Grapes

It is not uncommon to walk a vineyard row and find some vines with red leaves somewhere in the canopy. Red leaves can appear at any time in the growing season and are caused by many biotic (viruses, bacteria and fungus) and abiotic (nutrient deficiencies, cold injury and damage to root systems, etc.) stresses.

Winter injury is the single most limiting factor to grape production in the Eastern United States. Although we had experienced limited damage in the last 20 years, many vineyards in the Mid-Atlantic reported winter injury following the harsh winters of 2013-14 and 2014-15. Although it has not been utilized by a significant number of growers in the past, many vineyards that have experienced damage recently should consider “hilling up” (mounding soil over graft unions) for protection again winter damage.

Damage from low winter temperatures is arguably the greatest risk to sustainable profitable winegrape production in the eastern US. The majority of Maryland vineyards had not experienced a significant amount of low-temperature damage over the past decade or so, however, vineyards throughout Maryland have experienced damage over the past three winters. The following “TimelyVit” will give an overview of how vines attempt to prevent damage, the conditions which influence the level of damage, and types of damage.

profitable winegrape production in the eastern US. The majority of Maryland vineyards have not experienced a significant amount of low temperature damage over the past decade or so, however some vineyards have experienced damage this winter (2013/2014). The following “Timely Vit” will give an overview of how to assess the damage and how to modify your pruning based on the assessment.

Pruning a vine causes it to deacclimate similarly to a warm spell, so do not prune (especially very sensitive varieties) when you know you will experience very serious cold shortly afterwards.

A major theme of viticulture is that for a vine to consistently produce high quality fruit it must be “in balance.” That means that the amount of vegetative growth (shoots and leaves) is just right to properly ripen the reproductive growth (fruit load). Too little fruit may lead to an over-vigorous vine, shaded fruit and lower quality. Too much fruit may decrease vigor to a point where there is not enough photosynthetic area to properly ripen the crop leading to under-ripe fruit and reduced quality.

“Timely Viticulture” Balanced Pruning 2 dealt with the timing of pruning relative to dormancy, deacclimation, and bud break. The best thing to do is to try to delay pruning as long as practically possible. If you could accomplish all of your pruning in the last two weeks of March that would probably be best, although that is typically not enough time do to the size and labor limitations of most commercial vineyards.

Many fruit growers get understandably concerned in January and February when we get a run of “warm’ weather like we have been experiencing. When a deciduous vine or tree experiences weather warm enough to start the deacclimation process, there is an increased risk of winter damage to buds and wood. Here is a simplified model of dormancy.

There is a lot of new vines going in and many people are asking questions about grow tubes. The following is a short list of considerations for using (or not using) grow tubes with your new planting.

Most have finished or already finished pruning. Remember, if you have a site where there is a history or severe risk of bud damage from late frosts with early budding varieties (such as ‘Chardonnay’), it is best to prune those last as this will help to delay bud break. You can also prune to long spurs (5-6 buds) or long canes initially to take advantage of apical dominance and then do a quick final pruning down to your final spur bud count when the risk of frost has passed.