Grape Phylloxera: Biology and Genetics of Rootstock Resistance and Cause of

Our understanding of phylloxera biology, damage and variation has changed appreciably over the past few years due to research partially funded by the American Vineyard Foundation. Biology: Pylloxera populations do not accumulate from year to year. Populations reach a peak midsummer and then decline until harvest after which they rise again for a second peak, falling again as the soil temperature drops below 18°C, their threshold. Populations stay low over the winter until temperature again exceeds the threshold in spring. The fall of populations midsummer begins at veraison and reaches its nadir at harvest. We hypothesized that this fall is due to competition between phylloxera and the susceptible vine for sucrose released from starch stored in the phloem parenchyma at the feeding site. This hypothesis has been supported by 1) a series of month-long population studies on roots in the vineyards, and 2) experiments in which we measured sucrose released from starch and the disappearance of starch in excised roots. In addition, our study of variability of insects in the native range indicates that there are sexual forms of phylloxera in the leaf galls of desert phylloxera on wild vines. Damage: Our population studies (above) demonstrate that the weight of all phylloxera on vine roots is very small and cannot account for the damage seen in the vineyards. However, over the last four years we have demonstrated initially in greenhouse experiments and then in the field that soilborne phytopathogenic fungi that enter feeding wounds of phylloxera can cause sufficient necrosis to account for the vineyard damage. Many fungal species are involved; the primary ones are Fusarium and Pythium. Root necrosis changes over the season and can cause as much as 25{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} root loss in one summer. The rot is minimal at the end of summer and highest in early spring. Roots of all sizes appear to be equally affected. Soil conditions influence the prevalence of the rot. Survey data suggest that the organically managed soils have less root necrosis than conventionally managed soils, though populations of phylloxera in both soils may be similar. Variation: Phylloxera populations vary genetically and in their abilities to use particular root types as hosts. Our work with biotype B and AXR#1 demonstrated this variability many years ago. Recently, we have been looking at phylloxera colonies originating on various rootstocks for evidence of increased virulence. We found populations in California, Germany and Hungary which have increased virulence on 5C and S04 when compared with phylloxera that did not come from the roots other than V. vinifera or AXR#1. The increased virulence is primarily on immature roots though there is some ability to utilize mature roots as well. Reports of damage in the field in Germany suggest that damage is due to feeding on immature roots rather than mature roots (as occurs with V. vinifera or AXR#1 in California). The virulent colonies from California and Europe appear to be genetically related. These results need further research to determine relevance with regard to stability of rootstocks.

Cultural Control of Phylloxera in Root System Conversion Treatments

Root system conversion methods were evaluated at the White Hills Vineyard near Santa Maria, Ca. This study consisted of two experiments which utilized Gewurztraminer and Chardonnay in separate locations. Root system conversion treatments included inverted side grafting using cuttings, approach grafting using rootings and an ungrafted control for Gewurztraminer. The Chardonnay experiment investigated the suitability of selected rootstocks for root system conversion using the inverted side graft and approach grafting. Freedom, Harmony, Teleki 5C, Teleki 5A, Kober 5BB, and Couderc 1613 were the rootstocks used in this experiment. Yield data were collected for Chardonnay on October 6, 1994. The Gewurztraminer experiment was harvested and yield data collected on October 13, 1994. Berry samples were collected at harvest and fruit composition determined for both experiments. Vine growth and graft union assessment data were collected for Chardonnay on January 27, 1995. Graft union assessment data for Gewurztraminer were collected on January 27, 1995. As in previous seasons, the type of rootstock used was not an important factor in the response of Chardonnay vines to rootsystem conversion. Rootstock treatment had little effect on growth, yield or fruit composition. Gewurztraminer vines displayed a positive response to root system conversion in 1994. Vines which had been converted using approach grafting or inverted side grafting produced significantly higher yield than control vines.

Cultural Control of Phylloxera in Existing Vineyards by Root System Conversion

Root system conversion methods were evaluated at the White Hills Vineyard near Santa Maria, CA during the 1993 season. The study consisted of two experiments which utilized Gewurztraminer and Chardonnay in separate locations. Root system conversion treatments included inverted side grafting using cuttings, approach grafting using rootings and an ungrafted control. The Chardonnay experiment also investigated the suitability of selected rootstocks for root system conversion. Freedom, Harmony, Teleki 5C, Teleki 5A, Kober 5BB, and Couderc 1613 rootstocks were used in these experiments. Regrafting of vines not previously successfully converted was done in February 1993. Periodic inspections of the plots were made during the growing season. Graft union formation, rootstock growth, and vine growth were assessed during these inspections. Yield data were collected for Chardonnay when the vines were harvested on September 16, 1993. Gewurztraminer vines were harvested and yield data collected on September 30, 1993. Berry samples were collected at harvest and fruit composition determined. Gewurztraminer and Chardonnay graft unions were assessed ({aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}conversion) on April 9, 1994 and June 2, 1994, respectively. Approach grafting increased the percentage conversion for Chardonnay vines. Approximately 80{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of vines have been successfully converted. For Gewurztraminer, the percentage conversion remained approximately the same. We observed that a number of rootstocks died between the 1992 and 199 3 seasons which had a negative impact on percentage conversion. Root system conversion method and rootstock had little effect on vine performance.

Cultural Control of Phylloxera in Existing Root Systems

Root system conversion methods were evaluated in small research blocks at the White Hills Vineyard near Santa Maria, CA and the Meridian Vineyard near Paso Robles, CA during the 1992 season. Larger scale commercial blocks were evaluated at the previously mentioned vineyards as well as the Douglas Vineyard near Santa Ynez, CA, the Cat Canyon Vineyard near Los Alamos, CA, and the Sierra Madre Vineyard near Santa Maria, CA. Varieties used in these experiments were Gewurztraminer (White Hills), Chardonnay (Cat Canyon, Douglas, Sierra Madre, and White Hills), Cabernet Sauvignon (Meridian) , and Syrah (Meridian). Root system conversion treatments included inverted side grafting using cuttings, approach grafting using a rooting, interplanting between existing vines using a benchgraft, and an ungrafted control. In certain experiments, the suitability of selected rootstocks for root system conversion was tested using inverted side grafting (cutting). Freedom, Harmony, Teleki 5C, Teleki 5A, Kober 5BB, and Couderc 1613 rootstocks were used in these experiments. Grafting was done in February 1992 by Ken Coates, Coates Grafting, East Wenatchee, WA. Periodic inspections of the plots were made during the growing season. The extent of graft union formation was subjectively assessed during these inspections. Data on the cost of grafting and after-grafting care in commercial scale blocks were collected by Hampton Farming Company personnel. Yield data for Gewurztraminer was collected when vines were harvested on September 9, 1992. Syrah vines were harvested and yield data collected on September 11, 1992. Harvest of Chardonnay vines occurred on September 25, 1992. Berry samples were collected at harvest and fruit composition determined. Percentage take was measured on December 2-4, 1992. Chardonnay and Gewurztraminer vines were pruned during February 1993. Approach grafting produced the highest {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} take. The percentage take obtained for inverted side grafting using cuttings was extremely low as in 1991. This method of root system conversion is not recommended for further testing. Root system conversion method and rootstock had little effect on vine performance. Economic analysis of approach grafting indicated that it would cost approximately $5,210 / acre to achieve 100{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} conversion during a 5 year period with a 76{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} initial take. This is a conservative and high estimate. Factors influencing the estimated cost of root system conversion by approach grafting were vineyard density (83 0 vines/A), the initial {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} take, and the cost of grafting which was relatively high at $3.00/vine.

Cultural Control of Phylloxera in Existing Vineyards

Root system conversion methods were evaluated at the White Hills Vineyard near Santa Maria, CA and the Meridian Vineyard near Paso Robles, CA during the 1991 season. Varieties used in these experiments were Gewurztraminer (White Hills), Chardonnay (White Hills), and Syrah (Meridian). Root system conversion treatments included inverted side grafting using a cutting, approach grafting using a rooting, chip budding on the rootstock, interplanting between existing vines with a benchgraft and an ungrafted control. In certain experiments, rootstocks were evaluated using the inverted side grafting (cutting) and chip budding on rootstock methods. Harmony, Freedom, Teleki 5C, Couderc 3309, Salt Creek, Dogridge and Richter 110 rootstocks were used in these evaluations. Grafting was done in February 1991 by Ken Coates, Coates Grafting, East Wenatchee, WA. Periodic inspections of the plots were made during the growing season. The extent of graft union formation and rooting of cuttings were subjectively assessed during these inspections. Yield data for Chardonnay and Gewurztraminer were collected when the vines were harvested on October 7, 1991. Yield data were not available for Syrah vines. Berry samples were collected at harvest and fruit composition determined. Percentage take was measured on December 9-10, 1991 for Chardonnay and Gewurztraminer and on January 16, 1992 for Syrah. Vines were pruned and prunings weighed during January and February 1992. The {aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} take obtained during the 1991 season was low for the inverted side graft (cutting) and approach graft methods. This result was probably influenced by the rootstock wood used in grafting. Little suitable rootstock wood was available during 1991. Rootstock rootings or cuttings used for the inverted side graft or approach graft should have at least 6-8″ of 1/4″ minimum diameter cane. When rootstock wood meeting this criteria was used, inverted side grafting and approach grafting were successful. Chip budding on roots was a uniform failure and cannot be recommended for further evaluation. Root system conversion methods and rootstocks had almost no effect on vine performance. Yield and pruning weight were not significantly affected by treatment at any of the locations in the study. It is likely that differences in vine performance will become evident when the “new” rootstock becomes predominant over the existing root system.