What Every Homeowner Needs to Know About Their Aging Trees

Where did all the Cankerworms go in the spring of 2019


 Cankerworm Page

Cankerworms 2007/2008

The information below is part of a program given at Myers Park Methodist Church on October 27, 2007 by Jack McNeary. There are a few photographs here.  There are more photos at the link above (Additional Photos).  The photographs show some of the problems encountered in installing cankerworm traps.

If you do not want to read through the entire program, there is summary of how and when to band your trees for the cankerworm on page number ten.

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You would not be here if you did not know something about the fall cankerworm.  I am not interested in going over a lot of old details about which you are already familiar, but do want to tell you of some new things and treatments that we have learned.  I am convinced that if you monitor your traps properly throughout the season, you will protect your trees.

To get to the point of discussing new treatments for cankerworms, we need a little review of what works and what does not work in keeping the insects from feeding on our trees.

Tree Spraying for Cankerworms

At this point I want to say that I am all in favor of the city spraying the trees in the spring, however, you will still need to band your trees in my opinion.  Here is why.

1.  The area to spray has increased to 73,000 acres.  The first spray in 1992 was over 1600 acres.  It did little good.  In 1998 the city sprayed 6000 acres twice, and the spray was considered effective.  The second spray was done 10 days after the first spray.  The earlier spray was done with a helicopter and the spray in 1998 was done with a fixed winged aircraft.  This spring, (2008) the city is planning on spraying 73,000 acres one time.  Steve Ketner, Supervisor of Tree Maintenance who works with Donald McSween, the city arborists told me that they just want to keep most of  the leaves on the trees and do not want to or expect to wipe out the population of cankerworms.  If the trees retain some leaves, and we have rain, hopefully nature should take over.

2.  What if it rains or is too windy at the time of spray?  It will take approximately seven days to spray.  Will there be good weather that entire time?  I don’t think you can count on having perfect conditions over your house when they spray.  In 1998 when they had the successful spray, the city sprayed twice, at the hatching of the insect and ten days later at what is called the first instar.  That is the time when the small caterpillar sheds (molts) its hardened skin.

The 1998 spray was delayed a day because of rain and a second day because it was too windy.  This spray was rather successful, at least over my yard, but in the afternoon it became windy.  In the parts of town where the spraying was being done in the windy afternoon, it was not nearly as effective.  As I recall, the area around Wendover Road and Forest Drive had heavy cankerworm damage that year.  That area was sprayed in the afternoon after the wind increased.

The spray that will be used is bacillus thuriengiensis  BT for short and Dipel as a trade name.  It is harmless to people, dogs, cats, fish etc.  BT causes the caterpillars to stop eating within minutes after they have ingested a leaf with some of the BT on it.  BT is referred to as a biological control, and in this case is a stomach poison.  It is not a contact insecticide, and as I understand it, the insect only dies if it eats some of the BT. **

I have been messing with these critters since right after Hurricane Hugo back in September of 1989.  We actually had some defoliation as far back as 1987, two years before Hurricane Hugo.  I am able to observe them because I live in the midst of large trees in one of the most heavily damaged areas in Charlotte.

Also, I have been trapping the female cankerworms on one large willow oak in my front yard every year since about 1990 or 1991.  I would check the trap daily and mash the insects to get an accurate count.  At the time I started this I wanted to know when the females started up the trunk and how long did this migration last.  In general I found that about Thanksgiving time after the first hard frost (a couple of days in a row below freezing) the wingless females moved up the trees to lay eggs.  Had I know the cankerworm problem would have been as large as it has become, I would have kept records a little differently.  (as time has passed, the starting date is later like up in December)

In those early years I observed the migration of female cankerworms started slowly, peaked by Christmas and slowed down in January.  By February first, they were finished.  At the time we told people that they could take the traps down in February.  This has changed in that we must keep the traps up until mid to late April.  (the insects hatch in the spring and go up and down the trees in the spring and the trap captures a lot of them)Additional Photos 2007


I learned these past two seasons that there are some other factors involved that have changed the way we need to treat the cankerworms.


The original trap was a band of tarpaper about a foot wide with a swath of Tanglefoot on the tarpaper almost ten inches wide.  We found that some insects could crawl up behind the tarpaper, so some type of batting material needed to be used to block this path.

We also found that leaves could be blown up on the Tanglefoot and form a bridge over the sticky Tanglefoot.

**  Unlike typical nerve-poison insecticides, Bt acts by producing proteins (delta-endotoxin, the "toxic crystal") that reacts with the cells of the gut lining of susceptible insects. These Bt proteins paralyze the digestive system, and the infected insect stops feeding within hours. Bt-affected insects generally die from starvation, which can take several days.

The above was taken from an article written by W.S. Cranshaw... Colorado State

Now the band that we recommend is about 9 inches wide with a 6-inch band of Tanglefoot, 1/8 to of an inch deep.  The city of Charlotte requires the tree companies banding city trees to use the Tanglefoot method.

I will show you soon some of the other materials which probably work pretty well and can be used as a substitute for tarpaper.

Bug Barrier

  • The other favored method of banding has been using the Bug Barrier.  This is a plastic material that has sticky stuff on the inside of the band.  The entire band is only 6” wide, and we are supposed to put a fiber batting that is supplied with the band on the upper part of the band close to the tree.  This batting is about two inches wide and is there to keep insects from going under the plastic.   That means if installed properly, there will be a maximum of 4 inches of sticky surface to capture insects.
  • This did work OK if one had a very small infestation.  If there were a large number of insects, the cankerworms would overwhelm the band and crawl up the tree anyway.
  • At this point I need to tell you a little story.  Last year before I sold my business, we sold a lot of banding products from our office to homeowners.  Mainly we liked the BugBarrier because it was easy to put up and not as messy as the Tanglefoot. It was touted to be as good as any of the alternative traps.
  • Our office was located close to Plaza Midwood, Eastover, Myers Park and in general most of the areas close to the heavy infestations.  In the spring, this fairly short man came storming into my office.  He had on a T-shirt that said in effect I Am a Marine.  I knew I was in for trouble.
  • Well he started off telling us how the bug barrier had not worked.  I let him speak for a time, and I told him not to feel like the Lone Ranger because I had five trees in my yard and four of them had Bug Barrier on them and one had Tanglefoot.  All of the ones with Bug Barrier were completely defoliated just like his trees so he should not feel that he was alone with this problem.  I explained that we had recently revised our opinion about the spring infestation.
  • He seemed appeased since I had an equally bad experience with the BugBarrier.  I will show you some photos about that in a few minutes.
  • Some people felt the Bug Barrier worked OK, but I believe those traps work only were there are low infestations of cankerworms.

Improperly Installed Trap

  • What also does not work is the trap that is put up improperly.    The trap shown below was photographed on November 4, 2007 in Freedom Park.  There are a number of things wrong with it.

The first observable problem is that the band of Tanglefoot is too narrow and not thick enough. (The band of Tanglefoot should be 6 inches wide and 1/8 to of an inch thick).  The second is that no batting or other material was placed in the indentation in the bark.  Cankerworms can crawl right through this opening.  I stuck a stick in it as well as a Sharpie to illustrate the point.

There were many trees banded in Freedom Park similar to the illustration below.  In most cases every trap has a problem.  Most traps did not have enough Tangle foot applied.



  • Some people put them up too late, and every cankerworm that gets by the trap in the fall can lay 200 or more eggs. 
  • On windy days leaves can blow up on the trap and create a bridge for the cankerworms to crawl over.  To a lesser extent, fewer leaves blow up into the Bug Barrier type of trap.
  • Falling leaves and tassels cause the same type of problem in that they stick to the Tanglefoot.
  • Dust and other debris will blow up into the Bug Barrier trap and toward the end of the season, there is little stickiness to the two inches on the inside of the trap that is supposed to catch insects.Some people do not follow instructions.  The illustration below concerns a Bug Barrier trap.  The trap comes with two strips of batting material.  The idea is to put one strip on top of the other.  By doing this, the plastic is held away from the trunk.
  • In this case, the batting material strips were placed side by side thereby taking up four inches of the six-inch trap.  Also, in this instance, they did not finish the job, and I hope whoever installed this trap has come back to complete the job.

A second issue is that staples in this type of trap cause the plastic to come into contact with the bark allowing the insects an easy way to get up the tree.



  • The photograph below shows how staples have distorted the trap and how little room is left on the inside of the plastic to catch insects.


Below shows what happens when staples are used.  The plastic touches the bark in many places.  In addition, the tree is a Tulip Poplar which to my knowledge is unaffected by the cankerworm.  In other words it is a waste of money to place a trap on the certain trees.



The problems mentioned above are things that you as a homeowner can control depending on the type of trap you choose.  If you hire the work to be done then you need to know what is going to work.


Lets assume you have the traps installed by someone, and you inspect and decide the traps are installed properly.   If you do not look at the traps until the insects hatch in the spring you probably will have a problem.   The actual Tanglefoot tends to be absorbed into the tarpaper.  Leaves or tassels or dirt can remove the stickiness of whatever you are using.  If you use the Saran like plastic wrap instead of tarpaper, I do not think it is absorbed as readily.

(Photo on web site shows Tanglefoot trap with cankerworms crawling over Tanglefoot)

Springtime Infestation

This brings me up to a second story I want to relate.I

In the spring in late March on Sunday 28th, I decided I wanted to freshen up the Tanglefoot on my trap.  As I looked at the trap I saw a bunch of very small green worms about 1/8th of an inch long.  I looked at them with a magnifying glass and saw that the legs were exactly like the cankerworms.  I decided that the small cankerworms had hatched on the tarpaper and were crawling around looking for food.  There was no food and the worms soon got stuck in the Tanglefoot and died.  As a note, the male cankerworm searches for the female and since many females are on the trap in the fall. They mate there and clusters of eggs are laid on the trap.

It was not many days later that I started seeing inch long worms crawling up from the ground.

At the same time, I realized that I had four other willow oak trees that had ineffective Bug Barrier bands on them, and these worms were in the grass and crawling around the yard, looking for something to eat.  Cankerworms apparently don’t feed on grass. They tend to crawl upwards in their search for food. Before long there were hundreds; in fact I estimated there were over 1000 small caterpillars on the trunk of the willow oak below or in the Tanglefoot.  If each of those insects gets up the tree they can do a lot of feeding however, the ones that get into the top of tree in the fall are all able to lay 200 or more eggs.

I mentioned that I wanted to freshen up the trap.  I pulled off a few leaves and also some tassels. (Those are left over flower parts from the willow oak that cover the sidewalk in the spring.)  These tassels hang straight down, and so if a few of them get on the trap they can rapidly create a bridge.

I pulled a few leaves, removed a tassel or two and then used a putty knife to spread on some more Tanglefoot in a one-inch band at the top of the existing band.  In my case the tarpaper band was 9” in height and I put the 5 to 6 inch band of Tanglefoot toward the bottom of the tarpaper leaving me three to four inches to add fresh Tanglefoot.  I only spread this one-inch band on top of the existing Tanglefoot although I could have spread it on the clean tarpaper if I had chosen.

In the spring, the actual caterpillars are only crawling for a few weeks at the most so the monitoring in the spring does not have to be done every day.  Other literature says the worms are crawling around from early March to late April, but I have not observed that in my neighborhood.  The cankerworms spend about a week in the trees before we see much of them as crawling caterpillars on our shrubbery or trying to crawl up our trees.  You can expect to see them feeding after the insects hatch for approximately three weeks.


Spraying the Lower Trunk

April, 20, 2013... I decided to add this comment based on the fact that many people are concerned about pesticide use.  The professional companies that spray for the cankerworm caterpillar stage in the spring use materials that are safe for humans, but deadly to caterpillars  That means that some butterflies that we enjoy and need could be destroyed if they are in the caterpillar form at the same time the BT is sprayed.  BT stands for Bacillus thuringiensis which has several trade names.  Here is a link that explains details about Bacillus thuringiensis

If you are concerned about spraying as suggested below, then you should contact one of the professional tree services that have the proper equipment and knowledge to perform this service.  The professionals also might suggest using a systemic insecticide which is taken up through the vascular system of the tree or shrub.  If the insect eats the leaves it ingest the chemical and dies.

Back to Spraying the Lower Trunk

The last thing I did that is slightly controversial is I sprayed the lower truck with a simple garden insecticide.  You should be aware that a professional company that sprays needs to use the chemical exactly the way the label says it can be used. PERIOD!!  We have such an unusual situation with the cankerworm; it is not addressed specifically on any label that allows us to spray the trunk of a tree for the cankerworm.

  • In general, insecticides for homeowner use are much weaker than those that require a pesticide license to use.
  • However, if the label on the chemical at the local hardware store says you can use the insecticide for controlling caterpillars, then the cankerworm at this stage is a caterpillar.
  • I have a label here for a pyrethrin called Bug Buster –0     Pyrethrin is made from chrysanthemums and has a very low toxicity.  It also does not have a long residual.  It last about three days when exposed to the elements and does not like sunlight which will cause it to become less effective.  If you use it in that fashion it is a contact insecticide. You would want to inspect in a day or so to make sure there are no or few crawling caterpillars.
  • Do not be misled by a synthetic spray similar called Permethrin which can be very harmful to cats and fish.  Permethrin is a synthetic insecticide that behaves much like Pyrethrin but it has a much longer residual.  It is used in tick sprays and has low toxicity to humans.  However, it can kill fish and cats.  Cats lick their fir and it just does not get along with fish.

Bottom line for pesticides is … read the label 


I have checked at the local hardware stores and they all carry insecticides for homeowners use.  You can buy one like this _( held up Bug Be Gone container)_.  Or you can get a small tank like this _(small 1 gallon spray tank)_.


Bottom Line Regarding Your Trees.

Monitor the traps all season long, especially in the spring in April when the caterpillars start crawling up the trees to continue feeding.

Add and renew Tanglefoot as needed to stop the wingless females or the caterpillars.

Consider spraying the trunk of the tree with Pyrethrin type or other safe insecticide as the caterpillars overwhelm the trunk in the spring.

Continue to Page 10 for a recap of things to do.  (In this article page 10 is directly below.)

To recap what needs to be done.

  • Bands are put up after the first hard frost.  If you can, do it before November 15th.  A few insects will go up the tree early, but the frost is usually not until about November 25th.  (in general, the starting date is getting later.  I suppose we could cause this an effect of Global Warming. posted jan 2012)
  • A day hovering around 32 degrees will not do it.  A hard frost seems to me to be a couple of days in a row with the temperature around 29 degrees.
  • If you put up bands early, you will have to remove some leaves and possibly add a little more Tanglefoot.  In 2006 the insects started crawling November 16th.
  • Bands need to be put up correctly.
  • Tarpaper or other material needs to be wide enough to put a 6-inch band of Tanglefoot on the band.
  • Tanglefoot needs to be approximately to 1/8th of an inch thick.
  • It will take a little over one pound of Tanglefoot for a 24-inch tree.
  • On large trees the undulations in the bark need to be filled with batting material of some sort to keep the insects from going under the band.
  • Bands need to be monitored for damage from squirrels,
  • Bands will collect leaves and other debris that will create a bridge for the cankerworms to traverse.
  • Bands will absorb some of the Tanglefoot into the tarpaper.  Additional Tanglefoot must be added.
  • Add a small band of Tanglefoot about one-inch wide on top of the existing Tanglefoot.  If needed you should still have space above the original Tanglefoot to add more Tanglefoot if you think that will trap the insects better.
  • Female cankerworms will stop migrating up the tree by February 15th
  • Bands with Tanglefoot will continue to dry out.
  • Replenish Tanglefoot in mid March. 
  • Watch for cankerworm caterpillars in early April and make sure the Tanglefoot you have recently applied is still doing the job.
  • If you have a heavy infestation, and the trap is in danger of being overrun, consider spraying the truck and insects on it with a low toxicity caterpillar spray such as one containing Pyrethrin.  Pyrethrin is made from chrysanthemum blossoms and breaks down very quickly. Read the pesticide label and make sure it says it will control caterpillars.
  • Do not use Permethrin which is a synthetic insecticide similar to Pyrethrin but has a longer residual and can be harmful to fish and cats.  READ THE LABEL

Directly above is the last of page of the program (page 10). This is assuming you are able to see the photographs.

If you would like the other nine pages which are the basic text of this program, as well as some of the photos shown as slides, send an E-mail to Jack McNeary at jack(removethis)@jackmcneary.com.  (Added in 2011 .... check into the website at  www.jackmcneary.com.  On the first page there is a link in the left side bar that will take you to the current canker worm information as well as buttons that will take you to yearly information.).  

October 27, 2007

After the program there was a vigorous question and answer session.  I thought it would be good to voice some of the questions.

    What Tree Are Affected Most

  • Someone asked what trees did the cankerworms like most.    Willow oak is the most common tree, but other trees mentioned were White Oak, Southern Red Oak, Sugar Maple, Japanese Maple, Siberian Elm, Lilac (rare here in the south)  Cherries.  Although it was not mentioned, I assume that the water oak also is on the list since it is such a close kin to the willow oak. It is interesting to note that farther north, the elm tree is the favorite host.  Here the winged elms are not bothered.
  • Note dogwoods and Japanese maples are both under story trees and often are attacked by cankerworms crawling down from other trees, or parachuting down on silken threads.  Cankerworms are close kin to the silkworm.
  • When is the most cankerworm activity?
  • Last season in the fall,  2006      in November on the one tree at my house, I counted 26 female cankerworms.  In December, the number was 1987.  In January there were 3901, and in February there were 27.  You can see that January was the big month with almost twice the number of cankerworms as in December.
  • Another question was about where to locate the batting material …..Myers Park Hardware, Little Hardware, and Blackhawk Hardware.  These are all convenient to the Myers Park area and there many other stores that carry these materials.  Three inch pipe insulation works pretty well and is readily available this time of year.
  • Does the batting go at the top or bottom of the tarpaper?   As long as it keeps the insects from going up underneath the batting and on up the tree it does not matter.
  • However, for convenience and appearance, I think it is best to place the batting at the top of the tarpaper.  Place it just below the edge of the tarpaper so that the color does not show.  These traps are ugly enough without looking at white or yellow batting above the tarpaper.
  • Also if the batting is just at the top, and you have placed the trap so you can see the top then you can stuff batting into openings rather easily.  If the batting were at the bottom then it would be much more difficult to fill in the voids.  Also any insects that get trapped underneath the tarpaper are that many fewer to clog up the Tanglefoot.
  • One person stated that he had mature cankerworms crawling out of the ground at a seam in his driveway. (by the thousands).  I asked what had they been feeding on down underground or anywhere else to obtain that size.  I noted that the cankerworm upon hatching is about 1/16th of an inch long. We could not come up with an answer for how they got so big if they were hatching in the ground.  We are going to look at the situation this spring since he said the cankerworms have appeared two years in a row.
  • How much Tanglefoot does it take per tree.  This depends of course on the size of the tree.  The tree we banded at Myers Park Methodist Church was approximately 24 inches in diameter and, we used a one pound container.  Actually the container is 15 ounces and in this case it did not quite do the job.  The coating is a little thin and will be replenished soon.
  • As of December 5th, I have seen no female cankerworms.  Go to the Additional Photo link below.

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