Richard T. Nagaoka
St. Helena, CA, in the heart of the Napa Valley
(I) Cornelius T. Ough and Richard T. Nagaoka. "Effect of Cluster Thinning and Vineyard Yields on Grape and Wine Composition and Wine Quality of Cabernet Sauvignon." American Journal for Enology and Viticulture, Vol. 35, No. I, pp. 30-34 (1983).(II) W. E. Wildman, Richard T. Nagaoka, and L. A. Lider. "Monitoring Spread of Grape Phylloxera by Color Infrared Aerial Photography and Ground Investigation." American Journal for Enology and Viticulture, Vol. 34, No. 2, pp. 83-94 (1983).
American Journal for Enology and Viticulture, Vol. 35, No. 1, pp. 30-34 (1983).
[Please note: Most tables have been omitted. Please contact the office if you wish to receive a complete photocopy.]
The effects of overcropping have been reported to delay maturity (9) and to reduce acidity, quality grade, vine size and wood maturity (11). It has been hypothesized that reduction in crop level could benefit the grape quality by accelerating maturity and improving wine quality. Other experiments have indicated a rather wide range of crop, in the intermediate crop level, has a relatively small effect on composition or quality of the must or wine. However, very low crops or very high crops caused adverse quality (5,7,8). Some of the obvious effects are lowered color, lowered acidity, lowered pH and lesser quality with a very high overcrop (9). In an undercropping situation, acids, nitrogen compounds and salts accumulate in the grapes, and the wines made are unbalanced in flavor (8).
In this experiment, these extremes were not investigated. The vines were cropped normally and part of the clusters thinned in the trials.
Materials and Methods
All locations were planted in 1971 and 1972; Location III was field budded. All vines were trellised on a three wire trellis system on 7 ft stakes with one wire at 45 in and two foliage support wires at the ends of a 24 in crossarm at 60 in. Vine spacing was 6 ft X 10 ft with vigorous foliar growth responding to soils up to 20 ft in depth. The vineyard was non-irrigated and produced over three and up to almost eight tons per acre during the course of the experiment.
The three cropping levels were established by cluster removal approximately two weeks after bloom: unthinned check, no clusters removed; one-third thinned, one out of three clusters removed; and tow-thirds thinned. Two out of three clusters removed.
At each location, thirty vines of each level were thinned, plus an unthinned check. Four replications were produced at each location.
° Brix, titratable acidity and pH were sampled at intervals to established harvest date. Each vine in the plot was picked and weighed separately. Approximately three pounds of fruit were selected from each vine’s weigh pan and combined for a wine lot from each thinning level and replication.
The fruit was delivered the same day to the University of California winery at Davis for crushing and production into wine lots of analysis and taste panel comparison.
Vines were thinned from 1979-1982. No yields or wines were produced in 1979 due to heavy Botrytis infections associated with rains. Data are reported for 1980, 1981, 1982.
The fruit was crushed and fermented at 21° C in polythylene containers. Each replicate was treated with 75 mg/L of SO2 , and then a yeast starter of Saccharomyces cerevisiae, Montrachet was added. Daily °Brix readings were taken. The fermenting musts were pressed at about 5° Brix and allowed to finish at 21° C. An initial juice sample was taken for must analysis. ° Brix, total acidity and pH were measured immediately. Also a sample of the juice was frozen for future analysis.
When the wines were dry, they were removed to the cellar and racked, cold stabilized and handled in the usual manner. In the early spring, the wines were tasted by a panel of experienced judges for quality scores. The methods described by Amerine and Roessler (2) were used for the quality evaluations and for the other sensory tests.
Wine and must analysis were done as described by Amerine and Ough (1). Special analysis of the amino acids were made as reported (6).
Results and Discussion
For the three years for Locations I and II, the effects of years, locations and thinning treatments were statistically analyzed for the ° Brix, total acidity and pH as shown in Table 2. Because of variable thinning results, Location III was not included. There is no question that the three years had different juice compositions. The heat treated material had significantly more sugar, a slightly higher pH and a trend to a higher acidity. The thinning resulted in significantly lower ° Brix at the same harvest date, but no significant differences in total acidity or pH.
In 1982, some further analyses were done on the juices. These are shown in Table 3. No significant differences were found in the ° Brix, total acidity, pH, free a -amino nitrogen, total nitrogen or fermentation rate (from start to press) because of thinning.; In Location I (heat treated) in the 2/3 thinned samples, the proline was greater than in the control or 1/3 thinned samples. In the other locations, the proline values were not significantly different due to thinning. The locations showed some very distinct differences in nitrogen analyses of the juices and in the resulting fermentation rates of the musts. The free a -amino nitrogen is almost three-fold greater for Location I than Location III, and the total nitrogen also shows significant difference. Clearly the fermentation times, by locations, from start to press were noticeably (and statistically) different. The a -amino nitrogen appeared to relate to this fermentation rate better than proline or total nitrogen. This is expected since the proline is essentially not assimilable by the yeast, and the total nitrogen values are greatly influenced by the proline content. Figure 1 demonstrates the relationship of the a -amino nitrogen to the fermentation. This is an extremely good relationship considering that the fruit from three vineyards and three variations of Cabernet Sauvignon were used.
Locations and years in the wine data showed considerable differences. Differences in low acidities and high pH values in 1981 at relatively low crop levels, when compared to the high crop, high acidity and low pH of 1982, are very noticeable. The generally low color in 1982 and the much better color of the 1982 Location III compared to the same year for Locations I and II are shown along with the higher phenol content for Location III in 1982. The potassium was generally lower for Location III every year. Also, Location III tends to have more enthanol. The average ºBrix for the locations for the three years were: Location I, 21.50; Location II, 20.43; and Location III, 21.37. The average ethanol values (% v/v) were 12.00, 11.65 and 12.52. The calculated percent EtOH/° Brix are 0.558, 0.570 and 0.586, respectively, for Locations I, II and III. However, a more careful evaluation was done on the 1982 samples to check for possible raisining or shriveling effects. That was done by taking the ° Brix about 18 hours after crushing and before significant fermentation had started. The ethanol/° Brix ratio for Locations I, II and III were 0.555, 0.561 and 0.573 using the juice sample from the crusher, respectively, compared to 0.532, 0.534 and 0.535 if the ethanol/° Brix was calculated on the must sample taken after the skin juice contact. This indicates the effect of increased ethanol/° Brix was due to raisins or berries which were possibly shriveled and did not release their higher sugar juice as readily.
The results of the panel quality scores are given in Table 5. The wines were tasted by the same general group of experienced tasters each year, and the analysis of variance was done each year in an identical manner. The effect of thinning was mixed. The first year, the check was judged the better vine, but not significantly different from the 2/3 thinned. The level of significance was only 5%. In 1981 and 1982, the quality judgments were in favor of 1/3 and 2/3 thinned over the control. The score differences were small, but very highly (0.1%) significant. The vineyard locations had distinct effects on the wine quality. In 1980, Locations I and III were significantly preferred over Location II; in 1981 and 1982, Location III was significantly preferred over Locations I and II; and the latter two were judged similar in quality.
The aroma intensities of the samples were investigated for the 1982 experiments. The tasters were asked to smell each sample and rate the intensity of the aroma from 1 to 10 and then to describe the aroma. A number of replications were done. A choice of commonly used terms for Cabernet Sauvignon aroma were furnished. Table 6 gives an abbreviated analysis of variance showing the critical values and the average values associated with each location. As can be seen, the thinning treatment had little or no effect on the aroma intensity as perceived. The types of aroma were different from each of the locations. The values assigned showed the most intense aroma was associated with Location I and the least intense with Location III.
The variation in terminology used was fairly extensive, but the most common terms used were "weedy" and "minty." The "weedy" term was most often associated with Location I and the "minty" with Location III. Location II seemed to be a combination of these odors. The most used equivalent terms are given in Table 7. Also, this table gives the number of times one experienced taster assigned the terms "weedy", "minty-weedy" and "minty" to the wines from the three locations. The Chi² value was highly significant, indicating that this taster could recognize a real difference between the wines from the three locations by quality of the aroma. Some of the less experienced tasters tended to be confused and use many different terms for the same wine sample when triplicated. The more experienced tasters were generally more consistent in their judgements.
Whether these small sensory differences, due to thinning, are worth the loss of 1/5 to 1/3 the crop is a moot question not answerable by this report. However, some consideration must be made to the fairness of payment. What is more noticeable, and certainly worthy of more follow-up, is the effect of location on quality. Generally, the crop from Location III was equal to or greater than that from Locations I and II, yet consistently received better scores. Whether this is due to soil, location, clone or rootstock effect, it is impossible to tell from these experiments. Carbonneau, et al. (4) have recommended, for Bordeaux in years of large crops, to thin bunches by 50% to removes leaves in the area of the bunches at véraison and to summer prune to leave about five feet of foliage. While this is for France, they did find that these factors gave better wine both in composition and quality.
Thinning of the clusters had a minimal effect on ripening time, must analysis, wine analysis, and wine aroma. There was a small, but significant, increase in wine quality due to thinning.
Location (as differentiated by rootstock and virus status) has a considerable effect on composition of the fruit, fermentation rate, composition of the wine, intensity and quality of the aroma, and an effect on general wine quality.
The quality gain due to thinning is a factor which should be weighed carefully by the winery and the grower against the losses in tonnage in these mid-crop level areas.
American Journal for Enology and Viticulture, Vol. 34, No. 2, pp. 83-94 (1983).
The grape phylloxera, Phylloxera vitifolia (Fitch), commonly known as the grape
root-louse, is found native on the wild species of Vitis in North America east of
the Rocky Mountains. It exists compatibly on these wild vines as a leaf-gall forming
insect. A century ago when the insect was taken to plantings of the European grape, Vitis
vinifera, the root infesting form dominated, massive root destruction occurred and
vine death resulted.
Materials and Methods
Aerial photography: In late summer of 1978, it was decided that annual aerial
photography would be helpful for monitoring the spread of phylloxera and directing ground
confirmation. About 70 infested vines had already been removed from one location on the
east side of the vineyard (Fig. 1, Block B-1). The second location, on the west side of
the vineyard, (Fig. 1, Block F-2) consisted of a somewhat fewer number of infested vines.
On 4 October, 1978, 9 X 9 inch color (Kodak 2448 film) and color infrared (Kodak 2443
film) photos were taken of the entire vineyard by U.S. Forest Service photographer Jule
Caylor (Fig. 1), using a Zeiss RMK A 21/23 aerial camera (8 1/4" lens, 9"
format). On 31 August 1979, 15 October 1980, and 29 August 1981 (Figs. 4-6, 8-10) 2 1/4 X
2 1/4 inch color infrared (Kodak 2443 film) photos were made by the senior author using a
Maurer P-2 camera with 76 mm lens. These photos were of individual blocks and were of a
scale and quality comparable to the 1978 9 X 9 inch photos.
Aerial photo interpretation: Interpretation of aerial photos was largely accomplished by studying individual photos with magnification on a light table. Stereo pairs were not available for all years and were not found to be helpful even when available. Aside from knowing the locations of the 1978 infestations and general confirmation of satellite outbreaks, vine counts were made from the aerial photos independently of the ground confirmation. It was assumed in 1978 that the spread of phylloxera would be outward into vines adjacent to known centers of infestation. Thus, in 1978 and 1979 only the dead or depressed vines in or immediately adjacent to the two test locations (B-1 and C-3) were counted. By 1980, however, a new and unexpected pattern was emerging. While each original infestation did increase in size by the degeneration of vines around its periphery, the most striking feature was the development of new satellite outbreaks near, but completely separated form, the original. The satellite outbreaks appeared on an aerial photo first as light colored spots showing more soil and less vine foliage than in normal areas. On close examination of the photo, vines in these spots were usually still living, but had not produced any long shoots. Thus each vine appeared to be only a pinpoint of red foliage (on the color infrared photo) that was readily distinguishable from its neighbors because of the bare soil surrounding it. This stunted vine condition is similar to the "cabbage head" appearance of head trained vines described by Davidson and Nougaret (2). It is interesting to note that in their survey of phylloxera infestations in Fresno and Tulare Counties between 1915 and 1920, Nougaret and Lapham (5) found this "cabbage head" appearance to be so characteristic of infested vines, that they did most of their phylloxera mapping by observing this condition rather than by inspecting the grapevine roots. In similar fashion, the stunted cordoned vines are quite distinctive on a color infrared photo, and with experience, a photo interpreter should be able to recognize phylloxera and monitor its spread with only an occasional ground check.
Differentiation from other vine maladies: In this vineyard at least, phylloxera
damage to vines is readily distinguishable on aerial photos from any other vine malady
both by its rapid rate of increase and by the form of new outbreaks. It can be
distinguished from oak-root fungus, Armillaria mellea, if annual photos for three
or more consecutive years are available. Oak-root fungus does not spread so rapidly and
does not establish satellite colonies. This is evident when two oak-root fungus
infestations (Fig. 7) are compared with the same infestations photographed three years
later (Fig. 10). Even with a single years photo, phylloxera could probably be
inferred from a round or oval "bright" soil area containing stunted vines
appearing as individual pinpoints of foliage on the photo. Pierces Disease, found
nearby but not in this vineyard, has an entirely different pattern on an aerial photo,
showing a more random scatter of infected vines with a higher proportion of those adjacent
to riparian refuges affected. Two soil problems affect the vineyard under study. The
strips of light colored vines (Fig.1) are caused by gravelly soils with low water holding
capacity. These become most evident in the fall and affect a constant area from year to
year. These strips are particularly evident in Blocks C-1, C-2, C-3, and B-2 (Figs. 1, 2).
In Block A-1 dark colored clay soils with a water table near the surface caused premature
vine defoliation in 1978 (Fig. 1). In 1979, drainage lines were installed and vine growth
has improved since then.
Ground confirmation: Ground confirmation of a suspect area was made by examination of roots to identify either adult or nymphal phylloxera in the fall following photographic survey. Inspections were made on vines with depressed foliar growth, using a shovel or tractor mounted backhoe. No attempt was made to examine the roots of all vines appearing healthy around a confirmed phylloxera location, but all those checked had phylloxera present.
Computer analysis: An alternative to manual aerial photo interpretation makes use of a density slicer and computer. An aerial photograph may be divided into 256 shades of gray. One or a combination of a few gray shades may characteristically identify phylloxera. The 1978 through 1981 photos of Block B-1 were analyzed by video digitizing equipment manufactured by Measuronics Corporation.
Annual increases of phylloxera: Figure 2 shows the entire vineyard in 1981 in
comparison with the 1978 photo in Figure 1. Figures 3, 4, 5, and 6 are large scale photos
of Block B-1 in 1978. 1979, 1980, 1981. Figures 7, 8, 9, and 10 are the corresponding
photos for Blocks C-3 and C-4. Both sets of photos show the dramatic annual increase of
phylloxera. Figure 11 is a computer-generated diagram of part of Block B-1 that emphasizes
the annual increase and the pattern of the infestation. Table 1 lists the numbers of
grapevines judged to be infested with phylloxera at the two locations, Block B-1 and
Blocks C-3/C-4. Manual and computer counts were made from the aerial photos for each of
the years 1978, 1979, 1980, and 1981. Ground counts were made in 1977, 1979, 1980, and
1981. The ground counts for Block B-1 only are shown.
For the ground counts, there is a four year spread between the first and last counts, so the first year count would be multiplied by an additional x:
Projection of future phylloxera increases: In Table 2, the average increase factors developed in Table 1 are sued to project the numbers of infested vines and percentages of the blocks over the total period from the first year of phylloxerated vine counts to a future year in which complete infestation will prevail. The table predicts that by 1985, the eight year after discovery of phylloxera, Block B-1 (28 acres) will be dead or largely unproductive. However, since the increase is exponential, 90% of the increase is predicted to occur during the last three to four years. This relationship is emphasized in the graph in Figure 12. Depending on market prices and productivity of the vines not interpreted as infested, Block B-1 may be economical to harvest through 1982, 1983, or even 1984. The infestation in Block C-3, discovered one year later than that in Block B-1, shows approximately the same projection. By 1986, again the eight year following discovery of the outbreak, the predicted acreage of dead or unproductive vines is 70 acres, or 90% of the acreage of Blocks C-3 and C-4 from which the 1981 vine counts were made. Again, these blocks may be economical to keep in production through 1985, the seventh year following discovery of the outbreak. From these projections, it appears that under these conditions a vineyard manager has about five years from the time he discovers a phylloxera outbreak to plan and schedule removal of the stricken vines and order new vines on resistant rootstocks.
Nature of spread of infestation: Figure 2 is the 1981 photo of the entire Cabernet Sauvignon portion of the vineyard. Blocks A-1, A-2, and A-3 were planted on a resistant rootstock and are not experiencing phylloxera outbreaks. In addition, the easternmost 10 vines in each row in Blocks B-1 and C-1 were on rootstocks, based on the assumption that those vines would somehow block the entrance of phylloxera from neighboring vineyards. All of sub-blocks under B, C, and F are own-rooted vines, and the various satellite outbreaks that are suspected from the aerial photography to the phylloxera infestations are circled. Most of these suspicious areas were checked on the ground, and phylloxera was present on the vine roots. Every block, with the possible exception of F-1, has one or more confirmed phylloxera infestations. Three or four suspicious areas in Block F-1 did not enlarge significantly from 1978 to 1981 and may, therefore, be caused by oak-root fungus. The random nature of the outbreaks in the remaining blocks leads us to predict that all own-rooted blocks will undergo massive phylloxera infestations and will need to be replaced within the next five to seven years.
Manner of phylloxera spreading: Phylloxera does occasionally develop winged
forms in California, but these are thought to be incapable of causing new infestations.
Other possible methods of spreading phylloxera are: 1) introduction of infested rooted
vines; 2) Infection of new vine roots by "wanderers" which travel over the soil
surface or through soil cracks; 3) contamination by soil brought into the vineyard or
moved about in the vineyard by farm equipment; or 4) movement of soil by erosion.
The Grape Pest Management Manual (4) states, "Experience has shown that
phylloxera will eventually reach every vineyard in an infested district despite heroic
preventative efforts." This statement has certainly been true of the north coastal
grape growing counties. These areas are almost 100% infested, and the few own-rooted
vineyards that have been planted there in recent years have all developed phylloxera
infestations (1). In other parts of the state, vast new plantings of own-rooted vines have
been made in the last 20 years. It is estimated that 75% of the vines in the state are on
own roots, and the figure exceeds 95% for plantings in the new districts of the central
and south coast, Sierra foothills, and Lake County (A.N. Kasimatis, personal
communication). Thousands of acres of own-rooted vines have also been planted in the San
Joaquin and Sacramento Valleys in recent years. These new plantings represent a wide
variety of soils, some of them surely susceptible to the rapid spread of
seems only a matter of time until the accidental introduction of contaminated roots, soil,
or vineyard equipment creates infestations in these hitherto phylloxera free areas.
©1999 by The Grape Doctor, Richard T. Nagaoka,