Two-spotted spider mite
Tetranychus urticae [Acari: Tetranychidae]
Adult female two-spotted spider mite(l) and juvenile two-spotted spider mites (r).
Diapause coloration on a female two-spotted spider mite (l) and adult two-spotted spider mite (l) and predatory mite (r).
Damage to rose leaf by spider mites.
Spider mites and their webbing.
DESCRIPTION OF THE PEST
Twospotted spider mite adults (TSSM), as the name suggests, have two large
dark spots on the sides of their yellowish green bodies.Twospotted spider
mites are important pests in many agricultural systems and are the most important
arthropod pest of fresh cut roses. Both immatures and adults feed by extracting
fluids from plant cells. All stages are typically found on leaf undersides.
Mite lifestages include egg, larva, protonymph, deutonymph and adult. The
larval, protonymphal and deutonymphal stages are further divided into feeding
and resting stages (the active stage precedes the resting stage). These are
nymphochrysalis (larvae), deutochrysalis (protonymph) and teliochrysalis (deutonymph).
Eggs are deposited on leaf undersides. They are spherical, clear and about
0.14 mm in diameter. The egg becomes opaque as it develops and two red eyespots
appear just before hatching. The larva has 3 pairs of legs, while the protonymph
and deutonymph have 4 pairs. Development time on rose from egg to adult is
8.3 days at 77-95∞F (night-day) and 28.2 days at 50-68∞F (night-day).
Two spotted spider mites have many generations per year and can rapidly increase
in number.
Additional photographs and information on mite biology can be found at http://www.ifas.ufl.edu/~apkweb/entomol/B853a2.htm and at http://www.ipm.ucdavis.edu.
DAMAGE
High numbers are usually associated with dry, dusty conditions. Spider mite numbers may greatly increase if their many natural enemies are killed by broad-spectrum insecticides applied for other pests. The removal of plant fluids caused by mite feeding results in leaf stippling; mite feeding also results in desiccation and disruption of photosynthesis. High mite levels can cause unsightly webbing.
MANAGEMENT
Mites are currently managed primarily by chemical control. Miticides used include Avid, Sanmite, Cinnamite and Pentac (no longer sold, but old supplies may be used).The dense canopy produced by the bent cane system can interfere with good pesticide coverage, thus hampering mite control. TSSM management is further complicated by resistance to Avid, the most commonly used miticide. Some growers use the mite predator Phytoseiulus persimilis.
SAMPLING METHOD
Current technique: Some growers spray for mites on a regular basis without
scouting. Most will walk through their ranges to look for mites or rely on
their employees to spot mites as they are working. Some growers have scouts
who regularly inspect all plants and keep records on mite location and severity.
Protocol for this program:
Walk through all rows starting at the beginning of the house and flag all
plants with mites above the hook (i.e. on the harvested portion of the plant).
Randomly select 20 plants/10,000 sq. ft. house and examine 2 leaves at the
crown area of each plant. A leaf is all leaflets on a petiole (there are usually
5 leaflets). Note on the scouting form if there are fewer than 5 mites/leaf
or 5 or more mites/leaf and if one lifestage predominates.
FORMULATING AN IPM STRATEGY
The need for TSSM management is based mite density and location of mites
on the plant.
If greater than 20% of plants have 5 or more mites per leaf, then release
Persimilis.
If greater than 50% of plants have 5 or more mites per leaf, then spray with
a compatible miticide and release Persimilis when dry.
If there are fewer than 10 plants with mites above the hook, cut out the infested
shoots.
If there are 10 or more plants with mites above the hook, spray with a compatible
miticide and release Persimilis when dry.
Western Flower Thrips -- aphids -- whiteflies -- powdery mildew -- two-spotted spider mites -- other pests
How to implement IPM in cut roses
Photographs on this page by J.K. Clark.
Feedback should be sent to piflaugher@ucdavis.edu