There was quite a lot of dieback on woody shrubs and trees this spring and summer, some of it is still just showing up. Vertical cracks in juvenile trees are nothing new for us in Ontario. But this year we are seeing a little more than our fair share.
Let’s take a peek back into 2017. Remember how cool and rainy it was? Remember all those leaf diseases? Cool, rainy conditions promote vegetative growth and many of our trees and shrubs responded with big, fat growth rings.
Then we moved into a hot, dry September, the temperature hovered around 30 C several days in a row. It finally stopped raining in the central part of the region. Soils dried out and root hairs in the top few inches of the soil died off. The warm, dry weather continued into October. It was still warm in November, even the beginning of December was quite mild. Trees and shrubs weren’t losing their leaves. The mild autumn slowed the plant’s acclimation for winter, by stalling the onset of dormancy and natural dehydration processes.
Winter came with a vengeance in mid-December and the temperature hammered down rapidly, down to -20 C by early January. This rapid temperature shift can be very devastating to plant tissue, causing cells and tissues to freeze and crack open like you would not believe. The results are death of conductive tissue and sapwood. Leading to rapid xylem tissue freeze pops and vertical cracks from the exterior of the bark.
Although the wounds usually heal up and callus nicely on their own, you can always spray fresh wounds and cracks with rubbing alcohol to decrease the chance of pest invasion. Callus growth will compartmentalize the damaged tissue but yes, the discontinuous tissue will be there forever.
Fast forward to summer 2018. The other end of the spectrum. Hot and dry conditions in much of the province for much of the growing season… at least up until last week. Imagine what it must be like to be a tree?
We need to remember that trees are perennial species that suffer in silence with the cumulative stresses that they experience in the urban landscape. Trees and shrubs can modify their metabolism and adjust for negative impacts on growth for months and years. Years of metabolic tweaks and adjustments will catch up with them, kind of like the nursery grower with the bad back….who had to go to the hospital after he tried picking up a snail (true story, I swear).
So when we come across a tree that our client says “looked healthy last year”, maybe we should stop and review all of the climate and site challenges before we start looking in the photo index of Diseases of Trees and Shrubs. Where leaves are looking crispy, try scraping at the phloem just under the bark and peel open a bud for next year’s growth. If you see green juicy tissue, there is a good chance the tree will live through it. Continue slow, deep supplemental irrigation where soils are dry into the fall months and protect the tree from physical harm. And snails!