Greenhouse growers need to watch for aphids and two spotted spider mites

Scout begonias for aphids, and tropicals for spider mites. Take appropriate control measures if easily detected as warmer temperatures will increase pest numbers.

Visits to area greenhouses in recent days have indicated that after a few sunny days some insect and mite numbers have increased. Insect development is generally driven by temperatures and day time temperatures of 70°F or more in the greenhouse will speed up development of both aphids and spider mites.

Aphids have been observed on numerous types of begonias including wax begonias (Begonia x semperflorens) and Dragon wing type begonias. Also check peppers and dahlias from both cuttings and seed as these plants also seem to be favored by aphids. Look on the undersides of the leaves for small colonies of aphids. They will be either light green or melon colored.

Green peach aphids blend into the foliage well and you will often see signs of aphid activity before seeing the actual aphids. Green peach aphids are typically located on the terminal growth of plants.

Melon aphids tend to be located on the inside parts of a plant and congregate in groups on the stems and flower buds. Foxglove aphids are often found on the lower leaves and may drop off of the plant. Foxglove aphids also tend to cause more foliar distortion that the other types of aphids. Look for shed white skins, shiny honeydew, the presence of ants, curled new leaves, and distorted growth. The key is to find the hot spots early and treat with the proper insecticide. According to David Smitley, MSU Extension ornamentals entomologist, the best products for aphids include: Aria, Azatin, Benefit, BotaniGard, Decathlon, Discus, Distance, Endeavor, Enstar II, Flagship, Kontos, Marathon, Ornazin, Orthene 97, Precision, Safari, Tame, Talstar,and Tristar.

Left, aphids on Calibrachoa. Right, green peach aphid.
Left, aphids on Calibrachoa. Photo credit: Tina Smith, UMass. Right, green peach aphid. Photo credit: Whitney Cranshaw, Life Cycle.

Two spotted spider mites have been showing up on tropical type plants that growers are bringing up from the south as either prefinished or rooted liners. Since these items were grown in the south, they may have been exposed to conditions that favor more spider mite activity such as sunny, dry and warm weather which facilitate increased development of the mites. Spider mites cause severe chlorosis in attacked plants because the mites feed by “stabbing” cells with their piercing mouthparts and sucking up the juices that exude. Spider mites will remove chlorophyll from plant cells and reduce photosynthesis. Removal of chlorophyll produces the characteristic stippling or mottling of foliage and sometimes causes leaf drop. When populations of this pest are low, the mites prefer to attack the lower surface of leaves, but may move upward as populations increase. In severe infestations, the plants may be covered with the mites’ characteristic webbing, which is why they are referred to as spider mites. Water-stressed plants are particularly susceptible to spider mites.

To control mites, Smitley suggests the following products: Akari, Avid, Floramite, Hexygon, Judo, Kontos, Ovation, ProMite, Pylon, Sanmite, Shuttle-O, Suffoil-X (> 1% may be phytotoxic), Tetrasan, Kanemite.

Left, two spotted spider mites on Angelonia. Right, two spotted spider mite on Ipomoea "Blackie."
Left, two spotted spider mites on Angelonia. Photo credit: Leanne Pundt, UConn. Right, two spotted spider mite on Ipomoea “Blackie.” Photo credit: Leanne Pundt, UConn.

For further information on greenhouse issues contact either: Jeanne Himmelein (.(JavaScript must be enabled to view this email address)) or Tom Dudek (.(JavaScript must be enabled to view this email address)), your MSU greenhouse floriculture educators.

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