Identification

The three most common spider mite species on grapes are the Pacific spider mite (Tetranychus pacificus), Williamette spider mite (Eotetranychus willamettei) (photo above) and the two-spotted spider mite (Tetranychus urticae). European red mite (Panonychus ulmi) are also common in some reasons such as the Eastern United States. All these spider mites by the distinctive webbing the create on the undersides of leaves. A 10x hand lens is usually needed to correctly identify spider mites.  Spider mites feed on plants by sucking from the leaves, creating bronze, or yellowing on leaves in early infestation.

The Pacific spider mite is more common in hotter areas where grapes are grown, such as the San Joaquin Valley in California, though they can also occur in cooler, coastal areas. Pacific spider mite female adults can vary from orangish-red to slightly green in color, typically turning red or orange later in the season. Two large spots on the front of the mites and two smaller spots on the rear portion of the abdomen appear once feeding has begun.

The Williamette spider is yellow in color and prefers cooler micro-climates. For this reason is seen more often early in the season, and is found more often in shaded parts of the plant. It is also more common in cooler, coastal, climates.

The two-spotted spider mite is distinguished by having only the two pronounced dark spots on the front part of its body, with no spots on the rear. It is very common in some crops and does effect grapes, but in most areas it is not as serious as a threat as the Pacific and Williamette spider mites.The management and control of these three species are the same.

Spider Mite Management on Grapes

Applying water on dirt roads, and reducing speed of vehicles can prevent dust, which will help decrease spider mite populations. Using overhead sprinklers can also be used to control lighter infestations of spiders mites, and also can be used to reduce dust and increase humidity. Avoid irrigation stress which will make the plants mores susceptible to spider mites

Spider mites have many natural enemies. Predatory mites are very common in most grape growing regions. They can be identified by the clear, light amber color and they are typically more oval, or tear-dropped shaped than spider mite pests. Avoid spraying materials which may harm or disrupt predatory mites.

Commercially reared Western predatory mites and Neoseiulus californicus are also for purchase and release. These can be very effective at controlling spider mite populations in grapes. Releases should be target to areas of the vineyard where spider mite populations are highest, or where most damage is present. Natural predators should also be scouted and monitored. Releasing beneficial mites at multiple times may be need to establish their populations.

If miticides are needed for heavy infestation, be careful to choose products that are selective and will not kill the natural predators present. Spraying at times of the day when natural predators are least active can also help to not disrupt them.

Learn More: Complete Guide to Spider Mites