Fungicidal control of Phytophthora root rot of blueberry in a high-density bark bed planting in north Georgia, 2006

摘要

Fungicide treatments for control of Phytophthora root rot of blueberry were evaluated in newly-planted bark bed research blocks in Griffin, GA. Blueberries had been grown previously in one bed thereby increasing natural levels of Phytophthora cinnamomi, but fresh pine bark was utilized for the other bed. Treatments were applied in a randomized complete block design with four replications. Each plot consisted of four plants. Rows were spaced 4 ft apart, with 4-ft spacing between plants. Four fungicide applications were made to roughly correspond to root growth flushes in the spring and fall. Spring applications were delayed until significant leaf tissue was available for foliar fungicide uptake. Application dates were 10 Apr, 8 May, 4 Sep, and 9 Oct. An untreated check was included. Ridomil Gold was applied as a drench (0.02 fl oz per quart final solution applied to each plant), whereas AgriFos and ProPhyt (phosphonates) were applied to bushes until runoff with a backpack wand sprayer (57.5 gal/acre spray volume). Cabrio, which provides control of leaf spots but not root rots, was applied as an additional control treatment, since the phosphonates also control major leaf spots of blueberry, and Ridomil would not have been effective for these foliar diseases. Irrigation was applied to insure that the beds were wet enough for disease development. All other cultural practices were in keeping with methods commonly used in southern highbush blueberry production. For assessment of root rot severity, plants were rated visually on 10 Nov. Root segments of untreated diseased plants were plated on PARP selective media to confirm the presence of P. cinnamomi.