The insects are in their larval stage and appear as little green worms defoliating ash trees.
While the damage is generally not severe, their presence indicates homeowners are not treating their ash tree for emerald ash borer, a life-threatening pest.
“Strong streams of water will remove the sawfly larvae if they have fallen onto a deck, for example, and most will not reestablish themselves in the tree after being dislodged,” the Extension’s Dana Freeman said. “Larvae are preyed upon by beneficial insects and provide food for birds. Once the larvae drop to the ground, they pupate in the soil and will not emerge as adults until next year. This is a very short-term issue.”
As a proud owner of an American mountain ash tree, you know that this gorgeous tree makes a stunning focal point in any landscape with its bursts of bright red berries and graceful form. However, these trees are prone to infestations from various destructive worms that can quickly defoliate and weaken the tree if left unchecked. In this comprehensive guide, we’ll explore the most common worms that attack mountain ash trees and provide proven solutions for getting rid of these pests while keeping your tree healthy and thriving.
Identifying Worm Infestations
The first step in treating a worm problem is identifying exactly which pest you’re dealing with Here are some of the most common worms that infest mountain ash trees
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Caterpillars – Caterpillars are the larvae stage of moths and butterflies. They have soft, segmented bodies and multiple pairs of legs. Tent caterpillars, fall webworms, and gypsy moth caterpillars frequently attack mountain ashes.
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Sawflies – Sawfly larvae resemble caterpillars but have six or more pairs of fleshy abdominal legs. The mountain ash sawfly is a major defoliator of these trees.
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Leaf miners – These tiny flies lay eggs inside leaves. The larvae tunnel between the leaf surfaces, creating winding trails.
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Borers – Borers are larvae that bore into tree trunks and branches. Emerald ash borer is an invasive borer that can kill untreated ash trees, including mountain ashes.
Keep an eye out for chewed leaves, larvae on foliage, frass (insect waste), webbing, and dieback. If you spot any of these signs, it’s likely worms have infested your tree. Identifying the pest will help you choose the right treatment method.
Natural Worm Treatments
For mild infestations, natural and organic control methods may be sufficient to get rid of worms on your mountain ash:
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Manual removal – Pluck caterpillars, sawfly larvae, and other worms off leaves and branches by hand. Drop them into soapy water to kill.
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Pruning – Prune off heavily infested branches and leaves to reduce pest populations. Dispose of infested plant parts.
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Beneficial insects – Release predators like ladybugs, lacewings, and parasitic wasps that naturally consume tree pests.
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Neem oil – This organic pesticide damages the exoskeleton and repels worms when sprayed on foliage.
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Insecticidal soap – This soap solution kills soft-bodied insects through contact. Spray on larvae.
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Horticultural oil – Coat tree with dormant oil in late winter to smother overwintering pests.
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Bacillus thuringiensis (Bt) – This bacteria-based spray specifically targets and kills caterpillars when ingested.
Chemical Worm Treatments
For severe worm infestations, you may need to use chemical insecticides. Here are some effective options for getting rid of mountain ash worms:
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Carbaryl – This common insecticide kills worms on contact. Apply as a foliar spray and repeat as needed.
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Imidacloprid – Systemic insecticide taken up by the roots and makes leaves/stems toxic to pests. Controls borers.
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Permethrin – Broad-spectrum contact insecticide that kills many leaf and wood boring pests. Low toxicity to mammals.
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Spinosad – Derived from bacteria, this organic pesticide causes larvae death after ingestion. Low toxicity.
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Methoxychlor – This organochloride insecticide is effective on sawflies, webworms, leaf miners and other mountain ash pests.
Always follow label directions carefully when using chemical treatments. Avoid spraying insecticides during bloom to protect pollinators.
Preventing Worm Infestations
An ounce of prevention is worth a pound of cure when it comes to protecting your mountain ash from worms. Here are some tips to avoid problems in the future:
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Plant resistant varieties like the golden mountain ash, which is less prone to pests.
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Maintain tree health with proper watering, fertilization, and pruning. Healthy trees withstand pests better.
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Clean up fallen leaves, berries, and debris around the tree that provide shelter for overwintering worms.
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Apply preventative trunk sprays of systemic insecticides if emerald ash borer has been found in your area.
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Regularly inspect trees for early signs of worm activity and treat promptly before infestations escalate.
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Allow beneficial predators like birds access to your trees. They eat many tree pests.
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Avoid excessive pruning, damage to bark, and other stresses that make trees more vulnerable to borers.
When to Call a Professional
In cases of severe repeat infestations, it may be wise to have your mountain ash evaluated by an arborist. They have specialized tools and insecticides that may be more effective for large, mature trees. Professional removal may be required if worms have extensively damaged the tree. For emerald ash borer treatment in particular, specialized trunk injections are much more successful than homeowner sprays. An arborist can help devise a tailored pest management plan to restore your tree’s health.
With knowledge of common mountain ash pests and available control methods, you can protect your tree from destructive worms. Stay vigilant for early signs of infestation and take prompt action. Combining natural treatments, targeted insecticides, and prevention techniques will help keep your American mountain ash worm-free and beautiful for years to come. Don’t let worms ruin your tree’s ornamental features or jeopardize its health – implement an integrated pest management plan today!
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The top question at the Nebraska Extension office this week has been about ash sawflies.
The insects are in their larval stage and appear as little green worms defoliating ash trees.
While the damage is generally not severe, their presence indicates homeowners are not treating their ash tree for emerald ash borer, a life-threatening pest.
Treatment for emerald ash borer applied this year will manage the sawflies next year.
“Strong streams of water will remove the sawfly larvae if they have fallen onto a deck, for example, and most will not reestablish themselves in the tree after being dislodged,” the Extension’s Dana Freeman said. “Larvae are preyed upon by beneficial insects and provide food for birds. Once the larvae drop to the ground, they pupate in the soil and will not emerge as adults until next year. This is a very short-term issue.”
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Freeman said the extension also continues to receive pictures of birch trees not leafing out at the branch ends. This dieback is not uncommon for birch trees in this area and should be pruned out.
Not only do these trees have shallow roots that can be damaged by summer’s heat, she said, but they can be injured by freezing temperatures following warm, dry winter weather.
“Protect these trees from further damage by enlarging their bed of hardwood mulch and watering as needed to keep soils cool and evenly moist,” she said.
How to Remove Fall Webworms from Your Trees without Chemicals!
FAQ
How do you get rid of ash tree worms?
What are the worms on mountain ash trees?
How to get rid of tree worms?
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.
How do you know if a mountain ash tree has worms?
It emerges to lay its eggs on bark in April. The larva, which are light yellow worms with black heads, hatch and burrow into the trunk of the mountain ash. Signs of their activity are galleries in the trunk bark near the base of the tree, round holes about the diameter of a lead pencil, and frass (sawdust) nearby.
Do mountain ash trees wilt?
Fungicidal sprays containing chlorothalonil or mancozeb can be used to protect healthy foliage. Identification: Root rot is a common problem in American mountain ash trees caused by various soil-borne pathogens. Symptoms include wilting, yellowing foliage, stunted growth, and dieback of branches.
What eats mountain ash trees?
Holes In Lower Trunk Indicates Borers. The biggest nuisance pest of mountain ash trees is borers such as the flat-headed apple tree borer or the round-headed borer. The latter is the larva of a beetle that is about 3/4 inch long, brown with white stripes down its back. It emerges to lay its eggs on bark in April.