|Abstract or Summary
- Annual applications of fresh or composted dairy manure were assessed for
their effects on root rots of sweet corn and snap bean and damping-off of cucumber in
a field soil. Soil biological and physical properties were measured as possible
indicators of root rot suppressive potential. Regardless of amendment type or rate,
soils amended for two seasons with either a high (average = 39.2 Mg ha⁻¹ year⁻¹)
low (average = 16.6 Mg ha⁻¹ year⁻¹) rate suppressed root rot of sweet corn, root rot of
snap bean, and damping-off of cucumber by 54, 25 and 49%, respectively. Disease
suppression was sustained for less than 6 mo after amendment, Severity of these three
diseases was negatively (P<0.05) related to soil free particulate organic matter
content, fluorescein diacete (FDA) activity, microbial biomass, and percent water
stable aggregation. FDA activity was the best indicator of the soil's root rot
suppressive potential. When FDA levels were ≥ 2.88 μg min⁻¹ g⁻¹ dry soil, disease
suppression was observed.
In a container experiment, amendment with fresh (10% v/v) or composted
(15% v/v) dairy manure suppressed root rot of sweet corn in soils with a high root rot potential. Suppression was positively related to FDA activity in soil-i (R² = 0.70) and
soil-2 (R² = 0.91). Suppression was observed at FDA levels ≥4.00 μg min⁻¹ g⁻¹ dry
When sudangrass and oats were grown and incorporated in a container
experiment, severity of root rot of sweet corn was reduced by 22 and 18%,
respectively. Annual ryegrass and cereal rye had no effect on disease severity.
Disease suppression was not related to FDA activity.
Host range specificity of P. arrhenomanes, Drechslera spp. and Phoma spp.
was determined for crops grown in rotation with sweet corn. P. arrhenomanes and
Drechslera spp. were mildly pathogenic on annual ryegrass, perennial ryegrass and
cereal rye. Phoma spp. was pathogenic only to perennial ryegrass. None of the
pathogens were pathogenic on sudan grass and oats.
In conclusion, management of root rot of sweet corn through cover cropping
coupled with soil amendment shows potential for disease suppression and should be
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