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SPIDER
MITES…AGAIN One of the most comprehensive
articles dealing with spider mites is one by Dr. Ray Cloyd of the To begin, most rosarians
already 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, nitrogen and amino acids out
of them causing the leaves to die and fall off the bush. 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 applying the intensive spray
program described by Dr. Cloyd 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 adult mites. 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). You may be wondering why there
are no systemic miticides. Systemic pesticides enter the bush through its roots
(when applied as a drench to the soil around the bush) or through it leaves
(when applied as a spray) and then move through the plant’s vascular system
via the phloem and xylem. The phloem cells are laid
out end-to-end throughout the entire plant, and serve to transport the sugars
and other molecules created by the plant and
systemic chemicals. The
xylem of a plant is the system of tubes and transport cells that circulates
water and dissolved minerals and
systemic chemicals. Unfortunately, however, spider mites generally feed near the
midrib and plant veins, and not in the phloem or xylem, so they never get into
the plant’s vascular system and, in turn, would avoid any systemic chemicals. Without access to
systemic miticides, rosarians are left with contact sprays, which stay on the
surface of the leaves only where they are sprayed, and translaminar sprays
(sometimes referred to as locally systemic), which are absorbed by the plant’s
leaves and move from one surface to the other. That is, if one sprays the tops
of a plant’s leaves, a translaminar spray will migrate to the leaves’
bottoms – clearly, translaminar sprays are the best for mites which feed on
the bottoms of leaves. As noted above, and in Dr. Cloyd’s article, Avid is a
translaminar miticide, but it only kills the adult mites. Avid can be
supplemented with Hexygon which kills both the mites’ eggs and larva, but
Hexygon is a contact spray so great care must be taken to spray the bottoms of
the leaves. Dr. Cloyd also mentions Floramite, and notes that it kills all the
mites’ life stages but, like Hexygon, it is a contact spray and is not
translaminar. Let’s examine some alternatives. 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
appearing on the Rose Society’s website (www.chattanoogarose.org),
and in articles appearing in past issues of Basal
Breaks. This is great because MOA 6 has little or no potential for the
development of resistance – an analogy (a derivative of Dr. Cloyd’s
“napalm” analogy) 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. 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 (www.southernag.com)
in Most rosarians already have
Avid in their pesticide arsenals, so what’s needed is a translaminar ovicide/larvacide
– and there is one: TetraSan 5 WDG produced by Valent U.S.A. Corporation. The
active ingredient in TetraSan is etoxazole, a juvenile growth inhibitor – this
puts it in MOA 5 of the simplified MOA schema mentioned above. The label for
TetraSan carries a CAUTION toxicity rating, and specifies the usage rate as 8
oz. to 16 oz. per 100 gallons – this equates to ½ to 1 teaspoon per gallon. I
tank mix Avid and TetraSan to produce a translaminar miticide that kills all
spider mite life stages. And, I can buy a pound of TetraSan from Rosemania for
$99 – it’s packaged in eight 2 oz. water soluble bags, and should create 100
to 200 gallons of spray. So, if you have some Avid, get some TetraSan, and you
can produce a spray that’s as effective as Forbid 4F for one-third the cost.
And, even if you don’t have Avid, you can get 8 oz. from Rosemania for $99.95,
and still beat the price of Forbid 4F by $100. Be sure to use an adjuvant
like Indicate 5 so that your spray completely covers the leaves (at least their
tops), and also be sure to Read the
Labels of all the chemicals you use. |