Spider mites aren’t insects. Surprised? They’re actually arachnids, similar to spiders but much, much smaller. In fact, they’re so small (up to 1/20”) that they’re often difficult to see without a magnifying glass. They come in a range of colors, from red to brown, yellow and green, depending on the species and time of year.
American mountain ash trees are lovely additions to any landscape, providing vibrant fall color and clusters of bright berries that attract birds. However, these trees can sometimes be plagued by spider mites, tiny pests that feed on plant tissues and cause stippling, discoloration, and even defoliation. Getting rid of spider mites on your American mountain ash requires persistence and an integrated approach, but with the right strategies, you can protect the health and beauty of your tree.
Identifying Spider Mites on American Mountain Ash
The first step is learning to recognize spider mites on your tree. These tiny arachnids are usually red, yellow, or green. Look for stippling, speckling, bronzing, or yellowing of the leaves as common symptoms of spider mite damage. You may need a hand lens to see the mites themselves, which often congregate on the undersides of leaves. If populations are high, you may see fine webbing on the foliage. Regular monitoring will help you detect infestations early before they escalate.
Cultural Practices to Discourage Spider Mites
Certain cultural practices can make your American mountain ash less hospitable to spider mites:
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Keep trees adequately watered, especially during drought, to reduce moisture stress.
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Avoid over-fertilization, which can cause excessive foliage growth that attracts mites.
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Clear leaf litter and debris that provide shelter for mites.
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Increase air circulation around trees with proper spacing and pruning.
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Wash dust off foliage to allow natural predators access to mites
Biological Control Options
Natural predators can provide significant control of spider mites in American mountain ash trees. Beneficial insects like minute pirate bugs, big-eyed bugs, lady beetles, lacewings, and predatory mites all prey on spider mites. You can attract and retain these predators by avoiding broad-spectrum insecticides and providing nectar sources with companion plants. Releasing commercially available predatory mites can supplement naturally occurring beneficials.
Organic Chemical Treatments
Several organic sprays can helpmanage spider mites on American mountain ash trees:
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Horticultural oils smother mites on contact while being safe for most trees. For best results, apply oils when temperatures are between 40-85°F.
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Insecticidal soaps also desiccate and kill mites through direct contact. Target undersides of leaves.
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Neem oil disrupts mite growth and reproduction. Mix with water and spray leaves thoroughly.
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Sulfur dusts suppress mites, but may burn foliage if temperatures are high. Follow label directions carefully.
Conventional Miticides
Synthetic miticides effective against spider mites on ornamental trees include:
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Abamectin – Translaminar activity controls active mites and eggs. Repeat applications are needed.
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Bifenazate – Contact miticide that stops mite feeding quickly. Also ovicidal.
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Hexythiazox – Inhibits mite growth and reproduction. Apply before populations build.
Always follow label directions when using miticides. Rotate chemical classes to reduce resistance.
Removing Heavily Infested Branches
Pruning out severely infested branches can eliminate sources of spider mites, especially if biological and chemical controls have not contained the infestation. Dispose of pruned branches immediately to prevent spread. Then monitor for mite rebound and consider preventive treatments on remaining foliage.
Protect Your American Mountain Ash with Persistence
Controlling spider mites takes diligence and repeated monitoring and application of control measures. But with persistence, integrating cultural practices, biological control, and least-toxic chemical options as needed, you can minimize spider mite damage and keep your American mountain ash healthy and vigorous for years to come. Don’t let these tiny pests destroy the grace and beauty of this wonderful landscape tree.
Types of Spider Mites in Colorado
In the garden, look for the twospotted spider mite (Tetranychus urticae) on vegetables (e.g., beans, eggplant), fruits (e.g., raspberries, currants, pear) and flowers.
Evergreen trees are more commonly infested by other mites, such as the spruce spider mite (Oligonychus ununguis) on spruce and juniper, Oligonychus subnudus on pines, and Platytetranychus libocedri on arborvitae and juniper. Deciduous trees are attacked by yet other spider mites, including the honeylocust spider mite (Platytetranychus multidigituli) on honeylocusts, and a range of other mites on shade trees, such as elm, mountain ash, and oak. We also see a lot of spider mites on aspen trees, especially those in drier locations.
Spider Mite Control Options
Homeowners often inadvertently make spider mite infestations worse by trying to control them with “bug control” sprays. Unfortunately, these insecticides have little effect on spider mites but kill off their natural predators, such as ladybugs, big-eyed bugs, minute pirate bugs, and predatory thrips or mites. Plus, spider mites can quickly become resistant to typical insecticides, rendering them ineffective.
The end result is an explosion in the number of spider mites, with ensuing damage to their preferred plant targets.
Super Simple Spider Mite Control and Prevention
FAQ
Can a tree with spider mites be saved?
How do you get rid of spider mites on tall trees?
What is the best treatment for spider mites?
What is the best homemade spider mite killer?
How do you get rid of spider mites on a tree?
You can’t spray a tall tree forcefully enough to get rid of the mites for good, but trees benefit from a rinsing now and then. Spider mites thrive in dusty conditions, so rinse the branches as best you can and keep bare patches of ground lightly moist to eliminate flying dust. Predatory mites and lacewings are natural enemies of spider mites.
Do aphids damage American mountain ash trees?
They are a common pest that can cause damage to American Mountain Ash trees by causing leaf curling, yellowing, and stunted growth. Signs of aphid infestation include the presence of sticky honeydew residue on leaves, black sooty mold growth, and the presence of the insects themselves.
Do spider mites damage trees?
It’s surprising that such tiny creatures as spider mites can have such a big impact on trees. Even the largest tree can sustain serious damage. Read on to find out what to do about spider mites in trees.
Do spider mites attack trees during drought season?
Spider mites attack during drought season because they love stressed out plants. During hot and dry periods, keep your plant hydrated by providing at least one inch of water per week and adequate mulch. Is your tree showing symptoms of spider mites?