Effect ofPhytophthora megaspermavar.sojaeon Yield ofAsparagus officinalis

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Abstract
Field plots of the asparagus cultivar U.C. 157 established in Yolo loam at Davis [California, USA] in 1978 were inoculated in 1982 with field soil containing Phytophthora megasperma var. sojae and regularly (3-to 5-mo intervals) sprayed with metalaxyl at 1.12 kg a.i. ha to control Phytophthora rot. In 1983, metalaxyl treatment was discontinued on half of the plots that had been sprayed previously, and in 1984, treatment was begun on half of the plots that had not been sprayed previously. Sprayed plots yielded between 38 and 118% more than unsprayed plots and had higher yields with larger-diameter spears in 1983. Control of Phytophthora rot with metalaxyl also resulted in earlier production in 1983 but did not affect survival of plants or vigor of summer fern growth. A significant amount of spear and or crown rot occurred below the soil surface in unsprayed plots. Losses caused by Phytophthora rot were higher during wet seasons than during dry seasons and were higher during the early part of each season when soil conditions were cool and wet. Two consecutive years of severe Phytophthora rot in unsprayed plots may induce a long-lasting and possibly permanent decrease of productivity of established asparagus.

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