Mite Pests of Avocado—General Information
Spider mites (family Tetranychidae) and predatory mites (Phytoseiidae) are tiny eight-legged arthropods, except for first stage larvae, which have six legs. Persea mite is a key pest of California-grown avocados. Avocado brown mite and sixspotted mite are sporadic pests. Several beneficial mites are important predators of pest mites and certain insects. Natural enemies and certain management strategies vary among pest mites. Identify the pest and natural enemy species in your grove and learn their biology so you can manage these pests appropriately. For details about sampling techniques, see MONITORING PERSEA AND SIXSPOTTED MITES.
Description of the Pest
(View photos to identify mites)
The oval adults are about 0.01 inch (0.3 mm) long. Their body is lemon yellow, often with about six dark blotches on the abdomen, although some individuals have no distinct spots. Females lay tiny, globular, pale greenish yellow to translucent or pearly white eggs, which have a slender projecting stalk. About 25 to 40 eggs are laid over 10 to 20 days. Eggs hatch in 5 days to 3 weeks, depending on temperature. In summer, mites reach maturity in 8 to 12 days. Numbers are highest in spring and early summer.
Damage
Sixspotted mite is an occasional pest, mostly near the coast in foggy areas of San Luis Obispo and Santa Barbara counties. It generally is under good biological control in the interior growing areas (Riverside and San Diego counties) because of predators and warm weather. Sixspotted mite can become a problem anywhere trees are drought-stressed or where pesticide usage has disrupted mite biological control.
Sixspotted mite feeds only on the lower avocado leaf surface. It causes irregular brown to purplish discoloring, mostly along the midrib and larger veins. Sixspotted mite produces webbing, but not the dense roundish silk patches formed by persea mite. Densities of 25 to 30 mites per leaf may lead to defoliation.
Management
Enhance biological control by conserving natural enemies.
- Minimize dust.
- Avoid applying non-selective pesticides that are toxic to predaceous insects and beneficial mites that control plant-feeding mites and other pest insects.
- Limit any needed applications to spots where pests are most common.
Biological Control
(View photos to identify natural enemies of mites)
Sixspotted mite is controlled primarily by predatory mites (family Phytoseiidae). These phytoseiids include Amblyseius (=Typhlodromalus) limonicus and Galendromus helveolus. Euseius hibisci, a shiny pear-shaped predator, is important in part because it can maintain and increase its numbers on avocado pollen when pest mites are scarce. Typhlodromus rickeri also preys on sixspotted mite around Santa Barbara County. The spider mite destroyer lady beetle (Stethorus picipes) and sixspotted thrips (Scolothrips sexmaculatus) are other important natural enemies.
Cultural Control
Encourage predators by watering or paving main orchard roads to control road dust. Drive slowly when it is necessary to use dirt roads. Consider using a water truck or trailer to wet dirt roads, especially before travel during summer months when heat convection currents carry dust well up into the tree canopies. Individual backyard trees can be hosed down in early to midsummer to remove dust and enhance biological controls.
Organically Acceptable Methods
Use biological and cultural controls, sulfur and certain oil sprays in an organically certified crop.
Monitoring and Treatment Decisions
(View mite monitoring video)
- Look for sixspotted mite when monitoring persea mite, see MONITORING PERSEA AND SIXSPOTTED MITES. Be sure to distinguish the mite species present.
- When specifically monitoring for sixspotted mite, select trees in dusty and more humid locations of groves.
- Use a hand lens to examine along the midrib and lateral veins on the underside of interior canopy leaves.
- Look for brown to purplish discoloring, mite webbing, and mites.
Sixspotted spider mite can severely stress trees at relatively low densities by causing premature leaf drop. However, numbers rarely exceed an average of 2 to 3 mites per leaf. At this low level, sixspotted mite is not damaging, does not warrant treatment, and is easily overlooked.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. 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. Always read the label of the product being used. | ||||
| A. | NARROW RANGE OIL# | Label rates | 4 | 0 |
| MODE OF ACTION: Contact including smothering and barrier effects. | ||||
| COMMENTS: Requires good coverage to be effective. Check with certifier to determine which products are organically acceptable. | ||||
| B. | WETTABLE SULFUR# | Label rates | 24 | 0 |
| MODE OF ACTION: Unknown. | ||||
| COMMENTS: Do not treat with sulfur when temperatures exceed 90°F to avoid leaf damage. Sulfur sprays are often not effective in coastal areas where temperatures do not promote fuming action. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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. |
| # | Certain products are acceptable for organically grown produce. |