Submitted to: Blueberry Research Extension North American Workers Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/4/2006
Publication Date: 6/4/2006
Citation: Smith, B.J. 2006. Effects of Cultural Practices and Chemical Treatments on Phytophthora Root Rot Severity of Blueberries Grown in Southern Mississippi. Blueberry Research Extension North American Workers Conference Proceedings. pp. 148-154. Interpretive Summary: Phytophthora root rot is a serious disease of commercially grown blueberries in the southeastern United States. As the acreage of blueberries has steadily increased, so has the number of plants infected with Phytophthora root rot. Growers are now faced with the decision of renovating infected bushes, removing infected bushes from the field and replanting new bushes in the same field, or replanting a new field. This study was initiated to help determine if drainage and chemical treatments applied to mature ‘Tifblue’ plants infected with P. cinnamomi would reduce Phytophthora root rot disease severity. The greatest increase in plant height and weight of live canes following renovation of mature infected plants was a result of twice a year treatments with the fungicide metalaxyl. The effect of drainage and raised beds on reducing disease severity was disappointing. The renovated mature ‘Tifblue’ plants receiving the subsoil treatment were taller than those in the untreated control plots two years after drainage treatments were applied and the total cane weight of plants in the subsoil treatment was greater at the end of the study than that of the plants in the tile treatment. When young blueberry plants were transplanted into a field from which Phytophthora root rot infected plants had been removed, there were no significant differences in plant height, size or percentage living plants due to drainage, bed height, or fungicide treatment among the young ‘Misty’ southern highbush plants. Drainage and bed height only had a small impact on disease of young ‘Tifblue’ rabbiteye blueberry plants as indicated by a greater percentage of living plants among those planted on raised beds and treated with metalaxyl compared to those grown on flat beds receiving no fungicide treatment. These results indicate that in soils similar to those in the Poplarville trails, blueberry growers should replant in new fields with no history of root rot rather than trying to renovate old infected blueberry plants or replanting into fields from which infected plants were removed. This information will be used by blueberry growers and extension agents as they make disease control recommendations.
Technical Abstract: Phytophthora root rot, caused by Phytophthora cinnamomi Rands, is an important disease of highbush, southern highbush and rabbiteye blueberry. Southern highbush cultivars are being grown in the southeastern U.S. for their early fruit production and reduced chilling requirement; however, as the acreage of blueberries increases, the potential threat of losses due to Phytophthora root rot also increases. Phytophthora root rot is most severe when blueberries are grown in wet soils with poor drainage. Symptoms of Phytophthora root rot are small, yellow or red leaves, lack of new growth, root necrosis, and a smaller than normal root system. Infected plants generally have fewer and poorer quality fruit than non-infected plants. This five year study was initiated to evaluate the effect of drainage and fungicide treatments on Phytophthora root rot disease severity of mature infected rabbiteye blueberries and the effect of drainage, bed height, and fungicide treatments on Phytophthora root rot disease severity of young rabbiteye and southern highbush blueberries planted into infested soil. When drainage and chemical treatments were applied to mature ‘Tifblue’ plants infected with P. cinnamomi in an effort to reduce Phytophthora root rot disease severity, the greatest increase in plant height and weight of live canes was a result of twice a year treatments with the fungicide metalaxyl. Renovated mature ‘Tifblue’ plants receiving a subsoil treatment were taller than those in the untreated control plots two years after drainage treatments were applied. There were no significant main effects due to bed height, drainage, or fungicide treatment in the height, size or percentage living plants among young ‘Tifblue’ or the ‘Misty’ plants grown in a Phytophthora infested soil for four years. There was a significant interaction between bed height and fungicide treatment. After four years growth in infested soil young ‘Tifblue’ plants grown on raised beds treated with metalaxyl were taller and had a greater percentage of living plants than plants grown on untreated flat beds.