Five vine shelter types currently being investigated by Texas A&M for their impact on vegetative growth and winter injury potential
By: Patrick O’ Brien, Ph.D and Michael Cook – Texas A&M AgriLife Extension Service
The first few seasons in the vineyard immediately following planting are key growth stages and can be especially challenging in terms of their management requirements, even for the most seasoned of viticulturists. As young vines are not well established, they are particularly susceptible to various forms of damage from both biotic and abiotic sources.
Growers also assume a great financial risk and burden not only because, in most cases, it takes three to four years for vines to come into full production but even more importantly, as grapes are long lived perennial crops, mismanagement of a young vineyard can have negative implications that may persist for decades. A prudent grape grower will spend time to understand the inherent risks of their site and implement practices that will encourage healthy growth of both roots as well as shoots. One of the top threats to a young vine occurs when encroaching weeds compete with the vine for water and nutrient resources or rapidly grow tall enough so as to provide excessive shading, robbing the vine of vital sunlight. Additionally, left exposed to the open environment, young vines are at the mercy of excessive wind, intense solar radiation, and if using herbicides for vineyard floor management, potentially disastrous off-target herbicide damage. Moreover, to add insult to injury, vertebrate pests have no understanding or appreciation for the long-term goal of establishing a productive and healthy vineyard and are likely to view your leafy young wards only as an appetizing food source.
It is for this reason that vine shelters are commonly used to provide protection during early vine growth stages. Sometimes referred to as grow tubes, these shelters are available commercially in a range of colors, sizes, configurations, and material types. The choice of ideal shelter features for your vineyard site is a decision probably best determined by which risks present the greatest priority. Taller shelters may provide additional protection to the elements or vertebrates but may also prove a hindrance for ease of vine access for monitoring and training purposes. Cost of vine shelter type also varies greatly, with those made of stronger material types like plastic coming at a greater premium than those made of weaker materials like waxed cardboard. What may work well for a shelter design in one growing region may not necessarily work well for all regions or vineyard management strategies. In areas where hail is common for example, weaker vine shelters may not provide the durability required to protect their housed vines for an entire growing season, much less the multiple seasons required for full establishment.
Another factor to add to the decision-making process in vine shelter selection is that it is often recommended that shelters be placed on vines until sufficient periderm formation has occurred in order to reduce the risk of off-target herbicide injury, meaning that these shelters are utilized for the first two to four years of establishment. Some shelter types degrade rapidly, such as those made from cardboard, and may only last one growing season while others are much more resilient to the elements and thus their service life can be greatly extended.
Because of the protection that they provide you might think that the use of vine shelters for your young vineyard is an obvious choice. It is certainly a popular strategy, particularly in new world wine growing regions where their use is nearly ubiquitous. This decision may warrant a little more consideration however, because although vine shelters are effective in providing protection against certain forms of damage, due to the nature of their application, they may actually make vines more prone to other forms of damage as well. Research conducted by the Texas A&M AgriLife Extension Service demonstrated that the environmental conditions provided by different vine shelters vary based on their inherent features. In a trial investigating 12 commercially available vine shelter types, differences were observed in temperature and sunlight infiltration rates within the shelters. Light transmittance (lux) ranged from 2% to 48% compared to ambient conditions. Annual mean temperature was elevated for 3 of the 12 shelter types, with a maximum increase of 3% and reduced for 3 shelter types when compared to ambient demonstrating certain vine shelters do retain more or less heat than others
Figure 1
Figure 1: Growing degree days (GDD) were also calculated, with 6 shelters having up to 10% greater GDD accumulation compared to ambient and 2 with as much as 13% less accumulation Figure 2.
Figure 2
Previous research has also reported that the use of vine shelters may provide a warmer growing environment. Graham Due found that the use of polypropylene shelters at vineyards in South Australia led to an increase of 18°F over ambient temperature, while Hall and Mahaffee found that use of similar shelters on potted vines led to a maximum increase of 32°F! These findings have an important implication on vine development as air temperature may affect early vine growth. There is an optimum temperature range for vine growth, and the accumulation of growing degree days over the course of the growing season dictates total vine growth potential. Likewise, sunlight interception is an important growth factor. Based on this information, vine shelters could help to promote more rapid vegetative growth immediately following planting, desirable for getting young vines into a well-established state in preparation for training. Additionally, shelters help to guide the growth of shoots in a straight and vertical manner ideal for permanent trunk architecture and suppress the growth of lateral shoots meaning that vigor is not wasted on vegetative growth that is not constructive for training.
The higher temperatures that have been observed in certain vine shelter types are the result of a greenhouse effect caused by the insulative properties of the shelters themselves. Although this may be a positive feature in terms of providing sustained warm temperatures for promoting vegetative growth, especially throughout the growing season in cooler climates, it also means that vines housed in those shelters may be at an increased risk of heat injury particularly during heat waves in cool climates or for the extended period of high temperatures experienced in hot climates.
Another concern that can be easily overlooked is that the use of shelters could also increase cold injury potential during winter months or even encourage an earlier budbreak, making young vines more susceptible to spring frost events. This is because of the physiological sensitivity intrinsic to most grapevine species as it relates to dormancy. Grapevines enter dormancy rather slowly via acclimation beginning in the late summer to fall with dormancy peaking in mid-winter. They then begin to deacclimate, at a much more rapid rate, in late winter to early spring ultimately resulting in budbreak. Unfortunately, increased temperatures during these times can delay and/or disrupt acclimation as well as encourage premature deacclimation, making vines much more sensitive to cold injury.
To make matters worse, for those vineyards located in areas that experience frequent and drastic temperature swings the risk for injury markedly increases. One strategy that growers may use to mitigate this risk is removing shelters entirely in the late fall, and then replacing them once growth begins in the spring. Of course, removing and replacing shelters can be problematic not only because it is labor intensive and may require purchase of additional tubes if using “one-time-use shelters”, costing the grower more time and money, but this practice has not been supported by scientific studies.
Thus, in order to provide grape growers situated in environmentally high risk growing regions with the most up to date research-based recommendations on vine shelter use, a new project has been launched this year by the Texas A&M AgriLife Extension Service to further explore the impact of the insulative properties of 5 vine shelter types on vegetative growth rate, bud cold hardiness, and potential for summer and winter injury in the Texas High Plains. The shelter types under consideration for this trial were selected based on the results of our original trial as these shelters had the most significant insulative capacity out of the original 12 evaluated.
While the original trial was conducted on empty vine shelters, the new trial is focused on shelters housing actual young vines, allowing for direct measurements of plant growth response to the unique growing conditions provided by each shelter type. Preliminary results from this new study indicate minor visible differences in the rate of phenological development between vines housed in different shelter types. For example, by assessing the rate of growth, at intervals of once a week after planting, using the Eichhorn-Lorenz model, vines housed in 30” corrugated plastic shelters achieved a more advanced stage of development than their 30” waxed cardboard counterparts on four out of the five dates of assessment.
Over the next few growing seasons, we will continue to carry out this study and will provide results and recommendations to grape growers across the United States who are concerned about the potential for vine shelters to contribute to vine injury during the establishment of new vineyards and whether certain vine shelter types should be removed during fall to ensure vines acclimate to dormancy and deacclimate as best as possible.
