The following is from Mark Chien at Penn State University. He publishes a Wine Grape Information newsletter and I saw this article in there and thought it relevant to the Mississippi situation as well.
“Hurricanes and Vineyards: The trellis. It’s what holds the whole thing up. I know of bad trellis: at Temperance Hill Vineyard the people who developed the original part of the vineyard used inexpensive wires and stakes from India and I spent a decade cursing them for it. I recently met with Michael Schmidt, the owner of Spec Trellising, whom many of you know. Michael supplies the materials and hardware that grape growers need to develop their vineyards. I would say that Michael has a better overall view of the wine industry in the East than anyone I know. He truly sees the good, bad and ugly in our industry. In fact, he should be made an honorable extension agent because he probably dispenses more advice than I do about developing a vineyard. While we sat in his office the phone rang numerous times with novice vineyard owners asking questions about every aspect of vineyard development. I have seen his handiwork in the field and for those growers who get it, the results are very impressive. We got to talking about damage in 2011 to vineyards due to Hurricane Irene and how trellis modifications might mitigate the effects of high winds. Of course, no grape stake to our knowledge was ever tested, much less designed, to withstand hurricane-force winds. The failure most commonly seen last year was in notched metal stakes that collapsed at the lowest notch position. It is unlucky for us that we are the only significant wine region in the world that is smack in the path of hurricanes and that these behemoth weather systems strike just as the fruit is getting ripe and the trellis is carrying a full canopy and crop load. There are many factors that determine trellis vulnerability and most are obvious, including quality of grape stake and the relative strength of the entire trellis system. One might think that exposure of the vineyard might be important but I have seen vineyards in relatively closed conditions (hills, trees, etc) suffer damage. In my experience I have seen a few common factors among damaged vineyards. Hurricanes rotate counterclockwise and therefore winds usually strike from the north or west. In the case of Irene, the vineyards with blow-down that I saw all had east-west rows that took the brunt of the north wind. I am not suggesting that row direction should be determined by hurricane threat but it certainly can be a factor. The gauge, or thickness of the steel is very important and it makes sense that the 12-gauge stake will offer the most strength. I know the shape of the stake also affects its tensile strength but cannot say exactly which design would offer the most wind resilience. I know there are whimpy stakes and stout stakes and, in all cases, the latter is preferred – ask experienced growers for their suggestions. Notch design and position will affect the durability of the stake. Michael has asked Mannwerks, his stake manufacturer, to reduce the number of notches below the fruit wire position. In addition, he also asked them to redesign the notch so that a very small cutout in the old-style notch not be removed, which will make the stake stronger. I have been asked if a longer stake (more stake in the ground) would endure winds better but the problem is not the stake bending over but breaking at a weak point, so I don’t believe more stake in the ground will necessarily help, unless the soils are coarse/loose (such as sandy soils). Canopy height and width (density) are also a factor with taller and thicker canopies being more prone to blow-down simply because they catch more wind, but in my experience, there is not always a direct correlation – I have seen quite thin VSP knocked over. High winds hitting a vineyard is a curious natural phenomenon. A few years ago a large vineyard in southeast Pennsylvania with large east-west oriented Cabernet Sauvignon vines got hit and in addition to damaged outside rows there were intermittent rows in the interior that blew down. I have heard that the wind will actually “bounce” along and over the vineyard, knocking over random rows. This vineyard responded by placing wood end posts (6-8”) between every 4-5 panels. In our discussion, Michael and I thought that using a rib-back end stake every 5-6 panels would help to strengthen the exterior rows. There probably is nothing in wine growing more frustrating that having to raise fully loaded vines back to the upright position only weeks, or even days before, or during harvest. Hurricane proofing the vineyard is yet another added development expense but if you have a high value crop, like a wind machine for frost and freeze, it really makes sense to consider all of the threats, especially late season, and what is at stake in terms of crop and-or wine value, and whether mitigation is worthwhile. I welcome comments and ideas from the field about your experience and solutions to trellis knock-down. FYI – in our discussions, and based on cases of metal stake failure, both Michael and I recommend that galvanized stakes are used in vineyard development to increase longevity. “