Ask Your PCA: What are ways to manage mites in vineyards?

Cameron Jones Nutrien, Stockton


Mites are a damaging pest in vineyards. They put a lot of stress on the leaves by sucking out the nutrients and, eventually, the leaves stop photosynthesizing.

As mite populations stress the vines, they also stress the ripening sugars and impact ripening stages later in the season. In the San Joaquin Valley, the main problematic mites are Pacific and two-spotted. The Pacific is the more destructive of the pests, and its challenges can blow up very fast.

Dust on the leaves is a haven for mites, and they tend to hide underneath leaves that have the dust. Mites also thrive in dry conditions and love high heat.

As the vines head into véraison, they’re already under a lot of stress, and mite infestations can happen quickly without careful monitoring and treatment. Generally, mites start on the west or north end of the vineyard, where the wind blows, or where the dustier fields are found.

Dust control is an important aspect of mite control. Magnesium chloride or calcium chloride are applied to roads as a dust repellent. Plain water is also used.

Use of preventive miticides has been a common practice, but that is changing as grape growers move to sustainable programs. This transition has resulted in more frequent use of softer materials that preserves the beneficials, such as lacewing crawlers in the larval stage, six-spotted thrip, ladybug larvae and predator mites.

These beneficials will attack the mites, so it’s important to try to preserve them by using softer miticides and continue to rotate chemistries to prevent resistance from building.

A good rule of thumb is to use the softer chemicals early in the year to manage the mites and save the harsher miticides for later in the season if there is a flare-up of mites, to keep the numbers down and prevent damage.

Permission for use is granted. However, credit must be made to the California Farm Bureau Federation