PLANT PATHOLOGY HORTSCIENCE 34(6):1108–1111. 1999. ing vineyards may result in reduced phyllox- era numbers and phylloxera-related damage. The purpose of this work was to determine Differences in Grape Phylloxera- whether differences in phylloxera populations or phylloxera-related damage could be attrib- related Grapevine Root Damage in uted to organic or conventional management Organically and Conventionally regimes. Materials and Methods Managed Vineyards in California Two types of long-term vineyard manage- ment regimes were compared, organic and D.W. Lotter, J. Granett, and A.D. Omer conventional. Organically managed vineyards Department of Entomology, University of California, One Shields Avenue, (OMV) chosen for study were certified by the Davis, CA 95616-8584 California Certified Organic Farmers program (Santa Cruz) and were characterized by the Additional index words. Vitis vinifera, Daktulosphaira vitifoliae, organic farming, sustain- use of cover crops and composts and no syn- able agriculture, soil suppressiveness, Trichoderma thetic fertilizers or pesticides. Vineyards that had been organically certified for at least 5 Abstract. Secondary infection of roots by fungal pathogens is a primary cause of vine years and were infested with phylloxera were damage in phylloxera-infested grapevines (Vitis vinifera L.). In summer and fall surveys selected for this study. The time threshold of 5 in 1997 and 1998, grapevine root samples were taken from organically (OMVs) and years of organic management was chosen based conventionally managed vineyards (CMVs), all of which were phylloxera-infested. In both on experiences of organic farmers, consult- years, root samples from OMVs showed significantly less root necrosis caused by fungal ants, and researchers indicating that the full pathogens than did samples from CMVs, averaging 9% in OMVs vs. 31% in CMVs. effects of management by organic methods Phylloxera populations per 100 g of root did not differ significantly between OMVs and take 3 to 5 years to develop. CMVs, although there was a trend toward higher populations in OMVs. Soil parameters, In Spring 1997, a total of four OMVs that percent organic matter, total nitrogen, nitrate, and percent sand/silt/clay also did not differ fit these criteria were found in three California significantly between the two regimes. Cultures of necrotic root tissue showed significantly wine-growing counties: Napa, Sonoma, and higher levels of the beneficial fungus Trichoderma in OMVs in 1997 but not in 1998, and Mendocino. No vineyards could be found in there were significantly higher levels of the pathogens Fusarium oxysporum and the northern San Joaquin Valley that fulfilled Cylindrocarpon sp. in CMVs in 1998 but not in 1997. Implications for further research and the criteria for OMV. Conventionally man- for viticulture are discussed. aged vineyards (CMV) infested with phyllox- era were selected in the above three counties Grape phylloxera, Daktulosphaira vitifoliae Alternative management tactics for grape plus San Joaquin County to best duplicate the (Fitch) (Hemiptera: Phylloxeridae), is one of phylloxera and phylloxera-related damage soil and climatic conditions of the chosen the most important pests of grape because it would be useful for preventing or slowing OMVs. All of the CMVs were managed with kills vines, and once in a susceptible vineyard losses and for delaying the need to replace use of synthetic fertilizers, chemical pest and cannot be controlled. Use of resistant rootstocks declining vineyards with vines grafted to re- weed control, and, with the exception of one with parentage of North American Vitis pre- sistant rootstocks. Cultural methods for con- vineyard in 1998 (CV), no cover crops. CMVs vents vineyard losses caused by phylloxera. trolling phylloxera damage would be less sub- were rejected from the study if insecticides Phylloxera remains a viticultural problem be- ject to natural selection for biotypes and would were used to control phylloxera directly. cause the rootstock technology is not used spread replanting costs over time. They could All vines were on AXR#1 rootstock except universally, and because some of the more further provide a model for controlling other for the San Joaquin County vineyards, which virulent phylloxera strains are selecting for vine root pests and diseases. were own-rooted (Table 1). Vineyards on sandy certain rootstocks, especially those with par- Soilborne pathogens enter root wounds soils were rejected because phylloxera tend tial V. vinifera parentage (Granett et al., 1996; caused by phylloxera feeding and cause a not to colonize effectively or to cause vine Kocsis et al., 1999; Walker et al., 1998). Where substantial portion of the damage associated damage in these soils (Nougaret and Lapham, phylloxera damage occurs, vine losses are with phylloxera activity (Granett et al., 1998; 1921). high. No other generally applicable control Omer et al., 1995). A number of plant patho- Two sampling cycles, early summer (15 tactics are consistently effective (e.g., Weber gens have been implicated in the damage, June–15 July) and early fall (1 Sept.–1 Oct.), et al., 1996). including Fusarium and Pythium species. Soils were carried out in each of 2 years, 1997 and suppressive to these or other plant pathogens 1998. In 1997, one OMV, sampled in summer have been described for other plants and the (VE), was lost to the study because it was suppression may be related to soil organic replanted with resistant rootstock; we chose Received for publication 27 July 1998. Accepted for matter dynamics (Drinkwater et al., 1995; Hu another vineyard (KW) to replace it. The CMV publication 21 Dec. 1998. We thank Fetzer Vine- et al., 1997a; Schneider and Huber, 1982; van roster was reduced from eight to five vine- yards (Ukiah, Calif.), Robert Mondavi Vineyards (Rutherford, Calif.), the Univ. of California Sustain- Bruggen, 1995; Voland and Epstein, 1994). yards in the Fall 1997 sampling for feasibility able Agriculture Research and Education Program, Nonquantitative reports from researchers in reasons. In 1998, two CMVs (EL and SF) from the Organic Farming Research Foundation (Santa eastern Europe have described the recovery of the 1997 sampling roster were rejected be- Cruz, Calif.) for their cooperation and financial phylloxera-infested vineyards with use of cover cause of insecticide treatments for phylloxera support, and the U.S. Dept. of Agriculture for a crops and compost amendments (Riabchun, begun in Spring 1998. A third CMV (CH) was specific cooperative agreement (Fresno, Calif.). We 1971). lost because of vineyard replanting. These also thank Dr. Sean Clark (Sustainable Agriculture In California, vineyards may be certified as three were replaced in the 1998 sampling Farming Systems Project, Univ. of California) and “organic” by following strict management roster by CV, GC, and PO vineyards (Table 1). Dr. Jenny Broome (Sustainable Agricultural Re- rules, which include use of cover crops and In the 1998 summer sampling, one new (i.e., search and Education Program, Univ. of California) for critically reviewing the manuscript. The cost of organic matter amendments and not using not sampled in 1997) OMV (ZD) was substi- publishing this paper was defrayed in part by the certain types of chemicals. Such methods may tuted for the FE in order to add to the total payment of page charges. Under postal regulations, bear a resemblance to reported characteristics number of OMVs sampled in the 2-year pe- this paper therefore must be hereby marked adver- attributed to pathogen-suppressive soils. We riod. However, despite accounts that ZD had tisement solely to indicate this fact. therefore hypothesize that organically manag- been infested with phylloxera in 1994, it was 1108 HORTSCIENCE, VOL. 34(6), OCTOBER 1999 Table 1. Phylloxera populations and root necrosis in organic vs. conventional northern California vineyards. In 1998 only, resident vegetation and cover All vineyards were on AXR no. 1 rootstock unless otherwise noted. crop aboveground biomass samples were taken Season Vineyard County Comment Necrosis (%) Phylloxeraz in March, before disking or mowing, by har- vesting three samples of 1-m2 area adjacent to Organic where roots were sampled in each vineyard. Summer 1997 FL Napa 9.2 78 Samples were dried at 60 °C for 24 h, weighed, FE Mendocino 10.5 163 JR Sonoma 11.8 442 and used to calculate spring biomass inputs VE Napa 10.1 6008 per hectare. Mean 10.4 1673 Three soil samples were collected from 0- to 0.2-m-depth root at collection sites, com- Fall 1997 FL Napa 9.0 456 ° FE Mendocino 9.7 5 bined, dried at 60 C for 24 h, and analyzed by JR Sonoma 19.1 637 the Univ. of California Division of Agricul- KW Sonoma 13.7 85 tural and Natural Resources laboratory. Per- Mean 12.9 296 cent organic matter (OM%), total Kjeldal ni- Summer 1998 FL Napa 4.6 143 trogen (TKN), ammonium nitrogen (NH4N), JR Sonoma 5.3 89 nitrate nitrogen (NO3N), and percent sand, silt, KW Sonoma Flooded winter/spring 1998y --- --- and clay were determined for each sample. Mean 5.0 116 Individual grapevine root samples, aver- Fall 1998 FL Napa 6.8 6561 aging 30 g dry weight, were taken by digging JR Sonoma 8.4 329 a hole ≈0.6 m long × 0.3 m wide × 0.2 m deep KW Sonoma Flooded winter/spring 1998y --- --- within 0.5 m of the base of each of 10 vines in ZD Napa Control (uninfested)y [2.5] [0] each vineyard and collecting exposed roots. FE Mendocino 7.5 444 Individual vines were sampled only once. In Mean 7.6 2445 1998, control samples were collected from Mean (n = 134) 9.0 a 1132 a vines not infested with phylloxera for com- SE 2.2 631 parison of percent necrosis of infested vs. Conventional uninfested roots. In the case of CMVs, a Summer 1997 VP San Joaquin Own rooted–Chenin blanc 22.0 115 noninfested part of one vineyard was used for SF Sonoma 14.9 550 control samples.