How to Manage Pests

UC Pest Management Guidelines

Strawberry

Spider Mites

Scientific Names:
Twospotted spider mite: Tetranychus urticae
Carmine spider mite: Tetranychus cinnabarinus
Strawberry spider mite: Tetranychus turkestani
Lewis spider mite: Eotetranychus lewisi

(Reviewed 6/08, updated 10/14)

In this Guideline:


DESCRIPTION OF THE PESTS

Twospotted spider mite

Twospotted spider mite eggs are about 1/180 inch (0.14 mm) in diameter and are laid on the undersides of leaves. They are spherical, clear, and colorless when laid but become pearly white as hatch approaches.

Nymphs, adult males, and reproductive adult females are oval and generally yellow or greenish. There are one or more dark spots on each side of their bodies, and the top of the abdomen is free of spots.

Adult female twospotted spider mites may stop reproduction during the coldest winter months in production areas of colder inland valleys. Diapause is indicated by a change in color to bright orange. In coastal growing areas it is rare to have a significant proportion of the population undergo diapause. Mating and egg laying typically occur year round in all coastal strawberry-growing regions.

Carmine spider mite

Carmine spider mite, a close relative of the twospotted spider mite, is bright red in color. It is commonly found at low densities in Southern California, Central Coast, and San Joaquin Valley growing regions. Populations usually decline as temperatures warm in spring.

Strawberry spider mite

Both strawberry and twospotted spider mites look similar. They can only be distinguished by the morphological characters of male genitalia. Twospotted spider mite is the predominant species in strawberries grown on the Central Coast. Strawberry spider mite occurs in some of these areas, with mixed populations of both twospotted and strawberry spider mites seen particularly during the warmer parts of the production season.

Lewis spider mite

Lewis mite looks similar to twospotted spider mite, but the females are smaller than twospotted spider mite females. Lewis spider mites have several small spots, while twospotted spider mites have a single dark spot on either side of their body. Lewis spider mite is reported to infest some strawberry fields in the Oxnard area. Since Lewis mite is commonly seen on caneberries, nearby strawberry fields can suffer Lewis mite infections.

Take care to correctly identify these mites in the field, particularly in winter. Twospotted spider mites in diapause and carmine mite may be mistaken for the predaceous mite Phytoseiulus persimilis. However, the predaceous mite can be distinguished from these two mites by its much faster movement and shinier, teardrop-shaped appearance. For more identification information, see Emerging Pests.

DAMAGE

Twospotted spider mite and carmine spider mite damage to strawberries appears as stippling, scarring, and bronzing of the leaves and calyx.

  • Twospotted spider mite feeding is particularly damaging during the first 2 to 5 months following transplanting in late summer or fall. Mite feeding during this critical period of plant growth substantially reduces berry number per plant and overall plantation yield.
  • Yield loss is detectable at all mite infestation levels exceeding one mite per leaflet.

Plants are less sensitive to mite feeding after initial berry set

  • Substantial yield loss results from15 to 20 mites per mid-tier leaflet after berry set.
  • Plants that sustain infestations greater than 75 mites per leaflet may become severely weakened and appear stunted, dry, and turn red.

The highest numbers of twospotted mites are often observed following the peak spring fruit harvest. This peak is typically followed by a rapid, natural decline in mite numbers when the plant enters a vegetative growth cycle. Twospotted mite numbers may again increase later in summer as fruit production by day-neutral cultivars again increases.

MANAGEMENT

  • Cultural practices that favor vigorous plants are key to minimizing damage from spider mites.
  • Protect natural enemies as much as possible by choosing insecticides and miticides that are least harmful to beneficials.
  • If necessary, supplement natural enemies by releasing predatory mites.
  • When treating for mites, choose the most selective miticide and alternate it with a miticide of a different chemistry or mode of action to avoid the development of resistance.
Biological Control

Predator mites commercially available for release:

Of the commercially available predatory mites, only the first three are commonly used for spider mite suppression, most frequently Phytoseiulus persimilis. P. persimilis is an aggressive feeder, multiplies and spreads rapidly, and is a specialist predator that feeds exclusively on pest mites. However in the absence of these pest mites, P. persimilis feeds on its own species, causing the population to gradually disappear.

Predatory mite releases
  1. Monitor fields on a regular basis to determine spider mite numbers.
  2. Applying a short-residual miticide to reduce spider mite numbers before a predator release may improve biological control under some conditions.
  3. Make predatory mite releases early in the season before spider mite numbers begin to build or following winter spider mite treatments intended to reduce overwintering populations. On the Central Coast, spider mites are first observed typically in January or February, while further south spider mite infestations may first develop in fall.
  4. Following predator mite release, it is important to monitor spider mite numbers closely to evaluate the effectiveness of the predatory mites in maintaining the pest mites below economically injurious levels.

Insecticides, miticides, and fungicides that are not selective will kill the predators. Make releases only after residues are below lethal levels following any pesticide application.

Phytoseiulus persimilis has become established in most coastal strawberry-growing areas, and naturally occurring populations often move into spider mite-infested fields on their own. Neoseiulus (Amblyseius) californicus has also been found to naturally infest strawberry plantations in some growing areas and can effectively maintain spider mite numbers that are below threshold levels. Another predator mite, Phytoseiulus macropilus, occasionally occurs in strawberries early in spring.

Other natural enemies include minute pirate bug (Orius tristicolor), a small, black lady beetle (Stethorus spp.), a small, black rove beetle (Oligota oviformis), bigeyed bugs (Geocoris spp.), brown lacewings (Hemerobius spp.), green lacewings (Chrysopa spp.), sixspotted thrips (Scolothrips sexmaculatus), damsel bugs (Nabis spp.), and a predaceous midge larva (Feltiella acarivora).

Cultural Control

Strawberry cultivars vary in susceptibility to twospotted spider mite infestation and tolerance of twospotted spider mite feeding. When transplanted in fall, short-day cultivars are generally less tolerant of mite feeding than day-neutral cultivars, particularly later in the fruit-production season. When transplanted in summer, short-day cultivars are relatively tolerant of mite feeding.

Preplant chilling (vernalization) directly promotes plant vigor. Fall transplant, nursery location, preharvest chilling, nursery harvest date, and length of pretransplant supplemental cold storage can all affect a plant's vernalization. Plants with low amounts of chilling have low vigor and often develop intolerable mite infestations. Excessive chilling promotes increased vigor and reduces mite abundance, but other production factors are adversely affected (i.e., delayed flowering, large plant size, increased vegetative runner production). Be sure transplants have received adequate chilling and receive proper irrigation and fertilization.

Other controllable factors that can be used to promote plant vigor are

  • soil preparation and fumigation
  • use of polyethylene plastic mulch, and
  • proper irrigation to prevent water stress.

Road dust control is also important in inhibiting mite infestations.

Cultivars and cultural practices vary between production regions. Obtain information on cultivars and cultural practices pertinent to a particular growing region from your University of California County Cooperative Extension office or from transplant nurseries before making planting decisions.

Organically Acceptable Methods

Cultural and biological controls, including releases of predatory mites, sprays of rosemary oil or organic stylet oil, and entomopathogenic fungi such as Beauveria bassiana are acceptable for use on organically certified strawberries.

Miticide Resistance

Twospotted spider mites have a history of rapidly developing resistance to miticides when a miticide is repeatedly applied to the same population.

  • Alternating miticides that have different modes of action may reduce development of resistance to a specific miticide.
  • Avoid unnecessary spraying and treat only infested portions of the field.
  • Organophosphate, carbamate, and pyrethroid insecticide applications can induce twospotted spider mite outbreaks. If possible, avoid early season insecticide applications or apply insecticides that are less disruptive to beneficial arthropods. Careful selection and use of insecticides early in the season can potentially reduce the number of miticide applications.
Monitoring and Treatment Decisions

Vigorous plant growth during the first 4 months following fall transplant is a key factor in successful strawberry production. Monitor mid-tier leaves during this critical period when mite feeding is extremely damaging.

  1. Randomly select 10 leaflets per acre in small fields and 5 leaflets per acre in larger fields. When using a mite-brushing machine, the leaves from each acre can be brushed as one sample.
  2. Examine the undersurface of mid-tier leaflets with a hand lens to count the number of mites or use a mite-brushing machine.
  3. Record your observations on a sampling form (PDF).

The established economic threshold for this period is an average of five mites per mid-tier leaflet. Summer transplants have a higher threshold of an average of 10 mites per mid-tier leaflet during this same period.

Once harvest begins, strawberries become more tolerant of mite feeding and treatment thresholds increase to an average of 15 to 20 mites per mid-tier leaflet. Treatment thresholds may vary somewhat depending on location, time of season, cultivar, overall plant vigor, yield potential, and the availability of an effective miticide.

Common name Amount per acre R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
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. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. BIFENAZATE
  (Acramite 50WS) 0.75–1 lb 12 1
  MODE-OF-ACTION GROUP NUMBER1: un
  COMMENTS: Do not make more than one application per harvested crop. Two sprays may be made per year if more than one crop is harvested each year; minimum period between applications is 21 days. A good resistance management strategy is to use bifenazate as the winter spray (if needed) and as a rotational pesticide with abamectin and hexythiazox during the season. It has low toxicity to predatory mites and predatory insects. Bifenazate can be used once per year in strawberry nurseries.
 
B. ACEQUINOCYL
  (Kanemite 15 SC) 21–31 fl oz 12 1
  MODE-OF-ACTION GROUP NUMBER1: 20B
  COMMENTS: Do not use less than 100 gal water/acre and do not apply more than twice per year. Allow a minimum of 21 days between treatments. Crops other than strawberries may not be rotated for at least 1 year following treatment.
 
C. SPIROMESIFEN
  (Oberon 2SC) 12–16 fl oz 12 3
  MODE-OF-ACTION GROUP NUMBER1: 23
  COMMENTS: Do not make more than two applications per crop season.
 
D. ETOXAZOLE
  (Zeal Miticide) 2–3 oz 12 1
  MODE-OF-ACTION GROUP NUMBER1: 10B
  COMMENTS: A mite growth regulator that is most effective against eggs and immatures. Most effective when applied before high numbers develop, but it will eventually control even a large population. Effective against both twospotted and carmine spider mites but not against cyclamen mite. Do not apply more than 3 oz/acre per season.
 
E. FENPYROXIMATE
  (Fujimite 5EC) 2 pt 12 1
  MODE-OF-ACTION GROUP NUMBER1: 21A
  COMMENTS: Fujimite has been shown to eliminate predator mites for at least 6 weeks.
 
F. HEXYTHIAZOX
  (Savey 50DF) 6 oz 12 3
  MODE-OF-ACTION GROUP NUMBER1: 10A
  COMMENTS: Limited to one application per season. Follow label directions for last date material can be applied because this varies by region. Most effective against eggs and nymphs, so best used when mites begin to actively reproduce. Not registered for nurseries.
 
G. ABAMECTIN*
  (Agri-mek 0.15EC) 16 fl oz 12 3
  MODE-OF-ACTION GROUP NUMBER1: 6
  COMMENTS: Abamectin is less effective under cold weather conditions than in warm weather because movement into the leaf does not readily occur. Abamectin is most effective when used in paired applications 7 to 10 days apart when mites reach detectable levels under warmer temperatures in late winter and spring. Repeat the paired applications if necessary to maintain twospotted spider mite control. Do not exceed 16 fluid oz/acre per application or 64 fl oz/acre (4 applications) in a growing season. Do not apply in less than 100 gal water/acre (200 gal/acre is optimal). Do not repeat treatment within 21 days of 2nd application. Abamectin is not registered for strawberry nurseries.
 
H. NARROW RANGE OIL#
  (Omni Oil 6-E) 1–2% 12 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: The potential for phytotoxicity has not been fully evaluated. Growers are encouraged to test product or product mixes for phytotoxicity before field applications to determine safety margins. Acceptable for use on organically grown crops only when fruit are not present. Apply in 60 gal water/acre with air-assist, low-volume ground equipment or 200 gal water/acre with standard ground spray equipment. Use this miticide for low-to-moderate numbers; higher levels of mite infestation require treatment with more effective miticides. Make applications only during winter months when plants are semi-dormant to reduce the risk of phytotoxicity. Do not use oil from peak bloom through fruiting period or when air temperatures are expected to exceed 75°F within several days following application. Do not apply from Jan. 16 to May 30 in Orange and San Diego counties or the Oxnard Plains; do not apply from Feb. 1 to Jun. 15 in the Santa Maria Valley; and do not apply from Mar. 1 to Jun. 30 in Monterey and Santa Cruz counties.
 
I. ROSEMARY OIL#
  (Ecotrol) Label rates 0 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: The potential for phytotoxicity has not been fully evaluated. Growers are encouraged to test product or product mixes for phytotoxicity before field applications to determine safety margins. Danger of phytotoxicity is greater when used at higher rates and when temperatures are warm. Do not apply in less than 50 gal water/acre. No residual activity, so repeat applications at 10-day intervals while mite numbers are increasing.
 
J. STYLET OIL
  (Organic JMS Stylet Oil)#
  (JMS Stylet Oil) 72 fl oz in 75 gal 4 0
  MODE OF ACTION: Contact including smothering and barrier effects.
  COMMENTS: The potential for phytotoxicity has not been fully evaluated. Growers are encouraged to test product or product mixes for phytotoxicity before field applications to determine safety margins. There is a danger of phytotoxicity when oils are applied incorrectly, especially under conditions of high temperature and low humidity; not recommended for use in southern California. Use of ceramic spray nozzles is recommended by the manufacturer. Make applications at a minimum pressure of 400 psi. Lower pressures lead to larger droplet sizes, increasing the potential for phytotoxicity. Only organic JMS Stylet oil is acceptable for use on organically certified produce.
 
K. FENBUTATIN-OXIDE*
  (Vendex 50WP) 1.5–2 lb 48 1
  MODE-OF-ACTION GROUP NUMBER1: 12B
  COMMENTS: Pest resistance to fenbutatin-oxide has been widely reported and persists within a population. Two applications of 1–2 lb/acre can be effective at suppressing twospotted spider mites following an extended period of no use in controlling a given population, but resistance will again become prevalent in the surviving twospotted spider mite population. Fenbutatin-oxide is more effective in warm weather conditions and appears to work in some areas of the Central Valley. Do not apply more than 3 applications per season or more than 9 lb/acre per season.
 
L. PHYTOSEIULUS PERSIMILIS#
  COMMENTS: If low spider mite numbers are present in localized areas, make spot releases. Although research is lacking, experience suggests release rates of an average of two to three predators per plant when pest numbers are low. Release an average of five predators per plant when the pest mite population is at threshold level. For more widespread infestations early in the season when spider mite numbers are low, releases can be made at about 30,000/acre (about 1.5 predatory mite per plant) either as a single, large release or as three smaller releases of 10,000/acre, depending on severity of weather conditions and spider mite numbers in the field. Once mite numbers increase to threshold levels, inundative releases may reduce twospotted spider mite infestations, but these must be made at release rates exceeding 100,000/acre because once spider mite numbers begin to increase, it is difficult for predators to reduce their numbers below economic thresholds. Follow all releases of predatory mites with close monitoring of the spider mite numbers.
 
M. BEAUVERIA BASSIANA#
  (Mycotrol O) Label rates 4 0
 
Information not available.
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 R.E.I. exceeds the P.H.I. 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 ("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/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Strawberry
UC ANR Publication 3468

Insects and Mites

  • F. G. Zalom, Entomology, UC Davis
  • M. P. Bolda, UC Cooperative Extension, Santa Cruz County
  • S. K. Dara, UC Cooperative Extension, Santa Barbara County
  • S. Joseph, UC Cooperative Extension, Monterey County
Acknowledgment for contributions to the Insects and Mites:
  • P. A. Phillips, UC IPM Program and UC Cooperative Extension, Ventura County
  • N. C. Toscano, Entomology, UC Riverside

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