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:
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!).
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.