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. Read on for tips on monitoring and control.

Monitoring:

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, so susceptible crops should be walked and inspected regularly.  Damage can occur at very low mite densities, and looks like this:

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:

Is it broad mite? Or something else?

if damage from broad mite is suspected, it’s important to confirm the diagnosis by actually seeing the mites using a microscope (or having them confirmed by myself or an experienced scout), since broad mite damage can easily be confused with things like:

• Herbicide injury
• Nutritional (boron) deficiencies
• Physiological disorders (for example, under cooler temperatures and high humidity,  leaf curling can be seen on New Guinea impatiens).

You may not see the adult mites themselves, but spotting even 1 egg (see picture below), along with characteristic damage, is usually enough to confirm that broadmite is the culprit.

However, if you grow a lot of susceptible crops (refer to this list of “magnet” crops), or you’ve regularly had broad mite issues in the past, you may want to consider a more rigorous monitoring regime specific to this pest.  This involves taking random samples of meristems, washing them in alcohol, and inspecting the contents under a microscope on a regular basis.  Details of this technique can be found here.

I’ve confirmed broad mite: Now what?

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 details on biocontrol of broad mites, take a look at these articles from Michigan State Extension and Dr. Rose Buitenhuis (Vineland Research)

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.