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How to Manage Pests
UC Pest Management Guidelines
Apple
Webspinning
Spider Mites
Scientific Names:
Twospotted spider mite: Tetranychus urticae
Pacific spider mite: Tetranychus pacificus
McDaniel spider mite: Tetranychus mcdanieli
(Reviewed 8/06,
updated 8/06)
In this Guideline:
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Adult female mites are larger and more elongated than European red
mites and are green to yellow. Feeding mites have a dark spot on either side of
the body that may enlarge to cover most of the body. Overwintering females are
orange and hibernate under bark scales on the tree and in trash on the ground.
They move up the tree in late March and April, feeding on leaves. Rapid
reproduction occurs in hot, dry weather and the infestation peaks in July and
August. The tiny, spherical, colorless to straw-colored eggs are
distributed over the infested area.
Mites feed upon
leaves,
removing the cell contents and gradually giving leaves a finely stippled
appearance. Heavy infestations result in severe bronzing of foliage and
premature defoliation. Fruits on heavily infested trees fail to color and size
properly, and fruit production for the following year may be lowered.
Webspinning spider mites are typically most abundant during the hot
summer months, especially in dusty and water-stressed areas of the orchard.
Natural enemies keep spider mites below damaging levels in many orchards.
Monitor for mites and their natural enemies from June through August to
determine the need for treatment.
Resistant Varieties
Varieties such as Red Delicious, Golden Delicious, Rome Beauty, and
Jonathan are more susceptible to mite injury, while Gravenstein and Yellow
Newtown show less evidence of leaf damage from moderate populations.
Biological Control
The western predator
mite,
Galendromus (=Metaseiulus) occidentalis, is an excellent
predator of webspinning mites. Predator mites have been developed that are
resistant to carbaryl and most organophosphates used in apples. One predator to
10 webspinning mites is necessary for the predators to keep control of the pest
mites. Use lower rates of miticides to minimize destruction of predators and
allow some spider mites to survive. The apple rust mite is an alternative food
source for the predator mite. Avoid sprays containing lime sulfur, which will
kill rust mites. When alternative food sources are allowed to survive, the
predaceous mites can build up large enough numbers to control webspinning mite
populations.
Cultural
Control
Grass cover crops and sprinkler irrigation help to
minimize dust in orchards. Provide adequate irrigation to avoid water stress.
Do not mow the cover crop too short or let it dry, or the mites may move up
into the trees.
Organically Acceptable
Methods
Biological and cultural control and the use of resistant varieties are
organically acceptable methods.
Monitoring
and Treatment Decisions
From July to August, or if you encounter high mite populations earlier
in the season, collect five spur leaves at spaced intervals from one lateral
branch located at eye level from each of 20 marked trees that have been
established as representative trees in a block. Brush leaves in a mite-brushing
machine and count mites but not eggs. Sample every 1 to 3 weeks. Treat when
mite populations reach an average of 10 mites per leaf. Count predatory mites along
with webspinning mites. If you find one predatory mite per 10 mites, you may
not need a miticide application but continue sampling to be sure pest mite
populations do not increase. If treatment is required choose materials least
disruptive of biological control.
| Common name |
Amount to Use |
P.H.I.+ |
| (trade name) |
(conc.) |
(dilute) |
(days) |
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| When choosing a
pesticide, consider information relating to the impact
on natural enemies and honey bees and
environmental impact.
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| A. |
ABAMECTIN* |
| |
(Agri-Mek) 0.15EC |
10–20 oz |
2.5–5 oz |
28 |
| |
MODE OF ACTION: An
avermectin (Group 6)1 insecticide.
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COMMENTS:
Narrow-spectrum preventive material that can be applied early in the season
(from petal fall to 6 weeks later) when mite outbreaks are anticipated. Use with a horticultural spray oil. |
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| B. |
CLOFENTEZINE |
| |
(Apollo) 50SC |
4–8 oz |
1–2 oz |
45 |
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MODE OF ACTION: A
tetrazine (Group 10A)1 miticide.
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COMMENTS: For early and mid-season mite control; easy on natural enemies. |
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| C. |
FENBUTATIN-OXIDE* |
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(Vendex) 50WP |
1–2 lb |
4–8 oz |
14 |
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MODE OF ACTION: Unknown. An organotin miticide. |
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COMMENTS:
This material appears to be most effective when applied earlier in the season
rather than later. Do not apply more than twice a season in not more than 400 gal water/acre. Do not apply more than 4 lb/acre/year. |
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| D. |
PYRIDABEN |
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(Nexter) |
5.2 oz |
3.3 oz |
25 |
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MODE OF ACTION: A pyridazinone (Group 21)1
miticide.
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COMMENTS:
Can be used later in the season than preceding materials and is easier on
beneficials than dicofol. Do not use less than 100 gal water/acre spray volume. Most effective with use of a silicone spreader. |
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| E. |
ETOXAZOLE |
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(Zeal) |
2-3 oz |
0.5-0.75 oz |
28 |
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MODE OF ACTION: A mite
growth inhibitor (Group 10C)1 miticide.
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COMMENTS: Preliminary
research indicates it has an effect on the reproductive capacity of predatory mites. Most effective with use of a silicon spreader. |
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| F. |
BIFENAZATE |
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(Acramite) 50WS |
1 lb |
0.25 lb |
7 |
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MODE OF ACTION: A
carboxylic acid ester (Group 25)1 miticide.
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COMMENTS: Only one application/crop/year. Most effective with use of a silicon spreader. |
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| G. |
DICOFOL |
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(Kelthane) |
Label rates |
7 |
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MODE OF ACTION: A
Group 201 miticide.
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COMMENTS:
For use on late-season mite outbreaks. This material is harsh on beneficials so its use is best late in the season when necessary. |
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UC IPM Pest Management Guidelines: Apple
UC ANR Publication 3432
Insects and Mites
J. L. Caprile, UC Cooperative Extension, Contra Costa County
L. R. Wunderlich, UC Cooperative Extension, El Dorado County
P. M. Vossen, UC Cooperative Extension, Sonoma and Marin counties
W. W. Coates, UC Cooperative Extension, San Benito County
H. L. Andris, UC Cooperative Extension, Fresno County
L. G. Varela, UC IPM Program, Sonoma County
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to the insects and mites section:
C. Pickel, UC IPM Program, Sutter and Yuba counties
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