How to Manage Pests
UC Pest Management Guidelines
Cherry
Webspinning Spider Mites
Scientific Names:
Pacific spider mite: Tetranychus pacificus
Twospotted spider mite: Tetranychus urticae
(Reviewed 4/06,
updated 4/06)
In this Guideline:
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These two spider mites have similar life histories and are
controlled in the same manner. Overwintering
female mites are red or orange colored and are found under rough bark, in ground litter, and
on winter weeds. Adult males do not overwinter and are smaller than females.
During the growing season their color ranges from yellow to green to black
depending on age and host food. Both species have dark spots on their bodies.
Eggs are
laid on the foliage. Immature mites molt three times. Early in the season mites are found in lower to central areas
of the tree. The mites reproduce rapidly during warm weather between June and
September. During favorable conditions, mites develop within 7 days with eight
to ten generations per season.
Mites damage foliage by sucking cell contents from leaves. The
damage begins with leaf stippling. Leaves can turn yellow and drop off. High
populations cover tree terminals with webbing.
Crop reduction shows up the year after damage occurs.
In many cases biological control keeps spider mites under control.
Miticides may be necessary in some orchards in summer, but only when mite
populations reach damaging levels, which often occurs after pesticides have
been used that disrupt natural enemies. Keeping cherry orchards well irrigated
during summer will help reduce the likelihood of mite outbreaks that are severe
enough to warrant treatment.
Biological Control
Several species play a large role in mite control, including the western
predatory mite (Galendromus [=Metaseiulus] occidentalis), sixspotted
thrips, spider mite
destroyer, brown
lacewing, and green lacewing. The western predatory mite is the most
reliable mite predator. It is the same size as spider mites, but lacks spots
and ranges in color from cream to amber red. This predator maintains good
control unless the proportion of leaves with spider mites is higher than the
proportion of leaves with predatory mites.
Cultural Control
Reduce dusty conditions in orchards by oiling or watering roadways and
maintaining a groundcover. Prevent water stress, as this condition results in
higher mite densities and intensified damage.
Organically
Acceptable Methods
Biological and cultural controls and oil sprays are acceptable for use
on an organically certified crop.
Monitoring and
Treatment Decisions
Regular monitoring will help determine if biological control is keeping
spider mites under control or if treatments are needed. Begin monitoring leaves
for mites in March. From March through May, monitor every other week; monitor
weekly from May through August. Check trees at random throughout the orchard,
and separately sample trees along dusty roads, areas of the orchard that are
stressed, and areas that have had mite problems in the past. Sample at least 15
leaves from each tree, taking leaves from inside the canopy on the lower part
of the tree. Record the number of leaves with pest mites and the number of
leaves with predators. If the number of leaves with predators is nearly the
same as the number with pest mites, no treatment is needed. Return in a week or
so and sample again. If the number of leaves with pest mites is increasing and
the number with predators is not, then treat. Presence of a large number of
mite eggs is an indication that the population is increasing.
Spot treatments may be
sufficient because heavy infestations usually start in dusty or stressed areas
of the orchard. Use materials that are least harmful to natural enemies. Spray
oils can be used as long as trees are not stressed, but oils are not effective
on mite infestations that have developed heavy webbing. Oil sprays reduce mite
populations about 50% in two weeks, so monitor mite numbers again two weeks
after treatment to see if an additional spray is needed.
If treatment is needed
early in the season and predators are present, you can use below-label rates of
a miticide to reduce the pest population and help preserve predators.
Treatments are not needed after the first of September; mite populations
decline naturally at this time.
| Common name |
Amount to Use** |
P.H.I.+ |
| (trade name) |
(conc.) |
(dilute) |
(days) |
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| The following
materials are listed in order of usefulness in an IPM program, taking into account
efficacy and impact on natural
enemies and honey bees.
When choosing a pesticide, also consider information relating to
environmental impact.
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| SPRING-SUMMER |
| A. |
PROPARGITE |
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(Omite) 30WP |
2 lb |
0.5 lb |
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MODE OF ACTION: An
organochlorine (Group 14)1 miticide.
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COMMENTS: For
postharvest use only. Do not apply less than 40 days after or 30 days before an oil application. |
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| B. |
CLOFENTEZINE |
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(Apollo SC) |
2–4 oz |
0.5–1 oz |
21 |
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MODE OF ACTION: A
tetrazine (Group 10A)1 miticide.
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COMMENTS: This
material is more effective in the early part of the year; apply after
sampling indicates pest mites are increasing but before significant damage or
webbing is present. Kills eggs and young larval stages. Good coverage is a
must; use a minimum of 50 gal water/acre for concentrate and a maximum of 400
gal water/acre for dilute. To delay development of resistance, use only once/season. |
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| C. |
FENBUTATIN-OXIDE* |
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(Vendex) 50WP |
1–2 lb |
0.25–0.5 lb |
14 |
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MODE OF ACTION: Unknown. An organotin miticide. |
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COMMENTS: Do not
apply more than 600 gal dilute spray/acre. Do not apply more than 2 sprays while fruit is on the trees. |
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| D. |
NARROW RANGE Oil# |
4–8 gal |
1.5–2 gal |
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MODE OF ACTION: Contact including smothering and barrier effects. |
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COMMENTS: Do not
apply within 30 days of a propargite application. Be sure that trees are not
water stressed or injury may result. Not all oils are organically acceptable; be sure to check individual products. |
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UC IPM Pest Management Guidelines: Cherry
UC ANR Publication 3440
Insects and Mites
R. A. Van Steenwyk, Insect Biology, UC Berkeley
K. M. Daane, Kearney Agricultural Center, Parlier
J. A. Grant, UC Cooperative Extension, San Joaquin County
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