How to Manage Pests

UC Pest Management Guidelines

Bermudagrass Seed Production

Spider Mites

Scientific Name: Tetranychus spp.

(Reviewed 1/07, updated 4/10)

In this Guideline:


DESCRIPTION OF THE PESTS

Adult mites are tiny (about 0.06 inch in length), have four pairs of legs, are greenish, 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 egg; (2) a translucent, six-legged 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 midsummer 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 seed yield. Examine leaf blades with a hand lens for spider mites. Frequently infestations include a mixture of spider mite species.

MANAGEMENT

Biological and cultural controls frequently keep spider mites at low levels. Monitor for spider mites and predators before treating.

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 bermudagrass. 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 to provide significant control before 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. (Pest thrips, Chirothrips species, can be distinguished from the beneficial species of thrips by their smaller size and black color.) Monitor western predatory mites and the two species of thrips to determine if they are present in the field and to calculate 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 bermudagrass field. Good water management increases plant tolerance to these pests.

Monitoring and Treatment Decisions
No threshold is established, but when buildup is observed and no predatory thrips or predaceous mites are present, either spot treat or completely treat the field before webbing occurs.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to the impact on natural enemies and honey beesand the environment. Not all registered pesticides are listed. Always read label of product being used.
 
A. SULFUR DUST 20–25 lb 0 24
  MODE OF ACTION: Unknown. An inorganic insecticide.
  COMMENTS: Do not apply when temperature exceeds 90°F.
   
+ Restricted entry interval (R.E.I.) is the number of hours 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 the 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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Bermudagrass Seed Production
UC ANR Publication 3472

Insects and Mites

E. T. Natwick, UC Cooperative Extension, Imperial County
V. M. Barlow, UC Cooperative Extension, Riverside County
M. D. Rethwisch, UC Cooperative Extension, Riverside County

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