Viticulture Notes

Vineyard and Winery Information Series:
Vol. 16 No. 1, January-February 2001

Dr. Tony K. Wolf, Viticulture Extension Specialist

Table of Contents

III.Coming Meetings

I. Current situation:

January-February issue coming out almost in March? Well, things have been busy these last few weeks, and days have progressed to weeks. The information herein is relevant to the time of year, if not exactly coming at the January/February midpoint. The March-April Viticulture Notes will arrive in March and will have expanded coverage of pest management topics for the coming season.

2001 Pest Management Guides: Virginia Cooperative Extension's 2001 Pest Management Guides are available for purchase. Send check (payable "Treasurer, Virginia Tech") for $16.00 to Virginia Cooperative Extension Distribution Center, 112 Landsdowne St., Blacksburg VA 24061. Ask for a copy of Publication # 456-017 (Horticultural and Forest Crops). What does your $16 buy you? The first 40 pages of the pub deal with regulations, safe use of pesticides, pesticide toxicity, and basics of calibration. The balance of the pub is commodity specific, including the section on grapes. In that, you'll be provided with a "menu" of fungicides and insecticides which are registered for use on grape, including the target organisms, timing, and correct rates of application. Similar information is provided for chemical weed control. I encourage any serious grape producer to obtain and refer to this publication in designing a pest management strategy for the coming year.

Question from the field: I've been told that Surflan (pre-emergent herbicide) will be in short supply this year due to a fire at a production plant. What are my alternatives?

Answer (via Dr. Jeff Derr, Virginia Tech's fruit weed specialist): Surflan (oryzalin) is a pre-emergent herbicide registered for use in both young (including first year) and bearing vineyards. Prowl would be a good alternative to Surflan in nonbearing vineyards. Chemically, Prowl is very similar to Surflan and will provide similar control. Prowl, like Surflan, works best on annual grass and small-seeded broadleaf weeds. The manufacturer has never registered Prowl for use on bearing vineyards. Prowl should be applied as a directed spray to dormant grape vines. Prowl can stunt growth and cause abnormal leaves to form if sprayed over the top of plants after budbreak. Another substitute for Surflan would be Solicam, but only if the vines have been in the ground for 2 seasons. Watch the rate of application on sandy soils. Vines growing in heavier soils can tolerate higher rates of Solicam. The injury symptom from Solicam is bleaching of foliage, which is more likely to occur in sandy soils. Plants will outgrow any bleaching that occurs. Solicam works well in combination with Princep. Solicam controls annual grasses and certain annual broadleaf weeds, and will suppress nutsedge. Combining it with Princep will provide better broadleaf control.

Question from the field: In pruning my one-year-old Cabernet franc in the past few weeks (early February), I noticed that canes which I had hoped to retain as cordons had died back to below the cordon wire. The vines will be going into their second year in the vineyard. They exhibited very vigorous growth during the 2000 season. I had trained two shoots out on the cordon wire last summer and had planned to retain 18 to 24 inches of each this winter to begin to develop bi-lateral cordons. Whatıs really puzzling is that the canes looked well-matured in December when I got started on rough pruning. Did I do something wrong last year?

Answer: The cause of the die-back might relate to the vigorous growth that occurred last year, but I would not necessarily say that high vigor is undesirable. I saw a similar situation in a two-year-old Cabernet Sauvignon vineyard last spring. There, the affected vines had also grown well in the first two years, the grower had retained up to 24 inches of canes on the wire to serve as cordons, and that wood looked well ripened when pruned (dark, brown bark [periderm], green vascular tissues within). Following a relatively benign winter, those vines produced shoots only from the trunks, or vertical sections of the canes. In some cases, the die-back extended down the trunks as well. Clearly the wood was not as "ripe" as the visual appearance led the grower to believe -- as also appears to be the case with you. In the Cabernet Sauvignon vineyard, the affected vines were confined a dip or topographically depressed area of the vineyard. The vines outside of that depression were in better shape; that is, the extent of die-back was much less. Based on what I saw, I felt that the vines were showing signs of cold injury. I recommended that as the vines entered the third growing season, the grower retain shoots wherever possible, go easy on irrigation, even allow some weed competition, all in an effort to slow individual shoot growth down a bit. I spoke with that same grower recently and he told me that he had gotten excellent growth during the 2000 season, that wood appeared well ripened, and that they were moving to a "U-shaped", divided-canopy training system. Unfortunately, they may still have problems with cold injury at some future date, as Cabernet Sauvignon and "frost pockets" or even minor depressions in vineyard topography do not well mix. Letıs come back to the immediate question. The possible commonality of the situations described might be the vigorous growth of year-1 vines. One-year-old vines are not particularly in synchrony with the environment. That is especially true of the Cabernets, which have persistent vegetative growth even as the days of fall shorten. Even in an excellent site, with freedom of foliar pathogens, Cabernet Sauvignon more often loses green leaves to frost than to normal senescence. If you couple that extended vegetative growth with sharp transitions in temperature, the vines may not have the opportunity to mature tissues to optimal cold resistance. Cold acclimation of canes involves many processes, some of which include carbohydrate deposition, changes in lipids and proteins, and a dehydration of the tissue. These processes occur in an acropetal pattern (e.g., from the base towards the tip of a cane). Thus, the more basal nodes of a cane are generally more cold hardy than are the more distal buds ­ even where both groups show uniformly brown periderm. All growers, at some point, will have the occasion to see canes that have died-back to some point. It's normal, and our dormant pruning accommodates that die-back by retaining only well "ripened" or matured tissues such as the basal buds of a cane (as in spur-pruning) or by selecting canes with a predominance of well matured nodes (as in cane-pruning). I suspect that the tissues that died-back on your vines did not have ample carbohydrate storage or other biochemical features that we associate with optimal hardiness, despite their sound appearance last December. Recall too that we rapidly transitioned from relatively warm weather to unseasonably cold weather around Thanksgiving last fall. With December being very cold, the tissues might not have had the opportunity to brown and dry out, so your pruning at that point would have given a misleading impression of viability. The pattern of die-back that you're reporting is normal; the extent is greater than desired. Can it be reduced in the future? You reported good growth during 2000, and that's an indication of good vineyard management (ample moisture, minimal weed competition, disease-free status). Could it be too good? Possibly, if you had only trained two shoots last year. I recommend leaving a few shoots in year-one, and not pinching laterals, and this recommendation might be amplified for varieties such as the Cabernets. Allowing more shoots typically 'dissipates' some of the vigor tendency expressed by a single or double shoot system. The multiplex can be "thinned" down to two moderate-sized canes during the winter subsequent to the vine's first growing season. I won't guarantee that this will avoid the problem that you're seeing, but it should help. In terms of what to do now, I would recommend a course of action similar to the approach recommended to the Cabernet Sauvignon grower last year. Allow all possible shoots to develop this spring and position those shoots on the trellis wires in a fashion that avoids mutual shading ­ in other words, spread the foliage out so it's kept clean and exposed. DO NOT try to restrict growth to a couple of shoots that you hope to retain as canes next year. To do so will result in shovel handle-sized canes that would be of inferior quality for cordons. DO NOT apply nitrogen. Allow some weed competition by mid-summer to slow shoot growth. Go easy on irrigation water, withholding completely as long as shoots are elongating. And, where you can, keep up to several pounds of fruit on the vine. Even with the die-back, these vines, like most two-year-olds, are going to be vigor monsters this coming year; but the approach outlined here should give you some quality wood to work with next fall.

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II. Climbing cutworm alert:

This is a perennial warning that I offer each year as we approach bud-break. Climbing cutworms cause damage in vineyards every spring, although the incidence varies from vineyard to vineyard and may be influenced by the intensity of winter cold. Climbing cutworms are the larval stage of several moth species. The larvae feed on swollen grapevine buds and can cause significant destruction of buds and recently emerged shoots. Figure 1 is cutworm damage to recently emerged Cabernet franc shoots. Note the misshapen leaves and absence of a shoot axis on the lower bud. Injured buds appear hollowed-out, which is the same appearance of buds damaged by grape flea beetles. Cutworm larvae feed at night and seek shelter in soil and debris during the day. Thus, if you observe damaged buds, and cannot locate the pest, chances are that climbing cutworms are at work. Cutworm larvae are about an inch long. They are smooth, brown or gray, and may have stripes running the length of their bodies or diagonally. Figure 2 shows a cutworm larva coiled at the tip of the knife blade. A quick search around the base of an affected vine can usually reveal the pest. Vineyards that are most at risk often have mulch or weed debris around the base of vines, which offers a refuge for the larvae during the day. Feeding begins in the spring when buds begin to enlarge. The extent of damage depends on the cutworm population but also on the duration of the bud-break stage. During cool weather, when the period from bud-swell to bud-break is delayed, damage can be extensive because the larvae have an extended period during which they feed. Conversely, during hot weather, shoots emerge quickly and damage is minimal. Vineyards must be monitored carefully for cutworm feeding in the period around bud-break, and treated with an insecticide if feeding affects more than about 2% of the buds. Note: the 2% level of damage should be adjusted for your specific needs. One of the most damaging aspects of cutworms occurs when they feed on buds of canes that have been laid down on the wire to form cordons. Such canes that are deprived of uniform shoot emergence may need to be retrained the following year in order to provide uniform spur placement. On the other hand, older vineyards, that normally crop well, may tolerate 5% or more bud injury without adverse impact on yield or subsequent season spur development. Regardless, you need to walk the vineyard routinely after buds begin to swell to monitor for cutworm activity. Insecticides such as Sevin and Dipel (Bacillus thuringiensis [B.t.]), are registered and are marginally effective against cutworms. Guthion is more effective, but has a 21-day restricted reentry period. Cutworm control can be improved by spraying in the late afternoon or early evening to ensure that fresh residues are present when feeding commences. Read the insecticide label to determine the correct rate of product application and follow restricted reentry period restrictions.

Figure 1 Figure 2

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III. Coming meetings:

20-23 March 2001: Wineries Unlimited. Lancaster Host Resort Hotel, Lancaster, PA. 25th annual meeting and trade show. See the program at http://www.vwm-online.com Or, call 800 535-5670.

4-6 April 2001: New York Wine Industry Workshop. Geneva, NY. Topics include: wine laboratory management and analysis techniques, Brettanomyces growth in wines, micro-oxygenation for tannin and aroma development in red wines, special Cabernet Franc session. For information, contact Nancy Long at 315 787-2288 or email npl1@cornell.edu

29 June ­1 July 2001: American Society of Enology and Viticulture Annual meeting. San Diego, CA. For information call 530 753-3142 or see www.asev.org

10-13 July 2001: American Society of Enology and Viticulture - Eastern Section Annual Meeting. Niagara-on-the-Lake, Ontario, Canada. Includes a tour of vineyards and wineries on the Niagara Peninsula, space-aged grape growing symposium and technical meeting. Contact Ellen Harkness for information. 765 494-6704 or harkness@foodsci.purdue.edu.

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"Viticulture Notes" is a bi-monthly newsletter issued by Dr. Tony K. Wolf, Viticulture Extension Specialist with Virginia Tech's Alson H. Smith, Agricultural Research and Extension Center in Winchester, Virginia. If you would like to receive "Viticulture Notes" as well as Dr. Bruce Zoecklein's "Vinter's Corner" by mail, contact Dr. Wolf at:

Dr. Tony K. Wolf
AHS Agricultural Research and Extension Center
595 Laurel Grove Road
Winchester, VA 22602

or e-mail: vitis@vt.edu

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