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.

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.

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.

Chillin' in NC?

Today it was 56 F in Raleigh, NC. I am loving the warm temperatures, but I am getting worried about lack of chilling. As of 4 pm today, we have accumulated 119 chilling hours, last year on the same date, we had 399 hours. We usually get about 1000 or more hours in the area.

High chilling/low chilling. Most of the blackberries and raspberries we grow in NC need to accumulate a high number of chilling hours in order to break bud and grow 'normally' next summer. Contrary to what you may initially think, we don't want low chilling plants. We want high chilling plants that can stay dormant when we get January thaws. However, this year it does not look like we are making progress to that high chilling number. We will be keeping track of it over the next few weeks. 

If you live in the SEUS, you can find probably find out the chilling hours in your area.  The NC State Climate office has a great tool you can use if you want to calculate the chilling hours in your area. Here is a link. http://www.nc-climate.ncsu.edu/cronos/blackberry/