Submitted to: International Journal of Fruit Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/3/2008
Publication Date: 11/30/2008
Citation: Smith, B.J. 2008. Cultural Practices and Chemical Treatments Affect Phytophthora Root Rot Severity of Blueberries Grown in Southern Mississippi. International Journal of Fruit Science 8:173-181. Interpretive Summary: As the acreage of blueberries has steadily increased, so has the number of plants infected with Phytophthora root rot, one of the most serious diseases of commercially grown blueberries in the southeastern United States. 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 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 is an important disease of commercial blueberries and is most severe when blueberries are grown in wet soils with poor drainage. Symptoms of Phytophthora root rot include 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. Two five year studies were initiated in south Mississippi to evaluate the effect of drainage and fungicide treatments on Phytophthora root rot severity of mature, infected rabbiteye blueberries and the effect of drainage, bed height, and fungicide treatments on disease severity of young rabbiteye and southern highbush blueberries planted into Phytophthora infested soil. Significant improvements in the first study using mature ‘Tifblue’ plants were due to the subsoil treatment and to twice a year treatments with the fungicide metalaxyl. In the second study of young ‘Tifblue’ and ‘Misty’ plants grown in a Phytophthora infested soil, there were no significant main effects due to bed height, drainage, or fungicide treatment in the height, size or percentage of living plants with either cultivar; however, there was a significant interaction between bed height and fungicide treatment. After four years, young ‘Tifblue’ plants grown in infested soil on raised beds treated with metalaxyl were taller and had a greater percentage of living plants than those grown on untreated flat beds.