Adoption of Rootstocks for Sustainable Wine Grape Production in Columbia Valley, Washington

The research plan has two main objectives:

1. Evaluate different grapevine rootstock cultivars to determine which have the most promise for Washington wine grape producers in terms of growth, nutrient, and hardiness characteristics. (Years 1- 3).
2. Determine how different rootstock cultivars influence scion fruit characteristics, such as cluster weights, berry size, brix, titratable acidity (TA) and pH. (Year 3).

Trial Establishment. This research is being conducted at Inland Desert Nursery in Benton City, WA on a 1.1-acre demonstration vineyard that we chose because of known phylloxera pressure nearby, uniform topography and soil type (classified as a Starbuck silt loam with 0- to 5% slopes) and proximity to our farming headquarters for proper oversight and ease of customer touring. Before planting, we collected soil samples to quantify nematodes, chemistry/nutrients, and biology. Fertilizer was added before planting to correct any soil deficiencies, with formulations and amounts documented. One representative field soil test was taken to quantify nematode, nutrient/chemistry and biology levels of the whole field, for the purposes of assessing the effectiveness of inputs, comparing with leaf nutrient values, and monitoring nematode population progression over time. (See in Links 1 and 2)

Link 1: RM5 WSDA Soil nematode negative Xiphinema (1)  Link 2: RM5 Soil Nutrient Tests 2021 (1)

Rows were oriented North to South. Cabernet Sauvignon was planted on the western edge of the vineyard due to having 1 extra row that could not contribute to the other 5 trial replications. Therefore, we chose another common Washington State planted variety for grower interest/education, using a “salad bar” method of various rootstocks down the same row so vigor and resistance differences could easily be spotted when looking down a single row. Another side benefit to choosing a red cultivar on the outer edge of the block is that it will act as an early indicator for the presence of leaf roll infection from neighboring vineyards. The majority of the trial block was planted to 5 replications of Chardonnay Clone 15. Chardonnay-15 was chosen as the primary scion for analysis because it was a high in-demand variety in Washington State at the time of planting, and this particular clone has been widely farmed with standardized canopy management and growth practices, allowing our farmer-customers the ability to relate to the self-rooted version while analyzing the differences influenced by the various rootstocks chosen. Our Chardonnay-15 was grafted to the following five rootstocks: 1103 Paulsen (1103P), 101-14 Millardet Et De Grasset (101-14), 3309 Couderc (3309), Schwarzman, and SO4/Oppenheim #4 (SO4), and a sixth self-rooted “control” was also used (to which all performance characteristics will be evaluated against). All the non-vinifera rootstocks have high tolerance to phylloxera and some degree of tolerance to parasitic nematodes (Table 1). The trial was planted out in a replicated (5 replicates) block design. Randomization of the rootstocks were not to be implemented within each of the block replicates for ease of long-term tracking and management of the rootstocks (e.g., for potential future trials). Figure 1 shows a visual layout of the vineyard planting design; total vines planted will amount to 1,252, with roughly 200 vines per self-rooted or rootstock/scion combination treatments. After planting, the vineyard was maintained with industry standard integrated pest management and horticultural practices. The vineyard was planted using green growing, potted vines finished at 12 inches in length. All propagative material came from hardwood cuttings from Washington State Department of Agriculture certified mother blocks. Scion and rootstock combinations were “bench-grafted” in close succession using an omega-shaped graft punch. Grafts and cuttings underwent callusing in a controlled environment to heal and protect pruning wounds and the graft union. Once vines were adequately callused, both grafts and self-rooted control treatments were grown in pots in a controlled climate greenhouse, and the most uniform resulting plants were selected for planting in the demonstration/research vineyard. The majority of the specified trial vines were planted in June 2021 utilizing protective vine shelters, resulting in a 99.5% success rate. 278 vines are left to complete the trial planting in the Spring of 2022 as a result of short nursery material on 101-14 rootstock. Planting records confirming the 2021 grapevines are shown below in Figure 2- l. The same vine format, farming process and procedures were used to complete the block in the Spring of 2022.

Figure 1:

Objective 1: Rootstock performance evaluations. After June 2021 planting, we began collecting data for Objective 1. To understand how rootstocks will contribute to establishment success, we documented a survival rate of 99.5% across all combinations in the Fall of 2021, just prior to dormancy (See Figure 2.). We were surprised to see such a high survival rate given the extreme temperatures during the time of planting (a peak of 116 degrees, and a full month of +100 degrees). From 2022 to 2023, we saw little difference in the survival ratings. (See Figure 2a.)

To understand how growth was influenced, the following phenology ratings and measurements were to be taken annually: 1) phenological growth stage in May, July, and September; 2) tissue tests for nutrient status at véraison; and 3) weight, average diameter, length, and number of buds on pruned canes collected from November through February (dormant pruning). All measurements were collected from a minimum of 4 plants in each treatment replication. Phenology was rated on 6 buds/shoots per plant (a basal, proximal, and distal shoot relative to the vine trunk on each establishing cordon of the vine), for 4 vines per treatment replicate. To assess the impact of the rootstock/scion combinations on vine cold hardiness, we measured the lignification progress of flag shoots every week from August through mid-October. We updated the minimum quantity of plants to 4 from 10, as it was determined that a sample size of 4 would still yield statistically significant analysis and was more achievable to conduct.

As would be expected given the early age-stage of the vines 2021 phenology ratings and vine measurements were deferred to 2022, as vine growth was limited and not showing any material differences across the replications. However, we expect to complete the full scope of activities listed above for the 2022 planting year and beyond, as the grapevines will be waking up for a full cycle of growth and shut-down together. As would be expected given the early age-stage of the vines 2021 phenology ratings and vine measurements were deferred to 2022, as vine growth was limited and not showing any material differences across the replications. Unfortunately, due to labor shortages and limited insights to gather at this vine stage, we decided to only collect a single phenology rating in April of 2022. (See Figure 3) Based on the averages of this single phenology sample, the 1103P treatment replication advanced from dormancy slightly earlier than the others. In 2023, we were able to collect phenology ratings on all replications from around Bud Break to after Cane Harvest. Based on the phenology ratings, there were slight differences in the shoot and inflorescence development stage. However from Lag Phase til the end of the season, all replications showed similar growth patterns. (See Figure 3a. - Excel Spreadsheet)

For the nutrient tissue tests, we used the ANOVA statistical test to help measure the differences of nutrient uptake between the different treatment replications. (See Figures 4, 4a.) For 2022, there were measurable differences between the trial rootstock combinations in coordination with nutrient uptake. In Figure 4, the values highlighted in yellow show the highest statistical difference between the trial rootstocks and their nutrient uptake levels, values highlighted in orange show marginal differences. We can see these differences in Figure 4a. In 2023, there were even more measurable differences between the trial rootstocks and their nutrient uptake levels, significant values are highlighted in yellow, marginal differences highlighted in orange. (See Figure 4b.) We can see these differences in Figure 4c. This is where things got interesting. If certain rootstocks can uptake different nutrients better than others, this could benefit grape growers where the soil is deficient in these nutrients, and could help them take advantage of certain fertilizer application. However, we will need to collect more data points in order to become confident in this hypothesis. 

As seen in Figure 5, in 2022, the 3309C Treatment Replication weights have been slightly higher than the others. We expected low pruning weights for 101-14 MGT replications in 2022 as planting was only completed in Spring 2022. We decided not to take the diameter length and number of buds as the pruning weights were enough to interpret a growth pattern between the different replications. In 2023,  we saw a shift as the vines were in their second year of growth, with the exception of 101-14 MGT, as it was the first year for that replication. All across the board the pruning weights were higher than the previous year. In 2024, no significant differences were found.

In addition to the completed survival ratings, Dr. Moyer’s laboratory conducted cold hardiness tests using differential thermal analysis (DTA) to establish temperatures that produce an LT50 (http://wine.wsu.edu/extension/weather/cold-hardiness/). These samples were collected during the transitional time periods of early November (2 sampling periods) and late February (2 sampling periods). You can see the data for the DTA Testing in Figure 6 and Data for Objective 1 needs to be collected over a three-year time span to understand if characteristics imparted by the rootstocks to the scion are volatile or consistent over time.

Figure 2:   Figure 2a:

 Figure 3:      Figure 3a: Phenology Ratings 2023

Figure 4: Figure 4a:

Figure 4b:     Figure 4c:

Figure 5:  Figure 6:

Figure 6a:

Objective 2: Impact of rootstock on scion fruit quality. Objective 2 was achieved by measuring fruit before and at harvest in 2023. Fruit produced in prior years was inconsistent and unlikely to produce significant results due to immaturity of the plants. In harvest 2023, unforeseen personnel changes affected our ability to collect the data for Objective 2. We will continue to monitor the production and quality of the block in the next few years. We also believe that through our data and outreach in objectives 2 and 3, we have successfully addressed the viticultural basis of performance between these rootstocks.  We look to continue investigating the oenological impact of these differences in how they would impact wineries in regard to the quality of wine capable of being produced. 

All data will be subjected to an Analysis of Variance and subsequent means separation using Tukey’s HSD.

Table 1. Rootstock Characteristic Chart

Figure 1. Demo Vineyard Design