Lots and Lots of Lewis mites! (And how to go about controlling them in poinsettia).

lewis mite_UCANR

Lewis mite.  Photo from University of California.

You know how I just wrote a post on how you need to look out for unprecedented mealybug infestations in your crop this year?  Well I lied!  Now you need to look out for mealybug AND unusually high numbers of Lewis mites!

Read further for what consultants have been seeing out in the greenhouse and for effective control strategies.

Usually, Lewis mite is more of an occasional pest; it’s often just hit and miss which growers will end up with them.  However, 2016 is clearly trying to win an award for “The Year with the Most Widespread Lewis Mite Problem”.  So far this year, some consultants have been finding patches of them at almost EVERY grower they’ve visited. Outbreaks don’t seem confined to any one variety/colour, as in previous years.

Lewis mite, a species of spider mite, are exclusively a pest of poinsettia crops in the greenhouse (unless you’re also growing papaya or citrus in there.)  Early detection is difficult, since the symptoms are rather subtle at first: faint speckling and chlorosis (see picture below), which can resemble nitrogen deficiency. Additionally, the mite is almost impossible to see without a microscope.

Lewis mites poinsettia (1).jpg

Left: A new left just showing the characteristic stippling and chlorosis from Lewis mite feeding.  Right: Older leaves showing heaving Lewis mite damage.  Photo courtesy of Judy Colley, Plant Products.

Often, Lewis mite populations go undetected until mid-October,when populations build up enough to start causing noticeable damage: the upper foliage will turn brown and the mites will form unsightly webbing.

Webbing caused by a severe infestation of Lewis mite. Photo courtesy of Ohio State University.

Webbing caused by a severe infestation of Lewis mite. Photo courtesy of Ohio State University.

Given that they are difficult to detect, but end up causing a lot of damage, the easiest solution is a single,  preventative application of a miticide at the cutting stage.  (Something to keep in your back pocket for next year).

Since we are past that point now, but the canopy of the poinsettias is not yet filled in for 6 inch and 4 inch crops, the contact miticide Floramite appears to be be a good option. Floramite is relatively “soft” on bios (especially Eretmocerous), therefore it should have little impact on bio programs for Bemisia whitefly. 

 If you haven’t already treated for Lewis mite, walk your crop a little more often and look for the characteristic stippling symptoms.  If you find a spot on the bench, consider throwing out infested plants in the “Circle of Love”; i.e. throw out the centre infested plant and all those immediately surrounding it.  Or, simply do a spot spray of miticides.

As the season progresses (or with current 8-10 inch crops) control with contact insecticides like Floramite, Vendex and Shuttle will be much more difficult since the canopy is denser.  Many systemic miticides are effective (e.g.Avid, Kontos), but will likely interfere with whitefly biocontrol programs (being hard on parasitoids and predatory mites).   However, if you’re on a chemical program for Bemisia, this is the perfect time to apply Kontos to help control whitefly nymphs (see diagram below).

Grower Day 2016_Summary_Final

Estimated timeline to apply different control measures if you’re using an IPM-based program (top) vs. chemical only program. DO NOT APPLY DISTANCE AFTER BRACT FORMATION.  Diagram by S. Jandricic.

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This entry was posted in Lewis mite, Pest control strategies, pesticides, Poinsettia, Whitefly and tagged , , , . Bookmark the permalink.

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