathon (perhaps other nicotinoids; not yet tested), Mesurol.
Mealybugs/ Soft scales - Aria, Flagship, Orthene, Safari, Talus and Tristar.

From the article "Greenhouse insect management" by Dave Smitley, MSU Entomologist, in the January 19, 2007 edition of the Greenhouse Alert newsletter from Michigan State University Extension