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OSU Extension

College of Food, Agricultural, and Environmental Sciences

August 18, 2020 - 8:00am --

Late summer is prime time for two worm pests, of both coniferous and deciduous trees, to cause damage and frustrate those who are trying to keep their trees healthy and thriving. These pests are the bagworm and the fall webworm. Both pests can cause severe defoliation to the trees and leave trees either in poor health or with unsightly damage.  

The bagworm is typically found defoliating arborvitae, junipers, and other conifer and deciduous trees such as pine, spruce, locust, and willow. This worm can be found in a small, spindle shaped silk bag that is typically covered with pieces of the foliage and debris from the surrounding branches. The bagworm female can produce over 1,000 offspring and once they are mature and inside of the bags, they can no longer be killed with pesticides. When disturbed, they retreat into their bags, which is another reason as to why this pest is so difficult to control. When left untreated, the young larva can eat the buds on branches, causing dieback in the trees. Excessive feeding and defoliation over time will result in plant death. Another type of damage caused by the bag worm occurs when the worm wraps silk around the branch to hang its cocoon from and this ends up girdling the branch, resulting in branch death several years later. There are several options for control of bagworm. First is physically removing the bags from the tree. When there are a small enough number of bags, it may be feasible in the fall to locate the bags and physically remove them and dispose of them by either smashing them or throwing them away. Do not remove them and then leave the bags on the ground around the tree, the bags need to be destroyed or completely removed from the area. Another option to fight off bagworm is to use Bt. spray. Bacillus thuringiensis (Bt.) is a bacterial spray that is effective against bagworm when applied while the young larvae are feeding towards the end of June. Other insecticides such as pyrethroids are effective for control of bag worms, however, the challenge in using insecticides is that the plant foliage must be thoroughly covered to have full control.

Fall webworms, which may sound similar in name to the bagworm, are a completely different pest. The webworms cover trees with large webs that protect them from predators. These worms feed on deciduous trees in the fall and can cause significant amounts of defoliation. Fortunately, the timing of the damage caused by the webworm is typically late in the season close to when the trees would be starting to drop leaves anyway. This means that there is little impact on the long-term health of the tree, however, the large white silk webs are unsightly, so too is the defoliation caused by the webworms. The caterpillars feed for around 6 weeks while surrounded by their web. Chemical control measures are most effective when taken before the trees are covered in webs. If the tree is small enough or there are just a few small webs, the webs can be pruned out of the tree and destroyed or disposed of in a way that will not allow any of the worms to make it back to the tree. Bt. is another control option; however, it may be difficult to apply in larger trees with large clusters of webworms. In terms of the web that is left, the pesticides will not remove them, but a strong stream from a garden hose that is fitted with a spray nozzle can help remove the webs. For those larger trees that are more difficult to work with, it is best to work with professional arborists who can help apply the appropriate insecticides or help to remove the webs completely.

Wasps, Hornets, and Bees… Oh My!

            The extension office has been receiving a lot of calls about the big three stinging insects: wasps, hornets, and bees. The Extension office does not do any removal of any of these insects. If you have a swarm of bees that is on your property and you are looking for someone to remove it, there are resources listed on the Ohio State Beekeepers Association website. There is a tab listed as “Swarm Removal” which takes you to a page where you can click on your county and find a list of people who do swarm removals. For hornets and wasps, if the nest is around, on, or in your house and you are not comfortable with taking care of them yourself, it would be in your best interest to call a pest control agency. If the nest is below ground, the best time to treat the nest is in the morning just before the sun begins to rise. Use insecticidal dust and apply it down into the hole and then cover the hole with a shovel full of damp soil to prevent escape. There are some commercial traps available to use, however, these do not provide quick or complete control. If you decide to do any kind of treatment on your own, know and understand that there is a risk of being stung. You need to make sure to wear protective equipment such as gloves, hats, goggles, long sleeves, etc. If you are ever unsure about a wasp/hornet nest, it is highly recommended to call a professional or pest control company to kill the insects and remove the nest.


 Frank Becker is an OSU Extension Agriculture and Natural Resources Program Assistant and IPM Program Coordinator.  He may be reached at 330-264-8722.

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