United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Department of Plant Pathology, University of California, Davis 95616
USDA-ARS, 17053 N. Shafter Ave., Shafter, CA 93263
University of California Cooperative Extension, 1031 S. Mount Vernon Ave., Bakersfield 93307
USDA-ARS, WMRL, 9611 S. Riverbend Ave., Parlier, CA 93648
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Accepted for publication 15 May 2002.
Drip and sprinkler systems were compared for effectiveness as preplant metam sodium chemigation systems and conduciveness to late-season development of stem rot disease on potato. Sclerotia of Sclerotium rolfsii were used in a bioassay to test efficacy of metam sodium treatments. Drip application of metam sodium (532 liters/ha, 32.8% a.i.) through lines at 7 cm of depth in preformed beds (depths from bed top unless stated otherwise) killed all test sclerotia at 15-, 30-, or 46-cm depths. Drip application of the metam sodium through drip lines at 41 or 46 cm of depth resulted in 0 to 17 or 68 to 80% survival, respectively, of test sclerotia at 15 cm of depth; but all the sclerotia at 30 or 46 cm of depth were killed. Compared with the drip applications, sprinkler chemigation with metam sodium generally treated beds less effectively (8 to 100% of sclerotia survived at 15 cm, 62 to 100% at 30 or 46 cm). On flat ground, drip and sprinkler chemigation (metam sodium, 560 liters/ha) performed equally (4, 37, and 77% survival at 15-, 45-, and 75-cm depths, respectively). After potato planting and artificial soil infestation with S. rolfsii (5 to 6 weeks before harvest), subsurface drip-irrigated plots (line depth of 41 or 46 cm) had lower incidence of stem rot disease at harvest (13 to 23% on tubers) than that in sprinkler plots (56 to 62%). The low incidence of disease was associated with relatively dry surface soil. Subsurface drip chemigation with metam sodium in preformed plant beds does not consistently eradicate S. rolfsii sclerotia near the upper bed surface but, in an arid climate, it is less conducive than sprinkler irrigation to development of stem rot disease of potato.
The American Phytopathological Society, 2002