Article presented by: Donna Thrasher, Union County Extension Master Gardener 2011
PROTECTING TREES FROM FALL CANKERWORM DAMAGE:
Plan now for your "not so fun" Spring surprise.
It’s that time of year again and I’m not talking about the approaching holiday season!
And this year, rather than completely ignoring it and then thinking next spring “Darn, how could we have forgotten that yet again?”, given what we now know, we are purposefully trying to decide whether to do it all.
The “what” in this instance is band our trees against fall cankerworms – Alsophila pometaria, sometimes commonly known as “inch worms”, which turn into a dreaded spring menace in our area. In fact, fall cankerworm defoliation is a perennial Growline question each spring.
This problem is a cycle so it’s hard to know which came first – the moth or the egg, so to speak. We’ll start with the adult stage because, as I said, it’s that time of year. The female moth, which is wingless and has been lying in its pupal form in the soil since summer, emerges with the trigger of the cold temperatures of November & December. She climbs up to the top of the tree and lays her many, many, many eggs which then hatch as caterpillars in the spring. That’s when the actually defoliation attack begins as these caterpillars begin to eat the young spring leaves. To finish the circle, the now fully grown caterpillar enters back into the soil to make a cocoon and wait until the cycle begins again.
While cankerworms in our area seem most noticeably to feed on our oaks, they will happily munch on a variety of hardwoods and ornamental trees and shrubs.
Living in Charlotte for so many years with its beautiful street tree canopy, I was under the impression multiple years of the foliar denuding itself by cankerworms would ultimately kill the tree. For Charlotte, cankerworm control is all out warfare with periodic aerial spraying under the approval of the NC Department of Agriculture and a specific city/county website page encouraging homeowners to “Band Together” in the fight against cankerworms.
Although we lived in an old neighborhood with lots of established trees, we personally never seemed to have any problem with cankerworms – on so many levels, I think we moved to Union County just in time!
But, I now know the defoliation itself is not life-threatening to an otherwise healthy tree, which is able to tolerate it and leaf out again once the cankerworm feeding is done. However, it’s the continual defoliation year after year that adds to stresses that may already be present in the tree that is the issue – the stress from drought and the stress of an urban environment of autos and pavement.
In a perfect world, natural factors such as birds and rodents, parasitic wasp, and adverse weather conditions would keep the cankerworm population under control. When you see pieces of tree bark coming off, squirrels and birds are foraging for the caterpillars, which is certainly unsightly but is helping reduce the munching of hungry inch worms.
Beyond these chemical or natural controls and providing the tree with a good watering and fertilization program to help combat stress, the most common “other strategy” taken in our area is banding the tree with a physical barrier to capture the climbing females before giving them a chance to lay their eggs. Not just any physical barrier will work. It needs to be something “icky & sticky” to keep the females from just climbing up and over the barrier, and the sticky substance should not be applied directly to the tree itself.
According to the North Carolina State University, NC Cooperative Extension site, band your trees as follows:
Tree Banding- Tree banding in November and December can be an effective way to block wingless females from crawling to the tops of trees to lay eggs. Traps should be in place about mid-November through all January. A sticky agent such as Tanglefoot™ is applied to a band around the tree, rather than the tree itself to protect the bark. Some stores in the Charlotte area sell tree banding supplies and pretreated bands.
Step 1: Install a strip of batting or insulation around the tree a few feet above ground level and below all limbs.
Step 2: Position a band of tar paper or roofing felt 6-12 inches wide, around the trunk circumference covering the batting. Short staples may be used for this. Do not use nails. Electrical tape might be used for small smooth-barked trees.
Step 3: Apply the Tanglefoot or sticky material in a band several inches wide onto the tar paper. Wear disposable gloves for easy clean up. Bands must remain sticky and clear of excessive debris, and may need to be "refreshed" periodically.
So, why would we choose not to band against these pests? Although one of our few affected trees is directly over our front deck making the annual defoliation messy and unsightly, frankly, we have just too many trees on our property – it would physically be impossible to band them all, which means we wouldn’t be making much headway to eradicate the problem. Realistically, it will be much more effective for us to try to make sure our trees stay in the “otherwise healthy” category.
But that doesn’t mean this coming spring, we won’t wake up and say something along the lines of “Darn”!!
Some websites for more information can be found at:
North Carolina State University, NC Cooperative Extension -http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note153/note153.htm
Bartlett Tree Research Laboratories, Charlotte - www.bartlett.com/resources/Cankerworms.pdf
Charlotte Mecklenburg, Working Together To Save Our Trees -http://www.charmeck.org/city/charlotte/epm/Services/Landscaping/Pages/fall%20cankerworm.aspx
Fall Wingless Cankerworm Moth:
Fall Wingless Cankerworm Eggs:
Banding Process from NC State University:
Banding Process Complete:
Cankerworms Caught in Banding: