Banishing Broad Mite – New post in Floriculture IPM Blog

I’ve been getting a lot of calls lately about Broad Mites (Polyphagotarsonemus latus) in crops like New Guinea impatiens, torenia, begonias, exacum, ipomea and gerbera.  Broad mite can also attack chrysanthemums, so it’s time to start thinking about  control of this pest as you’re sticking your new cuttings.

Damage can occur at very low mite densities, and looks like this:

Broad mite damage on terminals of torenia.  Leaves have started to turn downwards and are coppery coloured.
Broad mite damage on torenia. Mites feed on new growth. The mite’s toxic saliva results in copper or purplish-colored damage on growing points. Leaves often turn downwards. Also look for stunted plant growth.

 And this:

broad mite damage 023_SJ

Buds become discolored and malformed. Flowers are prevented from fully developing. Petioles and internodes become shortened.

Unfortunately, broad mite’s small size (0.2 mm) means that spotting the mite is near impossible with just a hand lens. Damage is usually the first sign.  If broad mite is suspected, samples should be checked under a microscope (or brought to your friendly, neighborhood OMAFRA agent!).

Adult and eggs of broad mite.  Eggs have a characterisic "speckled" appearance that is used for diagnosis.

Adult and eggs of broad mite. 

Correct diagnosis is important since broad mite damage can be confused with herbicide injury, nutritional (boron) deficiencies or physiological disorders. For example, under cooler temperatures and high humidity,  leaf curling can be seen on New Guinea impatiens.

Biological control is an effective option.  Neoseiulus cucumeris, N. californicus and A. swirskii can all suppress this pest.  Beneficial mites should be introduced early in the crop cycle of susceptible crops to prevent broad mites from establishing.  For more information on biocontrol of broad mites, see http://www.greenhousecanada.com

Miticides are another option. However, it’s often unclear which miticides are effective against mite pests besides spider mites.  For broad mite, here are the effective products *:

  • Avid (abamectin):   has translaminar activity, making it a good choice since it builds up a reservoir of active ingredient in the leaf.  But, Avid is also toxic to predatory mites, so avoid this product if you’re using a biocontrol program that relies on predatory mites (i.e. programs for thrips and spider mites).
  • Forbid (spiromesifen) is active against both eggs and adults of broad mite.  It has translaminar activity.  However, Forbid has demonstrated phytotoxicity on impatiens and geraniums, and should be avoided on these crops. It is not compatible with the spider mite predator P. persimilis.
* Several applications may be necessary, as all life stages are present at once, and mites are well protected within growing points.  Always check the product label to determine how often applications can be made. For broad mite it is also recommended to confirm kill by checking plant terminals under a microscope.  This is because the mite’s toxic saliva can cause damage to continue to appear on plants for some time after control is achieved.
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This entry was posted in broad mite, chrysanthemums, insect pests, Miticides, New guinea impatiens and tagged , , , , , , , , , , , , , . Bookmark the permalink.

One Response to Banishing Broad Mite – New post in Floriculture IPM Blog

  1. Pingback: Spring crops that are “magnets”for certain pests. | onfloriculture

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