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Southwest Michigan Fruit Frost Report, 4/24/2002

In the Spring of 2002, over a week of summer like weather with highs climbing into the 80s and lows in the 60s caused rapid plant growth. We had cold wet rainy weather over the weekend with highs near 40 and lows near freezing. The weather cleared Monday evening resulting in wide spread frosts on Tuesday morning resulting in significant losses to all fruit crops. This was a classic radiation frost with clear skies and calm conditions. Reported lows reported for the region ranged from 29 to 20 F. Temperatures of 29 to 27 F were reported from the highest fruit sites while 22 to 20F were reported from the lower sites. Many good fruit sites reported temperatures of only 25 or 26.

In a radiation frost the ground cools by radiation to the open sky. The cold ground then cools the air above it. Since there is no mixing of the air due to wind the cold air layer becomes thicker and thicker and the bottom of the layer becomes colder and colder.  The cold dense air flows downhill like water, filling the hollows and valleys with cold air. This leaves hill sides and hilltops warmer than the surrounding area.  Wind machines are often used to mix the warm air above with the cool air below to keep fruit plantings warmer. On April 23, 2002 the difference between the cold air at the ground and the warm air above was only 3F. Growers reported little if any success using wind machines.

Dormant plants can withstand the severe cold of winter and subzero temperatures. As the  plants begin to grow in the spring the fruit buds become more and more susceptible to cold. Eventually the plant loses almost all the cold hardiness it had in the winter and temperature just below freezing will kill the actively growing tissue. (See Critical Bud Temperatures for Spring Frosts).

Most stone fruit are at or near the bloom stage where freezing temperatures of 28 or 27 F will result in 10% loss and 24 F in 90 % loss. From the temperature range we expect to see 50% or more loss in most fruit plantings. With large fruited fruits (apples, peaches, plums and pears) this is not significant but for small-fruited fruit such as cherries, blueberries and grapes where many small fruit are needed for good yields this frost is a disaster. Also fruit on higher sites will be less damaged than those at lower sites.

Small fruit

Grapes: After assessing grape damage on April 23 and 24, it appears we have lost 90% of the grape crop.   The warm weather had caused grapes to break dormancy earlier than normal. The average date for bud swell is April 27, but warm temperatures had caused buds to swell on April 16 and warm night temperatures caused the grapes to grow rapidly. Concord grapes in Berrien County have one leaf out. Grapes in Van Buren County were slightly behind.  At the one leaf bud stage, freezing temperatures of 27 F will result in 10% loss and 21 F in 90 % loss.  Wine Grapes were at bud burst.  The Paw Paw Lawton growing region recorded temperatures of 28 to 20 F. In the highest sites where temperatures of 28 F were recorded there was little damage.   For other sites the damage was total. All the actively growing points on the vines were killed. I was stunned by the damage done in grapes. Southwest Michigan has about 375 grape growers with 12,800 acres of grapes, about 95% of Michigan's total grape acreage. The grape crop in Michigan is worth about $20 million and it was all destroyed between sundown and sunrise.

Blueberries were at early pink bud. At this bud stage temperatures of 24 F or colder are need to cause damage loss. Tuesday's frost caused damage to early varieties in cold sites I estimate a 25% loss to the crop. Blueberry growers whose fields lie in the coldest sites because that is where the best blueberry soils are reported 24 to 18 F and lower.

In strawberries new leaves were emerging. The buds are still in the crown. Freezing temperatures in the 20s should have caused little loss, since the flower buds are still below ground. Strawberry growers report about 10% loss to their strawberries. Strawberry fields that were under plastic were beginning to bloom. Freezing temperatures will result in losses to open flowers. Closed buds can take 27 to 22 F.

To assess frost damage in tree fruits we need to wait several hours after the frost for the tissues to thaw out. The dead tissue will then turn brown and we can tear or cut the flowers open to see if the pistil or ovary of the flower has turned brown or black. This means there will be no seed or fruit from that flower. The pictures that follow show dead pistils. All these pictures were taken April 23 or April 24.

Apricots were in the shuck after the petals had fallen off the flower. Freezing temperatures of 27 F will result in 10% loss and 24 F in 90 % loss. Since most apricots are grown in high sites there was only moderate damage from Tuesdays freeze. Damage in Apricots is related to site and variety. All or nothing were killed: 75% Loss.

Peaches were still in bloom. Tuesday's frost will significantly reduce the crop: 90% in Van Buren County.  Less (25-50%) in Berrien County which has more peach acreage and more good peach sites near Lake Michigan with good air drainage. Since peaches have large fruit only a small number of flowers are needed for a full crop, the loss of a large number of flowers does not mean the crop is severely impacted. This means we could still have an excellent peach crop. The peach blossom on the left is alive while the one on the right was killed

Cherries were at or near bloom. Temperatures of 28 F will result in 10% loss and 24 F in 90 % loss. Crop losses due to freezing temperatures are significant. Cherries are small fruit. Due to the small size of the fruit the number of fruit needs to be large to have a full crop.
Sweet cherries were still in bloom. Crop loss 75 % loss. In sweet cherries the story is similar to apricots, good sites and hardy varieties suffered little damage while lower sites were wiped out. The sweet cherry blossom on the left was killed on April 23, 2002

Tart cherries were at white bud and scattered bloom had begun. Crop loss 50%. Losses are very site dependent. Some growers reported moderate losses, others reported little damage.

Plums were at full bloom. Crop losses due to freezing temperatures were significant and again site and variety dependent. Some growers reported heavy losses, other light losses.  At bloom temperatures of 28 F will result in 10% loss and 23 F in 90 % loss. Crop losses due to freezing temperatures on April 23, about 50%.

Apples were at pink and tight cluster. At tight cluster, temperatures of 27 F will result in 10% loss and 21 F in 90 % loss. At pink, when the petals are showing,   temperatures of 27 F will result in 10% loss and 21 F in 90 % loss. Most growers report light to moderate losses depending on the variety and site. Apple flowers are in clusters of 6. The center flower blooms first and has the potential to have the largest fruit. This flower is called the king bloom and is the most desirable flower to keep. The other flowers are called the side blooms and are usually thinned off to avoid a large crop of very small fruit. Unfortunately the king bloom is usually the first flower killed in a frost event. We have probably lost the king bloom and some of the side bloom so we still have fair crop potential at many sites. The picture on the left shows a dead apple flower, this was a king bloom. The picture on the right shows an apple flower cluster at pink.

Pears were at white bud.  It appears likely there was only light damage in pears.

For more information see my Freezing Damage to Fruit Page.

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Posted: April 25, 2002
Updated: April 30, 2009