I have had a lot of people ask me my thoughts about the latest freeze and its effect on plants and insects. My answer is “we have to wait and see.”
I can speculate on what possibly might happen, but because in horticulture, agriculture and nature in general, there are so many variables that come into play that it’s really hard to predict.
There are some things, however, that we do know and we can speculate and in the case of insects, we can hope, right?
For instance, Dr. Dave Shetlar, Ohio State University Extension entomologist shared some information on bagworm at a recent meeting. The literature indicates that bagworm eggs can be killed at -10F. Therefore, we MIGHT see some decline in the population of bagworms.
On the other hand, the parasitoids that feed on the bagworms are killed at 0F. We can’t win!
Robert Vennette , a U.S. Department of Agriculture research biologist, has found that emerald ash borer (EAB) larvae will die in extreme cold temperatures. He found through his research that roughly half of the larvae will die when the temperatures are -20 and at -30, roughly 90 percent of the larvae die.
In the plant world, we know that peach flower buds can be injured at -15. I know my area didn’t get that low but others might have.
Blackberries plants will survive our winters fairly well but if it gets down to -25 it can kill the entire plant. This winter might have caused cane damage but I don’t think it got cold enough to kill entire plants.
In all of these situations, there are also other variables that come into play. Take the EAB example for instance. The work was done in a lab with fairly consistent results.
Outside, despite a temperature of -20, the location of the tree and the exact location of the EAB larvae also impact the situation and may change the results.
And while it might be a good thing that 80 percent of the EAB larvae die in these temperatures, 20 percent still survive. This 20 percent will continue to spread, but the good news is that the spread overall will slow down a bit as it takes time for populations to rebuild.
The bad news is that the 20 percent that survived might have really tough genes that survive cold temperatures. Therefore, if these start to breed, there might a population that can survive extreme colds.
Another very important variable is snow cover. I was really disappointed that much of the Miami Valley, including my landscape, didn’t get as much snow as was predicted before the deep freeze.
Snow serves as a great insulator and can keep the temperatures 2 degrees higher per inch. I was hoping for snow to cover my newly-planted blackberries and very small Japanese maples.
In fact, I shoveled the little snow that we had to cover my Japanese maples that were near the sidewalk. I am keeping my fingers crossed for these.
I usually take this type of event in stride and adopt the wait and see attitude. There really wasn’t a whole lot we could have done to protect these plant. It’s the nature of gardening.
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