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.
enter temperatures etc. This entry is not complete. come back a little later. jmm
??????????? dates and temps here
I believe that what happened was that the wingless female cankerworms were on the verge of coming out ot the ground to climb the trees for laying the eggs. In the earlier days of the cankerworm issue, December was the month with the most numbers going up the tree.
get earlier graph for december Note the strong rise of cws. Over the years, the greater numbers have been in January with the cankerworms still hatching in late March. We will see them parachuting down on thier silken threads about 10 days after the females hatch. Since the females that are captured sometimes will lay eggs on the trap especially tar paper, and the males will find them there we will often see a cluster of eggs on the trap. If the eggs survive the early hazards some will hatch on the trap on the tree and you can observer them. They will be quite small about 1/16 of an inch long.
More coming soon. Bear with me. jmm
The first week of January turned out to be the coldest temperatures recorded in Charlotte since ?????
There is an interesting link that goes into some great details about how this affected other parts of North Carolina... an alligator frozen in the ice during this same cold snap in Wilmington NC. Worth reading: https://www.weather.gov/ilm/Jan2018snow
Jack McNeary, Retired Consulting Arborist