CHARACTERIZATION OF OPHIOMYIA SIMPLEX (DIPTERA: AGROMYZIDAE) ACTIVITY IN COMMERCIAL ASPARAGUS FIELDS AND ITS ASSOCIATION WITH FUSARIUM CROWN AND ROOT ROT

Fusarium crown and root rot, (Fusarium oxysporum f. sp. asparagi, F. proliferatum) has been implicated in the decline problems in production areas of asparagus. Pathogenic strains of both Fusarium spp. have been associated with Ophiomyia simplex (asparagus miner). The effects of asparagus stand maturity and harvest end dates on populations of and damage from O. simplex were examined. Commercial fields of various ages were sampled weekly in 2001 and 2002 for miner activity by trapping for adults and monitoring above-ground stem damage. Puparia and mined tissue were collected at the end of the season and were placed on media to detect the presence of Fusarium spp. Two peaks in adult activity were observed with the highest numbers of adult flies trapped in early to mid-Aug across all fields. Trap placement with consideration for the height of the canopy, was the key to our ability to record the second peak in activity. Mining damage was greatest in fields with a short harvest period and Fusarium was observed sporulating on up to 30% of the mined stems in those fields. At season end, there was no significant difference among the fields in number of puparia per stem (3-6). However, significantly more adults emerged during the season in fields with a short harvest period, than in older fields with a longer harvest period. Fifteen % and 3% of puparia from above-ground mines were infested with F. proliferatum and F. oxysporum, respectively while 11% and 17% of puparia from below ground mines were associated with F. proliferatum and F. oxysporum, respectively. Forty-four % and 4% of stem tissue pieces from above-ground mines were colonized by F. proliferatum and F. oxysporum, respectively. It is not known how significant the sporulation of Fusarium spp. on above-ground mines is to the overall spread of pathogen inoculum, but it appears that young fields with short harvest intervals are more vulnerable to mining damage and prolonged exposure to infection by Fusarium.