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UC Pest Management Guidelines


Injury to Pinot Noir grape foliage caused by Willamette spider mite, Eotetranychus willamettei.

Grape

Webspinning Spider Mites

Scientific names:
Pacific spider mite: Tetranychus pacificus
Willamette spider mite: Eotetranychus willamettei
Twospotted spider mite: Tetranychus urticae

(Reviewed 6/06, updated 10/08)

In this Guideline:


DESCRIPTION OF THE PESTS

The Pacific spider mite is the primary pest mite species in the San Joaquin Valley and may also be the primary pest mite in certain North Coast grape-growing areas. Adult Pacific spider mite females vary from slightly amber to greenish in color. Later in the season as they go into diapause or under high population densities adult females can turn orange to reddish. Upon emergence adult Pacific spider mites are almost void of food spots. As feeding begins usually two large diffuse spots appear forward and two smaller spots appear on the rear portion of the abdomen. Pacific spider mite prefers the warmer upper canopy of the vine. Although it can cause damage early in the season, Pacific spider mite generally prefers the hotter, dryer part of the season. Because they are so similar in appearance, it is difficult to discern between the Pacific and Willamette spider mites unless they are side-by-side. The Pacific mite is larger in size than the Willamette mite. Pacific spider mite forelegs are reddish in color and those of Willamette spider mite are translucent to pale yellow.

The Willamette spider mite is pale yellow. It is often considered an early-season mite. It prefers the cooler parts of the plant and is found mostly in the shady parts of the vine. In certain areas (e.g., North Coast) and during certain years, populations can persist throughout the growing season. Willamette spider mite is primarily a problem in the Salinas Valley and Sierra foothill production areas where it can cause economic damage to varieties such as Zinfandel. In the North Coast it can cause damage in early spring when shoot growth is delayed or later in the season in vines with small canopies. Willamette spider mite is seldom a pest in the San Joaquin Valley, especially on Thompson Seedless.

The twospotted spider mite, Tetranychus urticae, is almost identical in appearance to the Pacific spider mite except it rarely has spots on the rear of the body. It is only occasionally found on grapes in California and rarely causes damage.

DAMAGE

Damage caused by each species can help in identifying each species. Pacific spider mite damage begins as yellow spots. As damage progresses, dead (necrotic) areas appear on the leaves. High populations can render the leaves unfunctional with leaf burning and bronzing and copious amounts of webbing. Damage is worse along the shoulder and tops of the vine canopies. Willamette spider mite feeding in mid- or late season causes foliage to turn yellowish bronze, but usually no burn occurs unless vines are weak. In red varieties, infested leaves may turn reddish.

MANAGEMENT

Manage webspinning spider mites in a vineyard by integrating biological, cultural and chemical controls.

Biological Control
Many natural enemies help to control pest mite populations. The western predatory mite, Galendromus (=Metaseiulus) occidentalis, is commonly present in vineyards and can be quite effective in reducing all stages of spider mite populations. This mite is translucent to light amber, pear shaped, and quite active. The effectiveness of this predator depends upon its ability to increase its population size as the season progresses. Disruptive sprays applied early will reduce the survival of this beneficial mite. Naturally occurring predator mites will survive sulfur sprays and dusts, but released ones may not survive dusting sulfur unless they have sulfur resistance. Predator mites, including insecticide-resistant ones, are available commercially to augment populations in the field. Other predators, including sixspotted thrips (Scolothrips sexmaculatus), can also be important. To preserve these natural enemies, avoid using disruptive materials, especially carbaryl, dimethoate, dicofol, and methomyl.

Cultural Control
Apply water or other materials formulated to reduce dust on roads in the vineyard. If possible, maintain resident vegetation or other cover in the vineyard middles to further reduce dust. Irrigate in a manner that will avoid stressing vines. Although overhead watering has been shown to reduce mite problems, it can also increase some disease problems.

Organically Acceptable Methods
Organically acceptable methods include biological and cultural control methods as well as oil or soap sprays.

Monitoring and Treatment Decisions
Monitor for webspinning spider mites as part of dormant and budbreak spur monitoring as described in the DELAYED-DORMANT AND BUDBREAK SAMPLING (wine/raisin grapes or table grapes) and record observations on a monitoring form (example form81 KB, PDF). During rapid shoot growth, look for spider mites and predatory mites weekly on the first emerging leaves. During bloom, follow the guidelines for MONITORING INSECTS AND SPIDER MITES. When monitoring mites, note the presence of mite predators. The table below can be used in determining the treatment guidelines for various combinations of Pacific mite injury levels and predator-prey distributions in Thompson Seedless raisin vineyards. After bloom, record your observations on the insect and mite monitoring form (example form149 KB, PDF).

Pacific mite injury levels (% leaves infested) 1: Predator-prey distribution ratios for pacific spider mites in Thompson Seedless raisin vineyards1
Rare
(less than 1:30)
Occasional
(1:30 to 1:10)
Frequent
(1:10 to 1:2)
Numerous
(greater than 1:2)
light (less than 50%) delay treatment to increase predators delay treatment treatment not likely necessary treatment not necessary
moderate (50-65%) treat if population is increasing rapidly may delay treatment to increase predation treatment may not be needed if the predator-prey distribution ratio is increasing rapidly treatment not needed
heavy (65-75%) treat immediately may delay treatment a few days to take advantage of increasing predation treatment may not be needed if predators are becoming numerous treatment not needed, damage not increasing
very heavy (greater than 75%) treat immediately treat immediately teat immediately unless predator-prey distribution ratio increasing very rapidly; carefully evaluate damage treatment may not be necessary if population is dropping because of very high (greater than 1:1) predator-prey distribution ratios; carefully evaluate damage
1 Thompson Seedless vines are very vigorous and will tolerate more mite feeding than less vigorous varieties. Consequently, injury levels would be lower for other varieties, but predator-prey ratios and comments are applicable to all varieties.
Common name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
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. Not all registered pesticides are listed. Always read label of product being used.
 
A. PROPARGITE
  (Omite) 30WP 5–9 lb see comments 21
  MODE OF ACTION GROUP NUMBER1: 12C
  COMMENTS: Apply no more than twice/season. Lower rates allow greater survival of beneficials. Restricted entry interval is 14 days for wine and raisin grapes and 21 days for table grapes.
 
B. FENBUTATIN-OXIDE*
  (Vendex) 50WP 1–2.5 lb 48 28
  MODE OF ACTION GROUP NUMBER1: 12B
  COMMENTS: Do not apply more than twice /season. Lower rates allow greater survival of beneficials.
 
C. FENPYROXIMATE
  (Fujimite) 5EC 2pt 12 14
  MODE OF ACTION GROUP NUMBER1: 21
  COMMENTS: Apply in 50-200 gal water with higher volumes in vineyards with dense canopies.
 
D. PYRIDABEN
  (Nexter) 75WP Label rates 12 7
  (Pyramite) 60WP Label rates 12 7
  MODE OF ACTION GROUP NUMBER1: 21
  COMMENTS: Alternate with miticides of a different chemistry to minimize the development of resistance.
 
E. ABAMECTIN*
  (Agri-Mek) 0.15%EC 8–16 fl oz 12 28
  MODE OF ACTION GROUP NUMBER1: 6
  COMMENTS: Do not make more than 2 applications/growing season. Dust on leaves will inhibit absorption of this material. Effectiveness is also reduced by sulfur burn on leaves.
   
F. NARROW RANGE OIL#    
  (Saf-T-Side, etc.) Label rates 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: For Pacific spider mite, apply before bloom to get the best coverage and to delay the development of the population by 3–4 weeks. If an additional treatment is needed, apply 2 weeks after berry set (on raisin and wine grapes only; do not use on table grapes after bloom). For Willamette spider mite, apply oil after budbreak in a 1% spray. Do not apply within 10 days of a sulfur application. Check with certifier to determine which products are organically acceptable.
 
G. INSECTICIDAL SOAPS#
  (M-Pede) Label rates 12 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: Can cause berry spotting.
 
H. NEEM OIL#
  (Trilogy) Label rates 4 0
  MODE OF ACTION: Unknown. A botanical insecticide
  COMMENTS: For organically grown crops, check with your certifier for any restrictions that apply.
 
I. HEXYTHIAZOX
  (Savey) 50DF 3–6 oz 12  
  MODE OF ACTION GROUP NUMBER1: 10B
  COMMENTS: For use on nonbearing vines only. Do not make more than 1 application per year. More effective early in season on egg stage. If there is an abundance of adults, this material is not effective. Because this material is applied early in the season, it is best used in vineyards with chronic mite problems.
 
J. DICOFOL
  (Kelthane) 50WSP 2.5 lb 48 7
  MODE OF ACTION: UNC
  COMMENTS: May not be effective in all areas due to resistance. Disruptive to predaceous mites and lady beetles. Do not make more than two applications per season.
 
K. GALENDROMUS OCCIDENTALIS#
  COMMENTS: Releases are most successful when host plants (green beans) are placed directly on vines. Use a minimum of 1,000 predators per acre.
 
** Apply with enough water to provide complete coverage.
+ 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.
# Acceptable for use on organically grown produce.
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/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Insects and Mites
W. J. Bentley, UC IPM Program, Kearney Agricultural Research Center, Parlier
L. G. Varela, UC IPM Program, Sonoma County
F. G. Zalom, Entomology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
P. A. Phillips, UC IPM Program, Ventura County
D. R. Haviland, UC IPM Program, Kern County
K. M. Daane, Kearney Agricultural Research Center, Parlier
M. C. Battany, UC Cooperative Extension, San Luis Obispo County
Acknowledgment for contributions to Insects and Mites:
J. Granett, Entomology, UC Davis

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