Last May I wrote of the mild 2014-15 winter, the relatively early spring and how these conditions affect trees. Well, here we go again!
The sycamores that I noted breaking dormancy in 2015 about two weeks earlier than they did in 2014 have done it again. I saw the buds cracking open on Feb. 19. For practical purposes, that meant calling the pest control company early, again, to get the dormant oil spray on the trees ASAP to control the sycamore scale at the optimal time: bud break.
This newspaper reported local vineyards were at bud break — the very beginning of spring growth — about 10 days earlier this year compared with last year and 17 to 20 days ahead of normal.
After unusually mild winters, like 2014-15, trees and vines that require relatively little chilling begin growth early. This can set up problems with pests, diseases and sensitivity to a late frost. But for trees requiring significant chilling during their dormant rest, accumulated time between 32 and 45 degrees, mild winters may lead to delayed and erratic leafing-out and blooming, reduced growth, general weakening, reduced crops and susceptibility to disease. On that last point, note in particular the severe outbreak of fire blight in flowering pears and other susceptible trees last spring.
Last May, I noted signs of incomplete chill requirement in various trees including red maple, elms, Raywood ash, Chinese pistache, flowering cherry, apples, peaches and English walnuts.
We are only in early March, so it is too soon to tell how this will work out for those species this year.
Reviewing some websites for data on chill hours, I see the Oakville weather station recorded 1,020 chill hours in 2014, only 551 in 2015 and 757 as of the end of February this year. Many trees are still lacking the dormant rest needed before they can begin normal growth. Warm winter afternoons, about 60 degrees or higher, which we have seen often of late, can negate chilling that was accomplished earlier in winter.
The early emergence of tender shoots calls for extra diligence on the part of growers, since a sharp frost after bud break can be severely damaging to the crop. Likewise, relatively tender trees, like citrus, can be subject to the same kind of damage
I did not have the time or opportunity to follow up in any methodical way as to the eventual response of local trees that showed effects of insufficient chill hours. I can tell you anecdotally that my own October glory red maple tree eventually came into full leaf last spring, grew somewhat less vigorously with reduced lawn irrigation in its root zone than in previous years, and put on its usual show of autumn color.
And some English walnuts I had the opportunity to revisit eventually came into full leaf, but exhibited reduced shoot growth increments in comparison to the previous year. Those trees are in a non-irrigated area.
The advancing of spring and its effects on trees, plants, animals and ecosystems is discussed and documented at length in a wide range of literature. It is real and is having real effects. It is incumbent on us, especially those of us who work or have direct interests in trees, plants, farming and nature to be informed and to act positively in some way.
In my line of work, it means anticipating and preparing for certain tree pest and disease problems, and considering supplemental irrigation, where practical, to compensate for lack of rainfall.
For a home gardener, it might mean changing fruit tree selection to trees with low chill requirements. Examples include Anna, Fuji and Granny Smith apples, Babcock or Rio Grande peaches, and some of the plums that are already popular in our area: Santa Rosa, Green Gage and Satsuma.
Let’s watch and be hopeful. This winter and rainy season is not over yet.