How to Manage Pests

UC Pest Management Guidelines

Cucurbits

Spider Mites

Scientific Names:
Twospotted spider mite: Tetranychus urticae
Pacific spider mite: Tetranychus pacificus
Strawberry spider mite: Tetranychus turkestani
Desert spider mite: Tetranychus desertorum
Carmine spider mite: Tetranychus cinnabarinus
Brown wheat mite: Petrobia latens

(Reviewed 12/09, updated 6/12)

In this Guideline:


DESCRIPTION OF THE PESTS

Examine leaves with a hand lens for spider mites. Frequently, infestations include a mixture of spider mite species. Adult mites are about 0.06 inch in length, have four pairs of legs, are greenish to pink or cream colored, and have various sized black spots on the body. Under warm conditions spider mites move rapidly within the colony area. Spider mites have four stages of development: (1) the oval, somewhat translucent egg; (2) a six-legged translucent immature stage; (3) an eight-legged immature stage; and (4) the eight-legged adult stage. A generation may pass in as few as 5 to 7 days in mid-summer, or in a month during cool periods. Spider mites produce webbing that is often filled with cast skins, dust, and other debris.

DAMAGE

Mite feeding results in the destruction of chlorophyll; leaves become pale, stippled, and in later stages of infestation dry up and die. Loss of color is pronounced on the under surface of leaves before it becomes apparent on the upper side. Light infestations can be tolerated, but when heavy, can result in lowered yield and reduced quality of fruit.

MANAGEMENT

Biological control is an important component of mite management. Take measures to ensure the survival of predators and parasites.

Biological Control
Several predators play an important role in regulating spider mite populations, including the western predatory mite (Galendromus [Metaseiulus] occidentalis), sixspotted thrips (Scolothrips sexmaculatus), western flower thrips (Frankliniella occidentalis), lady beetles (Stethorus sp.), minute pirate bug (Orius tristicolor), and lacewing larvae (Chrysoperla carnea). The western predatory mite is the same size as spider mites but lacks spots and ranges in color from cream to amber red. It is available commercially, but research has not been done on the effectiveness of releasing these predators in cucurbits. Sixspotted thrips and western flower thrips are also effective predators, but naturally occurring populations of these insects generally do not develop to high enough levels that they can provide significant control until damage has already taken place. Both species are tiny, slender insects about 1 mm or less in length. Sixspotted thrips has three dark spots on each forewing; western flower thrips ranges in color from clear lemon yellow to dark brown. Monitor western predatory mites and the two species of thrips to determine if they are present in the field and their relative population density in comparison with pest mites.

Cultural Control

Minimize dust and encourage naturally occurring predators and parasites by limiting chemical rates and the number of applications. Control field bindweed growing in or at the edges of a cucurbit field. Good water management increases plant tolerance to these pests. After runners are 14 inches long, natural enemies such as sixspotted thrips or predaceous mites usually control pest mite populations.

Organically Acceptable Methods
Biological and cultural controls and sulfur sprays (not for use on sulfur sensitive varieties) are acceptable to use in an organically certified crop.

Monitoring and Treatment Decisions
Start monitoring for spider mites during the vegetative growth stage. No threshold is established, but when buildup is observed, either spot or completely treat the field before webbing occurs or before runners are 14 inches in length, providing no predatory thrips or predaceous mites are present. After the rows close over, ground equipment cannot get in the field, and chemical treatment must be applied by aircraft. Such treatments are less effective because it is difficult to obtain good coverage by aircraft.

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 3
  MODE OF ACTION GROUP NUMBER1: 25
 
B. ABAMECTIN*
  (Agri-Mek 0.15EC) 8–16 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 6
 
C. DICOFOL
  (Dicofol 4E) 1.25 lb 21 days 2
  MODE OF ACTION: UNC
  COMMENTS: Add a proper sticker spreader. Registered only on cucumbers and squash. Do not make more than 1 applications/season. Do not feed treated vines, forage, or crop residues to meat or dairy animals.
 
D. SULFUR# 15–20 lb 24 0
  MODE OF ACTION: Unknown. An inorganic insecticide.
  COMMENTS: Do not apply when temperature exceeds 95°F or use on sulfur-sensitive varieties. Not effective on Pacific mites.
 
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.
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/.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445

Insects and Mites

  • E. T. Natwick, UC Cooperative Extension, Imperial County
  • J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
  • C. S. Stoddard, UC Cooperative Extension, Merced & Madera counties
Acknowledgment for contributions to Insects and Mites:
  • R. L. Coviello, UC Cooperative Extension, Fresno County
  • L. D. Godfrey, Entomology, UC Davis
  • C. B. Fouche, UC Cooperative Extension, San Joaquin County
  • C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
  • J. B. LeBoeuf, AgriData Sensing, Inc., Fresno
  • M. Murray, UC Cooperative Extension, Colusa/Glenn counties

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