Need to spray - too cold?

General Fruit Growing
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I’d like to get a heavy dormant oil down on my trees but the overnight lows keep dropping into the 20s. But the afternoons are in the mid-50s and I’d like to get this done. What are the downsides if the oil gets cold on the tree? Wouldn’t it just take longer to set up and be more vulnerable to rain>

Thanks!

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If you look for recommendation for spraying dormant oil, you pretty much get following list:
No rain for 24 hours
Not temperature lower than 40F for 24 hours.
No sunny day
No wind.

It is almost impossible to get them all. Some of the recommendations obvious - like no rain or no wind. But none of the sources talks about how do you realistically select a day for spraying and none of the source explain - why temperature for 24 hours or cloudy weather is important. So I would like to see what our spraying guru tell us… :wink:

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if its not ideal the 1st time. i hit em’ again the next dry day.

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Why no sunny or no wind?

In fact, you don’t want to spray on a very calm day.

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That’s what is recommended - why - I don’t know. But wind - it could move your spray from where it should be, that I understand.

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I don’t mind a light breeze - lets me stay away from the mist if I plan it right.

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That is not correct about no spray on sunny day. If it is sunny 90F, then yes. Otherwise, sun or no sun, it does not matter.

Regarding wind, a little wind is fine. No wind or calm day, you should not spray. Chemical droplets will hang in the air and don’t move to where you intend them to go. Too much wind, you get spray drift.

Only temp and dry day should be taken into consideration when spraying.

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Which would be worse in your opinion, not spraying, or doing so under poor conditions?
I’ve done both. So far as I know, no damage done. (It’s hard to estimate what “wasn’t killed”).

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Gee, I thought the idea of a dormant-oil spray was to smother overwintering insects embedded in the bark. It has to stay on at least a couple of hours before evaporating, so you want an overcast day with no wind. You want it warm, though, enough for the insects’ metabolism to be waking up or they won’t smother.

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Oh, you’re going to smother insect eggs in a couple hours? (Before evaporation.)

Not sticking to wet surface or washing away in rain would be a much
greater cause of wasted oil than evaporation.

Last I knew, oil actually doesn’t evaporate. You can pour a whole bottle full into a open container and it will still be there next week.

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I just finished spraying a strong dormant mix. It’s 54 F, the sun is out, and there’s a very light air moving. One part of the tree would dry while I was spraying the next part - it was hard to keep track of what I’d hit and what I hadn’t!

Hard to believe I’m going to have a problem with it.

Thanks for all the comments.

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I don’t understand why they say over 40 degrees that night. What would be different on a 35 degree night? Does freezing cause some sort of harm and they want wiggle room? The tree has gotten cold all winter, so why would oil change things?

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All I know is not to spray during freezing temp. It is not the oil but the water that we should be worried about. You can’t really spray with freezing water.

Waiting for night temp at 40 is asking a lot for early spring spray. I don’t follow that suggestion. When I spray, I wait for temp to be over 32F. If it gets to 40 F when I spray, I’ll be happy.

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I hadn’t thought about the insect metabolism. I wonder if people have actually researched the best temperatures or if it is just tradition passed on to us?

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I couldn’t say, but Iowa State U. says something in that regard. I learned about apples at Tony Demski’s knee, and he said, “Apply dormant oil for aphids, scale, and mites as needed above 40° before silver tip.”

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The danger with freezing temps or too hot temps with oil is for leaves, as I understand it. Heavy oil on a dormant tree isn’t likely to hurt anything as far as I know. I am not an expert on this because I use hort oil on trees as they are pushing green, preferably around tight cluster. That’s when freezing temps can cause terrible damage, especially on frozen tissue in the morning.

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It rains often in spring here. I spray when I see a window of 3~4 days of dry weather and the day temperature is warm (in 40~50ish). I really didn’t pay attention to night temperature for I don’t spray at night. When the trees are still in dormant, how much they care at what temperature the oil was splashed on their barks

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