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Grape Chores – Winter 2020

UGA Extension Viticulture Blog

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Vines are generally at peak dormancy this time of year. The recent warm weather in late December/early January makes me question if this is currently true. Cold weather patterns are expected the third week of January. “Roller coaster” patterns of cold-warm-cold can cause the vines to prematurely de-acclimate during late winter and early spring, which increases the chance of cold injury to vine tissues. The following grape chores will last through January/February, when the next installment will be released through the Southern Region Small Fruit Consortium website (www.smallfruits.org).

  1. Put final vine orders into nurseries. Chances are you will not get the exact cultivar/rootstock/quantity combination you desire, but you may still find some of what you are looking for. Don’t wait any longer to order vines; in fact, now is a good time to put your vine order into nurseries for your anticipated plantings in spring 2021.
  1. Evaluate trellis integrity and repair. Check for broken posts and trellis wires and repair or replace them before bud break. The weight of the forthcoming season’s crop will can result in trellis failure if it is in poor integrity.
  1. Reflect on the previous season and talk to your regional colleagues – both industry members and extension personnel. What went right? What went wrong? Be prepared for next season by developing a plan to fix the “wrongs” and re-implementing the management strategies that worked well.  It helps to talk to neighbors and ask them their take on their season – they may offer advice and answer questions that will put you in a better position for success in the forthcoming vintage.
  1. Attend meetings, conferences, and workshops. The “big” statewide viticulture and enology conferences throughout the southeastern US (Georgia, North Carolina, Virginia) are coming up in the very near future.  The larger, regional conferences are also coming up.  Attend these to learn and network and be a supportive industry member. Here are the events that are happening in the near future:
  1. Evaluate cold injury in vine tissues. The closer to final pruning that tissue cold damage can be evaluated, the better, as the number of buds retained can be adjusted accordingly. In practicality, this may mean that cold damage is evaluated before starting to prune each block or cultivar.  It is impractical to wait until March to begin pruning in attempt to make it past the periods of greatest cold temperature threat.  Double, or “rough”, pruning (discussed below) is a good strategy to retain several buds before needing to make final pruning decisions.  Using a razor blade to cut a transect across buds will allow visual inspection of primary, secondary, and tertiary bud damage.For more on evaluation of grapevine tissue cold injury, please see the following resources:
  1. Dormant pruning. For those who practice spur pruning, “rough pruning” is a way to get a head start on final pruning. Many have already started this, perhaps in December 2019.  If rough pruning is practiced and brush is pulled from the trellis wires, the final prune will be efficient as the short spurs will simply fall out of the trellis after being cut.  Rough pruning to 4-5 node-spurs allows the grower to delay the final prune to late winter / early spring to assess bud damage and the risk of spring frost. Some “delay prune” by waiting until late winter / early spring before even starting to prune.  This is an attempt to force bud break on the apical bud positions of the dormant cane before those on the basal positions, hence potentially reducing the risk of spring frost damage to the basal buds (buds that will be retained).  We have seen mixed reviews with delayed pruning as it puts growers in a tough position to finish pruning while several other seasonal tasks are getting underway in early spring. Further, it has been reported that delaying pruning well into the spring can result in the failure of some basal buds to break, which negates the reason for practicing delayed pruning in the first place – to maintain crop production.If cane pruning, there is not much logic in delayed pruning, and certainly not much logic in “rough pruning” (don’t prune the canes you intend to lay out!).  Cane pruning is becoming more popular throughout the region; these trends are perhaps due to the reduced need to shoot thin cane pruned relative to spur pruned vines.  Cane pruning also removes older, grapevine wood that potentially contains pathogens that cause wood diseases. This brings up a note on when to replace cordons.  The easy answer is “whenever you are unhappy with the performance and health of your current cordon,” mainly as related to disease incidence and the height and spacing of your current spur positions. In general, it is time to lay down a new cordon (a “cane” in the first year) if there are several instances where adjacent spur positions are sporadic and/or when past pruning choices have resulted in a significant amount of one-year old buds being retained at 5-8” above the cordon.  It is further important to assess for common wood diseases that are often observed in cordons, such as Eutypa dieback, etc.  More on disease considerations at pruning time can be found in this document, written by Virginia Tech grape pathologist Mizuho Nita: https://farmcreditknowledgecenter.com/Farm_Credit_Knowledge_Center/media/Images/Disease-Consideration-at-Pruning-Time-2017.pdf.A final note on pruning – tools.  Using sharp, well designed tools helps reduce operator fatigue.  Sharpen your hand pruners as necessary, and use loppers (large pruners/shears for making larger cuts) that require relatively little exertion. These tactics will enable you and your crews to prune at optimal efficiency. Poorly designed pruners with dull blades require much more operator exertion resulting in fatigue.
  1. Service and check active frost protection machines/equipment and be prepared to avoid spring frost. The most ubiquitous active frost protection method in eastern US vineyards is using a wind machine (photo, below) to mix air in attempt to mitigate spring frost injury.  Wind machines have been noted to protect 10-12 vineyard acres.  Fiscal estimations suggest that wind machines can “pay for themselves” if they save the crop on only one acre if that crop is turned into wine and sold.  If your site is frequently threatened by spring frost, such an investment may prove to be economically beneficial.  Combining air movement with heaters or burning brush piles may offer additional protection when the 1-3 °F of protection offered by air mixing alone is anticipated to be ineffective at preventing frost damage.  Other methods, such as delayed pruning, spray materials, and irrigation may help in some instances, but each of these methods have drawbacks.  For example, highly variable results have been reported regarding the effectiveness of spray materials advertised to lower frost risk through bud break delay, cryoprotection, or preventing ice nucleating bacteria.

    Use a wind machine to mix air to mitigate spring frost injury

  1. I’m going briefly comment on shoot thinning in case bud break occurs earlier than normal (which will happen if warmer weather patterns continue). However, I’ll also comment on shoot thinning again in the March/April edition of Small Fruits). Shoot thinning is the first “canopy management” practice of the growing season.  As with most management practices, all vines require shoot thinning at the same time.  To optimize efficiency, shoots should be thinned by manually by hand removal.  This is best accomplished when shoots are roughly 5-7” long.  Inflorescences are clearly visible at this stage, making it easy to retain fruitful, and thin unfruitful, shoots.  It is NOT advised to wait on this practice, as it becomes much more difficult to efficiently thin shoots when shoots are approaching a foot to 18” in length, and the junction between the spur and shoot becomes lignified. You have waited too long if you need to use pruners to thin shoots. Optimal shoot density is around three to five shoots per linear foot of row for single-fruiting zone systems, such as VSP systems.  It is impossible to count to this number throughout commercial vineyards.  Thus, it is advised to thin a panel or two to the desired shoot density and get crew members to take a mental image of what this looks like (below); they can then implement in the rest of the vineyard with decent precision. Our recently developed and published Viticulture Management Poster (https://site.extension.uga.edu/viticulture/2019/01/viticulture-management-poster-available-at-a-conference-or-workshop-near-you/) can help you plan and implement sound seasonal viticulture practices, including shoot thinning.

    Panel thinned to desired shoot density

  2. Plan for pesticides needs. Order chemicals to manage pests – weeds, insects, and diseases. Make a management plan before the season starts. Again, consider using the new Viticulture Management Poster (https://site.extension.uga.edu/viticulture/2019/01/viticulture-management-poster-available-at-a-conference-or-workshop-near-you/) to help you target important seasonal management periods for specific insect and disease pests.

That’s about it.  We will likely be seeing some bud break in more southerly-positioned vineyards in the southeastern US by the time the next “grape chores” list is published in the next edition of Small Fruits News.  This will be here soon – SO GET OUT AND GET PRUNING!