Grow tubes have shown some distinct advantages for establishment. Grow tubes get the vine off to a quick start by promoting upright rapid growth without the added labor of tying to stakes. During dry periods without irrigation they can provide moisture at the base from condensation that aids in establishment. With new planting are under drought conditions, grow tubes may add enough moisture to the ground to be the difference between significant survival and almost complete death of newly planted vines. The tubes also protect young vines from pests such as rabbits and deer if other means of protection are not in place. From the new grower’s standpoint, maybe their best attribute is to reduce the danger to the vine when applying post emergence or contact herbicides.
The utilization of grows tubes is a fairly recent technique, gaining popularity over the past 10 years. Consequently their utilization has become fairly widespread and accepted before adequate short and long term research has been conducted, or even before experience has been obtained under actual vineyard conditions in the region. The object of this article is to present some of the potential “downside” issues. My goal is not to stop growers from using them, but to raise some points to consider along with all of the other options when making decisions about establishing new vines.
Speed of Growth
There have been many anecdotal reports of the rapid rate of growth promoted by grow tubes and based on how quickly the plant emerge from the tubes. The tube acts a “mini-greenhouse” and creates a warmer microclimate during the spring that increases the growth rate. The vines do grow out of the tube quickly, however is this “extra” growth persistent through the season and is the wood that is produced under these conditions desirable for long term survival of the vine?
Research conducted by Zabadal and Dittmer (1998) at the Southwest Michigan Research and Extension Center near Benton Harbor, Michigan can give us some answers. Newly planted vines were thinned to three shoots per vines when shoots averaged 6" in length and grow tubes were installed on half of the vines. Measurements of plant height 67 days after planting indicated that vines with grow tubes were significantly taller than those without. However, the number of leaves and leaf area of vines grown without grow tubes were significantly greater than those with tubes. Similar measurements taken 110 days after planting indicated that vines with grow tubes were no taller than those with all shoots retained and no grow tubes, and vines without grow tubes still had greater numbers of leaves and more leaf area than those with grow tubes. This indicates that there is no season long advantage of the grow tubes.
If you have ever heard me discuss training systems, you know that I recommend at least two trunks for vinifera vines grown in our region. Having multiple trunks increases the odds for some part of the vine to survive and/ or quickly recover from winter trunk damage. The additional permanent wood also has the ability to buffer fruit quality from season to season and increases final brix (Howell). Grow tubes tend to promote the dominance of one shoot or trunk during the first growing season. Therefore one would have to concentrate on growing and training a second trunk during the second leaf, adding additional training time and labor and delaying the establishment of the permanent scaffold of the vine.
Quality of Wood
The next question is regarding the quality of the wood produced in the tubes. The trunk of the vine is critical for long term survival, providing structural support and nutrient holding capacity that is critical for winter hardiness. The Michigan study discovered that measurements of these vines in the winter after their first year of growth indicated no differences in diameter of canes produced with and without tubes. More importantly, the total cane weight per vine was greater for vines grown without grow tubes and the internode lengths on those vines were significantly less than for vines grown with grow tubes. This may indicate that the wood being produced in the tubes is of substandard quality and may have significant impact on long-term survival and fruit quality potential. Alice Wise, the Cornell University Viticulture Specialist on Long Island, has also noted a distinct twisting or spiral to the trunks produced in tubes and questions the long-term wood quality (Wise).
Cold Hardiness
The other critical attribute related to trunk quality is trunk cold hardiness. This the most important limiting factor for economically growing grapes in the Mid-Atlantic. The same greenhouse effect that promotes growth in the spring also promotes continued growth in the fall and may delay the hardening of the wood, possibly reducing its cold tolerance. This has been noted in many places in the eastern US (Wise, Peterson, Zabadal and Dittmer). Again Zabadal and Dittmer’s study raise questions on the utilization of grow tubes. They tested the primary buds on these canes at the 3rd, 4th and 5th nodes from the base of the canes for hardiness in February 1999. The results indicated that buds on vines grown with grow tubes were significantly less hardy than those grown without grow tubes. The buds on the vines without grow tubes would be able to withstand close to 3 degrees lower temperatures (-6.2 oF) then grow tube vines (-3.5 oF) before receiving significant damage. This can play a significant role in the survival of our new plantings.
Pest Management
A significant plus of utilizing grow tubes is the protection they afford the young vines from vertebrate pests such as rabbits and deer. However the same “greenhouse” effect that promotes rapid growth of the vines also promotes rapid growth of fungal pathogens. Anyone who has used the tubes will attest to the significant powdery mildew infections present within the tubes. They also provide warmth and protection for Japanese Beetles and therefore high populations of insects can accumulate quickly within the tubes.
Due to the size restriction of the tubes it is very difficult to spray pesticides down into the tube and get thorough coverage. And spraying pesticides into the very warm and humid 3 microclimate created by the tube is a very questionable practice and may be phytotoxic. The high infection rate inside the tubes may provide long-term inoculum for future infections and contribute to the reduced cold hardiness of the trunk.
Economics
It is an expensive proposition to establish a vineyard, so every input needs to be weighed for cost effectiveness. The cost of the tubes range from about $.60 to around $1 each and the better ones are typically rated to have a three-year life, or about $.33 per year of use. The Michigan study estimated the annual cost of the tube and the time to install and removal (assemble, transport, install, remove, transport, and place it in storage) would be about $.65 (labor @ $6.00/hr) without any associated equipment and any other materials such as those used to fasten the tube. At $.65 per vine, a planting of 700 vines to the acre amounts to $455. The labor and materials cost for the herbicide program used in the trial was estimated at no more than $150 per acre, and its use without grow tubes produced larger and hardier vines than those with tubes.
Summary
Considerably more evaluation of grow tubes in controlled research as well as growers fields will be required before the full benefit/drawback impact of this technology can be understood ongrapevine establishment, performance, and longevity. Despite the impressive early shoot growth obtained with grow tubes, the impact of grow tubes on vine growth may not be totally positive and the factors presented here suggest caution.
I strongly suggest installation of a drip irrigation system in new vineyards and would rather see money put toward irrigation than grow tubes. However, planting new vines under drought conditions without either irrigation or grow tubes could result in major plant losses. So the final question of "To tube or not to tube?" will require considerably more evaluation. The decision depends on the specific situation and as with any other decision in a vineyard, a grower should carefully evaluate his circumstances and consider all options. But remember, “the wine is made in the vineyard,” and the quickest way to a great vineyard is the slow way!”
References
Howell, S. 2001. Personal Communication.
Wise, A. 2001. Personal Communication.
Zabadal, T.J. and T.W. Dittmer. 2000. GrowTubes: Are They Cost Efficient? 2000 Research Executive Summaries of the Southwest Michigan Research and Agricultural Extension Center
Peterson, David V. 1997. Using Grow Tubes for New Vine Establishment. Proceedings of the 5th annual Lake Erie Regional Grape Program.