Description of the Pest
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 coastal 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. 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), during certain years or conditions, and on certain varieties, 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 specific to each species can be helpful in identification. 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. In Sonoma and Napa vineyards, the most abundant predatory mite is Typhlodromus pyri; when present in spring, it can prevent the establishment of phytophagous mites. Predatory mites are 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. The western predatory mite, Galendromus (= Metaseiulus) occidentalis and Neoseiulus californicus are both available for release from commercial insectaries. G. occidentalis is used most commonly in hot inland valleys and N. californicus is more adapted to very cool coastal areas. The optimal timing for releases is in the spring when spider mite populations begin to appear.
Other predators, including sixspotted thrips (Scolothrips sexmaculatus), can also be important.
To preserve these natural enemies, avoid using disruptive materials.
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 form—). 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 .
| Pacific mite injury levels (% leaves infested) 1 |
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 | treat 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 |
Footnotes
- 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.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|
Galendromus occidentalis # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
NA |
See comments | — | — | Releases are most successful when host p... | — | — | — | — | — | — | — | — | — | — | — | 12/2016 | |
|
|
Neoseiulus californicus # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
NA |
See comments | — | — | Releases are most successful when host p... | — | — | — | — | — | — | — | — | — | — | — | 12/2016 | |
|
|
Agri-Mek SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
6 |
1.75–3.5 fl oz | 12 | 28 | Do not make more than two applications p... | moderate | moderate | low | moderate/high | moderate | high | low | extra high | low | intermediate | 12/2016 | ||
|
|
Acramite-50WS | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
20D |
0.75–1 lb | 12 | 14 | Only apply once per season. | narrow | low | low | low | short | — | — | — | — | — | 12/2016 | ||
|
|
Apollo SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
10A |
4–8 oz | 12 | 21 | Apply only once per year. More effective... | narrow | moderate | low | low | short | low | low | high | low | high | 12/2016 | ||
|
|
Nealta | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
25A |
13.7 fl oz | 12 | 14 | — | — | — | — | — | — | very low | low | intermediate | very low | very low | 12/2016 | ||
|
|
Zeal | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
10B |
2–3 oz | 12 | 14 | Only apply once per season. | narrow | high 13 | low | — | short | low | low | intermediate | very low | very low | 12/2016 | ||
|
|
FujiMite 5EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
21A |
2 pt | 12 | 14 | Apply in 50 to 200 gal water with higher... | narrow | high | low | low | long for predatory mites | intermediate | low | extra high | very low | low | 12/2016 | ||
|
|
Onager | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
10A |
12–24 oz | 12 | 7 | Only apply once per season. | narrow | low | low | low | short to moderate | low | low | intermediate | low | intermediate | 12/2016 | ||
|
|
various products # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNM |
Label rates | See label | See label | Narrow range oil. For Pacific spider mit... | broad | low | low | low | none to short | — | — | — | — | — | 12/2016 | ||
|
|
Trilogy # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
UNE |
Label rates | 4 | 0 | For organically grown crops, check with... | broad | low | low | low | short | low | low | intermediate | very low | low | 12/2016 | ||
|
|
M-Pede # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
— |
Label rates | 12 | 0 | Insecticidal soap. Can cause berry spott... | broad | moderate | moderate | moderate | short | low | intermediate | intermediate | very low | low | 12/2016 | ||
|
|
Envidor 2 SC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
23 |
16–34 fl oz | 12 | 14 | Only apply once per season. To protect h... | narrow | low | — | — | — | — | — | — | — | — | 12/2016 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b c d e Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides 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; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 ↩ Acute toxicity is low but reproductive capacity is reduced.
Important Links
- Delayed/dormant budbreak monitoring form
- Insect and spider mite monitoring form
- Photos of natural enemies of spider mites
- Photos of spider mites and their damage
UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
L.G. Varela (emeritus), UC IPM and UC Cooperative Extension Sonoma County
D.R. Haviland, UC IPM and UC Cooperative Extension Kern County
W.J. Bentley (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier
L.J. Bettiga, UC Cooperative Extension Monterey County
K.M. Daane, Kearney Agricultural Research and Extension Center, Parlier
R.J. Smith (emeritus), UC Cooperative Extension Sonoma County
L.R. Wunderlich, UC Cooperative Extension Central Sierra
F.G. Zalom (emeritus), Entomology, UC Davis
Acknowledgement for Contributions to Invertebrates
M.C. Battany, UC Cooperative Extension San Luis Obispo County
J. Granett (emeritus), Entomology, UC Davis
P.A. Phillips (emeritus), UC Cooperative Extension Ventura County
A.H. Purcell (emeritus), Environmental Science, Policy, and Management, UC Berkeley
