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A NEW DEFENSE AGAINST SPIDER MITES
by Roger Bryan

All rosarians know that the two-spotted spider mite (tetranychus urticae) is a serious rose garden pest. This nearly invisible insect works on the bottoms of leaves sucking the chlorophyll out of them. Spider mites can take a healthy bush to a leafless stick in a matter of days unless thwarted by constant vigilance of plant health and condition, and by an intensive spray program using Avid to kill the adult mites and Hexygon to kill the eggs and larva, or Floramite to kill all life stages. The aforementioned chemicals all work as contact or, at best, translaminar (i.e., Avid) sprays so special care must be taken to spray the undersides of the leaves – Avid, being translaminar, does penetrate the leaf structure and will move from the top surface to the bottom, but it only kills the adults. The life cycle of the spider mite – from egg to adult – is five to 20 days depending on factors such as temperature and humidity. If you don’t get all life stages when you spray, the mites will probably return, and they may have become resistant to the spray(s). But help is on the way!

Bayer Environmental Science has just announced the registration of a new miticide, based on a proprietary new chemistry with a unique mode of activity. The name of this new miticide is Forbid 4F, and its active ingredient is spiromesifin, a tetronic acid, which blocks fat synthesis so the mites dry out and die. This mode of activity, inhibiting lipid biosynthesis thus causing dessication (i.e., drying-out), is virtually the same as that of soaps and oils. That is, the MOA for Forbid 4F can be considered, for the sake of simplicity, to be MOA 6 as defined in papers elsewhere on this website, and in articles appearing in the Rose Society’s newsletter, Basal Breaks. This is great because MOA 6 has little or no potential for the development of resistance – an analogy[1] would be a flamethrower: you may miss some of your targets, but when they return they’ll be no less vulnerable to the flame.

Another feature of Forbid 4F is that, like Avid, it is translaminar. The active ingredient, spiromesifin, while not systemic (i.e., it does not move through the plant’s vascular system like, for example, Merit does), is absorbed by the plant’s leaves and will move from the tops of the leaves to the bottoms where the mites feed. This ability to move from the tops to bottoms of leaves significantly reduces the tedium of the spray process – while care should still be taken to cover the entire bush, rigorous spraying of the undersides of leaves should not be required. Moreover, according to Bayer, Forbid 4F controls mites at all life stages and offers an excellent residual of four to eight weeks for mites.

The label for Forbid 4F indicates its toxicity rating is CAUTION (be aware that the Avid label carries a WARNING designation). The label further specifies a usage rate of 2 to 4 fluid ounces per 100 gallons of spray. This equates to 1/8 to 1/4 teaspoon per gallon of spray – Bayer recommends, however, using the lower rate. Also, Forbid 4F may be tank mixed with sprayable fertilizers, insecticides and fungicides, although Bayer recommends a jar compatibility test. This product is available through Bayer distributors, such as Southern Ag ( http://www.southernag.com ) in Boone , NC . A very knowledgeable contact at Southern Ag is Mike Presnell (e-mail: sagrinsct@bellsouth.net ). It will also be marketed by OHP (Olympic Horticulture Products) under the name Judo. Lastly, it’s available in 8 oz. bottles which cost $224.20 from Southern Ag. The cost per gallon of spray is about the same as Floramite, but remember this product is translaminar – Floramite is not. And, this product has a longer residual effect.

REMEMBER: Read the Label!


[1] This analogy is a derivative of Dr. Ray Cloyd’s “napalm MOA.”