One of the keys to a successful scouting program is being able
to accurately identify the pests and diseases you come in contact with. The
following is a review of the most prevalent greenhouse mites.
Two-spotted Spider Mite (Tetranychus urticae):
style='font-weight:normal'> The two-spotted spider mite is the most commonly
encountered greenhouse mite. Less than a millimeter in size, the two-spotted
spider mite normally has two distinct spots on each side of the body beginning
at the forward part of the body and ending just beyond half of the body length.
The larval stage has six legs, whereas adults have eight. Spider mites can
attack virtually every ornamental crop, including most species of foliage
Indications of mite damage include a stippling or mottling,
yellowing or bronzing of foliage causing early leaf drop. Where severe infestations
exist, plants may be covered with the characteristic webbing produced by these
mites, thus the term spider mite.
Spider mite infestations occur most often during hot, dry
conditions and develop faster on water-stressed plants. Infested plants should
be marked and re-inspected with a hand lens several days after treatment to
Two-spotted spider mites commonly migrate via wind and plant
material. Weeds can serve as an alternative food source and should be
eradicated. Should any of these conditions exist near your greenhouses,
appropriate measures should be taken to prevent and/or eliminate them.
Cyclamen Mite (Steneotarsonemus pallidus):
style='font-weight:normal'> This tiny mite hides in protected locations on the
host plant, usually buds and flowers. They are serious pests of a number of
flowering and foliage plants, including cyclamen, African violet, ivy,
snapdragon, chrysanthemum, begonia and fittonia. The petals of infested buds
often become so curled and distorted that plants are unmarketable.
The injury they cause can resemble thrips feeding damage,
phytotoxicity or physiological disorders.
To avoid inappropriate control actions, plants that display
curled, distorted leaves should be carefully examined, using a hand lens, for
the presence of cyclamen mites.
Lewis Mite (Eotetranychus lewisi):
style='font-weight:normal'> The Lewis mite is a slender, tiny, straw or
greenish-colored mite with several small spots along each side of the body and
is smaller than the two-spotted spider mite. Like the two-spotted spider mite,
it infests greenhouses and is particularly injurious to poinsettias. Lewis mite
feeding causes leaf stippling and yellowing. Upper leaf surfaces usually
display a mottled or speckled appearance. These mites also produce visible
webbing, which can completely cover the poinsettia’s flowers and leaves.
Infestations must be detected and treated before leaves begin dropping off the
European Red Mite (Panonychus ulm):
style='font-weight:normal'> The European red mite is brownish-red and
elliptical in shape with four rows of spines that run down its back. It is
about one-eighth the size of a pinhead. It attacks deciduous shade trees and
fruit trees, as well as shrubs, resulting in leaf drop.
European red mites winter as bright red eggs laid in
clusters on twigs and branches of small trees. Frequently the twig crevices and
scars seem to be covered with red brick dust. They develop from newly hatched
nymph to adult in approximately 20 days at 55° F and sometimes as quickly
as four days at 77° F.
Southern Red Mite (Oligonychus ilicis):
style='font-weight:normal'> Southern red mites are typically found on
outdoor-grown woody ornamentals such as azalea, camellia and Japanese Holly.
This mite species is most active in cool weather, with the most serious
infestations usually occurring in fall and spring. The Southern red mite reproduces
rapidly then becomes almost inactive in winter and summer. Generally, summer
populations are controlled predaceous insects and mites.
The female adult has a dark reddish or brown abdomen,
pinkish or red cephalothorax and a pale mid-stripe. The male resembles the
female but is smaller in size, usually darker in color and lacks the pink or
Spruce Spider Mite (Oligonychus ununguis):
style='font-weight:normal'> Spruce spider mites are tiny and almost impossible
to detect with the naked eye. When young, they are yellow-green, turning
grayish-black at maturity. They reproduce rapidly with eggs that are
reddish-brown. Spruce spider mites feed on many conifers, including: spruce,
pine, cedar and yew. Indications of mite damage include yellow stippling,
yellow foliage and dieback. Spruce spider mites are most active in the cool
weather of spring and fall, with greatest damage occurring from March to June.
Spraying is recommended when 10 or more mites can be tapped from the branch and
no beneficials are found.
Each week, the grower and scout should review the scouting
information gathered from plant inspections and data from indicator plants.
This data will help prioritize a strategy. Looking at trends over a period of
time will help you decide if controls are needed.
When control of a pest population is necessary, there are
many control activities available. The specific method selected should be based
on the type of pest causing the problem and the severity of the loss if the
desired control is not achieved. Control methods fall into four basic groups:
• Cultural practices: in general, any activity that promotes plant health and vigor.
• Mechanical methods: crop management activities often performed by hand labor in greenhouse
• Biological controls: utilizing predators, parasites and pathogens to manage pest
• Chemical controls: when cultural and mechanical methods cannot provide the desired
Now that you know how to implement a scouting plan, it’s time to start scouting with help from this second article of a two-part series.