Ask Your PCA: What is best way to control spider mites?

Issue Date: March 11, 2020
Edgar Godoy PCA/CCA, AG RX, Santa Maria
Edgar Godoy

On the Central Coast, spider mites are a year-round problem in strawberries. There are four species of this pest that are economically important for strawberries, but twospotted spider mite is the main one. During the 2019-20 growing season, there were about two and a half months of overlap between summer and fall plantings. The mites migrated from the older plantings to new fields, which increased pressure.

The temperate climate on the Central Coast also contributes to spider mites becoming a year-round problem. Spider mites attack the young, new plants and stunt them, as well as resulting in yield reduction.

The first indication of mite damage is yellowing on the leaves. Depending on the variety, it could show bronzing or a purpling color as well.

Before starting treatment, it's important to monitor for mites. The fields should be checked a couple of times a week by taking random samples from the oldest and mid-tier leaves of the plants, then counting the mites using a hand lens. Five mites per leaflet this time of the year, on average, is an indication treatment should begin, or there will be an impact on the plant and yields.

An integrated pest management approach is recommended that includes releasing beneficial mites and spray applications of miticides. Predatory mites—Phytoseiulus persimilis and Neoseiulus californicus—are the main beneficials used to control the mites. The persimilis is a very aggressive predator mite, and it will feed heavily on the twospotted spider mites. Approximately 20,000 beneficial mites are released per acre. Depending on the pressure of a given field, more beneficials could be released.

If the spider mite numbers increase more rapidly than the predatory mite populations, a miticide may be indicated. Some miticides are more toxic to beneficials than others, so it is important to choose miticides that won't impact them.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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