How to Manage Pests
UC Pest Management Guidelines
Monitoring Persea and Sixspotted Mites
(Reviewed 1/07, updated 6/10)
In this Guideline:
Spider mites (family Tetranychidae) and predatory mites (Phytoseiidae) are tiny 8-legged arthropods. Persea mite is a key pest of California-grown avocados, whereas sixspotted mite is a sporadic pest. See AVOCADO BROWN MITE for details on how to manage this occasional pest.
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.
Both species feed on the underside of leaves, and the similar appearance of these mites as well as their damage can be confused. Monitor mites about every 7 to 10 days from about mid-March through October using one or more methods.
Quick Counting Method
2. Looking at the underside of each leaf, start at the petiole end. Locate the second major vein that goes strongly from the midrib to the left leaf edge. Ignore any partial, small, or weak veins. Examine the upper (towards the leaf tip) vein edge through a hand lens.
1. Total the number of persea mites counted and divide the total by the number of leaves sampled (typically 10). Multiply by 12 to derive the average mites per entire leaf.
2. Also count the predaceous mites (e.g., Galendromus spp.) in the persea mite feeding patches. Divide total predator mites by the number of leaves sampled. Multiply this predaceous mite average by 6.
4. Manage persea mite if warranted based on sampling results and past experience.
Persea and Sixspotted Mite Damage Sampling
2. Visually estimate the percent of mite-damaged tissue on each leaf by comparing it to standards with known levels of damage, such as colored photographs of avocado leaves showing 1 to 50% feeding damage. Record results.
3. For each tree, total the percent damage on the 10 leaves, then total the percent damage on all trees.
4. Calculate the estimated average percent damage per leaf: Total percent damage/Total number of leaves sampled (e.g., 100 leaves) = Average percent mite damage per leaf.
5. Manage persea mite or sixspotted mite if warranted based on sampling results past and experience.
Although it has not been experimentally verified, the probability of leaf drop is believed to increase greatly once 7.5 to 10% of the leaf surface is damaged by persea mite feeding. Thus, control may be warranted before reaching this damage level.
Persea Mite Density Estimation
2. Using a hand lens or other magnifier to examine the underside of leaves, identify whether there are any live persea mites on each leaf.
UC IPM Pest Management Guidelines:
Acknowledgment for contributions to General Horticultural Information:M. L. Arpaia, Botany and Plant Sciences, UC Riverside
M. L. Bianchi, UC Cooperative Extension, San Luis Obispo County
C. J. Lovatt, Botany and Plant Sciences, UC Riverside
P. Mauk, UC Cooperative Extension, Riverside County
G. W. Witney, California Avocado Commission, Irvine, CA
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