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Mites in Greenhouse Environments

There are a number of mite species that can be found in greenhouse environments. While most of these mites tend to be more of a problem during production, some of them can persist after plants are installed into the landscape. This is especially true of the twospotted spider mite. It is frequently found in greenhouses and infestation can continue in the landscape if conditions are favorable for mite development.

There are several other species of mites that can be encountered in greenhouse environments. The Lewis Mite (Eotetranyhcus lewisi) is a mite species that can be found on poinsettia and other plants. Adults look similar to twospotted spider mites but appear to have 4-6 spots. This species has recently become a problem for greenhouses frequently using imidacloprid products for whitefly control. Damage appears as stippling or bronzing on the edge of leaves and bracts of poinsettia.

The caramine spider mite (Tetranyhcus cinnabarinus) can be confused with red, diapausing forms of twospotted spider mite and some taxonomists argue they are the same species. However, in my experience these mites are slightly larger than twospotted spider mite and have a dark red color. The damage they cause is also slightly different. Some stippling is seen but damage frequently appears as yellowing and browning leaves. Damage can occur very quickly from this mite species, but I have not seen this in outdoor environments.

Unique Mite Feeding Injury

Most of the discussion in this article has described mite feeding injury as stippling, leaf yellowing, leaf drop, bronzing and gall formation. However, there are two species of spider mites that can be found in greenhouse environments that cause stunting of new growth, leaf cupping and leaf thickening. They include the broad mite (Polyphagotarsonemus latus) and the cyclamen mite (Steneotarsonemus pallidus). These two mite species belong to the family Tarsonemidae while many of the other aforementioned species belong to the family Tetranychidae. Host plant characteristics might help differentiate between these two species. They are often too small to see with the naked eye or a hand lens. You are more likely to encounter the damage and possible see some mite shed skins. Broad mites prefer hosts with leaves that contain very few hairs, while cyclamen mites prefer those with abundance of hairs. Broad mite is typically found on the undersides of leaves while cyclamate is found on the upper sides of leaves and in an around buds. Chemical control is difficult, and I would recommend using a translaminar material because these mites can exist deep inside buds.

There are even some mites that are specific to orchids. One mite that I encountered was the Phalaenopsis mite (Tenuipalpus pacificus). I have only encountered this mite one time in my career. Phalaenopsis orchids have thick fleshy foliage and stippling was not present. What I did observe was numerous shed skins causing the undersides of the leaves to appear white and pitting, sunken areas and necrosis caused by mite feeding. It was not the stippling type damage you would expect to see with Tetranychid mites. Both of these mites are in the family Tenuipalpidae, the false spider mites and do not produce webbing. The hosts included Phalaenopsis and Paphiopedlum.

Understanding the seasonal activity of mite species improves scouting efficiency and early detection of mite infestations. Proper identification of mite species will enable you to make proper selection of the correct miticide. There efficacy of a miticide may be dependent on the species of mite you are trying to control. Plant characteristics can often help in identifying the type of mite that is causing damage to your plants, but this approach is not replacement for lab identification by a specialist.

If you encounter something you have never seen before do not be afraid to send it to a specialist for identification. As always if you discover something new and different the IDNR, Division of Entomology and Plant Pathology would love to hear about it. Call 1-866-NO EXOTIC or email us at DEPP@dnr.in.gov.