Richard T. Nagaoka             
Viticultural Consultant
St. Helena, CA, in the heart of the Napa Valley

The following research articles by Richard Nagaoka appear below:

(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).

(I)  C.S. OUGH AND RICHARD 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. 1, pp. 30-34 (1983).

[Please note: Most tables have been omitted.  Please contact the office if you wish to receive a complete photocopy.]

Abstract:  Cabernet Sauvignon vines grown in three locations at Rutherford, Napa Valley, were thinned at three levels for three years. Composition differences in the musts and wines were small due to thinning. Differences in the composition due to locations were more pronounced. The quality of the wine was slightly increased by thinning in two of the three years. The location had also a generally consistent effect on quality which could be related to composition changes. Fermentation characteristics could be related to locations, but not thinning. The aroma quality and intensity was demonstrably different between locations, but not related to thinning.

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
Three crop thinning levels were imposed on a mature Cabernet Sauvignon vineyard near Rutherford, Napa Valley, California. A randomized, complete block design was employed at three locations to address different rootstocks, soils and virus conditions. The locations are summarized below:

[table omitted]

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
The thinning treatment effectiveness is shown in Table 1. The thinning effects on the crop reduction were never quite as complete as intended. Part of this is due to the vines’ self-compensation. After thinning, the clusters remaining probably weigh more and the berries may be larger. By removal of 2/3 of the clusters after bloom, the crop is only reduced by about 1/3. Reducing the number of clusters by 1/3 only reduces the crop by about 1/5. In all cases, a significant crop reduction was achieved compared to the control except in Location III in 1980. In 1982, Locations III, the 1/3 and 2/3 thinning treatments were both done accidentally at the 2/3 level. The levels of thinning would have had sufficient effect to cause an economic impact on the yields of the vineyard.

[tables omitted]

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.

[table omitted]

The wines from these various locations, treatments and years were analyzed. The analyses (Table 4) were all carried out within four months of making the wines. None of the wines had undergone examinations were completed. The thinning treatment had relatively little effect on the wine analyses. Only three of the analyses showed any significant effects: 1) 1980, Location I had a significant decrease in pH due to thinning. This was also a trend in the other locations for 1980 and for 1981, but not 1982. Other work has shown that pH tends to decrease with increasing crop load (8). 2) 1980, Location I showed a decrease in ethanol with thinning. This was also a trend in the other 1980 locations and in 1981, but not in 1982. 3) 1980, Location II showed a significant decrease with thinning in the phenol content of the wines. Again, trends in other locations in 1980 and 1981 were similar. In 1982, the trends were reversed. There were no significant effects due to thinning in the total acidity, color at 420 or 520 nm or in the potassium, although the trends were much the same for the color and potassium as described or the phenols.

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.

[table omitted]

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.

[table omitted]

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.

[table omitted]

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.

[table omitted]

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.

Literature Cited

  1. Amerine, M.A., and C.S. Ough. Methods for Analysis of Musts and Wines. 341 p., J. Wiley, New York (1980).
  2. Amerine, M.A., and E.B. Roessler. Wines, Their Sensory Evaluation. 230 p., Freeman, San Francisco (1976).
  3. Antcliff, A.J., W.J. Webster, and P. May. Studies on the Sultana grape. VII. Comparison of crop regulation by pruning with regulation by debunching. Austral. J. Agric. Res. 12:69-76 (1960).
  4. Carbonneau, A., P. Leclair, P. Dumartin, J. Cordeau, and C. Roussel. Etude de I’influence chez la vigne du rapport partie vegative/partie productrice sur la production et al qualite des raisins. Connaiss. Vigne Vin 11: 105-30 (1997).
  5. Cordner, C. W., and C.S. Ough. Prediction of panel preference for Zinfandel wine from analytical data using differences in crop level to affect must, wine and headspace composition. Am. J. Enol. Vitic. 29:254-7 (1978).
  6. Crowell, E.A., C.S. Ough, and A. Bakalinsky. Determination of primary amine nitrogen in mussts and wines. Submitted Am. J. Enol. Vitic. (1983).
  7. Kasimatis, A.N., E.P. Vilas, Jr., C.S. Ough, and C.A. Heringer. Cropping level of Zinfandel grapevines adjusted by pruning severity and deshooting. Proceedings, Am. Soc. Enologists, 30th Annual Meeting, Las Vegas, Nevada, June, 1979.
  8. Sinton, T.H., C.S. Ough, J.J. Kissler, and A. N. Kasimatis. Grape juice indicators for prediction of potential wine quality. I. Relationships between crop level, juice and wine composition, and wine sensory ratings and scores. Am. J. Enol. Vitic. 29: 267-71 (1978).
  9. Weaver, R.J., M.A. Amerine, and A.J. Winkler. Preliminary report on effect of level of crop on development of color in certain red wine grapes. Am. J. Enol. 4:157-66 (1957).
  10. Winkler, A.J. Effects of overcropping. Amer. J. Enol. 5:4-12 (1954).
  11. Winkler, A.J., J.A. Cook, W.M. Kliewer, and L.A. Lider. General Viticulture. 710p., Univ. of Calif. Press, Berkeley (1974).

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(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).

    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.
    The insect was reported on cultivated vines in California as far back as 1858 (2). Infestations rapidly spread through vineyards of Napa and Sonoma Counties and ultimately to most of the grape growing districts of the state. It is estimated that 20% of California’s total grape growing area is infested phylloxera, and this figure is increasing slowly (4). The use of phylloxera resistant rootstocks is the final solution to reestablishing vines in these infested districts (3).
    It was noted early, however, that the rate of movement of the insect population through infested vineyards in California was much slower than that found in European plantings. This phenomenon was eventually shown to simplified life-cycle. The winged migrant, a part of the sexual cycle in the insects’ development, is not believed to be fertile under California dry-summer conditions (2). Thus, the primary means of introduction into a vineyard was by man’s transporting of the insects on infested vine rootings and on farm equipment. Once established, an important additional means of spread of the insect was by the migration of newly hatched larvae outward from an infested site. Population pressure causes these larvae to seek uninfested roots by wandering on and through the soil during summer and autumn.
    The severity of phylloxera infestation is partially related to the type of soil on which the vineyard is planted. Nougaret and Lapham (5) pointed out that wandering larvae are severely restricted in movement through sandy soils that produce little or no subsurface cracking. In their surveys during the 1920’s, phylloxera infestations were not generally found on the deep sandy loam soils of Fresno and Tulare Counties, but were found particularly on soils underlain by hardpan. Though detailed studies have not been made to correlate phylloxera infestations with soil types in the coastal valleys of California, experience has shown that the most severe infestations have occurred on clay loam and clay vineyard sites.
    This study was undertaken the rate and manner of phylloxera spread in a mature own-rooted Cabernet Sauvignon vineyard on the floor of the Napa Valley. The soils are medium to fine textured and are similar to other soils in the valley that are known to readily support the migratory activities of phylloxera larvae. The original objective of the study was to test the use of aerial photography as the principal means for monitoring the rate of spread of known phylloxera infestations. As the study progressed, it became clear that aerial photography provided the earliest and easiest means of detecting new infestations that were separated from known ones. Ground confirmation is, of course, essential in both cases.
    Aerial photography, particularly combined with the use of color infrared film, is rapidly gaining recognition as a useful tool for detecting plant growth problems and contributing to improved management of many crops (6,9). Color infrared aerial photography can be particularly useful for annual monitoring of permanent crops, including vineyards (7,8). Aerial photography does not eliminate the need for other methods of diagnosis, but can often be an early warning system for a plant problem and then serve as the primary means of detecting the spread of the problem once the typical pattern is established in an area.

Materials and Methods
    In 1977, a large vineyard east of the Napa River near Rutherford, California was found to have two small infestations of phylloxera, one near the river on the west side, the other near a highway on the east side. Discovery of these isolated outbreaks near the edges of the vineyard suggests that phylloxera was entering from adjacent vineyards. The vineyard had been planted primarily from 1971 to 1973 on land that historically had been planted to pasture. The soils are primarily Yolo loam, Pleasanton loam, Cole silt loam, and Clear Lake clay. Some strips of Cortina very gravelly loam cut across the other soils. The soils were pre-plant fumigated using 3300 pounds per acre of carbon bisulfide. Weighing the risk of phylloxera infection against delays due to shortages of rootstock, the vineyard was planted mainly on its own roots. A portion of the vineyard was planted to St. George rootstock and field budded to Cabernet Sauvignon, and the balance planted to rooted cuttings of the same variety. Field run wood was selected from local vineyards and grown in a commercial nursery in fumigated soil. The plants were inspected and certified to be free of injurious pests. The vineyard is spaced 6 ft X 10 ft with wire trellis and rows running east to west. Irrigation can be provided by overhead sprinklers.

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.
    While reviewing the 9 X 9 inch aerial photos in October 1978, the viticulturist for the vineyard noticed a suspicious looking spot of diminished vine growth that had not been observed on the ground. Examination of roots in that location confirmed the presence of phylloxera in an interior location of the vineyard. Blocks B-1 and C-3/C-4 were selected for aerial photo study of the spread of phylloxera in 1978, 1979, 1980, and 1981.

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 year’s 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. Pierce’s 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.
    Vine counts were made from aerial photos of those vines thought to be infested with phylloxera for each year from 1978 to 1981 (Table 1). Vines in the known phylloxera locations were counted as infected if: 1) the vine was removed; 2) the vine showed only a pinpoint of foliage; 3) the vine was on the periphery of a known phylloxera location and was judged to have half or less the normal amount of foliage.

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.
    Comparing the counts of Block B-1, some discrepancies are apparent during some years among the three counting methods. The manual aerial photo count was low in 1980 largely due to the seasonal lateness of the photography. Long shadows interfered and it was difficult to judge whether vines were yellow due to phylloxera or to natural senescence. The count was, therefore, conservative. For phylloxera counts, it would be desirable to take aerial photography near sun noon before 1 September to minimize shadows and reduce the confusing effect of dry and partly defoliated vines.
    To obtain the greatest detail for illustrative effect, the computer count did not record some outlying spots in 1980 and 1981 north and west of the main infestation in Block B-1. It is estimated that the computer counts would be about 10% higher for 1980 and 1981 if these spots had been included.
    The annual increase in phylloxerated vines for each year is obtained by dividing the number of phylloxerated vines counted in that year by the number counted in the previous year. As seen in Table 1, there is considerable variation in rate from year to year. This is undoubtedly because the insect population buildup is not uniform from year to year. For purposes of making a projection into the future, one would like to have an average annual increase rate. However, a simple average of the annual rates overestimates the average annual increase. The method of calculation used to obtain the average annual increase factor shown in Table 1 smooths out the year to year variations and provides a more accurate factor to use in the future projections of phylloxera infestations. It assumes a constant rate of annual increase and calculates this rate from the first and last year counts. The calculation is as follows:

Assume that x = average annual increase.
For the aerial photo counts:

1978 count × x × x × x = 1981 count.

Substituting first and last counts:

83 x3 = 955, x = 2.27 (manual).

80 x3 = 893, x = 2.23 (computer).

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:

1977 count × x4 = 1981 count; 67 x4 = 963, x = 1.95.

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-original infestation in Block B-1 could have started from infected rootstocks in the 10 vine buffer planted along the east edge of the block. Or it and the widely separated infestations in all blocks could have originated from contamination of the rooted cuttings, followed by varying rates of insect population buildup since 1972.
    Wanderers probably do not travel more than one or two vines in any one year away from their original habitat (2). Therefore, the spread due to wanderers would appear to be on the periphery of an existing infestation, causing more or less concentric increases in its size. Many satellite outbreaks observed in the present study appear to be associated with the original infestations and are likely the result of new infestations by wanderers. However, there are several outlying new spots that are many vines or many rows away from any other infestation. These appear to be too far away to be accounted for by wanderers.
    Spreading of phylloxera by farm equipment may have been a factor in some of the outlying infestations. This mode could certainly account for outbreaks several vines away from the original infestation. However, if this were the primary method of spreading, one would expect the largest amount of spreading to occur to the west of the nine rows of Block B-1 that were infested in 1978, and to both the east and west of the three rows of Block C-3 that showed infestation in 1978. Neither location shows a pattern of this sort. The spread in Block B-1 is predominantly across the rows in a northerly direction, while that in Block C-3 is northerly and northeasterly. So far, there do not seem to be any differences in the rate of spread among the different soils represented. If any significant differences occur, they should become more obvious as phylloxera spread throughout the vineyard.
    Regardless of the manner in which the insect has spread, there is a strong indication that it takes more than one year for a new infestation to build up a population large enough that the vines become visibly depressed. The implication is that by the time some vines are showing visible symptoms of phylloxera, the insect is already widely established on apparently healthy vines at locations some distance away from the recognized infestation. This effect would render useless any attempt to control phylloxera by removing only infested vines and treating the soil to kill the insect at that location. Attempts to halt the spread of phylloxera in this planting using chemical control were not successful in 1980 and 1981.


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 phylloxera. It 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.
    Whether or not a highly effective chemical control of phylloxera is discovered, early detection by color infrared aerial photography could significantly lessen the economic and management impacts of a phylloxera infestation. If a control is discovered, early detection would be essential to containment of the insect in a small area. Meanwhile, the primary defense against phylloxera remains the planting of vines on resistant rootstocks. Early detection of phylloxera in individual vineyards can provide the vineyard manager with a few years lead time in which to schedule replanting of phylloxerated blocks.

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