VIEW ARTICLE

Residual Dexon and the Persistent Effect of Soil Treatments for Control of Pea Root Rot Caused by Aphanomyces euteiches. J. E. Mitchell, Department of Plant Pathology, University of Wisconsin, Madison 53706; D. J. Hagedorn, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 61:978-983. Accepted for publication 16 March 1971. DOI: 10.1094/Phyto-61-978.

Plots in five Wisconsin locations were treated with Dexon [sodium-p-(dimethylamino)benzenediazosulfonate] at 30 and 15 lb. actual/acre in October 1968 and at 15 and 7.5 lb. actual/acre in May 1969. They were planted and harvested in 1969 in a manner simulating commercial pea production. Adjusted yields showed increases attributable to treatment ranging up to 550%. Yields of plots treated at 15 and 30 lb./acre in October 1968 averaged 252 and 364%, respectively, over those for control plots at three sites. The spring preplant treatments of 15 and 7.5 lb./acre increased the 1969 yield by 385 and 184%, respectively, at Arlington where root rot was most severe. In 1970, the increases due to the 15- and 30-lb./acre treatments in 1968 were 33 and 84%, respectively. The persistence of the effect of Dexon treatment for pea root rot control apparently involved both reduced pathogen populations and persistence of relatively low levels of Dexon in the treated plots. Data for residual Dexon in soil indicated a loss of 50, 70, 80, and 90% after 1, 7, 21, and 90 days, respectively. Approximately 1 µg of residual Dexon/g of soil is required to inhibit zoospore formation. This level is exceeded in treated plots which continue to show repression of pea root rot. A treatment of 30 lb./acre which would be required to provide this level of residual Dexon for more than one season would not be economically feasible.