June 04, 2014
Growing Degree Days (GDD) update for Columbus, Ohio
Wow, time does fly! Crabapples bloom and before we know it, the blooms are gone. Early in the season I committed to doing a weekly update on GDD as they accumulated, but it’s the same story: Things move at lightning speed during the spring season. In spring plants seem to be doing their best to get a head start on seed and fruit production, and it’s all we can do to keep up with these plants and the hosts of pests that soon follow. Incidentally, I started this document on May 27 and am only just now getting back to it to finish up!
I want to take a moment and discuss the main challenge we are facing this spring: Cold damage. Record low temperatures last winter caused major dieback on many plants. I have compiled a list of plants that usually are cold hardy in our zone but which apparently ride the fine line between just warm enough to survive and just cold enough to die. This winter was cold enough to kill. Here are some trees and plants which have not done so well:
1. Sweetgum (may survive – wait and see)
2. Weeping Cherry (may survive – wait and see)
3. Southern Magnolia (young ones are most likely dead)
4. Butterfly Bush (dead if not sprouting from base)
5. Sugar Maples (stressed trees did not make it through the winter)
6. Redbud (same as Sugar Maples)
7. Mountain Laurel (most likely dead)
8. Royal Paulownia (significant dieback)
9. Mimosa (dead if not sprouting from base)
10. Boxwoods (dieback on some)
11. Rose of Sharon (dead and mostly dead, depending on location and health of plant)
12. Rose (mostly dead to the ground but sprouting from base)
13. Japanese Maple (Mostly dead trees to trees with minor tip damage, depending on location)
14. Bamboo (most exposed stands are dead, but new shoots should emerge)
15. English Ivy (exposed stands look very bad)
16. Holly (varying degrees of dieback based on exposure)
Back to Growing Degree Days.
As of this writing, we have reached 719 GDD in the Columbus area. This means that several more insect pests have emerged since the last entry I made. Working backward, we find:
Right now, at 719 GDD, nothing of note has emerged since Bagworms, at 630 GDD.
Just before Bagworms, Two Spotted Spider Mites started emerging at 627. And sure enough, last week I was talking to a client and noticed one of the Arborvitae by her door looked kind of grayish, dusky green, and it turned out to be covered in this pest.
Based on the OARDC website, Japanese Tree Lilac has its first bloom at 622 GDD, just after Arrowwood Viburnum, which has its first bloom at 621. These would be good examples of phenological indicators for Bagworms and Two Spotted Spider Mites. We know that once we see these plants in bloom, two significant pests could be about to make their entrance into our landscapes.
Another phenological indicator I always look for is Black Locust coming into full bloom. This means that two problem borers are around, or soon to be: Bronze Birch Borer and Emerald Ash Borer.
Unlike me, Cindy has been faithfully performing weekly updates on GDD. She will walk around with her GDD chart in hand, usually on Monday mornings, announcing the arrival of various pests, and forecasting the imminent arrival of others. This has actually proven to be very helpful for me, since I don’t have to remember to stop what I am doing in order to take a look for myself. Thanks Cindy!
When you see this (Japanese Tree Lilac in first bloom):
Start looking for this (you may need a hand lens to get a good look):
Two Spotted Spider Mites. Actual size is a little smaller than a period on this page.
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