This week broad mites were observed on begonia. Broad mites (Polyphagotarsonemus latus) can be a serious pest of a wide range of greenhouse ornamental plants including: begonia, New Guinea impatiens, dahlia, fuchsia, gerbera daisy, English ivy, lysimachia, salvia, snapdragon, verbena, vegetative petunia, peppers, thunbergia, torenia, African violet, cyclamen, and gloxinia. Broad mites are extremely small and nearly impossible to see. Adults are approximately 0.25mm (0.0009 inch) long, shiny, amber to dark green and oval. Eggs are oval, white and covered with bumps. You can possibly see the mites using a high magnification lens (20-30X) with good lighting. UMass Extension's Plant Diagnostic Lab can provide help to determine if you have broad mites.
Broad mites have piercing mouthparts and feed on the underside of young leaves and flower buds, causing leaf margins to curl downwards and preventing flowers from fully developing. They inject a phytotoxin as they feed which causes twisted, hardened and distorted growth on the plant terminals, and bronzed rough undersides of leaves. Severely infested plants become stunted and may eventually die.
Broad mites can be dispersed within a greenhouse by workers or equipment or by movement of infested plant material into the greenhouse. The best way to detect infestation is to inspect crops regularly for broad mite feeding damage. Before pursuing treatment for broad mites make sure you have accurate diagnosis. If characteristic symptoms are seen, send samples to the diagnostic laboratory where they can be inspected under a microscope.
Weekly releases of predatory mites Amblyseius cucumeris are used successfully to suppress broad mites on greenhouse crops. It is important to apply the predatory mites early in the crop production cycle before broad mites become established. Broad mites are also easily controlled using selective miticides. Not all miticides labeled for spider mites are labeled for broad mites. Translaminar miticides such as Avid (or generic Abamectin), Savate (Spiromesifen) and Pylon (Chlorfenapyr) are more effective than contact miticides. Be sure to follow label precautions for crop safety. For example, the Savate label recommends not spraying impatiens species including New Guinea impatiens.
For more information on miticides labeled for control of broad mites on greenhouse crops, refer to the latest edition of the New England Greenhouse Floriculture Guide.
Photo of Broad Mite Damage on Dahlia: http://ag.umass.edu/greenhouse-floriculture/greenhouse-updates/photos?co...
Watch for Broad Mite in Spring Crops: Dan Gilrein, Cornell Extension - https://e-gro.org/pdf/2017_605.pdf
It’s the B Season – Watch for Broad Mites: Sarah Jandricic, Greenhouse Floriculture IPM Specialist, OMAFRA - https://onfloriculture.wordpress.com/2018/04/05/its-b-season-watch-for-b...
Geoffrey Njue, UMass Extension