Vineyard Alerts
Managing Freeze-Damaged Vineyards — Are You Farming for 2007 or 2008?
Posted May 21, 2007
Andy Allen, Eli Bergmeier, and R. Keith Striegler, Ph.D.
University of Missouri-Columbia, Institute for Continental Climate Viticulture and Enology
As shoots have emerged and continue to emerge from a variety of bud types, you must answer a serious question regarding the management of the vineyard. Are you farming for 2007 or 2008? That is, do you intend to try and harvest whatever crop is present or will you forego cropping the vines and concentrate on rebuilding vine structure and health? The answer to this question determines, to a large extent, how you will manage your vineyard over the course of this season. Regardless of whether you crop the vines or not, the vines will need greater care than normal this season to recover vineyard health and productivity.
Current Situation — We have recently completed a second round of assessing the vineyard situation around the state and region. At this point, recovery in most varieties looks promising and many vineyards will produce more crop than previously expected based on the amount of bud injury seen. Many blocks will, however, require extensive cordon replacement, but may otherwise be back in production next year. There are several factors that have influenced the amount of crop now being seen in certain areas of the state. Location is one. Vineyards further north that were not as far along in bud development had more primary buds survive the freeze than those further south, where almost all the buds were at bud burst or beyond (greater than growth stage EL 4). Variety is another factor. Varieties with late budburst, such as Norton and Vignoles, had more primaries survive the freeze than earlier developing varieties such as Chardonel and St. Vincent. Traminette has been a pleasant surprise in this category. In some vineyards, Traminette has primary shoot survival nearly as good as Norton and Vignoles in the same area. Another factor is pruning method. Where vines were pruned to longer fruiting canes rather than short fruiting spurs, we are seeing a greater number of surviving primary buds and shoots. As we've stated so often in our pruning workshops, longer bearing units (spurs and canes) can delay opening of the buds in the lower node positions. In this situation, it has resulted in more primary bud survival in many vineyards. Survival and fruitfulness of secondary and basal buds is also contributing to the number of clusters being seen in area vineyards now. This has been better than expected in some of the vineyards we have examined.
Crop Size and Variability — Soon you will need to determine the potential crop for each variety and whether or not it will be economical to produce. Will the size of the crop and the revenue it generates justify the production and harvest costs? The situation is complicated this year because of the mixture of bud and shoot types present and the inherent fruitfulness, or lack thereof, of each type. Crop load estimation and the associated economic concerns are discussed later in this advisory.
In most varieties there is a mixture of shoots arising from primary, secondary, tertiary, basal and latent buds. This warrants concern because clusters produced on these different types of shoots will likely ripen non-uniformly due to differences in shoot growth and development between shoot types. If fruit of different maturities are harvested together, the resulting wine quality may be reduced, and this is a concern to discuss with your fruit buyer. His or her tolerance for variability may depend on several factors. Among them may be the wine type for which the fruit is destined. Variability may be more tolerable in cultivars destined for blends than for varietal wines. Price point of the wine may also be a factor.
If variability is unacceptable, how will you minimize it? There are several means through which crop maturation variability can be reduced.
- Shoot thin in the early season to remove the outlier crop. In this season, that may mean removing the primary shoots and their crop and farming the fruit on secondary, tertiary and basal shoots.
- "Green harvest" at veráison to remove either the early or late maturing fruit depending on which is the lesser contributor to yield. If you select this or the preceding option, will the remaining crop justify the costs of production?
- Differential harvest by conducting multiple hand-harvests through the blocks to pick each crop at its peak maturity. If you select this option, will each of the separate crops be large enough to justify the expense of separate hand harvests?
These are questions that need to be addressed sooner rather than later so that appropriate decisions can be made and the necessary actions taken to promote fruit and wine quality.
Crop Protection — Whether you intend to try to produce a crop or not will have a significant impact on your spray program. If you decide to forego the crop from a particular variety this year, then there will be no need to protect the fruit of that variety from fruit rots and insect damage. In this situation, you will be able to save a few dollars from a reduced pesticide bill for the season. However, it is still very important to protect the foliage and shoots from diseases and insects. Healthy foliage will be needed to produce the carbohydrates necessary for vine function and growth. It would be a serious mistake to try to cut vineyard management costs by foregoing your disease management program entirely. A severe case of powdery or downy mildew could cause premature defoliation of the vines, or at the least severely reduce leaf function. Besides reducing the production and accumulation of carbohydrates needed to support the vines' growth and function both this year and next, the loss of photosynthetic capacity of the vines could also predispose the vines to further freeze injury this coming winter. Just as important, not protecting the vines could result in disease damage to the shoots. This disease injury can not only cause structural weakness in the shoot, making it more prone to breakage, but disease lesions on the new canes can overwinter and serve as a source of inoculum for new disease infections next year. Many vines will need to have spurs and cordons, and perhaps even trunks, replaced due to freeze injury. It will be critical to the success of these new vine structures that they be formed from healthy, sound wood. This includes any suckers that are being retained for possible trunk replacement. The sprayer coverage should be adjusted to be certain that retained suckers are protected.
Suckering, replacing trunks and cordons — While vine recovery appears promising in many vineyards, it is still wise to keep a couple of suckers at the base of the vine in case trunk injury expresses itself later in the season when the vines are under more stress. This is particularly true for cultivars that possess marginal hardiness for your location.
We have noticed phloem and cambium injury on some less cold-hardy varieties, but it is difficult to say if it will be severe enough to cause collapse of the vines when they experience greater stress. Retaining some suckers as potential replacement trunks would be a wise insurance policy against vine collapse. Remember that trunk failure could appear after the winter of 2007-2008 and that crown gall development in injured trunks is a very real threat. Having replacement structures available is the key to thwarting losses of these types. Also, if you have been considering changing from single- to double-trunk vine training, the retention of suckers this season presents a prime opportunity to develop a second trunk. Remember that when using double trunks, they should all arise from below or as near to the ground as possible on own-rooted vines. Grafted vines should have all trunks arising from the top of the graft union. Because trunk injury and crown gall commonly occur near the base of the trunk, having the second trunk arise from greater than 4 to 6 inches above ground on an existing trunk offers little protection against loss.
A more likely scenario, however, is cordon replacement. We have seen several vineyard blocks where growth along the cordon, including shoots from latent and basal buds, has been poor or lacking altogether. In these cases, replacing the cordon will be necessary. Attempting to retain the cordon in the hope that shoots will eventually emerge and produce a crop may result in keeping cordons in which fruiting positions are lost for as long as the cordon is retained. If shoots do eventually emerge later this season, they will be so far behind the rest of the shoots that any crop they may carry will not be useful. It will be much better to retain suckers near the head of the vine or shoots at the base of the cordons to train as replacement cordons. Buds that develop along these suckers or shoots will produce fruitful shoots next year, or if trained well during the season, will produce laterals that can be used as fruiting spurs or canes. Replacing marginal cordons offers a secondary benefit in the form of reducing disease inoculum.
Canopy Management — One set of practices that certainly can not be overlooked this season is proper canopy management. Maintaining a well-structured canopy with properly spaced and well-illuminated shoots will be vitally important to re-establishing spur positions and cropping potential for next year. Keep in mind that with reduced or no crop this season, vines with minimal wood damage will be much more vigorous than normal. This is expressing itself already through the development of numerous suckers and basal and latent buds on vines where the majority, if not all, of the primary shoots were killed by the freeze. Unmanaged canopies result in dense, tangled masses of shoots in which most shoots develop under conditions of heavy shade. Remember that heavily shaded canopies are the enemy of quality wine production. Shoots that develop under such conditions do not ripen their fruit very well. They also do not form periderm and acclimate to cold temperatures and do not survive the winter as well as shoots that have adequate sun exposure during the growing season. Shoots that are needed to save or reclaim a fruiting position may be lost to freeze injury next winter if they are not well-exposed during this growing season. Fruitfulness of the buds that develop on heavily shaded shoots is also reduced compared to well-illuminated shoots. Whether you are harvesting a small crop this year or do not have a crop at all, trying to cut vineyard management costs by neglecting canopy management can have negative repercussions this year and next.
- Shoot thinning — Most shoots developing on vines are non-count shoots arising from basal or latent buds. In some count nodes where primary buds were killed, secondary and tertiary shoots have pushed from the same position. In many cases, particularly on mature, vigorous vines, there may be several buds developing within very close proximity to each other or in areas where spur/cane positions had previously been lost. Base thinning decisions on how crowded the resulting canopy will become if shoot thinning is not performed and whether or not shoots are needed to replace lost spur/cane positions. Consider that you can improve uniformity of crop maturity can be improved by removing shoots whose clusters differ significantly from the majority. Growers must resist the urge to retain clusters by maintaining excessively high shoot densities. The temptation will be great in vineyards where expected returns are already marginal.
- Shoot positioning — Regardless of crop potential, you should position shoots as in a normal year according the trellis/training system used. This allows the individual shoots to occupy their allotted space and guarantees that they will harden in the position desired for spurs or fruiting canes in that system. Shoot thinning and shoot positioning result in a more open canopy with better illumination and air movement in the fruiting and renewal zones and better spray penetration into the canopy.
- Leaf removal — If you are carrying a crop this season, leaf removal may be necessary to promote fruit quality and to reduce disease pressure. This is always a good practice with rot-prone varieties like Vignoles, but may be important for many varieties this year. As mentioned earlier, with reduced crop loads, the vines will be more vigorous and thus the canopies will be denser, leading to increased disease pressure. Dense canopies will also generally lead to reductions in fruit quality. Leaf removal around the fruiting zone will open a window to allow more light and air into the zone, reducing humidity and disease pressure within the canopy and potentially improving overall fruit quality.
- Cluster thinning — It will be tempting to keep every cluster on the vine that sets fruit this season. However, fruit-bearing shoots on large-clustered varieties should still be cluster thinned according to shoot length at fruit set. Here, the 2-1-None rule applies. That is, if the shoot is 20 inches in length or greater at fruit set, retain 2 clusters (on large-cluster varieties, more on varieties with smaller clusters). If the shoot is between 8 and 20 inches in length, retain 1 cluster. And if the shoot is 8 inches or less in length at fruit set, remove all clusters. Carrying too much crop on weak shoots prevents the shoots from properly developing in length and leaf area. The fruit from such shoots will not be as ripe as from more vigorous shoots and if the shoot is needed to become a spur or fruiting cane, it may be too poor to serve as one. Also, remove any clusters that are obviously lagging behind in maturity to promote more uniform maturity of the crop. In what is shaping up to be a very challenging season for our wine industry, it is still important to do whatever is necessary to promote high-quality fruit and wine, and not just try to produce as much fruit as possible.
Fertilization and Irrigation — Given the reduced crop load and potential for excess vigor in high-vigor vineyard situations, we still consider it wise to reduce or withhold nitrogen fertilization where increases in vine size are not desired. Consider applying nitrogen as needed to maintain vigor and vine health through split applications rather than applying all nitrogen fertilizer in a single application early in the season. If vine vigor approaches excessive levels after the first application, withhold subsequent applications. Likewise, reduce irrigation or allow mild water stress to reduce shoot vigor and prevent vine size increases where necessary.
Estimating Vineyard Yield and Economic Return — While yield estimates typically are generated after fruit set (EL 27), a pre-bloom assessment this year will enable you to make an early decision regarding the economic feasibility of the crop. This estimate should be generated with the goal of answering a question of great financial significance: "If the clusters presently visible develop normally, will the potential yield generate sufficient revenue to at least recover the costs of producing the crop?" A follow-up assessment after fruit set will provide a more accurate yield projection.
Consider three primary factors when determining whether farming a particular cultivar's 2007 crop is a wise economic decision: 1) potential yield, 2) price earned per ton, and 3) the variable costs of production. Factors that determine potential yield include the following:
- Number of bearing vines per unit land area. Unfortunately, many vineyards have vine counts below their true capacity, and this will affect potential yield. Under the current conditions, where growers' margins may be slim at best, accuracy is essential and the number of bearing vines per unit area should be counted manually. This determination can be made on a block or per-acre basis.
- The average number of cluster inflorescences per vine. This is assessed by counting the average number of inflorescences per vine on a representative sample of vines. In blocks with uniform vine size that were pruned and have recovered from the April freeze similarly, a sample population of approximately 20 vines per acre should generate fairly accurate results. If the vines are non-uniform, however, the sample population should be increased to perhaps 30 to 40 vines, or the block divided into homogenous sample areas to improve accuracy. Representative vines should be chosen through a regular selection process that includes vines uniformly distributed throughout the block (every twentieth vine, for example). Due to strong basal and latent shoot emergence, some canopies presently feature excessively high shoot densities. Shoot thinning will need to be performed in these canopies to maintain fruit quality, and this will reduce crop load somewhat. Also remember that shoot thinning may be a critical component of your strategy to reduce variability in crop maturation. Count inflorescences on the shoots you will retain after thinning, and disregard those present on shoots you intend to remove through the thinning process.
- Average cluster weight at harvest. While it's true that cluster weights for a given variety will vary annually, they remain an efficient method of estimating potential yield. Long-term records collected from individual vineyard blocks over time improve accuracy of this estimation strategy, and thus, provide the rationale for measuring cluster weights (by cultivar) at harvest every year.
Over the past few weeks, we have encountered many growers who don't have long-term average cluster weights for their cultivars or sites. To abate this shortcoming, an extensive search was conducted to locate reliable cluster weight data. The product of this search references 29 sources citing data collected in 13 U.S. states or Canadian provinces, and the majority report data collected over multiple growing seasons. The results can be found in Table 1 at the end of this document.
It's imperative that growers understand the figures in Table 1 are relevant only for clusters borne on primary shoots. Many growers in the region presently have significantly fewer fruiting primary shoots than normal, with a majority of their fruitful shoots now emerging from secondary, tertiary or basal buds. Unfortunately, the clusters borne on these shoots are often smaller than normal. Accordingly, we strongly advise growers to survey the existing clusters, make a visual determination of their size relative to normal, and then make appropriate adjustments to the anticipated cluster weight. If the crop will be retained on shoots developing from a variety of origins, the accuracy of the grower's estimate will vary according to his/her diligence in estimating the portion of the crop developing from each and its' associated cluster size.
Once these measurements have been made, the following potential yield calculation can be performed:
| Yield (tons) = | (# of Bearing Vines X Average # Clusters per Vine X Cluster Weight) |
| 2000 |
If prior measurements were made on a block basis, a conversion to a per-acre basis is often useful and can be made by multiplying the yield estimate by the following product:
Your Bearing Vine Count / Total Possible Number of Vines per Acre
The latter figure can be derived by dividing the number of square feet in an acre, (43,560), by the product of your vine X row spacing. For example, an 8' X 10' vine X row spacing (80 ft.2) will accommodate 544 vines per acre (43,560 ft.2 / 80 ft.2 = 544).
Once you generate the potential yield estimate, you need to determine the revenue produced per ton of fruit. As the price paid per ton of fruit often varies significantly by cultivar and processor, it's imperative that growers discuss this individually with their prospective buyers. With potential yield per unit land area and pricing information in hand, growers can then make a seasonal revenue projection by multiplying tons to be produced per acre by the price earned per ton.
The third factor that must then be considered is the variable cost of production. In normal production seasons, profitability is determined by the crop's ability to produce revenues that exceed the sum of both variable and fixed costs of production. Unfortunately, given the reduced crop, this appears unlikely for many growers in 2007. In seasons such as this, the deciding factor should be whether the potential crop can offset the variable costs of production. The reasoning behind this is that growers will incur fixed costs of production whether they opt to farm the 2007 crop or not, although some variable costs of production can be reduced or eliminated if the decision is made to forego the season's harvest. However, if the potential crop will generate revenues at least equivalent to the variable costs of production, the grower may use any revenues exceeding those expenses to at least partially offset her or his fixed costs, and therefore achieve a somewhat improved financial position.
An important consideration here is the vineyard's relationship to a processor. If the two entities are engaged in a typical "sell/buy" arrangement, the grower may be forced to make a simple, but unpleasant decision: if the potential revenue is not adequate to cover the variable costs of production, the block or cultivar should be removed from production for the 2007 season and placed on a reduced maintenance schedule. However, if the vineyard is owned or managed by a processor, the latter may opt to allocate some of the profit earned from the sale of the finished product toward recovering the expense of producing the crop. Each grower and/or operation should carefully evaluate their position and options to determine the course of action that yields the greatest benefit. Therefore, the grower's next question becomes "what are my variable costs of production?" For those relatively new to the industry, this may be a difficult question to answer, and unfortunately, it's simply not possible to determine this without carefully examining the operation's financial statements and vineyard management plan. For those who haven't yet made these calculations, we suggest referring to one of the many publications that provide detailed estimates. One such publication is Production Budgets for Arkansas Wine and Juice Grapes, Arkansas Agricultural Experiment Station Research Report 976 (PDF). Growers must realize that the figures reported within this publication, and all others forecasting expenses or profits, are only estimates. While carefully and skillfully prepared, they may not accurately reflect the expenses individual growers will incur in producing their crops due to differences in available equipment, operational efficiency, the number of pesticide applications required, fuel cost increases, etc. Growers are urged to carefully examine the assumptions made in the production of any budget they wish to reference and to re-create the budget using their own estimates if at all possible.
The 2007 growing season has presented grape producers with a challenging set of circumstances. Under these conditions, it's imperative that growers manage each vine as a unique individual. We urge growers in the region to carefully examine the economic potential of their crops, make prudent viticultural and financial decisions, and to manage their vines such that the return to full production is an expedient one.
References: Coombe, B.G. 1995. Adoption of a system for identifying grapevine growth stages. Australian Journal of Grape and Wine Research 1(2):104-110.
© 2007 by the Institute for Continental Climate Viticulture and Enology. All rights reserved. No part of this document may be copied or reproduced in any form or by any means, graphic, electronic, mechanical, photocopy, recording, or otherwise, without written permission of the Institute.
Table 1. Average Primary Cluster Weights Reported by Multiple Sources for Cultivars Grown in the Midwest.
| Cluster Weight (lb./cluster) | ||
| Cultivar | Mean | Range |
| Aurore | 0.21 | 0.13-0.28 |
| Baco noir | 0.15 | 0.12-0.18 |
| Catawba | 0.27 | 0.16-0.34 |
| Cayuga White | 0.46 | 0.33-0.60 |
| Chambourcin | 0.39 | 0.17-0.54 |
| Chancellor | 0.32 | 0.15-0.50 |
| Chardonel | 0.38 | 0.29-0.44 |
| Chelois | 0.23 | 0.11-0.34 |
| Concord | 0.26 | 0.22-0.30 |
| Corot Noir | 0.40 | 0.33-0.46 |
| Couderc Noir | 0.40 | * |
| DeChaunac | 0.27 | 0.15-0.35 |
| Delaware | 0.19 | 0.16-0.22 |
| Frontenac | 0.29 | 0.27-0.30 |
| GR-7 | 0.23 | 0.15-0.31 |
| LaCrescent | 0.23 | 0.22-0.24 |
| LaCrosse | 0.26 | 0.25-0.27 |
| Landot Noir | 0.13 | * |
| Leon Millot | 0.18 | 0.16-0.18 |
| Louise Swenson | 0.23 | * |
| Marechal Foch | 0.18 | 0.10-0.21 |
| Melody | 0.31 | 0.25-0.44 |
| Niagara | 0.38 | 0.25-0.49 |
| Noiret | 0.33 | 0.26-0.39 |
| Norton | 0.18 | 0.12-0.22 |
| Prairie Star | 0.39 | * |
| Rougeon | 0.31 | * |
| Seyval blanc | 0.47 | 0.15-0.70 |
| St. Croix | 0.24 | * |
| St. Vincent | 0.43 | * |
| Steuben | 0.32 | * |
| Traminette | 0.26 | 0.17-0.33 |
| Valvin Muscat | 0.23 | 0.17-0.36 |
| Vidal blanc | 0.44 | 0.22-0.62 |
| Vignoles | 0.19 | 0.11-0.26 |
| Villard blanc | 0.31 | 0.20-0.42 |
| Villard noir | 0.51 | * |
| Vivant | 0.31 | * |
