Cold weather and blackberry and raspberry bud damage 2007

Blackberry bud damage in April 2007. Note that the primary buds were killed (browned leaves) and secondary buds growing (green leaves).

After an abnormally warm March, April is decidedly cooler in NC. Blackberry and raspberry plants have broken bud and many are beginning to flower. Temperatures are expected to be quite cool these next few days, with temperatures predicted to be 38F in Raleigh and 33F in the Asheville area according to Accuweather. So growers in western NC should be paying close attention to their weather this week.

Although we don't have data on critical temperatures for blackberry, we expect that damage due to cold would be very similar to strawberry. Tighter buds are less vulnerable, and open blossoms are the most vulnerable. These temperatures are:

Tight Bud: 22F
Popcorn stage: 26F
Open Blossom: 30F

Strawberry growers can use rowcovers or irrigation to protect open blooms. Blackberry growers do not really have these options. Rowcovers would be very difficult to spread over the rows. Overhead irrigation adds ice and therefore weight to the canes and will cause them to break.

We experienced a similar situation in 2007. There was lethal damage to primary buds. Fortunately, secondary buds broke soon after the primary buds were killed and the secondary buds produced approximately 70% of a full crop. Five to six weeks after the freeze, the secondary buds were open and you could hardly tell there was any damage earlier that year. Laterals were longer and harvest was later, I think it was at least 2 weeks. Given that we were early, this delay if it happens may not be a bad thing, we may  be able to reset our harvest to the normal dates.

For some insight into what happened in 2007, here is a link and some pictures.
http://www.ces.ncsu.edu/disaster/freeze/BlackberryRaspberryAssessment.pdf

There is also more information on strawberry protection and critical temperatures on the strawberry portal.
http://www.ncsu.edu/enterprises/strawberries