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Replanting Options for Establishing Phylloxera-resistant Vineyards

Additional Fact Sheets on Phylloxera:

Contributing List of Authors: Ed Hellman. Oregon State University. This fact sheet and others on grape phylloxera were produced as a set by a phylloxera task force at Oregon State University: Bernadine Strik, Extension Berry Crops Specialist; M. Carmo Candolfi-Vasconcelos, Extension Viticulture Specialist; Glenn Fisher, Extension Entomologist; Edward Hellman, Extension Horticulture Agent; Steven Price, Post-doctoral Research Associate, viticulture; Anne Connelly, Master’s student, horticulture; and Paula Stonerod, Research Aide, horticulture. The authors of this fact sheet acknowledge the help and guidance of others on this task force.

Phylloxera is spreading through Oregon’s self-rooted European winegrape vineyards (see Phylloxera: What is it?). Grape growers with infested vineyards or growers wishing to avoid infestation have several options available for replanting existing vineyards with phylloxera-resistant plants. This fact sheet reviews the available options and discusses advantages and possible pitfalls of different replant strategies.

The primary objective of replanting is to establish a new vineyard that is resistant to phylloxera. A second objective is to reduce the costs of the transition. These two objectives should be considered together. You should not use a replanting method that will impact the long-term health and viability of the new vineyard. Likewise, you must carefully weigh the economic realities of the transition to protect the financial health of your business.

When to Replant:

All self-rooted Vitis vinifera vineyards in Oregon are at risk from phylloxera (see Phylloxera: What is it?). It is possible that all of these vineyards will eventually become infested. However, a vineyard could become infested this year or it might take 30 years. Growers can wait to replant until they know a vineyard is phylloxerated, or they can replant to resistant stocks before an infestation occurs. Replant strategies may be different in these two situations.

Uninfested vineyards

Replanting a vineyard before a phylloxera infestation provides you with the most options. In this case, the replanting can be based on a long-term plan of vineyard replacement and rehabilitation. Thus you can anticipate financial implications of replanting and spread replanting costs over a longer period. You can base the order of block removal and replacement on block profitability. You can also order planting material well in advance, integrate the replacement process into a larger plan of vineyard rejuvenation and improvement. In short, your decisions are planned rather than dictated by the spread of phylloxera and the pattern of vine decline.

Replanting before an infestation is discovered should be considered first in vineyard blocks with problems. For example, replanting provides you with an opportunity to renovate or change trellis systems, change vine and row spacing, change varieties or clones, or add an irrigation system or drainage tile. In addition to conferring phylloxera resistance, rootstocks can also be used to correct problems with excess vigor, water stress, poor fruit set, or vine nutrition.

Replanting profitable blocks before a phylloxera infestation occurs is a more difficult decision. There are still advantages to replanting, particularly in the long-term. A vineyard on resistant rootstocks will provide a supply of grapes that will not be interrupted by phylloxera and resistant rootstocks substantially add to a vineyard’s resale value. You must keep re-establishment time to a minimum in any situation, but this becomes especially critical with profitable production blocks; time without fruit production must be kept as short as possible (see below).

Infested vineyards

In an infested vineyard, replanting schedules will be dictated by the decline of phylloxera-infested vines (see: How to Monitor Rate of Spread of Phylloxera in Your Vineyard). You will need to remove or replant blocks with declining production when they are no longer profitable to manage. Avoid spot replacement of visibly infested vines. Distribution of phylloxera in the vineyard is much wider than the area of visibly affected vines, and vines outside a weak spot will continue to decline. Also, the patchwork of different vine ages down a row that results from spot replanting is difficult to manage. Replant infested areas on a row-by-row basis, with the replanted area extending well beyond the borders of the visible infestation.

If you have an infested vineyard, be aware that phylloxera will eventually move through the entire vineyard. Prepare a replanting schedule for the entire vineyard. Your first priority should be visibly infested areas. As described above, replant the least profitable blocks next with the added goal of vineyard improvement. Replanting apparently healthy, productive blocks will be your most difficult decision. You must balance the temporary lost revenue against the potential value of an entirely phylloxera-resistant vineyard.

Planting resistant rootstocks in an infested site is not insurance against continued spread of phylloxera in self-rooted areas of the vineyard. Many phylloxera-resistant rootstocks will support phylloxera populations, and these can serve as a reservoir for continued spread (see: Buying Winegrape Plants).

Replanting Options:

Growers replanting vineyard blocks can choose to replant after vine and trellis removal, replant attempting to re-use existing trellis structures, or attempt to plant between existing vines (interplant). The most prudent course is a complete renovation of the vineyard; it is also the most expensive, both in costs of renovation and in time with lost production. Interplanting is the other extreme. There are potential cost advantages to interplanting, but it has a much greater risk of failure.

Traditional European viticulture recommends a “rest period” of five to six years before replanting a vineyard. This period can be shortened to three years if the soil is disinfected by fumigation. The primary justification for this practice is the possible presence of nematodes, fungi, and phylloxera–phylloxera can weaken young vines, even those on resistant stocks. It is unlikely that many Oregon growers will wait five years to replant, but it is important to recognize potentially serious problems associated with immediate vine replanting.

You should evaluate vineyard blocks before making replant decisions. The objective of the evaluation is to identify vineyard limitations and determine if replant strategies offer an opportunity for their correction. Is the production system efficient? What is the anticipated life span of the trellis? Could the spacing or trellis system be changed to improve quality or production? Should an irrigation system be installed or renovated? Are there limiting soil factors such as compaction, nutritional shortages, acidity problems, or poor drainage? Are there pathogenic nematodes or fungi present in the soil? Many of these factors can be corrected most effectively before planting, without existing plants or trellises obstructing access to the entire block.

Vineyard renovation

In a new vineyard, you have the most options and the greatest chance f success with complete vine and trellis removal before replanting. This is your only choice hen the existing vineyard has serious, correctable limitations. Renovation allows deep ripping to loosen hard pans and pull up old vine roots. You can leave blocks fallow or plant cover crops to improve soil health and reduce phylloxera and nematode populations. Fumigation is only an option in the absence of growing plants. Soil nutritional modification requiring deep incorporation of phosphorous, potassium, or lime is most convenient in the absence of plants or trellis structures. Permanent modifications of new blocks such as changes in trellis systems or vine spacing or installation of drainage tile also require a fresh start.

Replanting with the existing trellis

You should only replant within an existing row if the plan and organization of the vineyard is acceptable and the trellis system has a minimum of 10 years of life remaining. Many of the major vineyard modifications discussed above are not possible if the trellis structure is retained. How to remove the old vines may be a difficult decision. In some cases, large old vines cannot be removed without damaging the trellis system. In this case, the old vines must be cut off and killed with herbicides. The old root system is allowed to remain in place. It is possible, however, that the old roots may serve as a source of root diseases and could increase phylloxera population pressure on the new rootstocks.

Interplanting

The goal of interplanting grafted vines between producing, established vines is to get the new plants into production while the old ones continue to supply revenue. It is possible that a new grafted vineyard could be established with little or no loss of production. Do not consider interplanting if the existing vineyard has serious limitations that could be corrected by complete vineyard renovation. Interplanting places the new plant at a significant disadvantage. It must compete for water, nutrients, and light with a much larger, established vine. This difficulty is compounded by the conflicting needs of a producing vineyard and young, newly-planted vines.

If you choose this option, you must make the establishment of the new vines your first priority. Adjust vineyard management to favor the growth of the new vines. Management practices to consider are: provide irrigation to new plants, remove permanent cover crops that compete with young vines, use plastic mulch around young vines to reduce weed competition and soil water loss, root prune the established plants, and summer prune established plants to increase available light for the new plants. You should probably remove the established vines within two years, at the time the new planting is being trained to the fruiting wire.

The potential problems with interplanting are many. The most serious is competition. It is possible that your considerable investment in grafted plants may be lost if the new plants cannot successfully compete with the established planting. Poor take on new plants could result in a non-uniform vineyard made up of vines of different ages and different varieties, with and without rootstocks. Also, removing the old vines once the interplants are established may be a problem–associated with this are potential problems with nematodes, soil fungi, and high phylloxera populations on the older vines.

Inarch Grafting:

Self-rooted vines can be converted to vines with resistant rootstocks by a grafting technique called inarching. Resistant stocks can be planted next to the trunks of existing vines and grafted onto the trunk. The goal is to completely replace the root system of the self-rooted plant with the phylloxera-resistant stock. This technique has been tried in California with mixed results. In some cases, growers were able to change the root system of established vines without losing production. It is unlikely that this technique would work consistently in Oregon. Field grafting, of any type, has never been reliable under Oregon’s cool growing conditions. Cool, wet weather following the grafting process generally results in graft failure. Given Oregon’s propensity for unpredictable weather, growers are advised not to try this system except in small-scale experiments.

Whatever replant strategy is used, the most flexibility is available when the planning starts early. Start planning now! The more prepared you are, the more likely that replanting will be an opportunity for improvement rather than a desperate attempt to rescue a dying vineyard.