Agriculture: Apple Pest Management Guidelines

Webspinning Spider Mites

  • McDaniel spider mite: Tetranychus mcdanieli
  • Pacific spider mite: Tetranychus pacificus
  • Twospotted spider mite: Tetranychus urticae
  • Description of the Pest

    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 per acre** REI‡ PHI‡
    (Example trade name) (conc.) (dilute) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
     
    A. NARROW RANGE OIL 4 gal 1 gal 4 0
      MODE OF ACTION: Contact including smothering and barrier effects.
      . . . PLUS . . .
      ABAMECTIN*
      (Agri-Mek SC) Label rates 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. Certain abamectin formulations emit high amounts of volatile organic compounds (VOCs); use low VOC formulations of abamectin. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
     
    B BIFENAZATE
      (Acramite 50WS) 0.75–1 lb 12 7
      MODE-OF-ACTION GROUP NUMBER1: 20D
      COMMENTS: Harmless to predatory mites. Only one application per crop per year. Most effective with use of a silicon spreader.
     
    C. CLOFENTEZINE
      (Apollo SC) 4–8 oz 12 45
      MODE-OF-ACTION GROUP NUMBER1: 10A
      COMMENTS: For early and mid-season mite control; easy on natural enemies.
     
    D. PYRIDABEN
      (Nexter) 8.8–10.67 oz 3.3 oz 12 25
      MODE-OF-ACTION GROUP NUMBER1: 21A
      COMMENTS: Can be used later in the season than preceding materials. Do not use less than 100 gal water/acre spray volume. Most effective with use of a silicone spreader. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
     
    E. ETOXAZOLE
      (Zeal) 2–3 oz 12 14
      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. ACEQUINOCYL
      (Kanemite 15 SC) 21–31 fl oz 12 14
      MODE-OF-ACTION GROUP NUMBER1: 20B
      COMMENTS: Harmless to predatory mites.
     
    G SPIRODICLOFEN
      (Envidor 2 SC) 16–18 fl oz 12 7
      MODE-OF-ACTION GROUP NUMBER1: 23
      COMMENTS: Slightly harmful to predatory mites.
     
    H. HEXYTHIAZOX
      (Savey 50 DF) 3–6 oz 12 28
      (Onager) 12–24 oz 12 28
      MODE-OF-ACTION GROUP NUMBER1: 10A
      COMMENTS: Kills eggs. Need to apply early, before monitoring indicates a need; use in orchards where European red mite is a chronic pest. Apply only once per growing season.
     
    I. FENPYROXIMATE
      (FujiMite 5EC) 2 pt 12 14
      MODE-OF-ACTION GROUP NUMBER1: 21A
      COMMENTS: Harmful to predatory mites. Most effective with use of a silicone spreader.
    ** For dilute application, rate is per 100 gal water to be applied in 300 to 500 gal water/acre, according to label; for concentrate applications, use 80 to 100 gal water/acre or lower if the label allows.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 ("un"= unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.
    Text Updated: 03/09
    Treatment Table Updated: 10/15