What Happened To The Fall Cankerworms During The Fall Of 2018 And Spring Of 2019?
I am retired but still keep up with the members of the Charlotte Arborist Association. I do not make all their meeting but did so in June of 2019. We all agreed that there were virtually no cankerworms, and that there is no way they can make a comeback this year. I wrote this report several months ago and posted it here for you to look at and agree or disagree. I will put up a band with Tanglefoot in the fall of 2019 just to see if I capture any. BTW today August, 14 I saw and captured a small dark brown inch worm that had been on a willow oak. Over the years I have seen the occasional “cankerworm or inchworm” during the off season, but they are of a different species than the Fall Cankerworm.
Below is part of the Article I wrote. I have not finished yet so it is not complete. The reason I am posting a partial article is that I have some other irons in the fire and have promised that I would get this information out.
I am interested if you have comments.
Where did the Cankerworms go this spring?
If you have been in Charlotte any length of time, in the fall, you have noticed the cankerworm traps on many trees, especially the large Willow Oaks lining many residential streets. In the late fall, the wingless female cankerworms climb up the trees, lay their eggs in the tops of the trees, and the eggs hatch in late March. About ten days later we start seeing rappelling caterpillars (also known as inch-worms) and the defoliation of many trees. Because the wingless female climbs the trees, the sticky “Tanglefoot” traps or similar tree wraps capture them on the way up the tree.
One of my favorite photos of the cankerworm is this trap where someone on Lilac Road wrapped Duct Tape backwards around a large willow oak and thousands of cankerworms tried to go back up the tree in the Spring and were captured in the glue on the Duct Tape. It appears the person who put up this trap also used tarpaper with Tanglefoot on it which is the black band close to the top of the duct tape.
The traps also capture many young larvae on their way down in the spring. These are the cankerworms that do all the damage. This year was different; there were plenty of traps but no cankerworms.
I have been tracking the cankerworms since shortly after Hurricane Hugo paid us a visit on September 22, 1989. Back then we knew very little about cankerworms. We did not know when the wingless females would climb the trees, lay their eggs, when they would hatch, we did not understand how much harm the young larvae would do to our trees, and what it would cost to control the cankerworms. Over the years we have learned a great deal about the cankerworms and have seen some years where there was tremendous defoliation all over the Charlotte area. In any event, the cankerworm population has diminished significantly over time. Cankerworms prefer to feed on Willow Oaks in this area, and some years some trees are totally defoliated in the early spring. If trees are attacked year after year, then the cankerworms cause a big expensive threat to the tree canopies of Charlotte and Myers Park, and other neighborhoods that have many willow oaks. Trees in general do much to provide shade, cool the air, filter pollutants, and produce oxygen just for starters. Where did the cankerworms go?
In the spring of 2019 for all practical purposes, there were no cankerworms in the Charlotte area. Why did they just seem to disappear? I believe that I know the reason. During the first week of January in 2018, I noticed that it was very cold. For seven days the temperature was below freezing at some time during the day. I commented at the time that I had never seen it that cold for that long an extended period. Later I checked the weather map for Charlotte and found the high and low temperatures for the first week of January 2018.
Monday Jan 1,2018 Low Temp= 18 degrees F High Temp= 38 degrees
Tuesday Jan 2, 2018 Low Temp=10 degrees F High Temp= 34 degrees
Wednesday Jan 3, 2018 Low Temp= 12 degrees F High Temp= 34 degrees
Thursday Jan 4, 2018 Low Temp= 19 degrees F High Temp= 34 degrees
Friday Jan 5, 2018 Low Temp= 10 degrees F High Temp= 36 degrees
Saturday Jan 6, 2018 Low Temp= 14 degrees F High Temp= 34 degrees
Sunday Jan 7, 2018 Low Temp= 12 degrees F High Temp= 30 degrees
Monday Jan 8, 2018 Low Temp= 19 degrees F High Temp= 43 degrees
I believe that what happened was that the wingless female cankerworms were on the verge of coming out of the ground to climb the trees for laying their eggs. In the earlier days of the cankerworm issue, December was the month with the most female cankerworms climbing up the trees.
In the early years of gathering data, I made a graph of the cankerworms and how many female cankerworms actually climbed the trees on a daily basis. See photo Below
I made this graph for the month of December for 1997 / 1998. At the time the cankerworms were migrating up the trees mostly in December. Now the primary month for migration is January.
The first week of January in 2018 turned out to be the coldest continuous low temperatures recorded in Charlotte and Raleigh since 1887.
In the fall of 2018 I saw only three cankerworms going up two street trees or trees on residential properties. I looked in a lot of places, and no one seemed to have seen any cankerworms. I also asked other Tree Service companies what they were finding, and there were no positive answers. Interestingly enough the City had the companies that typically contract to install the bands sign a three year contract in 2018. It cost approximately $250,000.00 per year to treat the city street trees, and I doubt there will be many cankerworms captured in the fall of 2019. I did hear from one of the City Arborist that there was one area where there was a heavy infestation. I could be wrong, but I do not see how so few insects can cause any major defoliation this next season. I also believe there is a city program that gives money away to neighborhoods to spend on banding trees. I plan to find out more information about both of these issues.
Jack McNeary September 20th 2019
Coldest in Charlotte and Raleigh sine 1887.
The coldest its ever gotten in North Carolina was on the top of Mount Mitchell on January 21, 1985 ... at a record breading -34 degrees F
Read this article here : A look back on the coldest day ever:
There is also an interesting link that goes into some great details about how this cold snap of early January of 2018 affected other parts of North Carolina ... as and example there was an alligator frozen in the ice during this 2018 cold snap in Wilmington NC.
The temperature data I posted in the article about the cankerworms above came from this link” https://www.timeanddate.com/weather/usa/charlotte/historic?month=1&year=2018
Jack McNeary, Retired Consulting Arborist
end for now