Lack of Winter Chilling A Concern

December 14, 2007

If you grow deciduous fruit (peaches, apples, pears, blueberries, etc) then you are aware that these plants require a certain amount of cool temperatures during the winter in order to grow and fruit normally in the spring. We often refer to this as required "chill hours". While there are different methods that have been developed to record "chillings" the most basic method used in Alabama is to begin October 1 and record how many hours during each 24 hour period that the temperature is 45 degrees F. or less. The accumulation of hours at or below 45 are recorded from October 1 - February 15.
To see 2008 chill hour accumulations from various locations in Alabama go to the following site.

http://www.aces.edu/dept/peaches/peachipm/mesonet/

What happens to fruit trees that do not receive sufficient chilling? Flowering is delayed as well as vegetative development. If the lack of chilling is high enough then fruit growth is adversely affected.

The 2007 - 2008 "chill hour" totals for many areas of Alabama are running lower than we would like to see at this time of the year. Especially south of Birmingham, AL. Growers have seen the recent colder weather add to the total but, will this be enough by February 15th. Weather is one of those areas that is hard to predict. We have been hearing forecasts for warmer and dryer conditions for this winter and spring. However, over the past 10 days and continuing for another 7 days we are getting much needed rainfall and colder temperatures. Should we get to February 15th and continue with colder weather "chill hour" concern will be greatly reduced.

Over the years we have looked at "rest breaking" compounds. Products that have been reported to reduce the total number of chill hours needed for normal or near normal spring flowering and growth. There is one product labeled "Dormex" and we will again take a look at this product on higher chill peaches and perhaps blueberries. For central Alabama I've estimated that our "chill hour" total will range between 880 to 900 by February 15th. This would leave us in good shape for 650 - 800 chill hour varieties, perhaps a little short for vegetative buds on 850 chill hour varieties, and short for fruit and vegetative buds on 950 - 1050 chill hour varieties.