July 2020 - 14

dr. bugs
BY RAYMOND A. CLOYD
Revisiting Broad Mite
Question: Broad mites seem to be more of a problem and are very difficult
to control. What are your recommendations for managing this pest?
Answer: Yes, I would agree that broad
mites are becoming more of an issue
feeding on many greenhousegrown
horticultural crops
(ornamental and vegetable)
including: begonia, browallia,
chrysanthemum, cucumber,
dahlia, eggplant, English ivy,
fuchsia, impatiens, New Guinea
impatiens, pepper, salvia,
snapdragon, strawberry, tomato,
torenia and transvaal daisy.
First of all, what are
Raymond A. Cloyd
is professor and
Extension specialist
in horticultural
entomology/
plant protection
at Kansas State
University. He
can be reached at
rcloyd@ksu.edu.
broad mites? Broad mite
(Polyphagotarsonemus latus)
is a tarsonemid mite very
closely related to and similar
in appearance to the cyclamen mite
(Phytonemus pallidus). Adult broad mites
are about 0.25 mm (0.0098 inches) long,
oval-shaped, shiny and light yellow to
amber (Figure 1). The hind legs appear
whip-like. Broad mite has four life stages
including: egg, larva, nymph and adult.
Females can lay up to 40 eggs during
their two-week life span, although
the number of eggs laid depends on
temperature and relative humidity.
Unmated females produce only males,
whereas mated females produce females.
Eggs are oval, white and covered with
bumps (Figure 2). Six-legged larvae emerge
(eclose) from eggs, transition into egglegged
nymphs, and then become adults.
Development from egg to adult takes five to
six days at 70 to 80° F and seven to 10 days
at 50 to 65° F.
Broad mite populations can spread within
greenhouses by means of air currents,
especially those created by horizontal
air-flow fans, leaves of adjacent plants
touching, and workers (employees)
handling infested plants and then touching
noninfested plants.
Broad mites tend to aggregate in groups,
feeding primarily on leaf undersides and
flowers where females lay eggs. They feed
on plant cells within the leaf epidermis
using their piercing-sucking mouthparts.
While feeding, broad mites inject a toxic
salvia that causes twisted, hardened and
distorted terminal plant growth.
Additional symptoms include: leaf
bronzing, leaf margins curling downward
and becoming brittle, and puckered and
shriveled growth. Extensive populations
of broad mites will lead to individuals
migrating and feeding on the upper leaf
surface, which can result in severe leaf
distortion. Broad mite feeding damages
the meristematic plant tissues associated
with the growing tip or apical shoot, which
inhibits growth; decreases leaf number, leaf
size and area; and reduces plant height. In
addition, leaves may appear " roughened "
and darker green than normal (Figure 3).
Broad mite damage to salvia is shown in
Figure 4.
Broad mite damage resembles nutritional
deficiencies, herbicide damage, watering
problems, or improper environmental
conditions (e.g., temperature and relative
humidity). Therefore, to correctly identify
a broad mite problem, it is important to
verify using a dissecting microscope.
Broad mite management involves
disposing of all plants confirmed to be
infested with broad mites. In addition
to discarding plants exhibiting damage
symptoms, remove plants adjacent to
infested plants, even if they are not
COMMON NAME
(TRADE NAME)
ACTIVITY TYPE
Abamectin (Avid)
Contact and translaminar
Bifenazate + Abamectin (Sirocco) Contact and translaminar
Chlorfenapyr (Pylon)
Fenpyroximate (Akari)
Pyridaben (Sanmite)
Spiromesifen (Savate)
Spirotetramat (Kontos)
Contact and translaminar
Contact
Contact
Contact and translaminar
Contact and translaminar
Table 1. Common name (trade name) and activity type associated
with pesticides registered for use against broad mite
(Polyphagotarsonemus latus).
14 JULY 2020 GPNMAG.COM
Figure 1. Close-up of broad mite adult
Photo courtesy of Raymond Cloyd, KSU
http://www.GPNMAG.COM
July 2020

Table of Contents for the Digital Edition of July 2020
