A Comparison of Six Different Compounds for Control of Leaf Spot and Seedling Blight of N.Z. Seed Oats Caused by Pyrenophora Avenae Ito & Kuribay. (Conidial State: Helminthosporium Avenae Eidam)

Abstract

Six different compounds were tested as seed disinfectants for control of leaf spot and seedling blight of oats, caused by Pyrenophora avenae Ito and Kuribay., in a heavily infected sample of New Zealand seed oats. Two of these compounds were organo-mercurial compounds, the other four were non-mercurials. This sample of oat seed was naturally infected with P. avenae and carrying mercury-resistant strains of the fungus. Mercurial compounds gave relatively good control of leaf spot and seedling blight of oats but three of the non-mercurial compounds i.e. fentin acetate with maneb, captafol and thiram, were not effective in controlling the disease. Benquinox gave good control on agar but failed to give complete control in pot tests. It also depressed the germination of seed. Pot tests were carried out on eight other samples of N.Z. seed oats from the 1967 harvest which were shown in agar plate tests to be carrying mercury-resistant strains of fungus. Results agreed well with those obtained in agar plate tests. Although, there are strains of fungus which are resistant to mercury in N.Z, seed oats, the percentage of these is low and it would appear that organo-mercurial compounds are still the best available seed disinfectants for controlling leaf spot and seedling blight.