Results

Location 1: 'La Crescent'

The average yield per vine was 20.9 lbs in 2023 and 13.7 lbs in 2024.  Yields from vines pruned to 2-node spurs and canes were below the average in both years.  Yields on vines pruned to 3-, 4-, and 5-node spurs had yields above the average in both years.  There did not appear to be variability in the fruit chemistry based on pruning treatment (Table 1).

Table 1: Impact of pruning practice on the yield and fruit quality parameters on 'La Crescent' vines.

Location 2: 'Brianna' and 'Marquette'

The average yields of 'Brianna' were similar in 2023 (20.2 lbs/vine) and 2024 (21.6 lbs/vine).  In both years the lowest yielding treatment (~16 lbs/vine) was pruning to 2-node spurs.  In 2023 cane-pruned vines yielded the highest, while in 2024 cane-pruned vines yielded below the average.  In 2023 the both the 3-node and 5-node spur vines had average yields, but they were both above average in 2024.

In 2023 the lower yielding 2-node pruned vines, had the highest brix.  That trend was not observed in 2024 where the lowest yielding treatment of 2-node spurs also had the lowest brix.

Table 2: Impact of pruning practice on the yield and fruit quality parameters on 'Brianna' vines.

In 2023 the mechanical harvester broke down halfway through the 'Marquette' harvest, so the mechanical harvest values cannot be directly compared due to differing harvest dates of around 5 days.  That year we had hand harvested one half of the entire vine, from 8% of the vines of each treatment prior to the machine harvest.  Those values were extrapolated to total yield per vine and the brix and pH were quantified (Table 3).  In 2024 mechanical harvesting was accomplished for all treatments and those values are reported. 

Estimated average yield per 'Marquette' vines in 2023 was 19.2 lbs/vine, while in 2024 the actual yield was 16.7 lbs per vine.  In 2023 both the 2-node and 3-node spur vines had estimated yields below average.  In 2024 vines pruned to 2-node spurs yielded below average and vines pruned to 3-node spurs were at the total average.  Cane pruned vines yielded the highest in both 2023 and 2024.  Vines pruned to 5-node spurs had above average yields in both 2023 and 2024.  There were no obvious trends in fruit chemistry except perhaps in 2024 the lowest yielding treatment of the vines pruned to 2-node spurs may have a higher brix.

Table 3: Impact of pruning practice on the yield and fruit quality parameters on 'Marquette' vines.

Location 3: 'Frontenac Gris'

Average yields were lower in 2024 (7.8 lbs/vine) than in 2023 (17.8 lbs/vine).  In 2023 hand-pruned vines had the highest yields, while in 2024 the machine pruned vines had the highest.  In either case the values were between treatments appeared similar.  Generally, the machine pruned vines had a somewhat higher brix, but the values did not appear very dissimilar (Table 4). 

Table 4: Impact of pruning practice on the yield and fruit quality parameters on 'Frontenac Gris' vines.

In 2023 black rot infections were present on the foliage while in 2024 the phomopsis infections were prevalent.  In the case of both years, the incidence of disease on leaves did not appear to be impacted by the pruning treatments (Table 5).  But mechanically pruned vines appear to have a greater severity of infections than hand pruning, with mixed pruning being intermediate.  In 2024 shoot infections of phomopsis were also recorded and hand pruned vines had a lower incidence of nodes affected by phomopsis than with mechanical and mixed pruning.

Table 5: Impact of pruning practice on disease incidence and severity on 'Frontenac Gris' vines.

In 2023 hand pruning vines took nearly ten times as long to prune as 2 passes from the mechanical pre-pruner, and around 3 times longer than mixed pruning (Table 6), when the manual de-suckering that was done on all vine was not included.  In 2024 the hand pruning and mixed pruning were accomplished at a much faster rate than in 2023.  In 2024 hand pruning took more than 6 times as much time as fully mechanized pruning, while mixed pruning only took 1.5 times as much labor than fully mechanized pruning.

Table 6: Minutes of labor required to prune. 

The labor cost to prune a grapevine will vary based on the minutes per vine and the cost of the labor per hour.  Moving from hand pruning to mixed saved $420-$560 in labor per acre, while moving from mixed to full mechanical pruning saved $88-$199 in labor per acre.  Most of the costs savings were not from moving from hand pruning to full mechanical pruning but rather from moving from hand pruning to mixed pruning.  However, both options require a substantial increase in machinery costs.

Table 7: Labor Cost Breakdown of Mechanical, Mixed, and Hand Pruning

Discussion

Other growers in the region reported lower yields in 2024 than in 2023, which is consistent with most the observations in this study.

The positive of on farm research is that the project is done on a commercial scale, so the results represent a large number of plants that are treated like they would be in a commercial setting.  The drawback of on-farm research on this moderate scale is that practices like machine harvesting are needed, but it limits the ability separate out replications to do a typical statistical analysis on the results.  

Cane Pruning and Length of Spur Pruning  

'La Crescent' vines pruned to 2-node spurs or long canes consistently had below average yields.  In situations where higher yields are desired, without wanting to leave extra shoots which can cause shade, pruning to 3-, 4-, or 5-node spurs appears to be the best choice.  This could indicate that the nodes 1 and 2, and nodes past node 5 are less productive or that non-count shoots arising from the cordons on the spur pruned vines contributed to the yield.  The fruit quality parameters we quantified for 'La Crescent' did not appear to be impacted by pruning methods or the yield.

Cane pruning produced variable results for 'Brianna'.  In 2023 cane-pruned vines had the highest yields while in the second year, they yielded below average.  This is likely due to cane-pruned vines of 'Brianna' being overcropped in 2023, as indicated by the lower fruit brix.  While it was not quantified in this study, visually the cane-pruned 'Brianna' vines appeared to have a greater amount of cane dieback after 2023.  This over cropping may have led to the poorer performance of cane-pruned 'Brianna' vines in 2024.  Additionally, the growth habit of 'Brianna' may make yearly cane pruning a challenging practice to implement.  'Brianna' vines pruned to 3- or 5-node canes had at or above average yields in all years, making it likely a better long-term pruning practice.

For 'Marquette' cane pruning or pruning to 5-node spurs always produced yields above the plot averages, with cane pruning always being the highest yielding.  'Marquette vines pruned to 2- or 3-node spurs were always at or below average for yield.  The growth habit of 'Marquette' also appears to be more amenable to cane pruning as an annual practice, than 'Brianna' appears to be.

One point to consider is that the 'La Crescent' vines in this study were trained to a Vertical Shoot Positioning (VSP) training system, while the 'Brianna' and 'Marquette' were trained to the more common high-wire cordon (HWC) system.   Currently many growers and some production guides recommend pruning these cultivars to 2-node spurs for both training systems.  In this study spur pruning to 2-node spurs generally had a lower yield than vines pruned to longer spurs.  However, there was not a consistent trend with cane pruning.   In the HWC trained cultivars ('Brianna' and 'Marquette') cane pruning was generally above average in yields, sometimes to the determent of the vines ('Brianna' 2023), while with the VSP system, cane pruned 'La Crescent' always had below average yields.  The question remains if 'La Crescent' vines trained to the HWC, how they respond to cane pruning? 

Given the relatively homogenous fruit quality parameters between treatments of 'La Crescent' and 'Marquette', over cropping did not appear to be an issue when using pruning practices that led to a higher yield from the same number of nodes.  This could be due to the relative vigor of these plants or cultivar differences.  'Brianna' fruit chemistry in 2023 indicated that the highest yielding cane-pruned vines were likely over cropped since the fruit brix was lower than the rest of the treatments.  The 2024 'Brianna' fruit chemistry is perplexing.  Generally lower yielding vines of a similar vine size will have a higher brix, like was apparent in 2023.  But this was not the case in 2024, where the lower yield 2-node spur pruned vines also had the lowest brix.  Its unknown what may have caused this, other than it perhaps can be challenging to get a representative sample from a bin of mechanically harvested grapes.

Based on this work, we recommend that pruning 'Brianna', 'La Crescent', and 'Marquette' to 3-, 4-, or 5-node spurs is the best approach for vines with sufficient vigor, in place of the common practice of pruning to 2-node spurs.  If a grower decides that cane pruning is a viable option for their management and the vines have sufficient vigor for the crop load, 'Marquette' appears to be a good candidate for cane pruning.  'Marquette' is also known for producing many non-count shoots on old wood, so cane pruning may have additional advantages given that there are no cordons. 

Mechanical Pruning

There was not a clear trend for which pruning method (hand, mixed, or mechanical) leads to the highest yields.  In 2023 hand pruning trended towards slightly higher yields, while in 2024 mechanical pruning did.  Either way yield can also be adjusted by leaving fewer or more buds as needed by either pruning system.   There may have been a slight trend for mechanically pruned vines to have a slightly higher fruit brix.  Perhaps this could be attributed to there likely being more shoots on mechanically pruned vines and therefor more canopy to produce sugar, but generally the fruit chemistry between the three pruning systems was very similar. 

In 2023 black rot infections were present on the foliage, while in 2024 phomopsis infections were present.  No quantifiable fruit infections were present in either growing seasons, both of which had below average precipitation.  In spite of different diseases being present each year, the trends were very similar.  Pruning practice did not appear to impact the incidence of leaf diseases, but mechanical pruning trended to lead to a higher severity of infection than hand pruning, with mixed pruning being intermediate.  In 2024 shoot stem infections of phomopsis were also present, so they were quantified in addition to leaf infections.  The rationale behind adding this parameter is that the leaves will fall off the vines in the fall and therefore have a less likelihood for reinfecting the plants the following year, while shoots will persist in the canopy the following year.  Hand-pruned vines had roughly half the phomopsis infected nodes as mechanical- and mixed-pruned vines.  This is likely due to greater amount of old wood, dead wood, cluster rachises, etc. persisting and providing more inoculum in the mechanically pruned vines, given the pruning is less selective.  This may mean that mechanically pruned vines have a great risk of infections for the following year than with hand-pruned vines.  One consideration is that in both 2023 and 2024 were relatively dry growing seasons, and in a wet growing season, differences in disease may be more pronounced.

Hand and mixed pruning were accomplished more quickly in 2024 than in 2023.  This is likely due to the vines having been fully mechanically pruned prior to the implementation of the experiment.  So, it took longer to adapt the vines to hand and mixed pruning that first year.  We estimate that the 2024 hand pruning labor cost of $554 per acre is likely below average for vineyards in the Midwest.  However the speed of hand pruning these plots could also be quicker if counting of nodes was not performed.

In our plots mechanically pruned vines had two passes of the mechanical pruner, once each direction.  Our visual observation is that this is unnecessary, and the second pass removed very little additional material.  So, in practice the minutes of labor for mechanical are half those listed on Table 6.  We reflected this in Table 7 when estimating the labor costs for each pruning practice.  The labor required for mixed pruning was nearly cut in half in 2024 compared with 2023.  We conclude that the 2024 labor values for pruning are more likely accurate since in 2023 the vines were being transitioned from full mechanical pruning.

Many vineyards already own a skid steer or tractor on which a mechanical pre-pruner can be mounted on, however one must factor in the variable costs from increased use of the machinery for pruning.  Prices of pre-pruners also vary and the economic feasibility of such a purchase will vary with scale and the values individual vineyard owners assign to labor and equipment.  If we use 2024 as an example, for a 10 acre vineyard there is over a $4,200 savings annually in labor costs when moving from hand pruning to mixed pruning, and over $5,100 in labor savings when moving from hand pruning to full mechanical pruning (Table 7).  When this is extrapolated over the life of the vineyard, there are potential cost savings when factoring the additional machinery costs as well.  Additionally, the ability to complete pruning on a shorter time frame with mixed or mechanical pruning also has intrinsic benefits such as worker fatigue, availability of suitable weather dates for pruning, labor shortages, and the ability to conveniently apply products for trunk diseases at one time.

Based on this work, our suggestion is that mixed pruning will likely be the best long-term pruning option, if a grower has the scale to purchase a mechanical pre-pruner.  While quantifying the long impacts of mechanical pruning alone were not within the scope of this project, visually it is apparent that from several years of mechanical pruning alone, that soon retraining or hand labor would be needed to remove dead wood, complex arms/spurs, etc.  It's likely that the labor to do that every 3-5 years would be greater than or equivalent to with mechanical pruning annually with a hand follow up (mixed pruning).  If a grower does implement a form of mechanical pruning, there is risk of greater severity of black rot and phomopsis infections.  In this project those infections did not impact fruit quality, however with a growing season with more precipitation or a more disease prone grape cultivar, these issues may become more pronounced.