Plant and Insect Diagnostic Clinic Update - April 6, 2017

News Article

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


Twospotted spider mites with webbing.


Broad mite damage to New Guinea Impatiens


Broad mite damage to New Guinea Impatiens.