2014 Starting off COLD

January 1, 2014 Blackberry Crop Update:

Short version:

Buds are tight and still developing.
Chilling has not been met for most cultivars (500 hrs in Salisbury).
Low temperatures predicted in the next 10 days are nearing the level that we have some concern about damage.


Longer version: 
Bud Development. We are heading into the coldest part of the year and the blackberry and raspberry buds are tight and are at the hardiest stage of their lifecycle. Research done by Takeda and others in 2003 (http://www.ars.usda.gov/SP2UserFiles/Place/19310000/FTakeda/2003JASHS-blackberrypaper.pdf) followed stages of bud development of both thorny and thornless blackberry cultivars. In general in January buds are at stages 4-6. At this stage, the flowers are still developing, and the most terminal flower buds are furthest along.  See the table 1 below for a detailed description of the stages. So, I dont think that the buds have fully developed. Will there still be some damage? Possibly. I will be monitoring the situation. The good news is that we know that there are secondary buds that can produce nearly a full crop. 










Chilling. We have accumulated 508 hours of chilling as of today at the Piedmont Research Station in Salisbury, NC. This is based on the model found at http://nc-climate.ncsu.edu/cronos/blackberry. The model we use accumulates 1 chill unit when temperature is between 0 and 7° C. The plants should accumulate several more units this week, despite the predicted cold weather. Most of the varieties we grow are higher chilling and have not yet met their standard chilling units, which are estimated to be between 700 and 1100 hours. http://teamrubus.blogspot.com/2012/02/chillin-in-nc-part-2.html

Low temperature damage? Michelle Warmund did some research several years ago and found that with eastern types of blackberries, buds at this time of year have reached their maximum hardiness and are killed at −9 °F.  While the types grown in the western part of the country are often damaged when temperatures reach 12 °F. However, we have observed damage to plants at the Upper Mountain Research Station in Laurel Springs to eastern types when temperatures dipped into the single digits. However, I think most of the damage we saw occurred later in the spring when the flowers were more fully developed. 

What to do?

Monitor your crop. Monitor the temperatures. 

Walk through your fields now and look at buds. Are they tight? Slice a couple open longitudinally and see if they are white and green inside, this is a healthy bud. Black is not good. 

Use row covers? There has been success in the midwest using row covers over the RCA trellis. The trellis is in the lowered position allows for "easier" positioning of the row covers over the trellis. I am not sure how feasible this would be with the trellis system we use in NC. However, if you have a piece, it may be worth pulling it over the entire canopy, sealing up sides and ends. What you want to do is to hold in some heat that is captured during the day. Here is a picture of one of our RCA  plots with row covers.

Are you ready for spring?

Andy Rollins,  Clemson Extension Service sent me this image last week. In the circle are some basal buds breaking at the base of pruned cane as well as some buds further up the cane. Daylength, temperature (cumulative and current temperature) and plant hormones are key components that determine when buds on a plant will break.  The daylengths are getting longer, 12 hours and 7 minutes in Clemson SC last week when this was taken.  Chilling hours (cumulative temperatures between 34-45F) is at 325 units, according to one model, however, I think the real chilling is higher (the inception time depends on a temperature trigger of 28F and that first occurred this winter in January). The chilling unit accumulation at the Piedmont Research Station, in Salisbury NC, where some of our research plots are planted is over 1300 units. Daytime temperatures are getting warmer, although they are not staying warm, so continued growth will not occur for a while.

However, spring is not far away. Get pruning done, trellises repaired, irrigation system prepped, winter pesticide applications out (lime sulphur on blackberries has to go out at delayed dormant before buds are 3/4" long). See SRSFC IPM guide for the latest recommendations. http://www.smallfruits.org/SmallFruitsRegGuide/Guides/2012/2012BrambleSprayGuide.pdf

Navaho and it's amazing basal buds produce a crop after a freeze

Navaho blackberry plant. Upper oval shows fruit on a primary bud from a floricane, flowers were damaged by the April freeze and few fruit developed. Lower oval shows fruit from a basal bud, where abundant fruit is ripening. 

Each year I continue to learn more about the amazing blackberry plant. Last week I visited a farm in western NC. The farm had experienced the same cold spell that many of the growers had during the April 10-12 night freezes. Nearly all of the flowers from the primary buds that were present sustained damage. In the photo above, the smaller oval at the top of the picture shows what remains of the crop from those primary buds. The lower oval shows fruit that has come from basal buds. Each year Navaho sends out some basal buds, but this year, there were many more basal buds and the grower will be able to realize a much better crop than had been expected from just the primary buds.

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.

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.

Blackberry plants recovering after the freeze 2007

Image 1. This is a secondary bud that has emerged (semi vertical green stem). There is a remnant of primary stem, it is the brown nub on the right. 

Image 2. Regrowth of laterals after complete loss of primary buds in 2007. 

Reports are in, there was damage, laterals were wilting in the afternoon at some locations after the  freeze this morning and at other farms there was just bud damage (4/12/12).

Above are some images of the plants a couple weeks after the freeze in 2007. These were in a field  of Arapaho. The remnants of the primocane leaves are on most nodes, it is the brown nub on the right side of the node (Image 1).  A few days after the freeze I was in this field and noted 99% blossom kill and most of the fruiting laterals tissue appeared dead (wilted). I did not look for secondary buds at that time. However, about 2 weeks later, secondary buds were emerging, and I could not find the dead primaries (Image 1).

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