Monitoring Spread of Grape Phylloxera by Color Infrared Aerial Photography and Ground Investigation

Transcription

1 Monitoring Spread of Grape Phylloxera by Color Infrared Aerial Photography and Ground Investigation W. E. WILDMAN ~, R. T. NAGAOKA 2, and L. A. LIDER 3 In 1977, phylloxera was discovered in five year old own-rooted Cabernet Sauvignon vines. Interpretation of aerial photos taken annually shows that phylloxera is readily distinguishable from other grapevine maladies, and that the annual rate of increase averages 255%. Projecting annual increases at this rate, all vines will be dead or unproductive in the eighth year following phylloxera discovery. However, because of the geometric increase in infestation, production may still be economical through the fifth to seventh year. Annual aerial detection and projection of the increase rate will enable vineyard managers to determine the optimum time to replant infested vineyards with vines grafted onto phylloxera resistant rootstocks. 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 compatably 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 with 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 be due to the fact that in California the insect displays a 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 1 Extension Soils Specialist, University of California, Davis, CA; 2 Viticulturist and Technical Director, Napa Valley Vineyard Co., Rutherford, CA; and 3 Professor of Viticulture, Department of Viticulture and Enology, University of California, Davis, CA The authors wish to thank Pete Schumacher, Don Johnston, and Doug Laubach of Measuronics Corporation, Great Falls, Montana for making the image analysis and providing the computer print-out illustrated in Figure 11. Presented at the 33rd Annual Meeting of the American Society of Enologists, Anaheim, California, 25 June 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 to record 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

2 84 -- MONITORING PHYLLOXERA 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 Carbernet 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 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 40cto- ber, 1978, 9 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 (81A " lens, 9" format). On 31 August 1979, 15 October 1980, and 29 August 1981 (Figs. 4-6, 8-10) 21A 21A 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 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 (Fig. 1, Block C-3). 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 Fig photo of the vineyard. Phylloxera was discovered in 1977 in Blocks B-1 and F-2. This photo led to the discovery in Block C-3.

3 MONITORING PHYLLOXERA 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 confirma, tion. 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 from, 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 :Fig t photo of the vineyard. Phylloxera outbreaks (circled) were first identified on aerial photos; later most were confirmed on the ground. Am. J. Enol. Vitic., Vol. 34, NO. 2, 1983

4 86 ~ MONITORING PHYLLOXERA Fig. 3. Aerial photo of Block B-l, infested vines had been removed in 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 waterholding 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-l, 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.

5 MONITORING PHYLLOXERA Fig. 4. Aerial photo of Block B-l, Satellite spots are barely visible. Results and Discussion 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, 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 Average annual increase factor Manual 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 Ground counts were made in 1977, 1979, 1980, and The ground counts for Block B-1 only are shown. Comparing the counts of Block B-l, 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 diffi- Table 1. Aerial photo and ground counts of phylloxera infested grapevines. Infested vines Block B-1 Blocks C-3, C-4 Aerial photo Ground count Aerial photo Computer Vine Increase Vine Increase Vine Increase Vine Increase Count Factor Count Factor Count Factor Count Factor

6 88 m MONITORING PHYLLOXERA Fig. 5. Aerial photo of Block B-l, More satellite spots appear. cult 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 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 x 3 = 955, x = 2.27 (manual). 80 x 3 = 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 x 4 = 1981 count; 67 x 4 = 963, x Projection of future phylloxera increases: In Table 2, the average increase factors developed in Table 1 are used 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 eighth year after discovery of phylloxera, Block B-1 (28 acres) will be dead or largely

7 MONITORING PHYLLOXERA Fig. 6. Aerial photo of Block B-l, Satellite spots enlarge. 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 The infestation in Block C-3, discovered one year later than that in Block B-l, shows approximately the same projection. By 1986, again the eighth 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-l, 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 be 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-l, 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 ownrooted 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

8 90- MONITORING PHYLLOXERA Fig. 7. Aerial photo of Blocks C-3 and C-4, Only 16 depressed vines caused this "bright" spot (circled) on the photo. Arrows point to oak-root fungus infestations. vineyard by farm equipment; or 4) movement of soil by erosion. The original infestion 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 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 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 spreads 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 fromthe 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

9 MONITORING PHYLLOXERA- 91 Fig. 8. Aerial photo of Blocks C-3 and C-4, Infested vines had increased to 44 around the periphery of the original spot. using chemical control were not successful in 1980 and Conclusions 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 Table 2. Projection of future spread of phylloxera using calculated annual increase factors. Block B-1 Block C-3, C-4 Aerial Photo; Ground Count; Aerial Photo" Factor 2.27 Factor 1.95 Factor 2.74 Vines % of block Vines % of block Vines % of block (130) (186) 0.9 (254) (421) 2.0 (494) (2164) 10.5 (1875) (4907) 23.7 (3651 ) (11122) 53.8 (7109) (13841) ( )indicates value was calculated using the respective average annual increase factors derived in Table (44) (120) 329 (901) (2469) (6765) (18533) (50775)

10 92 MONITORING PHYLLOXERA Fig. 9. Aerial photo of Blocks C-3 and C-4, Several satellite spots (circled) start to show up. Fig. 10. Aerial photo of Blocks C-3 and C-4, 1981, Satellite spots (circled) enlarge and increase. Oak-root fungus infestations remain much the same as in previous years.

11 MONITORING PHYLLOXERA [ --: I!1 -: :.... In II I I [ I I I1 I[ I in. 4 L evlp III Ii. f m co 108 bj z H 9e > w 8o > H 78 P C) 6e o 50 i'1 Z 4~ n, o 30 r, 20 < uj le ACRES INCREASED EACH YEAR TOTAL INFESTED ACRES 1981" 1.23 MAP B1 CORNER A AVE. CONN RD. Fig. 11. Computer generated diagram showing annual phylloxera increases from 1978 to 1981 in Block B-1. BLOCK B- 1 AERZAL PHOT0 COUNT GROUND COUNT e YEARS AFTER PHYLLOXERA DZSCOVERY Fig. 12. The exponential rate of phylloxera increase is emphasized in this graph for Block B-I. Vineyard production may still be economically feasible up to 30% unproductive vines. Symbols represent actual aerial photo and ground counts; solid lines are the future projections of the best-fit curves. 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.

12 94- MONITORING PHYLLOXERA Literature Cited 1. Buchanan, G.A. The biology, quarantine and control of grape phylloxera. Study tour report series No. 37. Dept. of Agriculture, Victoria, Australia (1979). 2. Davidson, W. M., and R. L. Nougaret. The grape phylloxera in California. U.S. Department of Agriculture Bulletin No. 903 (1921). 3. Husmann, G. C. Testing phylloxera-resistant grape stocks in the vinifera regions of the United States. U.S. Department of Agriculture Technical Bulletin No. 146 (1930). 4. Kido, H., A. N. Kasimatis, and F. L. Jensen. Grape phylloxera. In Grape Pest Management, D. L. Flaherty, Ed. University of Calif., Div. of Agric. Sci., Publication No. 4105, Berkeley (1981). 5. Nougaret, R. L., and M. H. Lapham. A study of phylloxera infestation in California as related to types of soil. U.S. Department of Agriculture Technical Bulletin No. 20 (1928). 6. Wildman, W. E., R. A. Neja, and J. K. Clark. Low-cost aerial photography for agricultural management. Calif. Agric. 30:(4)4-7 (1976). 7. Wildman, W. E. Color infrared: a valuable tool in vineyard management. Proc. Seventh Biennial Workshop on Color Aerial Photography in the Plant Sciences. American Soc. Photogrammetry, Falls Church, Va. (1979). 8. Wildman, W. E., K. W. Bowers, and R. A. Neja. Aerial photography in vineyard pest, soil and water management. In Grape Pest Management, D. L. Flaherty, Ed. Univ. of Calif., Div. of Agric. Sci., Publication No. 4105, Berkeley (1981). 9. Wildman, W. E. Detection and management of soil, irrigation, and drainage problems. In Remote Sensing for Resource Management, C. J. Johannsen, Ed. Soil Conservation Society of America, Ankeny, Iowa (1982).