Tuesday, April 03, 2012

Critical Temperatures for Frost Damage!

With the burst of warm weather we had over the past several weeks, our apple trees are about three to four weeks ahead of schedule.  And now we have a frost/freeze warning for tonight and tomorrow night.  Normally we would be at or near green tip, but those 80+ degree days we had have placed the trees at tight cluster/pink.  The real problem is that we have accumulated about 230 - 240 growing degree days thus far this spring.  Last year at the exact same time we had accumulated around 20!  So we are at least a month ahead for degree days and more than three weeks ahead for tree growth stages, compared to 35-year averages.

This spring degree days have been accumulating faster than tree growth can keep up. The degree days are way ahead of the tree growth stages this year and may continue that way for the rest of the growing season.  As the trees develop in the spring and buds start to swell, they lose the ability to withstand the cold winter temperatures that they could withstand in dormancy during the cold winter months. The young, actively growing tissue can then be damaged or even killed. Swollen fruit buds can better withstand temperatures in the teens without any damage. As the buds open, temperatures in the low 20s can cause harm, but sometimes leave other buds undamaged.  As growth moves from green tip to 1/4” green to 1/2” green to tight cluster to pink in apple trees, temperatures in the upper 20s can cause considerable harm to an early blooming tree. Near bloom, the range between slight and severe damage can be very small. So the stage of bud development determines how susceptible any given fruit crop is when freezes occur.  For more information on what those critical temperatures are that can cause freeze damage to trees during development, I have uploaded two charts from Utah State University below that you can download by clicking on either chart below.

Critical_Temperatures_Frost_Damage_Fruit_Trees_Utah_Page_1  Critical_Temperatures_Frost_Damage_Fruit_Trees_Utah_Page_2

Given the weather patterns we have experienced so far this spring, and the fact that we have gotten snow as late as mid April, a spring frost is highly possible within the next few weeks.  We will need to constantly assess the stage of development our trees are at and their susceptibility to freeze injury. If we continue in this spell of warm weather, apple trees will continue to develop quickly and the critical temperature will rise from the low 20’s to the high 20s, to levels just below freezing at bloom time.


At 10:47 PM, Blogger Andrea said...

I just found your site. Wow! You have a lot of detailed information here. I will be referring to it in the future. Can I ask you a question? We just bought our first peach tree. Planted it about 3 weeks ago. It's leaves turned yellow and now it's lost almost all of it's leaves. The tree doesn't seem to be dead...yet. I'm sure you're busy, but I'm wondering if you can offer any insight? We are near Peoria, IL.

At 1:41 PM, Blogger Orchard Keeper said...

Hi Andrea!

There could be a number of things causing the extreme leaf drop.

Of course your new tree is not yet established. Some transplant shock is to be expected. Also, dropping of some older leaves if and when the tree is blooming in spring is normal, but the problem seems more serious than that. You are right to be so concerned about the leaf drop. Plants feed themselves through the process called photosynthesis. Peach trees also do this using their leaves. If your tree has no leaves, it will be unable to feed itself adequately.

Are you SURE that you are not over or underwatering the tree? Is the drainage adequate where the tree is planted? Peach trees are very particular about that. Their roots will not tolerate standing water, nor will they tolerate drying out. Too much or too little water is one likely cause of serious leaf drop. If drainage is not adequate, you could try digging a deep hole near the root ball and filling it with gravel to function as a drain.

Also, did you add manure and/or mulch when the tree was planted? Newly planted peach trees should not be fed at all until new growth is produced because they may have been generally fed at the nursery. Also, the soil of the planting hole should not be amended. If you do amend it, the tree's roots will not want to grow into the surrounding soil as they should. They will tend to stay within the confines of the amended soil in the planting hole. If your soil is primarily clay, the sides of the planting hole should be roughened. If left smooth, it's like planting your tree in a bathtub. Obviously, since the tree is already planted, you can't do anything about that now, but do stop feeding the tree until it recovers if you have been.

Extraordinarily high temperatures and low humidity can also cause leaf drop. Have you had either of these situations in your area? Have you had hot dry winds?

Pests and fungal diseases can also be causes, but your description does not seem to fit those types of problems.

Hope this helps! Thank you for writing. Please give me an update on your tree situation. I would like to know if it is recovering, and what you did for your tree to help it. I care about your peach tree, too! Hopefully it will bounce back. It may take a little time though.


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