Evaluation of Mechanical Thinning on the Yield and Quality of Mechanical and Hand Pruned Concord Grapevines © 2001

Progress Report to Viticulture Consortium and the New York Wine and Grape Foundation - 1/10/2001

Investigators:  Terry Bates, Justin Morris

Cooperators:  Rick Dunst, Gary Main, Barry Shaffer, Tom Oldridge, Bob Betts, Dawn Betts, Dave Vercant

Rationale and Justification:

Mechanical pruning of Concord grape vineyards significantly reduces pruning time and labor costs and therefore has the potential to increase profitability for juice grape producers. Typically, mechanical pruning retains more nodes per vine than hand pruning. Greater node retention can lead to a heavier crop with delayed ripening and decreased return fruitfulness because of a low and undesirable leaf area-fruit ratio. Fruit thinning, either by hand or by machine, has been used to achieve a higher and more desirable leaf area-fruit ratio, which increases the rate of fruit maturation and increases return fruitfulness. Therefore, the combination of mechanical pruning and mechanical thinning may be a powerful tool in decreasing production costs while maintaining vineyard productivity.

To determine if mechanical systems are a viable and sustainable vineyard practice, research is needed that investigates the physiological response of the grapevine to mechanical treatments. In the specific example of mechanical thinning, growers question the severity of physical damage caused by mechanical thinning and its impact on vine health. This project is directed at evaluating the response of both mechanically and hand pruned Concord grapevines to two thinning machines at two thinning speeds.

Objectives

1) Study the physiological effect of thinning on the yield and quality of hand pruned Concord grapevines.

2) Evaluate the effect of two thinning machines at two thinning speeds on the yield, quality, and return crop of machine pruned Concord grapevines.

3) Compare the yield, quality, sustainability, and economics of three mechanized production systems with traditional hand production of Concord grapevines.

4) Measure the effect of mechanical pruning and mechanical shoot positioning on the production of Geneva Double Curtain trained Concord grapevines.

Activity 1: Physiological Effect of Thinning on Concord Grapevines

Hand Thinning: At the Fredonia Vineyard Lab, a block of mature, dormant Concord grapevines were hand pruned and adjusted to 120 nodes (7 rows, 350 vines) in 1999. In three rows, 110 vines with cane pruning weights between one and three pounds were selected as count vines for the hand thinning experiment. At 27 days after bloom (7/6/99), 10 count vines were defruited by hand to estimate the full potential crop. On the remaining 100 count vines, the crop was reduced by hand thinning in 10% crop increments. The experiment consisted of 11 crop levels evenly spaced from full crop to no crop with 10 replicate vines per crop level for a total of 110 count vines.

Harvest: Individual vines were hand harvested on 9/16/99. Crop weight, juice soluble solids, and final berry weight were determined at harvest. Ripe nodes of periderm, return crop, and juice quality attributes (color, titratable acidity, pH) were measured over the winter and during the 2000 season.

Results from Activity 1: At 27 days after bloom, average berry weight was 1.4 grams. We predicted that the final average berry weight would be approximately 2.75 grams. Therefore we estimated that the berries were approximately 50% of final berry weight at 27 days after bloom. The average crop weight on defruited vines at 27 days after bloom was 20 pounds/vine, which translated into approximately 12 tons/acre potential crop at harvest.

Hand thinned vines showed an inverse yield-brix relationship between 4 and 11 tons/acre (Figure 1A). The linear slope on the 4-11 tons/acre portion of the curve was -0.5 (r² = 0.998). Removing an equivalent of two tons/acre by thinning resulted in a gain of one-degree brix in the remaining fruit at the same harvest date. This relationship was constant until a crop level of approximately 4 tons/acre. Additional hand thinning (from 4 to 1 tons/acre) did not translate into higher juice soluble solids concentrations in the remaining fruit.

There was a strong inverse linear relationship between yield & juice color and yield & ripe nodes of periderm (see 1999 progress report). Unlike the yield - brix relationship, juice color and periderm continued to go up below 4 tons/acre (Figure 1B). In conclusion, thinning an equivalent of 2 tons/acre resulted in a gain of 1 ^obrix, 42 ripe nodes of periderm, 0.10 absorbency units at 520nm, 0.04 absorbency units at 430nm, 0.05 g/berry, and 0.03 juice pH units (Figure 1A, B, and 1999 report).

The vines from the 1999 thinning experiment were all pruned to 120 nodes again in 2000 to measure the effect of the 1999 crop load on the 2000 yield. A 1999 yield of 12 to 0 tons/acre produced from 400 to over 700 ripe nodes of periderm, respectively (Figure 1A and B). When all the vines were pruned to 120 nodes, the vines that started with the greatest ripe nodes of periderm had the highest return crop in 2000 even though all vines were pruned to the same bud number (Figure 1E). Higher return crop in 2000 was a result of greater crop/node which was a result of more clusters/node and not because of greater cluster weight (Figure1C and D). Therefore, these data suggests that reducing the crop load or crop stress in year one allows the vine to ripen more buds to their maximum potential in year one. If all the vines are pruned to the same bud number in year two, the vines with the greatest population of mature buds will have the greatest yield potential in year two.

Figure 1A-F: The effect of 1999 yield on juice soluble solids, ripe nodes of periderm, and the 2000 return crop in 120 node, hand-pruned, Concord grapevines in New York.

It is also interesting to note that there is a limit to these relationships. As stated before, in 1999 there was no additional sugar benefit to reducing the crop below 4 tons/acre; however, the ripe nodes of periderm did continue to increase below 4 tons/acre. 2000 data suggests that there is also no additional return crop benefit to reducing the previous year's crop below 4 tons/acre.

In summary, 120 node vines that had 4-5 tons/acre in 1999 produced between 500 and 600 ripe nodes of periderm, set between 2 and 2.5 clusters/node, and had a return crop between 12 and 13 tons/acre. Having a greater yield in 1999 resulted in less ripe nodes of periderm, fewer clusters/node and lower return crop. Having a smaller yield in 1999 did result in greater ripe nodes of periderm but did not result in higher return crop in 2000.

This experiment was repeated in 2000 and return crop information will be recorded in 2001.

Activity 2: Machine thinning on machine pruned vines

In 2000, none of the commercial Concord vineyard plots where thinning experiments are conducted needed mechanical thinning because of mediocre fruit set. However, mechanical thinning was investigated in a commercial Niagara vineyard in 2000. All thinning was done with the Morris-Oldridge thinning unit. The treatments were: zonal thinning where the top beater bars were removed and the lower half of the canopy was thinned at a high thinning rate, full canopy thinning where all beater bars were used at the lower thinning rate, and an unthinned control. At harvest, the unthinned vines yielded 10 tons/acre and 13.5 ^obrix. Full canopy and zone thinning reduced the yield and raised the ^obrix at the rate of about 3 tons for every ^obrix (Figure 2). There did not appear to be a measurable negative effect of zonal thinning on the yield brix relationship. However, the aggressive nature of the zonal thinning removed just as many leaves from the lower half of the canopy as it did fruit. On the other hand, full canopy thinning at a moderate thinning rate appeared to be a reasonable method for crop control in Niagara vineyards.

Figure 2: The effect of mechanically thinning Niagara grapevines on Yield and Juice Soluble Solids in 2000.

Activity 3. Comparison of mechanized pruning systems

An experiment was initiated in 1999 to compare mechanical production systems on single-wire cordon trained vines.

Treatments:

In 1999, the potential crop was estimated at 30 days after bloom and the Arkansas and Minimal pruned treatments were mechanically thinned to target 11-12 tons/acre. The hand pruned and Betts treatments did not require thinning in 1999 and none of the treatments required thinning in 2000.

Results from Activity 3. In 1999, the hand pruned and Betts treatments were statistically the same in all parameters measured (Table 1). The Arkansas and minimal pruned treatments retained significantly more nodes, which greatly increased the crop potential. In 1999, those two treatments were thinned to comparable yields of the Hand and Betts treatments. At harvest, the yield ranged from 11.3 tons/acre in the Betts treatment to 12.3 tons/acre in the minimal pruned treatment; however, juice soluble solids ranged from 16.2 to 14.6 ^obrix, respectively. The hand, Betts, and Arkansas treatments adhered to the yield-brix relationship in Figure 1A (1 ton/acre » 0.5 ^obrix). The minimal pruned treatment did not follow the standard yield-brix relationship and did not meet the commercial fruit maturity standard in 1999.

In 2000, all of the treatments had similar yields and fruit maturity. Again, minimal and mechanical only treatments had significantly more retained nodes than the hand and mechanical with hand follow-up treatments. The increased node number led to greater clusters/vine but those clusters were smaller because of lower berry weight and fewer berries per cluster. Therefore, the yield of all treatments was the same without the need for crop adjustment. Hand pruning and mechanical pruning with hand follow-up were statistically similar in all measurements except for berries/cluster (Table 1).

Activity 4. Machine pruning and shoot positioning of GDC vines

An experiment was initiated in a commercial GDC vineyard in 1998 which compares two mechanized systems with hand pruning. Data collection is similar to the other mechanized pruning activity.

Results from Activity 4. In 1999, The hand pruned GDC vines had fewer retained nodes, lower yield, higher juice soluble solids, and higher ripe nodes of periderm than the two machine treatments (Table 2). Between the two machine treatments, the Vercant treatment had higher yield, similar juice soluble solids, and greater ripe nodes of periderm. These results suggest that shoot positioning machine pruned GDC vines delayed both fruit maturity (^obrix) and vegetative maturity (ripe nodes of periderm).

In 2000, the hand pruned vines again had fewer retained nodes, lower total yield (yield + yield missed by harvester), and higher soluble solids. The two machine treatments were statistically the same in all measurements taken. However, ripe nodes of periderm, the growth parameter most affected by shoot positioning, have not been measured yet.

Conclusions from 1999-2000

1) Fruit thinning of Concord grapevines at 30 days after bloom increases juice soluble solids, color, pH, and berry weight of the fruit remaining on the vine. In addition, thinning also enhances vegetative growth by maturing more nodes of periderm, which results in a higher return crop.

2) Moderate machine thinning can be an effective tool for crop control in Niagara vineyards.

3) Hand pruning and machine pruning with had follow-up were identical in 1999 and 2000. Minimal and machine pruning (alone) leaves more buds/vine and produces more clusters of smaller size. In 2000, this yield compensation mechanism allowed all treatments to have the same yield without crop adjustment.

4) Mechanical shoot positioning of machine pruned GDC Concord grapevines delayed the maturation of both the fruit and the wood in 1999. In 2000, yield and fruit maturity was identical and vegetative growth has not been measured, yet.

Table 1. Summary data from the mechanical pruning experiment at the Betts’ Vineyard.

Mean separation by Duncan's Multiple Range Test at 5% level. Significant year x pruning interactions are indicated by *'s.

Table 2. Results from mechanical pruning and shoot positioning GDC experiment.

Mean separation by Duncan's Multiple Range Test at 5% level. Significant year x pruning interactions are indicated by *'s.