Warm, Dry Weather Brings Out the Spider Mites

By Trisha Gedon, Oklahoma State University

First posted on 06-07-2013

With summer knocking on the door, Oklahoma gardeners may soon be dealing with more than increasing water bills.

As the weather turns hot and dry, spider mites can become real pests, said David Hillock, Oklahoma State University Cooperative Extension consumer horticulturist.

“Some species of spider mites are limited to one or a few kinds of host plants, but there are others that feed on many different types of plants,” Hillock said. “Tomatoes and marigolds are the most popular picks for spider mites, but there are only a few plants completely immune from all species.”

Damage occurs when the mites suck plant juices with their small, needle-like mouthparts. A light infestation will leave a pattern of small, pale spots on the infested plants. With a heavier infestation, gardeners will see where the individual spots run together and can cause the death of a leaf.

Hillock said this type of damage is the only sign of an infestation in species of spider mites that do not spin webs.

“One way to check for the presence of mites is to shake the plant over a white piece of paper. If you see tiny specks begin to move on the paper, they are likely mites,” he said. “Some species overwinter as adults, while others overwinter as eggs. As the weather warms they hatch or become active.”

Spider mites, often called red spiders, are barely visible to the naked eye. Newly hatched mites have six legs, but all other active stages have eight legs. They are related to spiders and ticks and are not insects. Hillock said there are several different species in Oklahoma. Some are reddish in color but others are brownish or pale greenish. Some have two or more darker spots on the back. Several common species spin fine, irregular webs over the infested parts of plants but other species spin little or no webbing.

He also noted hot, dry weather is favorable for most spider mites and during the summer months they can complete a generation in 7 to 14 days. Females can lay as many as 300 eggs in their webs or on host plants. This can result in a rapid infestation of spider mites and may cause extensive damage to plants in a short amount of time. Infestations will begin to decline later in the year when the weather becomes cooler and wetter.

Fortunately spider mites are relatively easy to control with a strong stream of water that knocks them off the plant.

“Using water to control them also helps conserve their natural enemies, including lacewings, lady beetles and predatory mites,” Hillock said. “Practices that encourage predators to the garden helps reduce the need for chemical control. If necessary, gardeners can use insecticidal oils and soaps, which are known as soft pesticides.”

Photo from wikipedia.com, submitted by Gilles San Martin