[Note: For an introduction to this insect pest and as background for this article, please read Part One here, if you have not already done so.]
What I Found, and What I Predict
I started working with Russell Tree Experts in April of 2012. Soon after that my colleagues and I became aware of a major epidemic of lecanium scale in communities on the east side of Columbus. Entire streets had trees that were covered in scale, noticeable to the eyes of discerning arborists because of how black the trees looked as we drove by. We watched in chagrin as the epidemic worked its way west. As the scale populations increased in my areas (central and western communities), I could no longer jokingly rib my colleagues about how they were not taking care of the trees in their areas. We were doing what we could, but many of the infested trees were larger ornamental pear, crabapple, and cherry trees that are not the best candidates for cover sprays. Recently one of my clients in Dublin ended up with three crabapple trees that had a heavy infestation of lecanium scale. We tried some treatments but the trees had declined and the client made the wise decision to remove and replace them.
Last year during a regular fertilization visit to this property, Andy, one of our Tree Wellness arborists, made a note that another tree had scale, this time in the back yard. I stopped out soon after to take a look. Here is what I found:
Second-instar nymphs that overwintered on the tree stems. Note white waxy covering beginning to form. Scales are in their final fixed position, actively feeding and growing. Note droplets of honeydew here and there.
Each of these nymphs will mature into adult females that will be about 10 times their current size by the time they lay their clutch of 100 or more eggs.
This is a new infestation. An old infestation would also have the dead female bodies of last year’s adults alongside the current generation. They would be dark brown and about the size of BBs used for air gun ammunition.
I made some notes for treatment recommendations and discussed options with the client. He decided not to pursue treatment. This was on April 23rd.
Nearly 6 weeks later in early June, I went back to this property for a different reason. While I was here I inspected the small crabapple. Much to my surprise, the second-instar nymphs had not grown. By this time they should have been at or near adult size, and they would be soft and slimy when crushed. I brushed some of the scales with my fingers and they rubbed off the tree stem like gray ash. They were dead. I checked the tree all over – no adults, all scales were dead. This tree had been treated with something very effective. You will recall from the first article that the insect stage most vulnerable to treatment is the first-instar nymph stage, which hatches from eggs laid by the adults that these second-instar nymphs would have become.
I knocked on the door.
During the ensuing conversation I found out that indeed, the tree had been sprayed with an unknown solution recommended somewhere on the internet. I encouraged my client, feeling very proud that they had taken matters into their own hands. “You killed every single scale!” I told him.
I shared the story with TJ back at the office and asked TJ to ask the client for the recipe when he talked to him to confirm our next visit to the property.
A week or two later, another client appeared on my calendar. Her problem was dieback on a crabapple, and Oakland nursery had recommended that she call us. As I walked around the front corner of the house I noticed lecanium scale on a shrub in the front bed. “Hmmm…” I thought. So I was not surprised when I saw the crabapple, a nice one, also had a heavy infestation of lecanium scale. There were the adults as expected.
Then I looked more closely. By this time of year there should have only been dying and dead adults on the tree, with possibly some first-instar nymphs feeding on the leaves. But here were dead adults alongside second-instar nymphs on the twigs. Not a single first-instar nymph to be found under a single leaf. I rubbed my finger across a few of the nymphs… Sure enough, they rubbed off easily, like ash.
Now my thoughts went back to the first client who had sprayed his tree with a home-cooked remedy. I carefully interviewed the current client and she was positive that no treatment of any kind had been made on her tree. I started to wonder.
This became a trend for the next few weeks, such that when I encountered lecanium scale several more times I was no longer surprised to see the same thing. This made me realize that the problem for the scale, and the blessing for the infested trees, had to be environmental.
Late winter of 2020 we had a two-week period of what I called “false spring”, when temperatures were far too warm for the season and I silently directed my thoughts to my trees, asking them not to believe that winter was over. Of course they ignored me and began to leaf out and flower. Then winter raged back in and the new growth was burnt, flower buds died, and spring looked less vibrant when it actually came on its normal schedule weeks later.
After that false spring, we had no less than 4 nights during two separate weeks when temperatures dropped well below freezing. I disguised my Japanese maples as ghosts using bedsheets to protect them from freezing after they had budded out. It was to no avail - all the new growth got burnt off. The same thing happened to many of you as well, since the cold snaps were widespread.
I propose the hypothesis that the second-instar nymphs of lecanium scale also believed in the false spring, and emerged along with their host plants. When the temperatures plunged below freezing four times during a prolonged cold spring all those nymphs were killed. Just like that, entire populations of this scale were dead. How many of you recall that we had snow on Mother’s Day last year? Well, if my hypothesis is correct, I present you with a blessing disguised as a late snow: For many of my clients the problem of a large population of a serious insect pest had been solved without applying a single drop of insecticide. That greatly helped me bear the disappointment of my disfigured Japanese maples!
Based on this hypothesis I close this article by making the prediction that this 2021 season my colleagues and I will continue to confirm a crash in the general population of lecanium scale. Those large trees that were not good candidates for topical sprays? No need to spray them after all. Though lecanium scales have their place within their ecosystem, when their population reaches damaging levels it is gratifying to see widespread control that has taken place with no human intervention. My only hope is that beneficial insects did not suffer in the same way.
As I close I have mixed feelings about how plants and insects are very much at the mercy of the environment. But I hope I have achieved my goal in sharing all this with you. By writing this I hoped you could see a little of what it is like when arborists try to decipher the clues they find from client to client, from tree to tree, from insect to insect. And I am still relieved to know that the lecanium epidemic may very well have been stopped in its tracks, at least for a time.
May you all be well, and may this coming season be full of “long days and pleasant nights.”
Your friendly neighborhood arborist,
José Fernández | Regional Manager, Russell Tree Experts
José became an ISA Certified Arborist® in 2004, and a Board-Certified Master Arborist® in 2015. Currently he is enrolled at The Ohio State University pursuing a Master’s Degree in Plant Health Management. José likes working around trees because he is still filled with wonder every time he walks in the woods. José has worked at Russell Tree Experts since 2012.