Blackberry crop damage spring 2020

Over the last week there have been cool temperatures at night that have damaged the blackberry crop. The crop in some areas was 10 days to 2 weeks earlier than usual. This year we saw damage to the primocanes, something that we have not seen before. Thanks to the many growers I have talked to over the past couple of days for sending in the pictures below.  My impression is that the site and not cultivar has more to do with damage. Higher sites on the same farm incurred less damage. Also healthier plants sustained less damage.

Flower bud damage
The first image below are from a field visit a few years ago. The first image illustrates how a fruiting lateral looks fine on the outside, however once you slice open that same shoot, you can see that many of the centers (technically receptacles) of the flower buds are black. If the centers of the buds are black, they will not develop into fruit. If they are green, the fruit will develop normally.

On most farms, the crop this year was further along and the damage is easier to spot, no need to cut open the buds. The blackened centers are the receptacles. Culitvars from top to bottom are: Prime-Ark 45, Natchez, Osage and Freedom.

Prime-Ark 45

Natchez

Osage

Floricane crop of Freedom. Date is not correct.

Damage to primocanes
This year we saw damage to the newly emerged primocanes.  We think that the winds that came through over the last week made the plants more vulnerable to the cold temperatures. The damaged tissue will die. However, there are still buds on the lower canes and they will emerge and start growing. The response of the plant will be similar to tipping. 

Traveler cane damage.

Traveler tip damage

Freedom tip damage.

Freedom leaf damage.

What to do this year?

• Wait a few days to determine the extent of the damage. Some areas in the region may sustain further damage this weekend and early next week.
• Secondary buds near the base of the primary shoots may start to grow into a secondary shoot. Here is a link to secondary bud information on this blog. The secondary buds/shoots are often very fruitful, and will produce a later crop. https://teamrubus.blogspot.com/search?q=secondary+buds
• When damage was severe, 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, the dead primocane and floral bud tissue in the field will be susceptible to additional disease infection.  

What to think about for the future? 

• Site selection. A few feet in elevation can make a big difference.  There are several online resources that discuss elevation. Here is an example for vinyards. http://www.evineyardapp.com/blog/2019/07/03/how-to-prevent-vineyard-frost-damage/
• Insurance. We have experienced cold damage to the blackberry crop frequently enough that this may be a good investment.
• Wind machines. Peach growers use these in parts of the state. They can be a "valuable tool for frost protection in areas where atmospheric temperature inversions occur during radiation freeze events. The warmer air inversion layer typically occurs at about 40-50 ft, and wind machines 30 ft tall with 18-foot blades mix the warmer air from the inversion with cooler air around the vines. One wind machine typically can provide 1-3ºF of warming for about 10-12 acres" (https://grapes.extension.org/frost-injury-frost-avoidance-and-frost-protection-in-the-vineyard/
• Heaters. Growers can buy commerical heaters or burn items such as large bales of hay. Both options are generally expensive and can be a source of pollution.
• Bare soil or closely mowed cover crop. Bare soils have a large heat capacity, during the day they can capture and store considerable heat. https://www.canr.msu.edu/news/bare_ground_is_warmer
• Shift type trellis and row covers. Growers in the midwest utilize the RCA or shift type trellis in combination with row covers to protect their crop in the winter. https://content.iospress.com/download/journal-of-berry-research/jbr044?id=journal-of-berry-research%2Fjbr044

Thanks to the many growers and to Karen Blaedow, NCCES Henderson County agent who shared their images with me.