03/02/05 Phosphorous acid in potato storage

Challenged by late blight and pink rot scientists at the University of Idaho and Washington State began working with phosphorous acid. U of I's Jeff Miller believed that phosphorous acid might prevent the spread of those potato diseases in storage. MILLER "What we found was the one location where the phosphorous acid seemed to work they had made a mistake and used it at a higher rate than was labeled. So we began looking at different higher rates than had been used in the past and then we started to see some results in our work." Miller says the phosphorous acid won't stop disease in tubers already infected in the field. But they did find that 99 percent of the potatoes exposed to extreme levels of pink rot fungi then treated with phosphorous acid on their way to storage escaped pink rot. That compared to only ten percent of the untreated spuds. Figures were very similar for late blight. MILLER "It is effective against strains of the pink rot pathogen that have been resistant to methanoxim. Methanoxim resistance is a huge problem in eastern Idaho and many growers have felt that with the change in the pathogen population to resistance they don't have any fungicide options anymore." The maker of one phosphorous acid product labels it as a post-harvest spray and Miller says about 450 thousand tons of North American potatoes were treated with that spray after last harvest last fall. Today's Idaho Ag News Bill Scott