Grape productivity is typically measured by grape yield per acre, expressed in tons. And while it’s not always possible to predict the exact yield you’ll produce each year, there are several things you can do to optimize grape production and ensure a crop of healthy grapes.
How Many Grapes per Acre Should You Expect?
Over the past few decades, grape yield per acre has been a point of contention in the table grape and viticulture world. Many grape growers held the idea that a lower yield (i.e. underproducing) would lead to higher quality grapes. However, grape quality is not only related to the density of production, but also to the quality of the soil, water, rootstock, and sun access.
With this in mind, grape growers are encouraged to aim for “balanced vines,” calculated according to the Ravaz Index as 5 pounds of fruit for each 1 pound of prunings from those same vines after the growing season. Generally, wine grape vines can be expected to produce around 3 to 5 tons per acre, and table grape vines will ideally produce 8 to 10 tons per acre.
Factors That Impact Grape Production
If your grape yield per acre is much lower than the expected range or you’re turning out low-quality, damaged grapes, there are several factors that could be involved. Here are some of the most common problems, along with suggested strategies for growing healthy grapes.
As alluded to previously, some growers may intentionally lower their grape yield per acre in order to produce “higher quality” grapes. This leads to more vigorous shoots and an increased rate of vegetative growth compared to the number of actual grapes on the vine.
If under-cropped, the shade created by the leafy canopy makes the vines more susceptible to disease and decreases grape yield per acre by reducing bud fruitfulness and blocking the sunlight from reaching the grapes.
- Solution: Aim for Balanced Vines
Instead of reducing grape production to improve quality, focus on soil structure, effective irrigation techniques, appropriate rootstock selection, and adequate access to sunlight. These factors should include grape quality without sacrificing grape health or yield.
Once you have a healthy grape yield per acre, you need to protect your fruit from competitors — particularly sparrows, house finches, American robins, European starlings, and crows. These common bird species peck at the fruit on the edges of the vineyard and the top of the vines, causing juice to spill onto bunches lower down and leading to a buildup of organisms and bunch rot.
In California, a failure to control bird damage can decrease producer surplus by 6.6%, whereas the cost of managing birds effectively increases producer surplus by only 1.3%. Customers benefit from effective bird management too, with a surplus of 11.5% when damage is prevented.
- Solution: Protect Your Vines from Birds
Fortunately, there are several techniques that you can use to protect your vineyard from bird damage and ensure a crop of healthy grapes. These include:
- Cleaning up potential nesting sites
- Applying nets
- Using frightening devices
- Flying falcons over the vineyard
- Shooting birds (requires permission)
- Trapping birds (requires permission)
- Applying repellents (check state restrictions)
Just like with stone fruit and citrus crops, diseases can reduce grape yield per acre by attacking the various parts of the plant. The diseases that most frequently affect grapevines include:
- Grapevine leafroll disease
- Grapevine red blotch disease
- Grapevine powdery mildew
- Pierce’s disease
- Trunk diseases
- Esca (measles)
- Eutypa dieback
- Botryosphaeria dieback
- Phomopsis dieback
- Solution: Follow Best Management Practices
In order to protect grape production in the face of disease, you’ll need to identify any diseases as soon as they appear (or research diseases in your area beforehand) and weigh up the different options available. In many cases, cultural and biological controls may be helpful for preventing damage without the need for chemical sprays.
Finally, frost damage can reduce your grape yield per acre by reducing the number of fruitful buds. Frost damage is most likely to occur in cool or cold climates, but cooler regions of California can be affected as well. The most common evidence of frost damage is burnt and/or shriveled leaves and buds, which leads to fewer buds that can then produce fruit. You can’t prevent the frost from falling, but there are strategies that are effective for protecting your grapes on a commercial or domestic scale.
- Solution: Implement Grapevine Protection Strategies
If you’re just starting out in grape growing, select a site on the upper side of a slope or hill so that cold air can flow downwards and away from your grapes. You can also select a variety of grapes with a later bud break (to avoid the frosts) as long as they’ll still have enough time to ripen.
If you already have an established vineyard, you can protect your grape yield per acre from frosts using delayed and double pruning techniques, giant fans, and/or giant sprinklers. For smaller or domestic vineyards, cover grapevines with blankets or tarps at night.
Improve Your Grape Yield per Acre with Fruit Growers Supply
Fruit Growers Supply has been a key player in the California fruit-growing industry since 1907 when we started to manufacture corrugated boxes for Sunkist. Now, our range of offerings has expanded to include custom irrigation systems and shipping pallets as well as grape-growing products like netting and sprays. If you’d like to grow healthy grapes season after season, contact our team or visit us in-store. Fruit Growers Supply is here for you — find out how we can help today!
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