HORTICULTURE
The 2007 Easter Freeze in SW Michigan
Just
before Easter in 2007, Michigan suffered a severe spring freeze event. The Easter
Freeze was a period of very cold weather that occured just before Easter.
Temperatures in March had beem relatively warm with lows about freezing allowing rapid bud
development. The initail freeze that caused the damage was an Advective Freeze or
wind freeze, not a radiation freeze. Most of the freezes
that cause problems in the spring in Michigan are radiation freezes. These freezes
occur after the passage of a cold front preceding a mass of cool dry air. Usually
there is a stormy period as the cold front moves through followed by clearing and light
winds. In a radiation freeze, the temperature falls during calm, clear nights and
then rises again after dawn when the sun comes up and warms the earth.
In 2007, we had several cold windy days with highs around freezing and lows in the mid to low 20s. The stormy weather before the clear calm conditions was several days long and caused a lot of damage by itself. Damage from these cold windy conditions were wide spread across the region. Finally on Saturady morning the winds fell to very low levels and a radition freeze occured.
A period of very cold weather occurred in February. Temperatures were close to zero and below several times in the first three weeks of February. This caused some damage to peach fruit buds in orchards away from Lake Michigan. Soils had good moisture early. Late March and early April were warm, with highs into the 70s and lows well above freezing. Warm weather caused rapid fruit bud development with bloom beginning in apricots, peaches and sweet cherries in early April with record high temperatures on Tuesday April 4 followed by frigid weather with snow and highs near freezing for the next four days. Lows near 20 occurred on Easter weekend Friday and Saturday (April 6, 7). Low temperatures were a few degrees higher close to Lake Michigan and the extreme cold did not last as long. Many fruit crops were damaged by the freeze. Most of this event was cold and windy--a classic advective or wind freeze. At the end of the storm there was a mild radition freeze on Saturday morning. Another radiation freeze (clear, still, relatively dry) occurred on Tuesday morning April 10, with lows in the low 20s close to Lake Michigan and below 20 away from Lake Michigan. The low temperatures away from the lake also lasted much longer than closer to the lake. This frost was very variable and many exposed sites, normally frost-free sites, had more damage than usual. States south of Michigan experienced severe cold damage to fruit crops. In evaluating this freeze I changed the way I looked at freeze damage in fruit crops and use critial temperatures especially grapes and blueberries.
These critical bud stage tables are for temperatures of relatively short duration no three days of snow, wind as cold arctic air moves through the region. The freeze Michigan and the entire Eastern United States Suffered was a classic Advective Freeze where cold air moves into a region. When you have a lot of cold air moving, everything quickly becomes the same temperature as the air and the cold can penetrate deeply into the tissues. I had hoped for conditions similar to the cold snow storm we had in 2005 when temps remained near freezing not to have temps in lower 20's for 6, 8 and 12 hours on successive days. It seems that the conditions were more similar to the wind freeze that affected Northwest Michigan’s cherry crop in 2002. Then cold winds killed swollen cherry buds at temperatures that were above the temperatures in the tables we use to estimate damage from recorded lows. There are other variables that can cause differences between the observed effect of cold and the predicted critical temperatures. Stan Howell, former MSU small fruit specialist and viticulturist, has done work showing that wet buds are killed at warmer temperatures than the predicted temperatures in the WSU bulletins determined in a freezer.
Some people may think that a freeze kills all the fruit buds. This is not always true depending on the temperature
The bottom line is that the published values are for specific conditions and if the conditions are very different the tables can be wrong. As I walked orchards and vineyards, I saw plenty of damage to exposed leaves that were brown, black or dark green and watersoaked and were obviously damaged from the prolonged cold. Many times when I cut open these obviously damaged buds the flowers inside looked fine and I wonder how that could be since the one next to it was dead. Warmer temperatures will make it easier to determine damage as this tissue dries out when we get above freezing for a couple of days this week.
Grapes
Blueberries
Finally, The Easter Freeze of 2007 caused extensive damage to leaf buds in Blueberries
especially the variey Bluecrop. This damage resulted in reduced shoot growth because
the growing point for the new shoots was killed so the number of fruit was larger than the
number of leaves could support.
