Although grapes are currently dormant, growers, whether backyard or commercial, should not abandon the vineyard entirely during the winter months.
This lull in work load is the perfect time to perform some vital tasks to ensure a smooth transition from the vines' dormancy period to bud break in early to mid-spring depending on the grape variety.
The primary tasks that can be carried out during winter months include proper fertilization, pest and disease management, sufficient irrigation, maintenance and avoiding practices that disrupt the vines dormancy. Other tasks that can be accomplished during this time include continuation of vine training and preparation for the next growing season.
Vines still require soil moisture even during the fall and winter months. Approximately 14% of the total seasonal water budget is required from harvest to leaf drop (Figure 1).
Although this amount is significantly less compared to the water requirements during the active growing season, growers should still be mindful of water needs during the off-season. This means growers may need to apply supplemental irrigation during periods of low soil moisture status. Fortunately most of us have seen ample, if not excessive rain events, so irrigation has not been necessary this winter.
During the winter months it is a good time to conduct routine maintenance and repairs of the irrigation system, which may include flushing of the lines and cleaning filters. Check that all emitters are performing as they should and inspect the injection system if applicable.
Vine training and pruning
You can continue to train vines, including cordons, by untangling them and tying them to your trellis or arbor with the appropriate vine ties (avoid bread ties or zip ties), but do not prune or remove any wood at this time as this can de-acclimate vines, causing them to wake up earlier than they should. If we receive a spring frost you could easily lose the one crop that is resting and already formed within the primary buds.
There is one exception to the above rule. For many growers who have lots of vines and not a lot of help it can be difficult and messy to prune the entire vineyard at once in early spring. Pruning grapevines is a necessary process that must occur each year and timing is critical in order to minimize risk of spring frost damage as well as reduced fruitfulness by waiting too long.
Many growers adopt a technique called double pruning. In double pruning you prune all 1-year-old wood, known as the canes, that are coming off of the cordon to about seven to eight buds. This first pruning is called rough pruning. Rough pruning can occur anytime during the dormant period, but most growers will begin during January or February. Doing this will allow the grower to remove the majority of pruning trash making the final pruning, which is done later in spring, more efficient.
While rough pruning will often wake the vine up prematurely, only the top buds of each cane will break bud. If they freeze, it does not matter as you will come back a second time, in early to mid-spring depending on each grape variety, to prune each position along the cordon to one cane and that single cane down to one, two or three buds depending on vine balance requirements.
Pruning will be discussed in greater detail at regional workshops that I put together across North Texas. Visit our Facebook page at Texas Viticulture and Enology to see when and where these workshops will occur.
Vines often benefit from a small dose of nitrogen post-harvest to encourage healthy foliage and storage for next season. Applying nitrogen at too high of a rate or too late in the season can reduce the vines’ ability to harden off.
Apply the appropriate concentration following harvest but resist the urge to apply nitrogen once the vine has entered dormancy (Figure 2). Application of other essential nutrients such as potassium, magnesium, iron and possibly phosphorous may be done during the fall or winter months via drip or banding/broadcasting. But only apply fertilizers if they are actually needed. More is not better in this case.
Pest and disease
Continue proper pest and disease management strategies to promote a healthy vineyard even during winter. Rogue (pull out) dead or diseased vines that were marked and replace in spring. Remove all mummified fruit before bud break and make sure to burn or trash all pruned wood.
If you compost these clippings, ensure they are properly composted. Studies have shown that fungal pathogens that infect grapes can remain active even on dead wood for five to seven years. There are also dormant season fungicides that can be applied to the whole vine during late winter to early spring.
You can consult our 2020 Texas Grape Pests Management Guide available at agrilifebookstore.org for more details. Also, don’t forget to sanitize pruning shears with Lysol or a 25% bleach solution when final pruning from vine to vine in spring.
Even during the winter, vines need to have their vineyard floor maintained. Applications of herbicide or mechanical practices to keep a weed-free strip under the row should have taken place in the fall. Furthermore, seeding out a cover crop within the row middle, if desired, needed to have been done at this time. Many will mow down the cover crop in spring.
If you mulch to prevent weeds, winter is a good time to replenish the mulch layer, keeping it about 3 inches thick. The use of pre-emergence herbicides labeled for vineyard are often recommended and can be applied in late February.
Other tasks that should not be overlooked in the vineyard include:
1. Perform irrigation maintenance and repair.
2. Review soil and plant nutritional tissue tests to make appropriate fertilization applications.
3. Order supplies such as pesticides, fertilizers, PPE equipment, trellis hardware, replacement vines, etc.
4. Winterize equipment as needed.
5. Conduct trellis maintenance and repair (Figure 3).
6. Apply soil amendments and/or mulch as necessary.
7. Review seasonal notes and make adjustments to management strategies for next season.
8. Rogue flagged vines.
9. Propagate, via hardwood cuttings, new vines if you are a hobby operation and would like to expand the vineyard.