Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2007
Publication Date: 1/11/2008
Citation: Bryla, D.R., Yang, W.Q., Linderman, R.G. 2008. Incidence of Phytophthora and Pythium infection and the relation to cultural conditions in commercial blueberry fields. HortScience. 43(1):260-263.
Interpretive Summary: Root rot is a major disease in blueberry throughout the U.S., with shoot symptoms ranging from pale yellow to reddish leaves and stunted growth to premature defoliation, and, in severe cases, plant death. Fifty-five commercial blueberry fields were sampled in northwest Oregon in 2001 and assessed for the presence of Phytophthora and Pythium root rot fungi. Phytophthora was detected in 24% and Pythium was detected in 85% of the fields sampled. Infection by Phytophthora, identified as P. cinnamomi, was significantly related to cultivar, with infection occurring more frequently than expected in 'Bluecrop' and 'Duke', two of the most popular cultivars grown in Oregon, and less than expected in 'Earliblue'. Incidence of Phytophthora, infection was not related to any other cultural characteristics examined, including the application of fungicides, or to field vigor. Any association of P. cinnamomi with low vigor was more likely related to localized conditions within an infected field. We noticed during sampling, for example, that weak growth usually occurred in low areas. Low lying areas often remain saturated following rain or irrigation, leading to problems with root rot. Pythium was detected in every cultivar included in the survey (11 cultivars total), but unlike P. cinnamomi, occurrence of Pythium was not related to cultivar. The percentage of fields with Pythium infection in each cultivar was simply a function of the number of fields sampled. Pythium infection was also not related to field characteristics or field vigor, nor was it related to the presence of P. cinnamomi. The results of this study provide important information on distribution and severity of Phytophthora and Pythium in the region.
Technical Abstract: Fifty-five commercial blueberry fields were sampled in northwest Oregon in 2001 and assessed for the presence of Phytophthora and Pythium root rot fungi. Phytophthora was detected in 24% and Pythium was detected in 85% of the fields sampled. The only species of Phytophthora identified in the study was P. cinnamomi. Root infection by P. cinnamomi was significantly related to cultivar, with incidence observed more frequently than expected in 'Duke' and 'Bluecrop'. Both blueberry cultivars are two of the most popular grown in the region, representing 42% of the fields in this survey and approximately 46% of the total area planted in Oregon. Two other cultivars found infected by P. cinnamomi were 'Rubel' and 'Briggitta Blue', together accounting for an additional 24% of the fields surveyed. Phytophthora was not detected in fields planted with 'Berkeley', 'Bluejay', 'Bluetta', 'Darrow', 'Earliblue', 'Elliott', and 'Powderblue', each of which represented only 2-7% of the fields surveyed. Pythium spp. were identified to genus only, but one or more species of Pythium was found in all 11 cultivars included in the survey. Occurrence of either Phytophthora or Pythium was unrelated to planting age of the fields or to cultural practices such as bed type, cover crop, mulch, irrigation system, fertilizer application, fungicide use, or the source of plant material used in the fields. Overall, most fields with Phytophthora or Pythium had similar levels of vigor as those without the pathogens and remained largely symptomless under good soil drainage conditions.