Protection of sugar beet seed plants against Phoma betae (Frank). Part I. Effect on seed health and quality.
In an attempt to reduce infection of sugarbeet seeds by P. betae [Pleospora betae], field trials were conducted on IHAR (Plant Breeding and Acclimatization Institute) breeding materials in ZDHiAR Kończewice, Poland during 1988-90. Out of the tested fungicides (triadimefon, triadimenol, imazalil, fenpropimorph, flutriafol, bupirimate, propamocarb, iprodione, fenarimol, captafol, prochloraz, propiconazole, thiram and carboxin), only Zaprawa Oxafun T (a.i. thiram 37.5% and carboxin 37.5%) and Sportak 45 EC (a.i. prochloraz 450 g/l) showed fungitoxic activity against the mycelium and pycnidia of P. betae. These fungicides were non-phytotoxic to sugarbeet seeds: their application did not negatively affect germination. Zaprawa Oxafun T at 2 kg/ha and Sportak 45 EC at 2 l/ha and 3 l/ha (1989-90) were used for spraying seed plants. The average level of seed infection in control samples in the succeeding years was 84.4% (1988), 24.2% (1989) and 55.5% (1990). Zaprawa Oxafun T reduced seed infection only in the dry season of 1989. Leaf spraying with Sportak 45 EC at a dose of 2 l/ha decreased the level of P. betae infection by 58.8% (1988), 63.0% (1989) and 43.5% (1990), as compared with the infection level of control samples (taken as 100%). Deep-seated infection of seeds from control plants, 49.3%, was reduced to 19.8% by spraying with Sportak 45 EC at a dose of 2 l/ha. Germinability of seeds from protected plots was increased by 3-4% compared with seeds from unprotected plots. Growing P. betae mycelium for 1 year on the medium containing 5 ppm of a.i. of the tested fungicides did not alter the susceptibility of this pathogen to these fungicides.