The purpose of this project was to reduce bud damage in vineyards by providing a targeted heat source to the fruiting buds during extremely cold weather. With the limited number of cold weather events in our area the past two winters, we were unable to see a significant difference between the application of the thermal protection versus the control area in terms of bud damage. The system did perform very well during the few below zero Fahrenheit events and kept the buds above that. It was also observed that on sunny days the black insulation absorbed the sunlight and maintained a slightly warmer temperature than those without the insulation. We will continue to utilize the system as an insurance against an extreme cold event in our region and potentially have more significant results to share with others.
Our proposal was to install electrical heat wire and insulation along the fruit zone of the vine to create a targeted zone of heat. The temperature inside the insulation was monitored with a digital thermostat which then activated the tape and provided heat when the temperature dropped below a threshold. The insulation is important to contain the warmth within the fruit-zone. Additionally, in the spring, when the insulation is removed for the growing season, the heat wire alone may be sufficient enough to provide protection from an early frost. While our pilot was targeted to grape vines, we envision that this system could also be used for other trellised fruit, including apples, pears, and stone fruit.
Our objective was to use the system described above to automatically warm the fruiting zone when temperatures are below a threshold to ensure that the primary buds survive and provide a full yield of fruit, as compared to a control.
The ability to guarantee a crop of fruit despite variable cold temperatures is of paramount importance for fruit growers situated in the northeast, and this has become more challenging in recent years. Climate change has modified the pattern of the polar vortex, causing both extreme colds and significant variability in temperatures. These factors have caused significant winter damage to the fruit buds over the past 3 years, causing yield losses, and financial losses for fruit growers. Additionally, in some cases, extreme temperature variability has caused fruit buds to deaclimate earlier in the dormant season, making the fruit buds vulnerable, and creating the opportunity for any cold temperatures to destroy the bud tissue.
We would like to explore a sustainable, automated solution to protect the fruit buds that involves using a combination of electrical heat wire and insulation along the fruit-zone of the vine to create a precisely targeted area of warmth to directly where the buds are located. While fruit growers have attempted to manage risk from extreme colds in several ways, each of these methods has specific weaknesses. We believe that it is imperative to find a more sustainable, automated solution that will effectively protect the fruit.
Installation of equipment (12/1/17 through 12/14/17):
- Cane Prune Vines (normal vineyard process)
- Install Heat Cable on Fruiting Wire. Unroll heat cable and attach to fruiting wire using the cable ties. Attach thermostat to the heat cable using 14 gauge extension cord. Connect thermostat to an appropriate power outlet (240v) and adjust settings for operation at 0 degrees F. This installation is a one-time event.
- Heat Cable: Briskheat Self-Regulating Heating Cable SLCAB10240BP ($3.20 per foot)
- Thermostat for Heat Cable: TC4X-2 Digital On/Off Thermostat ($99 each row)
- Cable Ties to attach heat cable to fruiting wire ($20)
- Extension cord (cut to desired connection length) ($400)
- 100 AMP Panel with eVolt reader to connect to all the rows ($5318)
- Installation labor (20 hours for 1800 feet of heat cable)
- Tie Canes to Fruiting Wire (normal vineyard activity)
- Install Insulation. Make a small incision in insulation tube and wrap it around the fruiting cane/heat cable/fruit wire for the length of the row. This task will be performed annually after cane tying.
- Armaflex COIL 5/8″ ID x 1/2″ Wall ($1/foot)
- Labor to apply and remove annually (45 minutes per 100 feet of heat cable)
- Install Data Loggers. Attach data loggers on end posts to measure and log temperature differences throughout the season.
- HOBO MX2303 – Dual Probe (Air vs Inside Insulation) ($180)
- HOBO MX2304 – Single Probe (used to measure the temperature inside insulation at end of a row to validate the full length of heat run) ($140)
Here is a visual of the steps involved:
1. Cane Prune Vineyard
I did find significant cost savings on the material by sourcing directly from the manufacturer (Briskheat).
We did have two weather incidents in 2018 that made use of the technology – one on the evening of 1/14/18 and one on 1/15/18. This allowed us to take measurements of the external outdoor temperature and the temperature inside the insulation adjacent to the vine buds.
The graph below is a result of the temperature data set being taken in 5-minute increments. As you can see in both evenings, when the cold outdoor temperatures dipped below 0 degrees Fahrenheit (the red line), the heat tape was activated and maintained temperature for the fruiting buds above that temperature (the blue line). Additionally, it appears as though the black insulation also had an additional warming effect from the sunlight even though the heat tape was not activated during the day.
In addition to the temperature, we were also monitoring the kWh consumption. For these 2 evenings and 4 hours of use, we consumed 1 kWh per 100 feet of heat tape.
Additionally, we did not see any significant temperature degradation throughout the row when measuring the temperature at the source and at the end of the row.
Lastly, when we performed bud counts in the spring of 2018, the difference between the bud damage of the control versus that of this experiment was insignificant (16% control to 18% treatment) . While 16% or 18% may seem relatively high, there are a number of factors that can contribute to bud loss, like water storage, insufficiently going dormant in the fall before cold temperatures begin, yield from the previous year, etc. Additionally, an expected loss for grape vines on any given winter is 9% – 11%. Also, we would not expect to see high bud mortality with the lows we did experience in January.
In 2019, we only had two evenings where the temperature dropped below our threshold of 0 degrees Fahrenheit to activate the heat tape. In the chart below, those two incidents occurred on February 1st and February 3rd. The lowest temperature recorded over those two evenings was -2.83 degrees Fahrenheit. Again, the heat tape and insulation demonstrated its ability to moderate the temperature in the bud-zone of the vines.
Our results of the kWh of usage were identical to those observed in 2018.
Lastly, we examined the bud mortality rate in the spring of 2019 and discovered that there was not a significant difference between our experiment and the control. The bud loss for the 2019 experiment was 3.2% and the control was 4.1% – well within our normal regional threshold of 9-11% bud mortality.
During the weather incidents of 2018 & 2019, we learned several things:
1. That, when activated, the heating element did not heat up above 50 degrees Fahrenheit – which would alert the vines to begin to come out of dormancy.
2. That the heating element can maintain temperatures within a certain range and stay above our desired minimum.
3. That the black insulation provides additional warmth to the buds inside the insulation when the sun is present.
4. We need more data. The four weather events over the past two winters were not cold enough to create the losses we would come to expect during a severe cold snap (~-15 F). The bud count loss between our experiment and the control was not statistically significant as a result.
5. That the insulation also protects against significant warming to the buds. As mentioned above, the buds begin to come out of dormancy if their temperature rises above 50 degrees Fahrenheit. When this happens, the cold temperatures that they can withstand also decreases. The insulation appeared to have a buffering effect on the warmer days as well, ensuring that they were not stimulated by the warming temperatures in the way that the rest of the controlled vineyard was.
Education & Outreach Activities and Participation Summary
I reached to several media outlets about the technology. There were stories from two – The Democrat & Chronicle which featured the technology and the other was from the blog of one of the leading wine industry writers on what vineyards are doing to combat the effects of extreme cold temperatures.
The Democrat & Chronicle Article:
Jancis Robinson (paid access)
Pertinent Text – “At Heart & Hands Wine Company, Tom Higgins is taking another approach. He has devised an automated heating system to protect against icy temperatures. Heating tape, more commonly used in roof de-icing, is permanently attached to the fruiting wire and then wrapped in plumbing tube insulation over winter, as shown above. Temperature probes inside the insulation are triggered to activate the heating tape at –17°C, and to turn it off at approximately –13°C. The system can also be used to ward off spring frost, using higher temperature settings. ‘For every 100 feet (30 m) of grapevine, it takes me 20 minutes to apply the insulation, and 10 minutes to remove it,’ claims Higgins.
The ease of use and relative affordability of his plan is a major part of its appeal. Higgins received a Sustainable Agriculture Research & Education grant from the United States Department of Agriculture to pursue his research. Initial results are inconclusive after a relatively mild first winter of use, but Higgins is confident that the long-term benefits will be tremendous.”
In addition to the articles, I have had a number of other vineyard owners visit the farm to inspect the system and ask questions about how the system works.
One of the critical elements that I was most fearful of was that the buds would become too warm inside the insulation next to the heat tape. If the bud temperature exceeds 50 F, it triggers the vine to “wake up” and be more vulnerable to the extreme cold temperatures. Additionally, it would trigger them to push their buds earlier than the other vines, also making them more susceptible to a late frost. Fortunately, the system did not even come close to the 50 F during its activation and we did not see any signs of an earlier bud push on the experimental vines versus the control.
I did field a handful of calls and visits from other growers wanting to learn more about the concept. I had growers as far as Canada come down to take a look at it to see if it might be an ideal solution for their cold problems.
I’m satisfied that we have the system installed and in place for any future cold events. While so far, the two seasons of this experiment (2017-2019) proved to be inconclusive with our trial, we’re hopeful that we will have additional winters where this technology will be valuable in saving some crop for the season.
I believe we have designed a system that can be utilized by other growers around the world. One of the biggest challenges and cost components that we faced was building a system that could record and log the energizing of the system. I suspect that future implementations of this system may opt for cost-savings and not want to record things like the consumption of kWh.
Unfortunately, the true test of this system will be a double edge sword. That is, if we have a catastrophic cold incident, it will mean a significant loss on the farm in our control acreage. I am still hopeful, however, that this system will work as designed and maintain warm temperatures for those protected buds and potentially in a frost event.
I feel that we still need additional data from the study and I’m confident that we will be able to use this system against a significant temperature event that creates additional crop loss on our controlled vineyard.