Vineyard Early Season Management
George Zhuang, UCCE Fresno County
Early season vineyard management is critical for several reasons. The grapevine microclimate directly effects fungal disease severity during the early season. Fungal disease outbreaks can have a large effect on yield. This is due to yield losses as fungal infection makes fruit unmarketability. Fungal infections can also affect fruit quality by lowering Brix and color in red varieties. Proper early season vineyard management can thus help to reduce these effects and save you money on late season disease management. Early season vineyard practices can also affect the follow year’s success. Bud fruitfulness next season is affected by early season light exposure this season.
The winter of 2020 was relatively dry based on historical average. The accumulated precipitation from 10/01/2019 to 04/19/2020 in Fresno was 8.29” (CIMIS Station #80 at Fresno State) compared to the historical average of 10.67” during the same period. However, spring of 2020 has followed the similar pattern as the spring of 2019 with abundant precipitation during the early canopy growth stage. So far, we have received 4.44” of rain in 2020 from the beginning of March to the end of April compared to the 4.41” of rain in 2019 from the beginning of March to the end of May. Therefore, we might end up with more precipitation in spring of 2020 compared to 2019. Wet spring favors grapevine fungal disease and requires deliberated vineyard management to offset any potential risks.
The most important steps during the early season vineyard managements include:
1. Irrigation
2. Nutrition
3. Pest/disease
4. Canopy management
5. Crop management
The objectives of early season vineyard management are simple and straightforward: to sustain yield with desired fruit quality at harvest with low disease/pest pressure. Irrigation, grapevine nutrition, pest/disease pressure, canopy management and crop level all play in the formula to decide the timing and severity of vineyard practices at the early growing stage.
Water Management
I have covered the basic concepts of water management at previous Vit Tips (https://ucanr.edu/sites/viticulture-fresno/newsletters/Vit_Tips_Previously_newsletter_VineLines58357.pdf). Here, I will focus on early season irrigation scheduling, and two keys are: 1) when to irrigate, 2) how much to irrigate.
When to irrigate:
1. Visual Assessment of Canopy
2. Soil Moisture Assessment
3. Plant Water Stress Assessment
Visual assessment of canopy (1) can be used to gauge the level of water stress. Assessment of items such as: shoot tips, tendrils, internode length, and even budbreak can infer the water stress of the vines. However, visual assessment needs experience and might not be accurate enough for real-time management.
Soil moisture (2) can be judged through different ways, including feel and appearance, soil matric potential (tensiometer), soil gravimetric measurement, soil volumetric water content. Most growers choose soil appearance or soil matric potential to schedule their first irrigation.
Plant water stress (3) can also be assessed by measuring leaf or stem water potential. If the midday leaf water potential is greater than -10 bars it indicates that the vine is water stressed. At this point the grower needs to start their first irrigation.
How much to irrigate:
After growers decide to start the irrigation, growers can follow the recommendation previously outlined in the Raisin Production Manual (Table 1). Crop evapotranspiration (ETc) can also be calculated from reference evapotranspiration (ETo) and crop coefficient (Kc). ETo can be obtained from nearby CIMIS stations and Kc can be calculated using the percentage of midday canopy shading.
Table 1. Vine water use (drip irrigation schedule) for a large canopy vineyard or one using a trellis with a crossarm* (reproduced from the Raisin Production Manual, UC ANR Publication 3393)
*Vineyard canopy covers 75% or more of the land surface during summer months. When used to schedule drip irrigations, amounts must be increased according to the efficiency of the drip system. $Divide values by number of vines per acre to determine gallons per vine per day. Divide values by 27,154 to calculate inches per day.
| Gallons per acre per day$ | Month | |||||
|---|---|---|---|---|---|---|
| Date | April | May | June | July | August | September |
| 1-7 | 700 | 2,050 | 3,550 | 4,700 | 4,900 | 4,100 |
| 8-14 | 1,000 | 2,400 | 3,900 | 4,900 | 4,800 | 3,800 |
| 15-21 | 1,300 | 2,700 | 4,250 | 5,050 | 4,550 | 3,500 |
| 22-30 | 1,650 | 3,100 | 4,500 | 5,000 | 4,400 | 3,200 |
Nutrient Management
Early season nutrient management should include N, Zn, and B. In addition, K and Mg may also need to be managed at this time. Growers need to consider irrigation amount and the amount of nitrate (NO3) in their water source. Vine tissue testing is a great way to take a snapshot of vine general nutrient status and can be beneficial to guide the nutrient application program. Typically, bloom tissue test, either from petioles or leaf blades, has the greatest value to tell the early picture of vine nutrient status. Growers can have enough time to adjust the fertilizer program to compensate any negative effects from nutrient deficiency or toxicity.
| Nutrient | Unit | Deficient (below) | Adequate | Excessive (above) | Toxic (above) |
|---|---|---|---|---|---|
| NO3-N | ppm | 350 | >500 | 2,000 | 8,000 |
| P | % | 0.1 | 0.15 | ||
| K | % | 1 | 1.5 | ||
| Mg | % | 0.2 | 0.3 | ||
| Zn | ppm | 15 | 26 | ||
| B | ppm | 25 | 30 | 80 | |
| Na | % | 0.5 | |||
| Cl | % | 0.5-1.0 | 1.5 |
General vine nutrient threshold of bloom petiole can be found at Table 2. Growers should be careful of vine N critical value since Table 2 N threshold were established on own rooted Thompson Seedless vines. Many factors can affect N critical value, e.g., variety, rootstock, weather, disease/pest pressure and more. Therefore, growers should gauge the vine N status using visual assessment of general vine health, historical records, yield, disease/pest conditions, and laboratory results. Recently, remote sensing has been explored in Dr. Fidelibus’ and Dr. Pourreza’s labs in UC Davis to assess vine N status covering large acres using non-destructive measures. Some early results are encouraging showing low cost field images can provide more information covering large areas through the whole growing season.
The general rule of N application is based on the crop removal. For every ton of fresh grape removes approximately 3 lbs of N. Therefore, growers need to adjust the amount of N to apply based on the yield per acre. With an average of 10 tons per acre of vineyard, the amounts of N recommended are approximately 30 lbs. per acre. However, growers need to consider the amount of N from irrigation water and add the amount of N into the calculation. For instance, with 10 lbs. of N per acre foot of water, and a typical vineyard requiring 2 acre feet of irrigation per year, this field would have already received 20 lbs. of N by just irrigating the vines. However, keeping the general rule in mind, growers need to adjust the amount of N based on: soil type, rootstock, irrigation type, vine vigor, and pest/disease pressure.
With the consideration of N amount, timing of N is also critical to achieve the maximum N application efficiency. Two timings of N application have been recommended: early season and post-harvest. Specifically, early season refers to one month after bud break and right after fruit set. The benefit of early season N application is that canopy is growing rapidly at this stage and N uptake efficiency is close to maximum. Post-harvest can be an alternative timing to apply N, however, photosynthetically functional canopy is required to achieve the N application efficiency. Therefore, post-harvest N applications are most appropriate for early to mid-season varieties.
Canopy Management
Pest and disease management are key targets during the early growing stages. Irrigation and nutrient management can indirectly affect the pest/disease pressure through changing the canopy size/density and microclimate. Shoot thinning and leafing are commonly applied to open the canopy. This increase cluster spray coverage and light exposure. It will also improve the air circulation within the canopy, which helps to reduce the relative humidity. The goal of this work is reduce pest/disease pressure while improve fruit quality.
Shoot thinning can be applied by hand or machine at shoot length of approximately 8”-10”. Leafing can be applied by hand or machine around fruit set on one side or both sides of the canopy based on the regional climate and row orientation. Recent studies have confirmed that pre-bloom or bloom leafing has minimal effect on yield with greater or similar benefit on berry quality as comparison of fruit set leafing (Cook, et al. 2015).
Disease and pest pressure are another reason why early season canopy management is critical. Wet spring condition favors Phomopsis and Botrytis, and the effectiveness of fungicides will depend largely on the timing and coverage. Typically, growers can adjust the timing of fungicide application based on local weather forecast or UC PM index. Canopy management (shoot thinning, leafing, and cane trimming) can help to open the canopy to improve the spray coverage. It will also increase light exposure inside the canopy and improve the air circulation to lower the relative humidity.
In conclusion, canopy managemnet should be integrated with water and nutrient management as the part of early season vineyard pratice with the consideration of pest/disease management, growing condition, e.g., climate, soil condition and irrigation water availiability and quality, and production goal in order to achieve the maximum production efficiency with low disease and pest pressure.
Reference:
Cook, M., Zhang, Yi., Nelson, C., Gambetta, G., Kennedy, J., and Kurtural, K. 2015. Anthocyanin Composition of Merlot is Ameliorated by Light Microclimate and Irrigation in Central California. American Journal of Enology and Viticulture. 66: 266-278.