An on-farm study in Wisconsin examined the effects of chisel plow, moldboard plow, and no-till on disease development and sclerotia placement. In this study, density and viability of sclerotia at three depths, 0-1 inches, 1-4 inches, and 4-8 inches, was followed over a three year period. (See Figure 1)
Sclerotia density remained highest in the uppermost soil layer in areas managed with no-till or chisel plow in all three years of the study. Also, the greatest proportion of viable sclerotia were found in the uppermost soil layer of no-till and chisel plow treatments. In contrast, sclertia placement, sclerotia density and sclerotia viability in the moldboard-plowed areas varied from year to year.
In 1995, sclerotia were buried and the greatest sclerotia density was found in the deepest soil layer. In 1996, the plow layer was inverted and sclerotia buried the previous year were brought to the soil surface. In 1997, the greates density of sclerotia in the moldboard-plowed areas occurred in the deepest soil layer. At the same time, it appeared that sclerotia were being redistributed throughout the soil profile by moldboard plowing.
See figure 2
Sclerotia viability was lowest in the uppermost layer (0" - 1") of the moldboard plowed area compared to sclerotia viability in the no-till and chisel plowed areas. Conversely, sclerotia viability was highest in the uppermost layer in the no-till plowed areas. A possible explanation for the effects of tillage is the activity of parasitic fungi and bacteria.
See figure 3-5
The concentration of viable sclerotia on the soil surface suggests that white mold incidence should be greatest in no-till fields.
Instead, the greatest apothecia density and disease incidence occurred in the molboard plowed areas. Apothecia dinsity and white mold incidence were not correlated with the density of soilborne inoculum.The most likey explanation for these results is the effect of canopy density on the environment for disease development. Establishing desired stands in the no-till area was a problem.
So, the highest plant population, and as a consequence, the greatest apothecia development and white mold incidence occurred in the moldboard plowed areas. In no-till area stands were low and the soybean canopy did not close in. Apothecia numbers throughout the growing season were higher in the moldboard plowed or chisel plowed area than in the no-till area. This indicates that conditions were more favorable for fungal development in the moldboard and chisel plowed areas.
Canopy development and conditions influenced by canopy development were more important than soilborne inoculum density or density of viable sclerotia in determining disease severity.
See figure 6
The relationship between white mold incidence and tillage system is not clear cut.
Results compiled from variety trials in Wisconsin indicate that white mold incidence is slightly but consistently greater in moldboard plowed soybeans than in no till soybeans.
Results from five years of variety trials where more than 50 varieties were planted each year on adjacent no-till and moldboard plowed fields were compared, and white mold incidence was greater in the trials planted and managed with conventional tillage, usually moldboard plowing.
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Figure 1: The Effect of Moldboard, Chisel plow, and Notill on the Vertical Distribution of Sclerotia
Rollover for larger image
Figure 2: Sclerotia Viability Observed at Three Depths in Three Tillage Systems Sampled in Spring 1997
Figure 3: Apothecia Observed in Three Tillage Systems During 1996 Growing Season
Figure 4: Average Apothecia Number Observed in 1997 Three Tillage Systems in Rotation/Tillage Study
Figure 5: Tillage Influence on Soybean White Mold, Yield and Incidence
Figure 6: Effect of Tillage on Incidence of Soybean White Mold
