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Frequently Asked Questions

Topic: Insects and Pests

1. Question: How badly can OPM damage trees?
Answer: Like all caterpillars, OPM feeds on the leaves of oak trees. High caterpillar numbers can result in severe defoliation, but so far no trees have been recorded as dying because of this. Normally defoliated trees produce leaves the following spring and recover. However, annual defoliation over a number of years can weaken trees which might over time result in oak tree decline.
2. Question: Are all oak tree species affected by oak processionary moth?
Answer: Kew Gardens contain many different species of oak. Recording of attacks on oak there indicates that OPM is mainly found on English, Sessile and Turkey oaks (Quercus robur, Q.petraea and Q.cerris).
3. Question: Can I still plant oak trees given oak processionary moth infestations?
Answer: Yes, there is no reason why oak trees should not continue to be planted. However, as a precaution, we suggest that anyone planning large-scale plantings in the London area, especially where there is public access, should be aware of the possibility that OPM could spread and pose a risk to human health.
4. Question: Can OPM be fatal to humans or pets?
Answer: To date no human, cat, or dog deaths have been recorded by people or pets coming into contact with OPM. However, the older caterpillars are covered in irritating hairs that contain a toxin. Contact with these hairs can result in skin irritation and allergic reactions such as rashes and conjunctivitis. If the hairs are breathed in, this can cause asthma or anaphylaxis. These problems are significant because OPM are mainly found on urban trees, along forest edges, and in amenity woodlands.

Learn more about the danger OPM poses.
5. Question: Are other tree species besides oak attacked by oak processionary moth?
Answer: Hornbeam, hazel, beech, sweet chestnut, and birch have been reported to be attacked, although mainly when growing next to badly defoliated oaks.
6. Question: If I find OPM nests or caterpillars in my trees, what should I do?
Answer: We strongly advise against treating this pest yourself. The health dangers posed by the caterpillar hairs, thousands of which can be in the nests are potentially high. In addition, to effectively manage OPM, the job must be done at just the right stage in the moth's life cycle by someone professionally trained to carry out the task.

Bartlett Tree Experts have highly qualified and trained staff who can advise and treat your tree. We offer a range of effective control methods that include surveying, bio-control treatments, botanical insecticides, insect growth regulators and systemic tree injections. Regular monitoring of oak trees in spring and early summer is recommended. Early detection can prevent infestation and aid in effective management.

Learn more about the treatment of OPM.
7. Question: Where in the UK has OPM been found?
Answer: At present West and Southwest London are the most severely impacted OPM areas. OPM has been confirmed in the following boroughs: Brent, Bromley, Croyden, Ealing, Hammersmith & Fulham, Harrow, Hillingdon, Hounslow, Kensington & Chelsea, Kingston, Merton, Newham, Richmond, Spelthorne, Wandsworth, and Westminster. Isolated cases of OPM have also been found in Pangbourne (Berkshire) and Bromley (Kent). Careful monitoring of OPM spread is ongoing but unfortunately all evidence indicates that this pest is slowly spreading beyond the London area.
8. Question: Does anything eat OPM?
Answer: OPM does have some natural enemies in its native range to include some species of birds, beetles, small mammals, and parasites. We can expect some of our ‘generalist’ predators and parasitoids to exploit populations of OPM in the UK, but it is not anticipated that these predators will have any significant effect on OPM populations.
9. Question: We have an Aspen tree that gets some kind of bugs on the leaves. The leaves get really sticky and, by summer, there are wasps and bees swarming around it all the time. It is right next to our neighbors house and along our driveway. The driveway gets this weird stuff all over it and the grounds actually looks darker under the tree from the substance. We've had the tree sprayed in the past, but it doesn't seem to work. What do you suggest?
Answer: There is a systemic insecticide that can be applied to the soil at the base of the tree that will be absorbed by the roots and transferred into the foliage. The treatment will provide season long control of aphids, as it is highly effective. This is a process that should be handled with great care. You can click here to make an appointment with one of our professionals.
10. Question: My Princeton Elm leaves are being eaten by a small green caterpillar a half- to one-inch in length. The damage has been fairly extensive for the last two years and this year it has started very early. The tree is 15 years old and about 50 feet tall.
Answer: It sounds like Winter Moth, an insect that has migrated into our area from Asia through Canada. It feeds on many deciduous trees in early spring, but prefers fruit bearing trees such as ornamental cherries, pears, and crab-apples. If the tree is attacked repeatedly, it could weaken it and kill it. Two treatments are necessary and will likely need to be done on a yearly basis until this pest subsides.
11. Question: Can the Emerald Ash Beetle be controlled in the healthy looking trees?
Answer: With the Emerald Ash Beetle, you would see exit holes and the tree would not survive the damage from the beetle. We recommend having the tree examined by a certified arborist to make sure it is not the Emerald Ash Beetle. If it looks like this particular insect, then the state should be informed. You can click here to schedule an appointment with one of our professionals.
12. Question: I have insects in one of my trees. Recently, a large branch fell, exposing the extent of the insect damage. Could you provide insight as to what I may be able to do to prevent further damage?
Answer: Insects can invade trees several ways. With what you described, it sounds like ants in dead heartwood of the tree. The condition mentioned should be evaluated by one of our Certified Arborists. You can make an appointment by clicking here.
13. Question: I have three Birch trees in my yard. They are starting to show signs of a beetle infestation. The top branches had leaves turning brown and dying just prior to the fall leaf drop. The trees are over 20 years old and I'd like to know if they can be saved.
Answer: We would like to arrange a time for our arborist to meet with you to evaluate your Birch trees. We do have a treatment to suppress the borers causing the damage to your trees. You can make an appointment by clicking here.

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