The following are highlights and updates about samples and questions recently received in the Plant and Insect Diagnostic Clinic. Visit the PIDC's Facebook page to ask questions and for updates and more pictures. For more information on a particular disease or insect problem listed, follow the article cited.
Insects & Mites
Insect and mite samples are starting to pick up in the Clinic. It's that time of year, again. In the past few weeks we have received plants from greenhouses with several different mite and insect pests:
Twospotted spider mites (Tetranychus urticae) are a common pest in greenhouses and outdoors during the summer. These tiny mites leave webbing on leaves, and their feeding causes yellowing or bronzing stippling of leaves. Dry weather favors these mites as they are naturally kept under control by a fungus that prefers wet conditions. Plants outdoors may succeed without applied controls but treatment in greenhouses with biological controls or miticides is usually necessary.
We received a sample with broad mite symptoms. Broad mites (Polyphagotarsonemus latus) are really interesting because they can cause very strange symptoms on plants. Russetting of fruit and twisting of leaves are two common symptoms. Often the damage looks similar to that caused by a growth regulator herbicide (such as 2-4 D or Dicamba). Broad mites are extremely small and difficult to find even with the superb microscope in the PIDC. I usually can only confirm infestations by looking for the small translucent eggs. Image at the Ohio State University "Greenhouse Industry Roundtable of the Midwest.")
The last greenhouse pest insect we diagnosed was shore flies. Shore flies are common in greenhouses and thrive in very wet conditions where they live in association with algae. Adults flying around are a nuisance and they leave small fecal spots on the leaves of plants. More at Purdue Extension Pamphlet E-111-W.
Bed bugs continue to be a common sample! Remember to be cautious of used furniture and to check hotel rooms when traveling. Bed bugs are not commonly transported on humans, but they do get around on the things we carry with us such as backpacks, purses, and luggage. See ISU Extension & Outreach Pamphlet IPM 0073A.
Twospotted spider mites with webbing.
Broad mite damage to New Guinea Impatiens.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on April 6, 2017. The information contained within may not be the most current and accurate depending on when it is accessed.