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How to Manage Pests

UC Pest Management Guidelines


Adult twospotted spider mite, Tetranychus urticae.

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 3/09)

In this Guideline:


DESCRIPTION OF THE PESTS

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.

DAMAGE

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.

MANAGEMENT

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 predatory 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** R.E.I.+ P.H.I.+
(trade name) (conc.) (dilute) (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. ABAMECTIN*
  (Agri-Mek) 0.15EC 10–20 oz 2.5–5 oz 12 28
  MODE OF ACTION GROUP NUMBER1: 6
  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.
   
B. CLOFENTEZINE      
  (Apollo) 50SC 4–8 oz 1–2 oz 12 45
  MODE OF ACTION GROUP NUMBER1: 10A
  COMMENTS: For early and mid-season mite control; easy on natural enemies.
   
C. FENBUTATIN-OXIDE*      
  (Vendex) 50WP 1–2 lb 4–8 oz 48 14
  MODE OF ACTION GROUP NUMBER1: 12B
  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.
         
D. PYRIDABEN
  (Nexter) 5.2 oz 3.3 oz 12 25
  MODE OF ACTION GROUP NUMBER1: 21
  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.
         
E. ETOXAZOLE
  (Zeal) 2–3 oz 0.5–0.75 oz 12 28
  MODE OF ACTION GROUP NUMBER1: 10B
  COMMENTS: Preliminary research indicates it has an effect on the reproductive capacity of predatory mites. Most effective with use of a silicon spreader.
   
F. BIFENAZATE      
  (Acramite) 50WS 1 lb 0.25 lb 12 7
  MODE OF ACTION GROUP NUMBER1: 25
  COMMENTS: Only one application/crop/year. Most effective with use of a silicon spreader.
         
G. DICOFOL
  (Kelthane) Label rates 48 7
  MODE OF ACTION: UNC
  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.
   
** For dilute application, rate is per 100 gal water to be applied in 300–500 gal water/acre, according to label; for concentrate applications, use 80–100 gal water/acre or lower if the label allows.
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals with a different mode-of-action Group number, and do not use products with the same mode-of-action Group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a Group number of 1B; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

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 Insects and Mites:
C. Pickel, UC IPM Program, Sutter and Yuba counties

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