Page 18 - Griffin Gazette Summer 2016

Broad Mites
Don’t let their size fool you!
By Rick Yates, GGSPro Technical Services Manager
Spring 2016 will be remembered for a
number of reasons, many weather related,
but broad mites (Polyphagotarsonemus latus)
certainly left their mark on this season as
well. Gerbera daisy and N.G. impatiens bore
the brunt of the damage, but GGSPro also
detected broad mites on begonia (Nonstop),
dahlia, ivy, impatiens (double, Sunpatiens),
fuchsia, peppers, salvia (farinacea), torenia Agrosciences Inc. Ronald stressed that curative treatments are not
and thunbergia.
Routine scouting usually doesn't detect broad mites. They often
avoid detection because of their microscopic size and ability to stay
out of sight. Broad mites are smaller than spider mites and are found
most often on tender young leaves in the growing tips. They also
feed on flower buds and have been found tucked in between the
petals of gerbera daisy blooms. The adults appear as various shades
of amber with larvae and nymphs appearing almost colorless. The
eggs have a unique geometric pattern on them that serves as a very
useful detection aide. They aren't that much smaller than the adults,
and the appearance of the eggs remains apparent for some time
even after the eggs hatch, making it easier to spot them.
While broad mites themselves may go undetected, the damage
they cause certainly does not. They inject a toxin as they feed which
causes dramatic symptoms to appear. (See Image 1) Damage
can vary widely from one type of plant to another which keeps
diagnosticians on their toes. Ivy geraniums with broad mites can be
easily missed as the primary symptom can be just very slow growth
and a lack of flowering. Most plants show more obvious symptoms.
Typically, the young leaves in the growing tip will start to lose their
normal shape. Leaves may become thickened, causing them to
become hard and brittle. The leaves and stems in the growing tip
darken over time. Twisting, cupping and curling also can occur,
making it easy to confuse broad mite feeding damage with other
problems such as herbicide damage, plant viruses, high soluble
salts and physiological disorders. (See Image 2) Broad mite flower
damage can even be confused with thrips damage on gerbera
daisies. (Check the Bonus Section of the Gazette for this and
other great pictures of broad mites and the damage they cause.)
This makes it imperative to positively identify the source of the
problem. GGSPro uses a microscope for identification, but a good
quality hand lens may be sufficient. If you don't have access to
this type of equipment, submit samples to a lab for assistance.
Damaged leaves won't recover even after the broad mites are
controlled, but if detected early enough the plants resume normal
growth and generally become saleable. Moderate damage might
be overcome by pinching out affected growing tips although
that adds to crop time. Advanced infestations usually result in
crop loss.
18 Griffin Gazette Summer 2016
Image 1: Gerbera Daisy- broad
mites causing hard, leathery growth.
Broad mites require live plant tissue to survive, making the removal of
all plant material including weeds between crops an important step
in assuring that they do not carry over from season to season. Broad
mites spread through air currents, when the leaves of adjacent plants
overlap and by hitching a ride by clinging to a whitefly1.
Biocontrol
There is conflicting information about the effectiveness of using
predator mites to control broad mites, so I reached out to Ronald
Valentin, Lead Entomologist and Bicontrol Expert at Bioline
going to be successful, although all of the Amblyseius mites will feed
on broad mites. Best success will be achieved when high numbers
of predator mites are present. An example would be the hundreds of
predator mites released over 4-6 weeks when utilizing mini-sachets
of A. cucumeris to control thrips on hanging baskets. During warm
summer time conditions A. swirskii can be expected to outperform
cucumeris, while A. andersoni is the best choice in cooler conditions
since it is active down to 43°F. Last but not least, A. californicus
shines under the low relative humidity conditions that hinders the
other Amblyseius mites.
Miticides
Not all miticides are effective against broad mites. Avid, Judo and
Pylon are examples of translaminar systemic miticides that have
good activity against broad mites. The translaminar activity is very
helpful in light of the reclusive nature of these tiny pests. Several crops
show sensitivity to Judo so please confirm plant safety with GGSPro
before making an application. Akari, Sanmite and horticultural oils
also control broad mites but are contact products requiring excellent
coverage which can be difficult to achieve with some crops. Drench
applications of Kontos also appear to be effective in controlling
broad mites. Control with Kontos drenches can take up to 3 weeks
and geraniums, dracaena and a handful of other crops cannot be
treated due to crop damage.
Always read and follow the entire pesticide label. Pesticides mentioned may not be
registered in all states and may be a RUP (Restricted Use Pesticide) in certain states.
Products other than those listed may be safe and effective.
1 Dr. Raymond A. Cloyd, Kansas State University, FloriBytes Newsletter, October 2010,
http://w w w.oardc.ohio-state.edu /floriculture /images /10-10_ Mites.pdf
(Image 2, Left): N.G. Impatiens- broad mite damage can resemble soluble
salts damage, (Image 3, Right) broad mite under a microscope. Photo credit:
Jim Willmott, U.S. Botanic Garden.