ISHS Acta Horticulturae 810: IX International Vaccinium Symposium
UTILITY OF PHOSPHONATE FUNGICIDES FOR MANAGEMENT OF PHYTOPHTHORA ROOT ROT OF BLUEBERRY |
| Authors: | P.M. Brannen, P. Harmon, D.S. NeSmith |
| Keywords: | Vaccinium corymbosum, southern highbush, phosphonate fungicide, Phytophthora cinnamomi, phosphite, phosphorous acid |
| Abstract:
Phytophthora root rot of blueberry, caused by Phytophthora cinnamomi, is a major disease of southern highbush blueberry, Vaccinium corymbosum interspecific hybrids, particularly in high-density pine bark bed systems. The industry fungicide standards for management of Phytophthora root rot had been mefenoxam (Ridomil Gold) and fosetyl-Al (Aliette). Other phosphonate fungicides had been developed, but these had not been tested on southern highbush blueberry. Therefore, tests were conducted with the foliar-applied phosphonates ProPhyt and AgriFos as compared to fosetyl-Al (2005) and drench-applied mefenoxam (2005 and 2006). ‘Millennia’ and ‘Southern Belle’ were transplanted into pine bark beds in 2005 and 2006 tests, respectively. To ensure that P. cinnamomi was present, bark beds were utilized which had previously contained blueberries, and the presence of P. cinnamomi in roots of symptomatic plants was confirmed by PCR. In both years, plant health, as measured by plant vigor and above-ground symptom development, was substantially increased by use of phosphonates and mefenoxam alike (P<0.05), and all fungicides gave statistically equivalent disease control. In a 2005 central Georgia trial, return flower bud counts were 501, 601, and 650% of the untreated control for Ridomil Gold, ProPhyt, and Aliette, respectively. In 2006 at the same location, results were similar, with return bud counts of 104, 136, and 145% of the untreated control for Ridomil Gold, ProPhyt, and AgriFos, respectively. Return bud counts were 382, 533 and 303% of the untreated control for Ridomil Gold, ProPhyt, and AgriFos treatments in a similar southern Georgia site. Based on these studies, the phosphonate fungicides ProPhyt and AgriFos provide control of Phytophthora root rot equivalent to that of either fosetyl-Al or mefenoxam. | |
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