Spider Mites: Little Bugs That Cause Serious Damage

Little bugs can do serious damage to Pennsylvania trees and shrubs, both native and otherwise. One example of this is a group of pests referred to as spider mites. Although mostly invisible to the naked eye (they are that small!), spider mites can do a significant amount of damage to the shrubs, trees and even flowering plants that make your landscape so beautiful.

What Are Spider Mites?

In the northeastern regions of the United States, landscape owners are “lucky” enough to have not one but two different types of spider mites.

spruce spider mite

Spruce Spider Mite Oligonychus ununguis (Jacobi). This little critter is considered one of the most destructive pests in the entire United States. Not surprisingly, spruce spider mites like to feed on various species of spruce trees as well as Douglas Firs, hemlock, juniper and a few other types of conifers. The females lay their eggs at the base of needles and in/around bud scales. The eggs overwinter there and then the newborns hatch and /flourish during spring and summer, making a tasty meal of the fluids they suck from your conifers’ needles.

Signs of spruce spider mites include needles that are spotted and yellowed in appearance. Prolonged infestation will result in needles that are rusty/brown in color and that begin to drop early.

Twospotted Spider Mite Tetranychus urticae (Koch). Relatively similar in appearance is the twospotted spider mite. It is also called a glasshouse spider mite or a red spider mite. This pest is not one bit picky and will be happy to set up shop in flowering plants, shrubs and shade trees. Once established, the females overwinter under the bark or in the groundcover at the base of the host plant. When spring arrives, they get to work laying eggs on the underside of leaves. These eggs hatch fairly quickly and the newly emerged spider mites get on with the business of living – by eating their host’s healthy plant material.

Signs of twospotted spider mites include leaves that look mottled in appearance. Leaves may have grey or yellowed spots, and can eventually turn brittle and brown. Flower petals may also brown and wither. Like spruce spider mites, the twospotted offenders don’t chew the leaf material but, rather, they suck out the juice inside the leaves so the foliage is destroyed from the inside out.

What Can You Do to Conquer Spider Mite Infestations?

There are a few things you can do to protect your trees, shrubs and flowering plants from the ravages of dreaded spider mites:

  1. Be observant. The most important step is to hone your observation skills and form a relationship with your landscape. The more familiar you are with your trees and shrubs the sooner you will notice any signs of stress. As with a human illness or parasite infestation, early treatment prevents more serious side effects or further complications. If you lead a busy life or have a larger landscape that seems to get away from you, contact a local arborist or landscape management company to give you a hand.
  2. Get out the garden hose and sprayer. You can take action yourself, armed with only the garden hose and a sprayer with a high-power setting. Even though spider mites are small, they aren’t overly clingy so a thorough spray from your garden hose can be enough to knock them out of your plants. Read up on their lifecycles (we hyperlinked to them in the individual mite descriptions above) so you know right where to hit them and when. This will help to diminish spider mite populations on your plants, which will minimize the damage they can do. Keep in mind, however, that your plants are also susceptible to damage from that high-pressure approach so be very, very careful that you don’t harm tender, healthy portions of the plant when spraying them with a pressurized stream of water.
  3. Use specific miticides. Here in the arboriculture world (aka Joshua Tree), we like to use spider mite-specific treatments. These have come a long way and many products are considered “green” because they only affect the specific species of spider mites and their eggs, without damaging other living creatures. These are your best bet because they stop the entire mite lifecycle in its tracks, keeping your trees and shrubs healthy and mite-free for the rest of the season.

Late summer is the time of year when long-term feeding from spider mites is the most apparent. Spider mites hatch and grow throughout the spring and early summer, and all the juice they’ve sucked makes for visibly damaged foliage.

Are your trees and shrubs showing signs of stress? Unsure whether or not it’s mite-related? Contact us and we’ll send a licensed arborist over to make a professional diagnosis and get you on the right tree insect treatment track.

Identifying tree and shrub insects, disease, and mites.

 Image Source:  spruce spider mite

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