Assessing Winter Injury in the Piedmont and Western North Carolina Class Exercise

Guest writer: Nicholas Basinger nabasing@ncsu.edu, Graduate Student, Department of Horticultural Science with data collection help from HS 422 class members. Edited by G. Fernandez

Deep cold, accompanied by snow came into the state the last week of January.  Some growers were reporting temperatures in the negative single digits.  After this weather came and went,  growers were wondering if the frigid air had affected their crops.

Samples of whole canes were collected from 3 locations: the Piedmont Research Station (PRS) in Salisbury, NC, the Upper Mountain Research Station (UMRS) in Laurel Springs, NC and a grower site located near Hendersonville, NC.  We looked at 4 varieties of blackberries and 3 varieties of raspberry.

These samples were brought back to NCSU and dissected on February 10, 2014 as part of a class exercise in HS 422, Small Fruit Production.  The objective of the exercise was to determine if bud damage had occurred due to the cold temperatures in the past few weeks. Three buds from an upper lateral, three from a middle and three from a lower lateral (see drawing below) were dissected and assessed for damage.

We observed the most injury in raspberry varieties from the UMRS (elevation 2800 ft), which saw temperatures of -9 ^oF during the late January freeze.  By the time the freeze hit on Jan. 30,  780 chilling hours had accumulated at this site. Previous days to the lowest recorded temperature were in the mid 40’s.  This is almost a 50 degree temperature shift in a matter of 2 days.   Raspberries do not tolerate large temperature fluctuations and are more susceptible to cold damage when their chilling requirements have been met.  Almost all of the raspberry canes at this site showed bud damage throughout the cane. Fortunately, the raspberries sampled were primocane-fruiting types and will be mowed to the ground in a few weeks. They will  produce a crop on the primocanes later in the summer.  

In all locations, we observed some injury to blackberry buds.  In general, injury was observed on buds furthest from the crown. And the colder sites, Hendersonville and Upper Mountain Research  Station in Laurel Springs had more injury than the Piedmont Research Station in Salisbury.

Below are some examples of what to look for when dissecting caneberry buds. 

The cold temperatures have permanently damaged this Navaho bud. Notice that in the center of this bud there is a dark dot (necrosis).  This will not produce fruit in the spring.  Photo: Gina Fernandez

This picture is a great example of healthy Navaho bud.  Notice that the bud looks green and there are no signs of necrosis. Photo: Nicholas Basinger

If you are interested in taking samples from your field, we suggest you sample an entire cane as is illustrated in the diagram above to determine where the injury has occurred. If the majority of the injury is on distal portions of canes and laterals, those buds can be removed by pruning. For more on how to sample read this posting: http://teamrubus.blogspot.com/2014/01/assessing-cold-damage-in-blackberry-and.html

ALSO, here is a link to an awesome (GF opinion) video, showing how to dissect and look at buds,  click HERE. When dissecting it is VERY important to cut down middle of the bud; if you do not cut down the middle you may not be able to see damage if there is some present. 

Assessing cold damage in blackberry and raspberry buds and wood at annual NC grower meeting

In early January, at the SE Vegetable and Fruit Expo in Savannah, GA, we set up a microscope and a magnifying glass (the kind you get in a craft store) to look at bud damage in blackberries. Most of the buds that I sampled looked good. http://teamrubus.blogspot.com/2014/01/buds-look-good.html

On Feb 6, 2014 we be looking at more samples at the annual meeting of the North Carolina Commercial Blackberry and Raspberry Association, in Shleby, NC. (Contact Daniel_Shire@ncsu.edu for meeting information). We will be looking at  samples collected  from our research blackberry and raspberry fields.

You are welcome to bring in some samples from your fields. We may not get to all of the samples, but we will train you to look at your own samples, so you can sample your own fields on a regular basis.

If you want to bring in some samples or prepare samples for evaluation at home, here is the protocol (courtesy of Michelle Warmund, University of Missouri):

• cut 3-4  8" cane sections from a low, mid parts of a main cane and some laterals from the fruiting area
• place each group of canes in  in a zippable gallon size plastic bag
• label each bag with name of cultivar and where the cane was taken from the plant (low, mid, laterals)
• store at room temperature for 4-5 days before the meeting.

At the meeting we will cut canes and check for injury symptoms. Dead cane sections and buds will have oxidized and turned brown after storage for 4-5 days in the zippable gallon size plastic bag. The sections from the lower and mid cane are needed to assess potential damage primarily to the canes. We will look at bud and cane damage on the laterals.

Here are some examples of bud and cane damage in West Virginia at the USDA Appalachian Fruit Research Station in Kearneysville, WV. The photos taken by Dr. Fumi Takeda.

Winter injury to blackberries. Plants with shriveled floricanes and primocanes are green and healthy. Photo: Fumi Takeda 

"Bark" scrapped off, showing oxidation of cambial/vascular tissues. Photo:Fumi Takeda

Primary bud is damaged as indicated by necrosis of partially differentiated inflorescence axis. Secondary bud is still undifferentiated, no sign of damage. Photo:Fumi Takeda.

Buds look good!

Here are a couple of images that show buds that we looked at yesterday. As I mentioned before, buds are tight and at the stage when they should be most dormant.  We did not see any damage to all but one of the buds we evaluated (20+ buds).

The first image is of a healthy bud, this is typical of the many buds we sliced longitudinally.

This image was from Navaho, but all other cultivars including those from the Pacific Northwest looked healthy.

Red arrow points to healthy bud.

This is from a small weak lateral, cut from the tip of a plant:

Red arrow points to damaged bud.

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. 

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.

Managing (?) older plantings of raspberries and blackberries

In our raspberry trials in the NC mountains, where raspberries are adapted and are capable of producing good crops, we have seen productivity decline after the 5th year of fruit production. While in the peidmont areas, we see a dramatic decline in the 2nd year of fruit production of raspberries (they are not adapted to the region). Blackberries on the other hand, tend to be more adapted and will live longer in most regions of the state. However, how long they will last is not known. In North Carolina and other states in the Southern US a recent rise in acreage of blackberries occurred in the past few years and as these plantings age, we need to monitor them to determine how long they will be productive both in terms of fruit and profits.

In the southern US, heat, drought, insects, diseases, if not controlled can take their toll on the productivity of a blackberry and raspberry field. Likewise, plant and soil health needs to be monitored in order to provide a plant with optimal nutrition.  Because this is a fairly new industry, we don't have long term experiences with the crop, however, below are a list of things to think about and address as needed as your plantings age.

Observation of annual growth. Growers should keep good records of individual fields and compare productivity from year-to-year. In addition to yield records, the plants health can be monitored by looking number of canes/plant, cane diameter,  and number of fruiting laterals. You do not need to count each of these, but a picture taken at the same spot in the field each year could help you identify any issues.

Diseases and insects. There is a long list of diseases that can negatively impact  blackberry or raspberry plant health.  In fields that are lightly managed, I most often see cane blight and viruses, and borers negatively impact productivity. 

Weeds. Perennial weeds harder to control over time and annual weeds will compete with crop. Both will impact productivity if left unchecked.

Fertility. There is no known long term research for caneberry fertility in the southern US. However, routine soil and plant tissue samples will help you determine needs and adjustments. Tissue samples should be taken each year and sent for evaluation. In NC, samples should be taken after fruit harvested from the plants. Leaves from the 3-5th node of the primocane plant should be taken and sent to NCDA and they will make recommendations for the following season. Keep your records so you can see if there are trends in your fields. Below are the recommended levels of macro and micronutrients.

Yield and prifitabilty. Good yield records for each field should be taken every year. A simple comparison each year will be your most useful indicator of planting productivity over time. Based on a budget developed at NC State University, when a grower is getting $14/flat, a 10% reduction in yield, their returns fall from $6036 to $4359/acre (see blue font below). You can get a copy of this budget and play with the inputs (any boxes that are blue can be edited).  http://ncsu.edu/enterprises/blackberries-raspberries/management/blackberry-raspberry-budgets-pricing/

Estimated Returns per Acre for Commercial Blackberry Production
for Varying Yields and Wholesale Prices per Flat.  Total yield 19,000lbs/acre, 80% marketable, so net of 15,200 marketable lbs/acre.
	Wholesale Market ($/flat)	Marketable Flats per Acre
		1,621	2,027	2,533	3,040	3,648
	$8.96	($8,173)	($7,533)	($6,732)	($5,932)	($4,971)
	$11.20	($4,542)	($2,993)	($1,058)	$878	$3,200
	$14.00	($2)	$2,682	$6,036	$9,390	$13,415
	$16.80	$4,538	$8,356	$13,129	$17,902	$23,629
	$20.16	$9,986	$15,166	$21,641	$28,116	$35,887

Estimated Returns per Acre for Commercial Blackberry Production
for Varying Yields and Wholesale Prices per Flat. Total yield is 17,100 lbs/acre, 80% marketable yield, so net of $13,600 lbs/acre.
	Wholesale Market ($/flat)	Marketable Flats per Acre¹
		1,459	1,824	2,280	2,736	3,283
	$8.96	($8,429)	($7,853)	($7,133)	($6,412)	($5,548)
	$11.20	($5,161)	($3,767)	($2,025)	($283)	$1,807
	$14.00	($1,075)	$1,340	$4,359	$7,377	$11,000
	$16.80	$3,011	$6,447	$10,743	$15,038	$20,193
	$20.16	$7,914	$12,576	$18,403	$24,231	$31,224

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.

Estimation of damage from a grower and his daughter

Blackberry shoot about to be dissected

A grower in western NC sent me this information that he and his daughter gathered as part of a math lesson. They used real data from the plants that had been damaged from the cold temperatures in April. I have asked them to follow up with pictures and yield data. I will keep you all updated. I have also instructed some of you to do the same in your fields.

Blackberry Freeze Damage/Production Estimate

Conducted 4/24/12
Frost and Freeze occurred 4/12/12 27 degrees on top of field and 25 at bottom
Randomly selected one Navaho plant and removed every fruit shoot and sliced each fruit bud to determine percentage of live buds at this development stage of Navaho.
Marked the plant to later determine new shoot generation.
Plant utilized was a 3rd season plant ¾ up the knoll and mid field.
Data collected:
107 fruiting shoots on the plant.
10 minutes to remove all shoots – (approximately $3334 of labor to remove shoots per acre)
Average of 6 fruit buds per shoot at this development and time of season (there were 5 open blooms on the entire plant)
340 buds were determined “alive” out of 642 buds examined – 53%
These plants have been under a vigorous fertilization/irrigation regiment following the freeze – to hopefully stimulate new growth.
Observations made:
0 buds were found alive the day after the freeze.
The live buds appear to be the ones that have developed after the freeze. The live buds are small ones surrounding the top dead buds or developed at a lower lateral of the fruit shoot.
It appears that there is a possibility of further new buds to develop at lower tiers of the fruit shoot.
There is concern of deformed fruit on some buds that appear to be “alive.”
Natchez were much further developed and 0 to very very few new buds are being found.
The 1st year harvest Navaho appear to have a more significant new bud development – no data at this time.

If you would like some help estimating your damage give me a call or send me an email. This is not like the 2007 freeze, so any information you can share will help us all learn from this experience.

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).

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.

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