Agriculture

Twospotted Spider Mite

  • Tetranychus urticae
Updated: 08/2012

Tools

PestManage: a decision support tool to view and compare pest management options

Description of the Pest

The adult female twospotted spider mite is oval-shaped and measures approximately 1/50 inch (0.4 mm). The adult male is smaller than the female and has an elliptical shape; its body is tapered at the end. Twospotted spider mites are usually translucent or greenish-yellow in color, but can also be brown or orange-red. Just prior to diapause, adult females change to bright orange. Twospotted spider mites have dark spots on each side of their body, which is due to the accumulation of body waste products.

Adults overwinter in soil cracks beneath plant debris or on living plant tissue. Females lay eggs on the underside of leaves and depending on temperature, eggs hatch in 4 to 5 days. The complete life cycle takes approximately 14 to 16 days and there are several generations per season.

Damage

Feeding damage appears on the upper surface of leaves as silvery or dry spots. Heavy infestations cause leaves to turn bronze in color and drop. Economic damage can occur from a reduction in oil yield and quality, and a shorter duration of productivity of mint fields.

Management

Infestations of twospotted spider mite can occur in all peppermint growing regions of California. Commonly, populations increase quickly during the hot and dry periods between June and August. Although most damage occurs during this period, economic populations have been observed during late April and early May. Control options include reducing plant stress through optimum irrigation and fertilization, biological control using predatory mite releases, and miticides.

Biological Control

The spider mite predator, Neoseiulus fallacis, can occur in all mint-growing areas of California. Adults have a pear-shaped body and measure approximately 1/50 inch long (0.4 mm). They are shiny with long legs and tan to light orange. Immatures are semi-transparent and cream colored.

Predatory mites can be distinguished from spider mites by their more active searching behavior. N. fallacis can also be purchased from commercial insectaries. Releases should take place when twospotted spider populations are well below the threshold of five mites per leaf. For optimum results, N. fallacis should be released at 2000 per acre when approximately 20% of sampled leaves have at least 1 spider mite. Preserve N. fallacis by using a compatible miticide.

Using biological control is an excellent tool to manage miticide resistance, because biological control organisms are indiscriminate in their feeding behavior.

Organically Acceptable Methods

Clarified extract of neem oil and predatory mites can effectively control twospotted spider mites. The efficacy of neem oil is slower than conventional miticides, because it is an insect growth regulator and does not kill by contact. When using neem oil, apply at a lower threshold of approximately three mites per leaf.

Cultural Control

Minimize water stress and control dust along dirt roads, especially during hot weather.

Monitoring and Treatment Decisions

There are two different monitoring methods: enumerative and presence/absence sampling.

  1. Twospotted spider mites tend to be distributed unevenly throughout peppermint fields. Therefore sample several different locations when monitoring.
  2. Sample a minimum of 7 locations for every 30 acres. Sample more locations, depending on the field's history.
  3. The sampled location should measure approximately 15 feet by 15 feet.
  4. Sampling methods and treatments:
    • Enumerative. Count all nymphs and adults on the underside of about 23 randomly selected leaves at every location. Treat if five mites per leaf or more are found.
    • Presence/absence. If a leaf has two spider mites or more, note the leaf as infested, otherwise it is considered not infested. Apply a miticide if 15 of the 23 leaves sampled (~65%) are infested. This indicates a density of approximately five mites per leaf.

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(fish) 9 Leaching(human) 10 Solution runoff(human) 11 Last updated 12
A
Neoseiulus fallacis # Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

NA

— — — Predatory mites can be released early i... — — — — — — — — — — — 08/2012
A
Agri-Mek 0.15 EC Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

6

10–20 fl oz 12 21 Contact or ingestion toxin that paralyze... moderate I high low moderate/high long high low extra high low intermediate 08/2012
F
Acramite-50WS Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

20D

0.75–1 lb 12 7 Contact toxin that targets all stages.... narrow II low low low short — — — — — 08/2012
B
Zeal Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

10B

2–3 oz 12 28 Acts as a contact toxin to eggs, inhibi... narrow II — 13 — — short low low intermediate very low very low 08/2012
D
FujiMite 5EC Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

21A

1–4 pt 12 14 Contact toxin to eggs, juveniles, and a... narrow III — low low short intermediate low extra high very low low 08/2012
C
Onager Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

10A

Label rates 12 28 Apply after sampling indicates pest mit... narrow II moderate low low short to moderate low low intermediate low intermediate 08/2012
G
Trilogy # Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

UNE

Label rates 4 See label Apply in a minimum of 25 gallons per ac... broad II low low low short low low intermediate very low low 08/2012
E
Omite-6E Application Timing Varies (See UC IPM Pest Management Guidelines and Label) 8

12C

1.5–2 qt 21 days 28 Contact toxin that targets juveniles and... narrow III moderate 14 low low short — — — — — 08/2012
NA
Not applicable.
—
No information.
I
Do not apply or allow to drift to plants that are flowering including weeds. Do not allow pesticide to contaminate water accessible to bees including puddles.
II
Do not apply or allow to drift to plants that are flowering including weeds, except when the application is made between sunset and midnight if allowed by the pesticide label and regulations. Do not allow pesticide to contaminate water accessible to bees including puddles.
III
No bee precaution, except when required by the pesticide label or regulations.
  • ‡ 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  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.
  • 14 ↩ Use lowest rates for best management of predatory mite to spider mite ratio.
UC Peer Reviewed Logo

UC IPM Pest Management Guidelines: Peppermint
UC ANR Publication 3457

K.E. Tollerup, UC IPM and Kearney Agricultural Research and Extension Center, Parlier

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