The most common species of spider-mites that affect hops is the Two-Spotted spider Mite. They can be very economically damaging during hot and dry parts of the season. They feed on the leaves, which can negatively affect both quality and yield.

Identification

Two-spotted spider mites are very small and a 10x hand lens is typically needed to identify them. Adults are identified by two dark spots on either side of the front portion of the mites. Larvae look similar, but are smaller and translucent. Eggs and small, clear and spherical.

Damage first appears as yellow spots on the leaves where feeding as occurs. In heavier infestations webbing appears on the undersides of the leaves. Severely infested leaves wilt and die as the spider mites continue to feed on the leaves through piercing-sucking.

Two spotted spider mites should be scouted for early in the season, before heavy infestation has a chance to occur. If mites are found early, control through biological or chemical options is easier to achieve. Spider mites prefer hot and dry climates. Their development can be tracked by using Growing Degree Days to help predict when different life-cycle stages will be met. This is important to know when considering chemical sprays, because different active ingredients will affect different stages of the mite’s life-cycle. For example, hexythiazox (Savey), is effective against nymphs and eggs, but not adults. The Pest Prophet app can be used to track growing degree days, using localized weather data.

Spider Mite Management on Hops

Two-spotted spider mites prefer dusty areas of the hop-yard so applying water on dirt roads, and reducing speed of vehicles can prevent dust. Stress due to irrigation deficient or other factors can also cause plant to become more susceptible.

Biological control is very important in spider mite management. Predatory mites are very common in most regions where hops are grown. They can be identified by the clear, light amber color and they are typically more oval, or tear-dropped shaped than spider mite pests. Many commonly used pesticides may have adverse effects on natural predator populations. Studies have shown that sulfur sprayed early in the season for Powdery Mildew control, can cause outbreaks of two spotted spider mites later in the season. Natural predators should also be scouted and monitored, before and after spraying.

There are a few species of predators that available for commercial production and release, such as Phytoseiulus persimilis and Neoseiulus californicus. Persimilis releases should be targeted to areas of the hop-yard where spider mite populations are highest, or where most damage is present. This will give the Persimilis a feeding source to begin building up their population. Re-releasing may be necessary to establish predator populations.

If chemical control is needed, be very careful to check the label of available products. Different active ingredients of miticides can be used to target different life-cycle stage of spider mites. Different products will also affect other insects, such as natural predators, in different ways.

Learn More: Complete Guide to Spider Mites