Shade cloth for fall bearing blackberry druplet abortion/malfunction problems in southeastern USA

Final Report for FS13-276

Project Type: Farmer/Rancher
Funds awarded in 2013: $6,458.00
Projected End Date: 12/31/2016
Region: Southern
State: South Carolina
Principal Investigator:
Walker Miller
The Happy Berry Bunch
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Project Information


The project tested hypothesizes of making a trellis made from locally sourced materials that enabled operation of tractors/ sprayers on steeply sloped hills of the inner Piedmont of the southeast as well as support shade cloth to provide cooler conditions for improved yield and quality of blackberries. The trellis did so successfully except for an unanticipated problem of reduced soil evaporation resulting in tractor sliding. The shade cloth failed to provide cooler conditions or the anticipated benefits. The reasons why and the outreach program are discussed.


The problem was to provide a consumer desired, quality crop product to harvest, which is not available in the fall (September to December) market window, not be exposed to excessive price competition globally or otherwise, and would not be damaged by spring frost. To “thumbnail it” develop a new alternative crop for growers to become more economically, environmentally and socially sustainable. Recently developed fall bearing blackberries by Dr. John Clark at the University of Arkansas represents such an opportunity. The problem is that high summer temperatures in the southeast are causing reddening, white and abortion of drupelets and resulting in malformed berries with lower yields. Dr. Clark points out in his presentations and reports that beautiful fruit is produced in research trials in the cooler climate of the Pacific Northwest and California. In a personal communication he suggested that flowers formed when temperatures exceed 85 degrees Fahrenheit are smaller and malformed. Personal observation is that the frequency of white, dried, aborted drupelets is greater when exposed to direct sun. Therefore, the problem becomes to reduce the temperature and direct exposure to sunlight.

While hosting an extension researcher from Israel he pointed out that 30% shade cloth was used to produce berries free of similar problems in spring and summer bearing berries in Israel. Since we are about 850 feet in elevation and perhaps cooler, we planted a very small test planting of Black Magic and Prime Ark, both fall bearing and both with relatively soft berries when compared to commercial variety like Navaho. The soft berry means a very short marketing time line, an ideal situation for direct marketing, and local food shed growers in the southeast. The 2012 season was a cool season with great blackberry growth but still we had reddening, white and abortion of drupelets and malformed berries associated with hot temperatures of summer. If you are to use shade cloth the problem becomes to create a shade cloth support structure/system in the field adaptable to uneven terrain, that uses locally available supplies, cost less than commercially available systems, provides for vegetation management and pest management, is retractable when temperatures are good for good flower formation for maximum photosynthesis, deployable when hot weather or freezes threaten. A potential side benefit would be freeze protection by reflecting heat back into the canopy instead radiating out during radiational freeze on windless, clear nights.

The final part of the problem is to verify that proposed benefits of lower temperatures, better quality berries, and prevention of heat loss can be realized. Lastly, sustainability is achieved by reduced risk in producing high quality blackberries and increased reliability of cropping in the spring, cropping in a now empty market window and prolonged cropping in the fall over ambient conditions.

Project Objectives:

Develop a trellis system for shade cloth deployment and retraction that would enable normal tractor operation for mowing, air assisted spraying and directed weed management sprays using locally available supplies. The second objective is to verify hypothesized impacts of lower summer temperatures improved quality berries, higher yields and reduced heat loss in frost events.


Materials and methods:

A fully executed agreement was completed May 7, 2014 and work was begun. The spring blackberry season (growth of fruit buds, flowering and developing fruit) had already begun. Materials (treated 4x4’s 12 ft long, Chain link fence top rails and high tensile wire (12 gauge) and associated hardware were purchased by the project leader, normal extra seasonal help hired and installation of the trellis system commenced. This was a busy time of year and we started out way behind the proposed timeline of the grant proposal. This meant a lost opportunity to use sweat equity of the project leader for installation.

The trellis was up and in place by the end of June despite the fact that is a very difficult time of year because of low cash flow (limited harvest and hence sales) and the project proposal does not cover these costs. A loan was obtained through Farm Credit (Ag South) to purchase the shade cloth and max-min thermometers (4), weather boxes and etc. Despite communication problems shade cloth was obtained and up by early August with everything in place by August 18, 2014. Data collection commenced.

The trellis system handled very nicely on the hilly uneven terrain of the western inner Piedmont plateau. Tractor, sprayers and equipment easily moved about under the trellis as long as it was not wet. The area under the trellis with shade deployed remained moist significantly longer and a problem developed with tractor/equipment sliding into blackberry V trellis rows which run perpendicular to downhill. Pictures of the trellis system are in the Power Point attached to the First Annual Report. Details on the trellis construction materials are also included in the Power Point.

The cost for shade trellis was $1800 for the project area or $7850 per acre in 2014 dollars. The cost of the Aluminet shade cloth for the project area (10,000 sq feet) was $3046 or $13,268 per acre. These figures calculate to $21,118 per acre which was 1/5 or less than what a commercial Turn-key automated system would cost. Cost could have been reduced using cheaper shade cloth. Such an automated system might have helped with the wind-run issue discussed below.

Deployment and retraction of the shade cloths by hand took about 6 hours for the project area. During the two year period storms were not a problem. At one point a tree fell on the project area. The damaged area was quickly fixed with locally available materials. Because spring/early summer harvest was done by this time, no data was collected on spring/early summer harvested berries. In addition there was 50 percent crop loss due to late spring freeze on April 16. The primocane bearing berries Prime Ark and Black Magic were in their third leaf from plug starters. Primocane production was vigorous with lots of fruit terminals. Typically, as reported by the breeder, Dr. John Clark of the University of Arkansas, fall yields are 10% of spring yields. This should be contrasted with yields of 4 to 10 tons per acre of fall bearing blackberries in the cool climates of California and the Pacific Northwest. We were only getting 1 plus quarts of berries per 500 feet of row per day which was further compromised by spotted wing drosophila and a undiagnosed malady we called “blackberry etch.” Conversations with another grower that had a planting that was in its’ fourth leaf getting 20 quarts a day from 600 feet of row so we were optimistic that we would get much better yields next year. Because of this an “executive decision” was made to use phenotypic indicators, measuring floral competence as a predictor of berry normality (not in original proposal), to evaluate the performance of the shade cloth. This data, along with temperature data, was collected daily till frost on November 2 and 3, 2014.

The results of 2014 were reported at the Southeastern Fruit and Vegetable Conference (SEFVC) in Savannah Georgia, January 8, 2015 in the Bramble Session and are attached here as a Power Point presentation. After the presentation at the SEFVC several individuals approach me to discuss the results. A commercial company selling automated shading suggested we were measuring temperature of the air and not the fruit…that we should be using infrared thermometer measurements. In 2015 we consulted with the USDA about infrared thermometers and learned how they work considering resolution and field of view. Good instruments start at about $600 which we could not afford, or find, or borrow. There was no additional money in the budget for this contingency so we bought a $20 infrared thermometer From Lowes in 2015 for daily infrared measurements, continued to monitor the max/min thermometers in and out of NOAA boxes and in and out of the sun as well as do floral competency measurements. At the same conference we learned that it is approximately 50 days plus or minus from bloom to harvest for primocane blackberries. For our area of the country the average first killing frost is November 1. This meant that any flowers that developed after approximately September 15 would not be harvestable due to killing frosts.

In summary after the 2014 and 2015 season after analyzing the data collected using Max/Min thermometers making measurements at approximately 1 PM each day as well as measuring floral competence using phenotypic indicators (number of flower petals, number of sepals, the presence of leaf out growths on the sepals looking at 10 flowers per variety per day) we were not observing cooler temperatures in the shade. Floral incompetence was not different between sun and shade but was higher in the higher temperatures of mid August (around 50%) when compared to Mid September. A probable significant difference was observed between the two varieties used with Black Magic being closer to normal than Prime Ark as far as phenotypic indicators. Bottom Line…Shade cloth was not helping… yields were terrible! The shade cloth did help extend the season by a few days through reduced berry freezing incidents but not enough to justify the investment. Perhaps Black magic, which appears to be day neutral, continuing to flower and fruit until frequent freezing temperatures shut it down and resuming immediately upon warm up could be manged as a primocane only system year round in a temperature controlled environment during the winter months.

What is happening? We consulted several times with Clemson University retired meteorologist Dr. Dale Linville trying to understand why 2015 results were the same as 2014 and the shade cloth was not cooling as anticipated. Temperatures in the shade were higher than or equal to temperatures in the sun. Phenotypic indicators increased with increasing temperatures starting in June and declined as temperatures cooled in September. Black magic had less deformity than Prime Ark. Each day at approximately 1 PM temperature of ten green, red and black fruits in each primocane variety and in the Kiowa variety were measured. The numbers were variable due to the use of a cheap infrared thermometer. What we found was there was no apparent difference in temperature between colors of fruit, or in, or out of the shade.

Based on the discussion below what we should have been measuring were hourly temperatures of fruit during the day. What we probably would have observed was a delay in temperature gain but ultimately a higher temperature in the shade than in the sun and that the delay was inadequate for an impact on yield and appearance of berries. The conclusion is that shade cloth does not work for southeastern North America. The questions are "Is this a dead horse?" and "Why did it not work"? With Dr. Linville’s Help we learned, using instruments he supplied, that wind run under the shade cloth was reduced in the sun. The problem was to understand and explain our observations.

In addition to the lack of positive impact that we hoped for, we noted other morphological changes in the plants such as deeper green tissues both at the canopy surface and interior of the canopy. Also greater moisture levels in the soil and some changes in branching. Who has not walked under the shade of a tree and not felt ten degrees cooler? After consultations with Dr. Linville and literature on the physics of temperature, here is what we found was going on. The discussion below was prepared for 2015 field day at the farm. The full report is at our website and is attached here. After two years of observation what did we learn? Air has lower heat holding capacity thus it warms very quickly after sunrise and cools rapidly after sunset. Plant tissues have much higher heat holding capacity because they are mostly water which is much denser than air. Color makes very little difference. The physical principle involved is that heat energy always moves from the hot to cool. So as the day progresses plant tissues absorb heat both from energy wave lengths from the sun and ambient air until the tissues are equal to, or are greater than, the air temperature when heat from the tissues moves to the surrounding air. This process is impacted by air movement both when the plant tissues are cooler or hotter. When plant tissues are hotter wind takes heat away. Therefore when shade cloth reduces wind run it reduces heat removal from plant tissues. The shade cloth for the first part of the day reduces the rate of heat gain by plant tissues through reduced solar radiation but eventually it reaches the ambient air temperature as heat from the surrounding air flows toward the plant tissues and then because of lack of wind run the temperature goes higher than ambient temperatures.

The white drupelet problem was reduced in blackberry but processes like flower initiation, development, pollen viability and success in fertilization and white drupelet formation may vary in sensitivity to heat stress. It takes 50 days plus or minus to go from flower to harvestable fruit. So fruit from flowers formed within 50 days of first frost will be killed on average. Only flowers formed that successfully went through the process above prior to very early September will be successful. Bottom line shade cloth delays but does not stop plant tissues from reaching high temperatures in the southeast… with number of days above 95 degrees increasing from 10-15 to 30- 35. This means that yields experienced in cooler regions of the world will not happen in the hot southeast unless temperatures are modified in some other fashion.

Shade also impacts Photosynthetic Active radiation (PAR). Light from the sun is unidirectional. Shade changes it to multi-directional. Reduced intensity and multi-directional light can result in different organization of the chloroplasts for greater efficiency. Therefore PAR is increased throughout the canopy thus 50% shade does not result in 50% loss in PAR. Finally, Photosynthetic capability of the plant can become light saturated…blackberries possibly do not need full sun. Several plants are light saturated at 25 to 50 % full sun. The photosynthetic saturation point for blackberries is unknown and needs to be determined.

Is this a dead horse? Perhaps not! Let’s go back to the walk in natural shade. The cost of the trellis system still seems high for a small grower. An even less expensive system might be to use living pine trees. Pine trees are not epicormic, thus when a branch is removed it does not grow back. If pine trees, loblolly for example, were planted in north - south rows for maximum shade impact or east-west rows for minimal shade impact that were widely spaced, shade could be managed. The vision is that the trees would be totally limbed up till they were 4 -5 feet above the production canopy. For the next 30 feet branches would be removed in the north - south direction to minimize shade (sun goes over east west) impact. Over 40 feet the canopy would be allowed to expand in all directions. The distance between the rows would be determined by the number of hours of direct light required (e.g. photosynthetic saturation) and the threshold hours for flower and fruit damage. Remember that diffuse/multidirectional light results in more light in the interior of the plant, changed chloroplast organization and thus the presence of 50% shade does not mean a 50% reduction in photosynthectically active radiation. The advantages beside price are passive frost protection from east-west branches; diffuse or indirect light feeding the producing canopy; reduced damage from violent summer thunder storms; increased carbon sequestration; on-farm adaptation and mitigation to global warming; mulch production from needles on site for weed and water management. Disadvantages possibly would be increased disease and insect management, for example botrytis and blackberry psyllid and bird depredation.

Instead of loblolly perhaps a nut bearing pine could be used like Italian stone pine (we have a few growing at the farm). Major municipalities around the globe are betting major portions of their budget on the cooling effect of living trees in an attempt to address the impact of global warming on cities. The principle involved is evapo-transpiration. Incident solar radiation, as it heats the foliage, results in the cooling of evaporation. As the air surrounding the plant heats up rapidly, due to low heat capacity (less dense) and from solar radiation that energy flows from the air to the cooler plant where it is dissipated by evapo-transpiration. The result is keeping the air cooler in the canopy, as well as the plant cooler, while at the same time reducing incident radiation to plants and animals below. The result is both cooler air and less rapid heat buildup by plants and animals below with high heat capacity because of high water content. It seems reasonable to the author that the blackberry community should be looking to the future by addressing changes to our culture system.

Research results and discussion:

Growers get ideas and believe they see solutions or opportunities to improve their success. It is hoped that this negative report will prevent another grower from making a major investment in something that does not work in southeastern parts of North America. It is hoped that through the educational adventure of trying to understand the observations and the outreach program we have made it will stimulate the research community. The objective should be to develop a low input and carbon positive system of growing blackberries.

Participation Summary

Educational & Outreach Activities

Participation Summary:

Education/outreach description:

Project Outcomes

Project outcomes:

Economic analysis: Building a trellis that works on rolling hills including the shade material cost about $2100 per acre can be successfully done. This price could be reduced using different shade materials but there is an interaction with projected life of the shade cloth. The life of the trellis system itself is probably in excess of 15 to 20 years. The farm sees no future use for the trellis and shade materials. The farm’s direct investment for the trellis and shade cloth was $4846 of which it is estimated that the farm will salvage maybe $1000 less the salvage labor costs of removing it. The rest will be recycled in our local recycle center.


Potential Contributions

Extension/Outreach: The farm is visited each year by about 6000 families/clients. By the time we got the trellis up we had the explanation of what a SARE Producer Grant Project was by our family and employees as well as what we were trying to do “down pat.” Therefore a lot of folks learned about SARE. We were a featured tour during the September 15 to 17, 2014 meeting of the Southeastern Professional Fruit Workers conference held at the Clemson University Madren Center. The group is made up of horticulturists, entomologists, pathologists, area and county agents from all southeastern states. Thirty one were in attendance at the field day and observed the plots. Numerous questions and discussions were held about the objectives and observations made to that point in time. As discussed above a status report was given at the 2015 South Eastern Fruit and Vegetable Conference (SEFVC) in Savannah GA. The proceedings are digitally available to all 2000 plus attendees. In the Blackberry Association’s program there were about 65 growers, university and supporting industry individuals in attendance. Interest was very high as 8 or more individuals queried me after the presentation and another approximately dozen sought me out for further discussion during the rest of the conference. In mid October 22 of 2015 a field day was held at the farm with the cooperation of the local Clemson Regional Extension. Forty three people were in attendance representing 19 farming operations in the upstate of SC, western NC and Northeast Ga. Dr. John Clark, blackberry breeder and developer of primocane bearing blackberries from the University Arkansas, was in attendance at the field day as provided in the grant. His roll was adviser to the project and aid in interpretation of the observations. He was provided a copy of the handout for the field day prior to the field day. The hand out entitled “Shade cloth for blackberry drupelet abortion and white drupelet problems in the southeastern USA” is attached at the SARE website.

The program, conducted at the field site, consisted of the author presenting the objectives, reviewing how it was conducted, explaining the observations and why the hoped for results were not obtained. Dr. Dale Linville, Meteorologist retired, Clemson University attended to help explain the physics of temperature and why wind run or air mixing is important. Also present at the site were pine trees, 20 feet tall, which had been planted by the author prior to project initiation for passive frost protection. Many in the audience sought out the shade of these trees and were able to experience temperatures below the shade cloth, in the sun and temperatures under a tree. An infrared thermometer was used to demonstrate/observe temperatures of plants in the created environments as well as white and black surfaces. There was a lively discussion and Dr. Clark “picked it up” from there with history of the development of primo cane varieties. He reiterated that fall yields in the southeast were not good but that floricane production on these varieties were excellent and had attributes that fit well for Southeastern growers. He also reviewed attributes of recent releases and what looked good in the pipeline. A popular press article was prepared and has been submitted to Fruit Growers News. It is also attached to SARE website.

Future Recommendations

As outlined above living shade should be investigated.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.