Blackberry flowering

Blackberries are in full bloom or beyond at the Piedmont Research Station today. Here are some shots  taken from the RCA trellis plots. All cultivars have some flower kill as can be seen by the black dots in the centers of the flowers. Flowers with those blackened centers will not develop into fruit. We will take viable flower counts next week.

Apache

Oucahita

Von

Bud removal to mimic freeze damage in the spring

This spring we set up demonstration trials at 2 locations in the state to monitor what would happen if we mechanically removed buds at critical times during flowering. We wanted to mimic what may happen when we get bud kill to flowers in the spring due to freezing temperatures. One of the trials is at the Sandhills Research Station in Jackson Springs, Josh Mays is overseeing the trial on the cultivar Ouachita. He removed buds at four times in the spring, has taken lots of data and lots of pictures. Here is a short video of what we saw today. He will be sharing more at grower meetings this upcoming year.

The other trial is at the Mitchem Farm in Vale NC. I'll post about that one later...

Blackberry Freeze Damage Sample Evaluation in Savannah

Growers and Agents: I will be at the 2014 Fruit and Vegetable Conference in Savannah, GA later this week. Debby Wechsler, Executive Secretary of the North American Raspberry and Blackberry Association is sharing her table space outside of the Blackberry and Raspberry Conference on Thursday afternoon, January 9, 2014.  I will be looking at blackberry bud samples that may be damaged by the cold temperatures over the next couple of days.

Please bring in your samples. I will have a microscope and some sharp scalpels to slice open the buds.

Protocol:

- take samples from laterals that occur at the top, middle and base of the canes. Bring in several buds from each section. 

-place samples in bags, make sure that the samples are labeled with top/middle/base of cane and variety. 

-below is an example of a bud, this was taken last spring so the buds are further along than what you may see in your field. 

-if you are doing it on your own, longitudinal slices are better. I suggest you go out before the temperatures drop and after as well, to see if there are any differences. 

RCA trellis with covers

RCA trellis with rowcover, Piedmont Research Station, Salisbury, NC. Photo: K. Snider. 

Blackberry canes with emerged buds, under rowcovers. Photo: K. Snider. 

At the Piedmont Research Station in Salisbury, NC, we have a set of four RCA trellises oriented  North/South and East/West. The primary objective of this project is to evaluate attributes of fresh blackberry fruit. We are most interested in the level of sun scald based injury to fruit based on canopy orientation.

However, the RCA trellis is used in colder regions of the country as a way to grow varieties that are not cold hardy. In North Carolina, twice in the past decade, we have experienced low temperatures (8 April 2007 and 12 April 2012)  that have resulted in significant crop loss. Developing flower buds and therefore the blackberry crop were killed by late season frost/freeze events. So, we are looking at this trellis system as an option for protection from cold in NC.

Temperatures at the Piedmont Research Station in Salisbury, NC, for the have been cold, 20F on 21 March. We had emerged buds so we protected blackberry plants under rowcovers. Although the buds would likely have survived, we wanted to protect them, just in case. We have data loggers recording temperatures under the covers and will download them next time we get to the field and update this post to include those temperatures.

Frost 2012 damage to blackberry crop

I was able to visit blackberry growers earlier this week in Western NC.  The current situation is very complicated. I saw a lot of flowers and buds with blackened centers (Figure 1). The center part of the female part of the flower, (technically the pistal), it is attached to the receptacle. Both of these flower parts form the blackberry fruit that we eat, and....both were damaged.

Temperatures. Temperatures dipped to 25-27 F degrees and stayed there for 4-6 hours depending on location the first night, but temperatures likely varied due to location as was evidenced in variation in the amount of damage we saw. (In 2007, it got to 20 F and was widespread across the entire state, damage was severe and killed the entire fruiting shoot).

Crop stage and location. According to most growers, the crop was about 2 weeks early, so all cultivars were well ahead of their normal schedule and many were flowering.   Natchez was at or near full bloom and Ouachita had some open flowers and many flowers that were at popcorn stage. Navaho was behind with just a few open flowers. However, these stages varied depending on the location of the field, location within the field (higher spots had less damage), and location within the canopy (upper wire had more damage than lower wire). 

Crop damage. Damage ranged from very little to severe depending on the location  and cultivar.  In some cases, just the king flower was dead (Figure 2). In other cases, flowers only in the upper portion of the canopy were damaged. I estimate that in some severe situations, there was 80-90% damage and in others only 30-40% damage. 

As I mentioned above and in earlier posts, the 2007 freeze killed the entire primary shoot and the secondary buds emerged and were able produce a crop. However, this year only flowers were damaged, the primary shoots are still viable and they will likely remain attached to the canes. This will likely inhibit the growth of the secondary buds and the crop that they would produce. 

Figure 1. Blackberry flower after 2012 frost. Photo courtesy of Amy Lynn Albertson.

Figure 2. Navaho fruiting shoot. Area circled shows king fruit dead, but subbordinate flowers are viable. 

What to do this year? There are a couple of options, these are some that come to mind at this time.

• You could just wait and see what happens, some buds lower on the primary shoot may not have sustained damage as is seen in figure 2. They will produce fruit, in general the tips of the shoots have the most fruit, often 3-5, while lower down the shoots, only one fruit per node is produced. 
• Prune off primary shoots. You would have to do this close to the cane, but be careful not to prune or damage the 2nd bud (leave approx 1/4 inch). This MAY allow the secondary buds to develop.
• Prune out the entire canes, removing all the dead flowers and the canes that they are attached to. 
• In all cases, maintain a fungicide program, in the first two scenarios, you will have more dead tissue out there that will be susceptible to disease infection.  

Future? Wind machines or helicopters may help if inversions are present. Helicopters or wind machines are often used in peach orchards and grape vineyards. When inversions are present these machines are able to mix the air,  bringing the warmer air down and mixing it with the cooler air, and keeping the temperatures above lethal stages. 

We are also evaluating a movable trellis. This trellis can shift positions. So when it gets cold, the trellis can be laid down and row covers can be placed over the entire row. Finally, we can hope that we are not 2 weeks early in the upcoming years. The earliness of this years crop really elevated the amount damage we saw.

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