Influence of Soil Type and Climate on the Population Dynamics of Grapevine Phylloxera in Australia K.S. Powell*1,2, W.J. Slattery1, J. Deretic1, K. Herbert,2, and S. Hetherington1,2 1 Department of Primary Industries-Rutherglen, Rutherglen Research Institute, RMB 1145, Rutherglen, VIC 3685, Australia. Fax: +61 2 6030 4600 e-mail: kevin.powell@nre.vic.gov.au (*Corresponding author) 2 Cooperative Research Centre for Viticulture, PO Box 145, Glen Osmond, SA 5064, Australia Keywords: Daktulosphaira vitifoliae, Vitis vinifera, demography Abstract A comprehensive study was conducted to monitor the population dynamics and potential for spread of grapevine phylloxera Daktulosphaira vitifoliae (Fitch) in the King Valley, Rutherglen and Upton regions of NE Victoria, Australia. Field monitoring from spring to autumn, commenced in October 2000 at four commercial vineyards. Populations were monitored on grapevine roots, the soil surface, and within and above the vine canopy using a variety of destructive and non-destructive techniques. Bimodal populations were evident on vine roots with a relatively large peak in summer. Dispersive stages, mainly first instars, were also observed above ground. These were relatively low in the spring, reached a single peak during early summer and declined from mid-to late-summer. Consistent features in the phylloxera demographics at all four sites were (a) the relatively high abundance of first instars compared to other life stages (b) the relatively low abundance of alate forms (c) the occurrence of bimodal peaks in crawler abundance on vine roots and (d) between-site differences in the timing of peak crawler occurrence. Populations were influenced by temperature, rainfall distribution and soil characteristics. INTRODUCTION Grape phylloxera (Daktulosphaira vitifoliae Fitch) is regarded as the world’s worst grapevine pest. It is geographically widespread in most major grape growing regions of the world. In Australia it was first recorded in 1875 in Geelong, Victoria and is currently geographically restricted to small quarantine areas, referred to as phylloxera infested zones (PIZs), in Central and North East Victoria and New South Wales. Unlike most other major grape-producing countries Australia maintains the majority of its vineyards on ungrafted Vitis vinifera L. varieties which are highly susceptible to attack by the insect and relies on a combination of quarantine protocols and rootstocks to manage phylloxera. In Australia, phylloxera outbreaks outside quarantine boundaries in the King Valley in 1991 and Upton in early 2000 highlighted the vulnerability of the Australian viticulture industry to the insect. Few studies have been conducted in Australia to quantify the population dynamics of grapevine phylloxera across a range of viticulture sites. King and Buchanan (1986) compared the dispersal of phylloxera populations at a single Australian vineyard site and in three vineyards in New Zealand. The objectives of our study were to quantify the incidence of phylloxera under natural infestation pressure, during the growing season at four commercial vineyard sites in North-East Victoria. Phylloxera abundance and dispersal is also related to soil characteristics and weather patterns and the relationship between these factors is described. MATERIALS AND METHODS Site Details Field trials in phylloxera infested ungrafted Vitis vinifera L. were conducted in four commercial vineyards. Two sites were located in the King Valley region, NE Proc. on Phylloxera Infested Vineyards Eds: E.H. Rühl & J. Schmid Acta Hort 617, ISHS 2003 33 Victoria; site 1 was located 5 km east of Cheshunt, where phylloxera was first discovered in the vineyard in May 1997 and site 2 was located 5-6 km west of Whitfield where phylloxera was first recorded at the site in November 1991. Site 3 was located in the Upton region where phylloxera was first recorded in April 2000. Site 4 was located in the Rutherglen region where phylloxera was first discovered in 1899. Soil Classification and Analysis Soil surveys were conducted at all sites in August 1999 except site 3 where samples were taken in August 2000. Soil samples (1x10 cm diameter cores) were taken at each trial site from depths of up to 1 metre. Samples were taken at three points on a transect within each infested block. All soils were dried immediately after field sampling in a fan-forced oven at 40°C for 24 hour, rumbled through a 2mm sieve and stored in sealed bags at room temperature. Soil analyses were conducted at the State Chemistry Laboratories, Werribee, Victoria. Weather Data Weather data (rainfall, relative humidity, temperatures (air, soil and canopy), wind speed and soil moisture) was recorded over 15 minute intervals for all sites throughout the trial periods and was kindly supplied by Serve-Ag, Tasmania and local growers. Experimental Design The experimental design differed for each site. Preliminary ground surveys of each site were conducted by physical examination of infested roots and results formed the basis for the experimental design for each trial site. At each site 12 to 16 vines were selected for sampling, in 4 vine rows, throughout each vine growing season (October though to July). Ungrafted Vitis vinifera L. vines of the cultivars Sauvignon Blanc (site 1), Chardonnay (site 2), and Cabernet Sauvignon (sites 3 and 4) were selected as sample vines. Sampling Techniques Phylloxera populations were monitored from October 2000 for 9 months at all sites, with the exception of site 3, which was monitored from January 2001 onwards. 1. Estimation of Phylloxera Levels on Roots. Commencing in October 2000 phylloxera populations on infested roots were quantified by destructive sampling at all sites. Root populations in infested study blocks were monitored every four weeks by randomly removing a 1-3g sample of roots by digging around single vines adjacent to sampled vine in order to avoid disturbing phylloxera populations on vines used for trap sampling. On removal, roots were collected in sealed polythene bags. In the laboratory roots were divided into storage or fibrous components, based on root diameter, then washed in distilled water, insects were collected in a 65µm sieve and stored in 70% ethanol for microscopical examination. Once insects had been removed, root samples were ovendried at 40°C for 48 hours and weighed. 2. Emergence, Pitfall and Trunk Sampling. The seasonal abundance of first instars (crawlers) and alates (winged adults) emerging from below ground onto the soil surface, moving across the soil surface and moving up or down vine trunks was measured at all study sites using pitfall, trunk and emergence traps as described in Powell (2000). Single emergence, trunk and pitfall traps were established on each of the twelve to sixteen sample vines and collected at fortnightly intervals and replaced with fresh traps. Collected insects were counted using a low power binocular microscope. 34 RESULTS Soil Classification and Analysis Soils were classified on the basis of soil texture and chemistry (Isbell, 1996) as dystrophic brown kurosol (Site 1); mesotrophic brown chromosol (Site 2), dystrophic brown and red kandosol (Site 3) and subnatric brown sodosol (Site 4). Soil texture at all sites demonstrated a duplex nature with loam A horizons over sandy to heavy clay subsoils (Table 1). Sites 1 and 2 showed a higher clay and silt content (>66%) than at sites 3 and 4 where the A horizon contained clay and silt content of 23 and 43% respectively. Concentrations of exchangeable aluminium were highest in the surface 20cm soil layer at sites 1 and 2 and were very low at sites 3 and 4. However, concentrations of Aluminium were high below 20cm and increased with depth at sites 1 and 3 and reduced with depths at sites 2 and 4. This trend was also observed with exchangeable calcium and pH both decreased with increasing soil depth at sites 1 and 3, but remained unchanged with increasing depth at sites 2 and 4. Total soil C values were highest at sites 1 and 2, and exchangeable magnesium, sodium, nitrogen, potassium and exchangeable cation exchange capacity (ECEC) were not significantly different between sites (data not shown). Temperature Soil temperatures were the lowest at Site 2 during the November to February period compared to other sites. At Site 4 temperatures declined by an average of 6°C in March and remained low through to the end of June. The patterns were similar for ambient temperatures (data not presented). At all sites peak average soil temperatures were recorded in January and February (Table 2) coinciding with a peak in phylloxera crawler abundance recorded in emergence, trunk and pitfall traps (Table 3). Similar temperature patterns were recorded in previous seasons at Sites 1 and 2 (Powell et al., 2000). Rainfall Distribution Rainfall distribution for all sites is shown in Table 2. Total rainfall during the vine growing season (October-April) was markedly higher at Sites 2 (436 mm) and 3 (480mm) compared to site 1 (206mm) and site 4 (295mm). At all sites peak phylloxera populations emerging from the soil, moving across the soil surface or moving up the vine trunk generally coincided with months in which the lowest levels of rainfall were recorded (December to April). Similar patterns were recorded in previous seasons at sites 1 and 2 (Powell et al., 2000). Relative Humidity Relatively low humidity values (<60%) were recorded at all sites, with the exception of site 1, during the study period. These low humidity values were recorded in December and January. Phylloxera Demography Phylloxera demography was quantified on roots and proportionally first instars were consistently higher than all other life stages at all sites (data for site 2 shown in Figure 1). Alates were observed at all sites, but were recorded at higher levels at site 2 (Figure 1). Timing of peak first instar abundance on roots differed between sites. Bimodal peaks of first instar populations on roots were observed at all sites (Figure 2). In both King Valley sites the major peak was observed in January with a minor peak occurring in June and March at sites 1 and 2 respectively (data not presented). At sites 3 and 4 relatively large first instar peaks occurred in March with a secondary peak post-harvest in June. The highest density of first instars found on vine roots was at Site 1 with nearly 100 first instars per gram of root (Figure 2). The lowest root population density (2 first instars per gram (dry weight) of vine root) was observed at Site 4 (Table 3). The largest peak in 35 crawler populations on roots coincided with peaks in populations recorded in above ground traps. First instars and alates were the only life stages recorded in traps. First instars were the most abundant above-ground active stage of phylloxera located at all sites in all traps used (Table 3). DISCUSSION There are a number of factors which can influence phylloxera population dynamics under field conditions and it is important to quantify these so that management practices can be manipulated where possible to reduce the risk of both inter and intra vineyard phylloxera dispersal. Interactions between the susceptible host plant and phylloxera, phylloxera genetics and site related factors are all likely to influence the population dynamics of the insect. However, there are few published studies which examine the effect of soil and weather variables on phylloxera populations. Consistent features in the phylloxera demographics at all four sites were (a) the relatively high abundance of first instars compared to other growth stages (b) the relatively low abundance of alate forms (c) the occurrence of bimodal peaks in crawler abundance on vine roots and (d) between-site differences in the timing of peak crawler occurrence. Peak crawler populations on roots are closely associated with root phenology. Two peaks of root growth occur during the season (Freeman and Smart, 1976). Fibrous root growth commences in the spring resulting in an abundance of roots in the summer (Freeman, 1983). This coincides with an increase in crawler populations in the spring reaching a peak in summer. The secondary peak in crawler populations is likely to be associated with a secondary root flush, which occurs post harvest in the autumn. Of the four sites studied, three showed relatively high phylloxera population levels on roots and above-ground compared with the Rutherglen site (site 4). The only distinct difference between the measured chemical characteristics of the soil at site 4 was its low Aluminium exchange capacity and higher pH throughout the soil profile. High aluminium levels can reduce plant vigour through reduced root elongation, which could, in turn, weaken the vines making them more susceptible to phylloxera damage. Temperature, humidity and rainfall play a significant role in phylloxera population dynamics. Turley et al. (1996) observed that phylloxera couldn’t initiate feeding sites and develop when temperatures fall below 18°C. Soil temperatures rose above 18°C at all sites in December coinciding with an increase in phylloxera populations both above and below ground. Maximum root growth occurs between 20-30°C that coincided with the period of maximum phylloxera populations observed at all sites. However temperature fell well below 18°C from April to June yet a secondary peak in first instar development occurs on the roots. Further studies are required to determine what if any host plant-insect interactions may be involved with the production of the over-wintering stage. This is likely to be associated with the post-harvest root flush. Some authors have suggested that hot dry seasons and insufficient irrigation result in higher phylloxera populations and rapid vine decline (King and Buchanan, 1986; Helm et al., 1991). In our study, the site with the lowest rainfall (Site 1) had relatively high phylloxera root and above-ground populations compared to other sites. Whilst the sites with the coolest soil temperatures (Sites 2 and 4) throughout the season had the lowest populations. Buchanan (1990) observed that phylloxera cannot tolerate relative humidity values of <50% and suggested that low humidity could restrict the spread of phylloxera above-ground. Relative humidity did not drop below 50% in this study. However, relative humidity values of less than 55% were recorded at sites 2 and 4 coinciding with relatively low above-ground phylloxera populations. In conclusion, site conditions including climate and soil type influence phylloxera population dynamics. However, further studies are required to examine the tritrophic interactions between host plant, insect and environment in order to fully realise the potential for managing phylloxera in ungrafted vineyards. 36 ACKNOWLEDGEMENTS Research was supported by the Grape and Wine Research Development Corporation, the Phylloxera and Grape Industry Board of South Australia, the Cooperative Research Centre for Viticulture and the Victorian Department of Natural Resources and Environment. The cooperation of vineyard staff in Upton, Whitfield, Cheshunt and Rutherglen is gratefully acknowledged. Literature Cited Buchanan, G.A., 1990. The distribution, biology and control of grape phylloxera, Daktulosphaira vitifolii (Fitch), in Victoria. PhD Thesis. La Trobe University, Australia. 177 pp. Freeman, B.M., 1983. At the root of the vine. Aust. Grapegrower & Winemaker. 232, 5864. Freeman, B.M. and R.E. Smart., 1976. Research note: A root observation laboratory for studies with grapevines. Am. J. Enol.Vitic. 27 (1): 36-39. Helm, K.F., Readshaw, J.L. and Cambourne, B., 1991. The effect of drought on populations of phylloxera in Australian vineyards. Wine Ind. J. 6 (3): 194-202. Isbell, R.F., 1996. The Australian Soil Classification. CSIRO Publishing, Collingwood, Australia. King, P.D. and Buchanan. G.A., 1986. The dispersal of phylloxera crawlers and spread of phylloxera infestations in New Zealand and Australian Vineyards. Am. J. Enol.Vitic. 37 (1): 26-33. Powell, K.S., 2000. Management of Grape Phylloxera in South-east Australia Phase I and II. GWRDC Final Project Report. GWRDC/PGIBSA/DNRE, pp 171. Powell, K.S., D. Brown, R. Dunstone, S.C. Hetherington, & A. Corrie., 2000. Population dynamics of phylloxera in Australian vineyards and implications for management. In: Proceedings of the International Symposium on Grapevine Phylloxera Management, January 21st 2000, Melbourne, Australia. Powell, K.S. and J. Whiting (Eds) DNRE, Rutherglen, Australia. Turley, M., Granett, J., Omer, A.D. and DeBenedicts, J.A., 1996. Grape phylloxera (Homoptera: Phylloxeridae) temperature threshold for establishment of feeding sites and degree-day calculations. Env. Ento. 25, 842-847. 37 Tables Table 1. Soil physical and chemical characteristics from four phylloxera-infested commercial vineyards in NE Victoria Site Horizon 1 2 3 4 38 Depth (cm) A1 0-30 A2 30-40 B1 B2, 1 40-55 55-65 B2, 2 65-90 B2, 3 90-100 A1 0-20 A2 20-30 B1 30-70 B2 A1 70-100 0-13 B1 13-38 B2 B3 A1 38-60 60-100 0-12 B1 12-40 B1,1 B1,2 40-80 80> Texture % Fines pH pHAl Total C Ca (clay & silt) water CaCl2 exchange (% w/w) (meq/100g) (mg/kg) fine sandy 75 6.9 6.3 0 2.3 8.9 clay loam sandy clay 74 5.4 4.6 110 3.4 4.3 loam light clay 77 4.9 4.2 270 1.2 0.99 medium 83 4.8 4 330 0.5 1.1 clay medium 82 4.7 4 320 0.3 0.61 clay medium 82 4.7 4 330 0.3 0.22 clay fine silty 66 5.5 4.9 130 8.2 8.1 loam fine sandy 74 5.6 5 88 5.8 8.1 clay loam fine sandy 77 5.6 5 67 4.6 7.7 clay light clay 80 5.8 5.2 10 2 7.7 coarse 23 6.2 5.2 <10 2.2 3.6 sandy loam light clay 41 5.9 4.7 47 0.59 1.4 (sandy) sandy clay 46 5.3 4.4 190 0.29 0.91 sandy clay 35 5.1 4.3 280 0.16 0.26 fine sandy 43 5.8 5.2 10 0.82 4 clay loam sandy light 50 5.9 5.4 <10 0.35 4.3 clay sandy clay 48 6.2 5.7 <10 0.2 3.6 heavy clay 68 7 6.1 NA 0.22 3.9 Table 2. Mean monthly weather data in four ungrafted V. vinifera vineyards in the King Valley (Sites 1 and 2), Upton (Site 3) and Rutherglen (Site 4), Victoria in the 20002001 growing season. Data Site 1 2 3 4 1 2 3 4 1 2 3 4 Rainfall (mm) Soil temperatur e (°°C) Relative humidity (%) Oct 2000 142 68 87 79 15 12 12 13 86 57 77 53 Nov Dec 31 181 184 81 18 14 16 19 75 72 78 72 4 5 34 8 22 18 19 22 61 52 59 83 Jan 200 2 28 71 33 23 20 23 25 62 55 59 52 Feb Mar Apr May Jun 20 81 29 43 23 20 22 24 72 68 60 64 4 15 62 35 20 18 17 18 72 69 65 71 3 58 14 16 16 14 13 14 67 70 59 68 4 32 15 15 12 11 6 0 42 9 10 9 84 79 8 92 80 93 94 Table 3. Mean first instar (crawler) phylloxera collected in below and above ground during peak periods in four ungrafted V. vinifera vineyards in the King Valley (Sites 1 and 2), Upton (Site 3) and Rutherglen (Site 4), Victoria in the 2000-2001 growing season. Site 1 2 3 4 Crawlers per root (g)1 98 19 34 2 Crawlers per emergence trap2 1123 62 126 3 Crawlers per pitfall trap3 Crawlers per trunk trap (lower)2 Crawlers per trunk trap (upper)2 448 9 40 11 8 0.3 17 3 1 0.08 1 Data represents average number of crawlers collected from washed root pieces of 12 (Sites 1,2 and 4) or 16 (Site 3.) grapevines. 2 Data represents average number of crawlers caught in 12 (Sites 1, 2 and 4) or 16 traps (Site 3.) 3 Data represents average number of crawlers caught in 12 (Sites 2) or 16 traps (Site 3). Pitfall traps were not recorded at sites 1 and 3. 39 Figures Eggs Intermediate Apterous Winged Crawlers Total 30.0 25.0 20.0 Insects/g/root 15.0 10.0 5.0 Total Crawlers Winged 0.0 Oct-00 Apterous Nov-00 Dec-00 Life stage Intermediate Jan-01 Feb-01 Sample month Mar-01 Eggs Apr-01 May-01 Jun-01 Fig. 1. Relative abundance of phylloxera life stages on ungrafted Vitis vinifera roots in a commercial vineyard (Site 2) in North East Victoria during the 2000-2001 growing season 40 100.0 Crawlers/root (g) 80.0 60.0 40.0 20.0 1 0.0 OCT NOV 3 DEC JAN 2 FEB Sample date MAR APR Site 4 MAY JUN JUL Fig. 2. Relative abundance of first instar phylloxera on ungrafted Vitis vinifera roots at four vineyard sites in North East Victoria during the 2000-2001 season 41