Individual and Combined Effects of Flooding, Phytophthora Rot, and Metalaxyl on Asparagus Establishment. Peter G. Falloon, DSIR Crop Research, Private Bag, Christchurch, New Zealand. A. S. Greathead, R. J. Mullen, B. L. Benson, and R. G. Grogan. Cooperative Extension, Monterey County, Salinas, CA 93901; Cooperative Extension, San Joaquin County, Stockton, CA 95205; Department of Vegetable Crops, and Department of Plant Pathology, University of California-Davis, Davis 95616. Plant Dis. 75:514-518. Accepted for publication 15 November 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/PD-75-0514.

Asparagus (Asparagus officinalis) crowns (cultivar U.C. 157) were transplanted into noninfested plots or plots that had been infested with both Phytophthora megasperma var. sojae and P. cryptogea before transplanting. Immediately after transplanting, metalaxyl was sprayed over half of the infested and half of the noninfested plots at 1.12 kg a.i./ha. Plots were then flooded for 48 hr every 2, 3, 4, or 8 wk or not flooded at all. In 1984, flooding frequency was the same, but flooding duration was reduced to two 8-hr flooding periods separated by 16 hr of drainage. There was no effect of Phytophthora on asparagus establishment in 1983, but emergence was delayed and survival was reduced as flooding frequency increased. In 1984, emergence was delayed, root and crown rot was more severe, and vigor and survival were lower in infested plots. Disease severity in infested plots increased as flooding frequency increased but was reduced by metalaxyl. Metalaxyl was more effective for controlling Phytophthora rot as flooding frequency decreased. There was only a small advantage from dipping crowns in solutions of metalaxyl at concentrations of 20–200 mg a.i./L or from in-furrow applications to seedling or crown transplants at 0.07–1.12 kg a.i./ha. Thus, Phytophthora-related establishment failures can be controlled with metalaxyl, or avoided by transplanting crowns or seedling transplants, when field conditions are dry and warm.