Aphids feed off of plants' juices by biting and sucking the plant stems and foliage. These critters may be small and almost unnoticeable, but they can weaken and kill greenhouse plants if not treated right away. Seal off your greenhouse to prevent new infestations, then treat the plants to eradicate this pest before it ruins your harvest.
Remove all weeds that are bordering the outside of the greenhouse in a 5- to 10-foot swath. Maintain a weed-free environment inside the greenhouse.
Seal all openings in the greenhouse to minimize the amount of aphids entering the area. Block out aphids' access to the greenhouse with a netting material that has a minimum mesh size of 434 mm, according to the Ontario Ministry of Agriculture. Cover all vents, windows and pipe entrances.
Release biological controls such as Aphidius spp parasitic wasp, Harmonia axyridis and Hippodamia convergens ladybeetle species into the greenhouse to naturally eradicate aphids. These insects can be obtained from many garden stores and nurseries.
Treat the greenhouse plants with chemical controls for faster removal. Spray the plants with a standard garden insecticidal soap if the infestation is light. Mist all exposed surfaces of the plant to smother aphids upon contact. Spray with a commercial garden insecticide formulated with kinoprene or pirimicarb and labeled for use against aphids if the infestation is heavy. Follow the product application guidelines for dosage, since toxicity varies by product.