Influence of tillage and method of metam sodium application on distribution and survival ofVerticillium dahliae in the soil and the development of verticillium wilt of potato

Abstract

The effect of plowing and deep-rip tillage, in combination with chemigation or shank injection of metam sodium, onVerticillium dahliae populations and disease development was assessed in two fields with differing soil types and potato rotations. Soil samples were collected on a geo-referenced basis at depths of 0 to 10 cm and 10 to 20 cm before tillage, after tillage, after chemical application, and before planting and assayed for the presence of the pathogen. Propagules ofV. dahliae were detected at 140 of 141 sites sampled prior to tillage. Most (74.4% in heavy, sandy loam; 63.1% in light, loamy sand) were concentrated in upper 10 cm of the soil profile. Plowing redistributed inoculum vertically while deep-rip tillage did not. In the non-chemical treated areas of both fields, theVerticillium population reached a maximum between 25 July and 8 August before declining to near pre-tillage levels. Overall, the population generally was lower in the field with heavy soil, higher organic matter content, and a 3-year crop rotation. Metam sodium appeared to be most effective when shank injected, as the levels of inoculum in both fields declined by 60% to 80% following this application method. Chemigation was ineffective in the lighter soil, but the inoculum density in the deep-rip tillage area of the field with the heavier soil declined by nearly 20% in the upper and 60% in the lower strata following this treatment. The number ofV. dahliae propagules at the 10- to 20-cm depth in the plowed area of the same field was reduced by 25% following chemigation, but remained unchanged in the upper strata. Wilt was reduced in both fields by as much as 50% with shank injection of metam sodium with concomitant increases in total yield, marketable yield and gross income. Increases in total yield were significant (P<0.05) for the main effect of chemical, in the plowed area of the field with the heavier soil type following shank injection. These data suggest that growers might benefit from altering their tillage and chemical application practices as part of an integrated approach to managing Verticillium wilt.