|Abstract or Summary
- Grape phylloxera, Daktulosp/iaira vitfoliae (Fitch) development was studied under field and laboratory conditions. The aphid-like insect feeds on Vitis vinfera L. roots producing swellings that decay and lead to vine decline. The only long-term economic solution for control of grape phylloxera (GP) is to plant vines grafted onto a resistant rootstock, but over 6000 acres of Oregon's wine grapes are planted with root-susceptible V. vinfera cultivars. Ten GP infestations have been verified throughout the state since August 1990. The objective of this research was to characterize GP development and within-site distribution in Western Oregon. Grape phylloxera were collected from roots dug at two depths (15-30 cm and 30-45 cm) in three infested vineyards in the Willamette Valley during the summers of 1992 and 1993. A sieve centrifugation method was used to extract GP for counting. The number of eggs, nymphs, n/adults (late-instar), and adults per 30 grams of roots were recorded twice a month. Mean population levels were calculated for each site, sampling date and depth.
Population development of GP varied between sites and between dates sampled. Population size appeared to be directly related to soil temperature. The site with the highest overall GP populations had the warmest soil temperatures but the least above-ground symptomatic vine decline ratings. Nymphal population peaks, identified at one site, may correlate with generation time or changes in root and soil environments. Similar numbers of GP were found at both depths sampled, but higher populations were collected from vine roots sampled on the downhill side of an infestation and from
vines immediately adjacent to satellite infestations. Sticky-trunk-wraps, placed on the base of vine trunks from June to November at the three sites, collected emerging crawlers (nymphs) and winged-alates in July/August of 1993. Development of GP populations collected from each of the three sites was studied in the laboratory at five constant temperatures (7, 10, 13, 16, and 21 °C). No significant differences in development were observed between the three populations. Grape phylloxera generally did not molt past the nymphal stage at 7, 10, 13, and 16°C. The first adults appeared before day 35 at 21°C and this was followed by a significant increase in first generation eggs. In contrast to the laboratory results, eggs were first recovered from field extractions in April/May when mean soil temperatures were 10.5 to 12.0°C in 1993. Eggs were not produced from laboratory populations below 16°C. These results indicate that either the field conditions allowed GP to develop at lower temperatures or the laboratory assay did not provide sufficient time to full development. The low temperature threshold
calculated for zero development from the laboratory assay was 5°C. A degree day
accumulation, which better reflects GP field development, was estimated at 437.5 using
maximum field soil temperatures and a vine development threshold of 10°C. Further use
of degree day models may help to predict generation time of GP.