Impact of animal manures on verticillium wilt, potato scab, and soil microbial populations

Abstract

This study examined the effect of chicken, liquid swine, and solid cattle manures on verticillium wilt and potato scab incidence at two commercial farms near Alliston, Ontario. The manures (chicken, 66 t/ha; swine, 55 hLJha; cattle, 100 t/ha) were spread in the spring of 1996 and incorporated with a Rototiller to a depth of 15 cm. Survival of Verticillium dahliae microsclerotia (MS) was determined by burying nylon mesh bags containing MS in the plots. After 4 weeks, the MS were plated on agaz medium. Soil samples collected after incorporation of manures were brought back to the laboratory and used for concurrent laboratory experiments. Ten-gram amounts of soil were placed into test tubes, bags of MS buried in the soil,and survival measured under controlled conditions. Potatoes were planted in the field 1 month after amendment. Potatoes were planted in 1997 and 1998 without any further treatment. verticillium wilt incidence was determined by isolation of V.dahliae from petioles. Scab incidence was determined from visual estimation of lesion coverage on tubers. Changes in soil chemistry, in soil microbiology, and in populations of plant pathogenic nematodes were also determined. Chicken manure reduced scab and wilt incidence and nematodes to near zero levels at both sites. Swine manure reduced scab incidence at both sites but reduced wilt and nematode populations at one site only. Cattle manure application caused a small reduction in wilt at one site. Disease incidence in the second crop was similaz for all treatments except for swine manure at one site where a lower scab incidence was observed and chicken manure at both sites where wilt incidence remainded below that in untreated plots. Scab incidence in the third crop was reduced at one site treated with swine manure, but one of the chicken manure treated plots had a higher scab incidence than the untreated plot. The viability of MS was similar for identical treatments in the field and laboratory assay and predicted which treatments decreased verticillium wilt. Reductions in viability of MS were found to be manure and soil specific.