ABSTRACTEVALUATION OF STRATEGIES FOR MANAGING SOILBORNE PATHOGENS OF ASPARAGUS IN MICHIGANByChelsea WoodsIn 2012, Michigan produced 8.8 million kg of asparagus spears for fresh market and processing worth $17.3 million. Asparagus is a perennial crop, with fields remaining profitable for 12 to 15 years. Fusarium crown and root rot (caused by Fusarium oxysporum f. sp. asparagi and F. proliferatum) and Phytophthora spear and root rot (caused by Phytophthora asparagi) contribute to early decline, and decrease the vigor of young stands in fields previously cropped with asparagus. Nine isolates of P. asparagi were tested for virulence using asparagus spears of five commercial cultivars and asparagus seedlings of three cultivars. Significant differences in isolate virulence and host susceptibility were observed on spears, but not on seedlings. Seedlings of 18 and 11 cultigens were screened for resistance to P. asparagi and Fusarium spp., respectively. While all cultigens were susceptible to the pathogens, significant differences in the degree of susceptibility were detected. Pathogen virulence varied, and the interaction between pathogen and cultigen significantly affected root rot severity. Fungicides and biocontrol agents were screened for efficacy as seed treatments against Fusarium spp. and P. asparagi in vitro. Two fungicides and one biocontrol agent increased germination of seeds inoculated with P. asparagi. Disease incidence was reduced when one biocontrol agent limited P. asparagi and Fusarium spp. growth. This is the first evaluation of modern hybrids and seed treatments for management of both Fusarium spp. and P. asparagi. Identifying resistant cultivars and effective seed treatments is important for the development of an integrated pest management system to control soilborne pathogens for Michigan asparagus growers.
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