Flowers damaged by cold temperatures

Last week, in one of our research plots at the Piedmont Research Station in Salisbury, NC, I noticed that some of the flowers had tiny black centers. This is the result of cold injury to the flowers earlier this spring just as the buds were starting to develop (23F on 3/27/14). The flower in the oval on the left, with the green center will develop into a fruit, while the two flowers in the ovals on the right will not develop into fruit. There were not many damaged flowers and I expect that the total yield will not be impacted by the amount of damage in this picture.

Blackberry Crop after 2012 Freeze

Image 1. All flowers killed by 27F, no fruit developing, crop loss was significant with this variety.

Image 2. Only the early flowers were killed,  this variety will produce nearly a full crop. 

Yesterday I was in a farmers field in the Piedmont region of NC and took several pictures. As with many farms in NC, on the night of April 10, temperatures at this farm got down to 27F. This farmer grew several different varieties of blackberry. Some were in full bloom, while others did not have any open flowers. The early varieties that were in full bloom now look like the top photo, while later varieties only lost their king flowers/fruit.

What to look for in terms of cold damage in blackberry and raspberry plants ALSO SEE POST 4/19/12

Image 1. Bronzed flower buds

Preliminary reports from across the state indicate that temperatures did go below freezing. It was 27 F in Davidson County,  and 29 F near Danville, VA.  To determine if your caneberry plants were damaged, you will need to wait a few hours. Around noon, go out to your field and start looking at your buds. Closed flower buds will show a bronzing on the sepals (green outer layer of flower buds) see an example in Image 1. However, there does not to be any visible damage, you need to look inside the buds.

Image 2. Blackberry flower bud after freeze injury. Note that only the ovaries and the receptacle are blackened. 

Slice the buds longitudinally and take a close look. In 2007 we saw that the male plant parts (anthers) were fine in some cultivars, but the female parts were damaged (ovaries) and the receptacle were damaged. See Image 2.

Image 3. Damage to blackberry buds in 2007, the entire flower, anthers, ovaries and receptacle are blackened, in most of these buds. 

However in some cases the entire bud was damaged as is shown in Image 3. In either case, no fruit will be formed.

In a few days you may see entire laterals wilting as was seen in the previous post. If you see this type of damage, you will loose the fruit from those buds. BUT you should see secondary flush of growth and based on what happened in 2007 you will get up to 70% of a full crop, later. Later in this year, means a normal fruiting season, I hope.

If you have damage, what should you do? With all the dead tissue, there is an increased risk of botrytis.  You should apply a fungicide to help keep the infection level down. Maintain your spring fertilizer regime and keep weeds under control to reduce competition for nutrients.