How to Manage Pests

UC Pest Management Guidelines

MITE PESTS OF AVOCADO – GENERAL INFORMATION

Spider mites (family Tetranychidae) and predatory mites (Phytoseiidae) are tiny 8-legged arthropods. 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 as needed. For details about sampling techniques, see MONITORING PERSEA AND SIXSPOTTED MITES.

DESCRIPTION OF THE PEST

Avocado brown mite (family Tetranychidae) is dark brown, oval, and tiny (about 0.01 inch or 0.3 mm long). Its tiny amber-colored eggs have a short projecting stalk. At low populations most eggs are laid singly along the midrib. Eggs are increasingly found throughout the upper leaf surface as populations increase. In summer there may be two complete generations per month. Temperatures of 90° to 95°F or higher usually kill these mites and their eggs, as does the first cold weather in fall or early winter.

DAMAGE

Avocado brown mite is a sporadic pest, mostly in coastal growing areas. Bronzing of leaves, mite cast skins, and partial defoliation of some trees by avocado brown mite is most noticeable from about July to September. Severe infestations tend to occur in border row trees along dirt roads, where road dust is detrimental to mite predators. Ash deposited on leaves from wildfires reportedly also causes brown mite outbreaks.

Avocado brown mite feeds almost entirely on upper leaf surfaces. It causes no significant damage when population densities are low to moderate (about 10 to 20 adult females per leaf). If the spider mite destroyer lady beetle (Stethorus picipes) is present and reproducing well at this time, brown mite does not become a problem. Damage occurs if avocado brown mite averages about 50 to 70 adult females per leaf (about 100-200 motile stages, adults and nymphs combined). At these higher densities mites also colonize the lower leaf surface and sometimes fruit, and partial defoliation can occur. These higher populations cause leaf bronzing along the midrib, then along smaller veins, and finally the entire leaf turns brown.

MANAGEMENT

Natural enemies and temperature (hot or cold weather) usually maintain this mite at innocuous levels. Maintain good biological control by conserving natural enemies. Control dust and avoid applying broad-spectrum pesticides for any pests. When treating any pests, including avocado brown mite during late summer or fall, spot treat individual trees where possible.

Biological Control
Naturally occurring populations of the spider mite destroyer (Stethorus picipes) provide the majority of brown mite biocontrol. Predaceous mites (especially Euseius hibisci and Galendromus helveolus) are also helpful, but predatory mites are primarily effective against sixspotted mite. Most other natural enemies listed as attacking persea mite also feed on avocado brown mite.

Cultural Control
Controlling dust, which improves predator activity, is critical for maintaining biological control. Oil or pave main orchard roads to reduce dust drift onto trees. When it is necessary to use dirt roads, drive slowly. Use a water truck or trailer to wet unpaved roads and prevent airborne dust, especially during summer months when heat convection currents carry dust well up into tree canopies.

Organically Acceptable Methods
Biological and cultural controls along with sulfur and some oil sprays are acceptable control methods in an organically certified crop.

Monitoring and Treatment Decisions
Look for bronzed leaves and brown mites during summer through fall monitoring for other pests such as caterpillars and persea mite, especially when monitoring in coastal groves. Consider monitoring specifically for brown mite in border rows along dirt roads during summer through fall where trees are dusty, were sprayed earlier in the season with a broad-spectrum insecticide, and after wildfires. Major outbreaks have occurred after spraying a broad-spectrum insecticide to control greenhouse thrips or omnivorous looper. To locate avocado brown mite and its webbing, use a hand lens (10X) to inspect along the midrib on the upper leaf surface. There is no suggested threshold for when treatment is warranted. Pesticide applications for avocado brown mite are rarely needed.

Common name		Amount to use	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact.
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	1 day	0
	MODE OF ACTION: Unknown. An inorganic miticide.
	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 (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 until harvest. In some cases the REI exceeds the PHI. The longer of these two intervals is the minimum time that must elapse before harvest. # Certain products are acceptable for organically grown produce.

PUBLICATION

UC IPM Pest Management Guidelines: Avocado
UC ANR Publication 3436
Invertebrates
B. A. Faber, UC Cooperative Extension, Santa Barbara/Ventura counties
J. G. Morse, Entomology, UC Riverside
M. S. Hoddle, Entomology, UC Riverside
Acknowledgment for contributions to Invertebrates:
P. A. Phillips, UC IPM Program, UC Cooperative Extension, Ventura County
M. Blua, Entomology, UC Riverside
P. Oevering, UC Cooperative Extension, Ventura County
D. Machlitt, Consulting Entomology Services, Moorpark, CA
T. Roberts, Integrated Consulting Entomology, Ventura, CA
B. B. Westerdahl, Nematology, UC Davis

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