Changing rotations and reduced tillage could explain why Rhizoctonia solani is becoming more prevalent in potato crops, believe experts.
As farms growing potatoes are now moving less soil between crops, reduced tillage has been shown to encourage survival of the pathogen in the soil. There are also more species of plants being grown in some rotations, whether that’s driven by a greater area of cover crops, environmental schemes, or more cash crop options.
In theory, this diversity could reduce available rhizoctonia inoculum for susceptible crops including potatoes, but it also provides more hosts for soil-borne persistence, says Professor Rumiana Ray from the University of Nottingham.
She believes there are knowledge gaps that require filling, particularly as farming systems have changed rapidly during recent years. “Growers and agronomists have to know the current soil-borne disease situation to assess the impact of these practices and implement alternative or corrective measures, if required.”
Control measures
Hutchinsons agronomist and potato specialist, Andrew Goodinson, says currently that leaves good husbandry combined with the application of soil- and seed-applied fungicides, as the main control measures where risk is identified.
In such instances he recommends use of in-furrow fungicides such as azoxystrobin or fluxapyroxad combined with a seed treatment if necessary. Consequently, Andrew sees liquid seed treatment options like flutolanil-based RhiNo becoming much more popular in the future as seed is treated in the shed over a roller table ahead of planting.
He says this takes an operation away from a busy planter operator already grappling with accurate seed spacing and in-furrow applications of fungicide and fertiliser, before even considering powder seed treatment applications.
However at the moment, most of Andrew’s growers are still using powder flutolanil formulation RhiNo DSG as it gives flexibility, particularly where seed is delivered ‘just-in-time’.
“But whatever seed treatment you decide to use, effectiveness does rely on excellent coverage. That makes correct setup, calibration and maintenance of on-planter applicators crucial,” he adds.
Plant health
Planting conditions and adequate early nutrition are the final considerations highlights Andrew, with timely cultivations and seed-bed preparations which avoid soil compaction key to seeing the crop grow away from the threat of rhizoctonia.
“Anything that can reduce stress and encourage crop development is a good thing; we’re using phosphite-based products as well. Other biological products will play an increasingly important role in potatoes, but we’re still learning how and when they’re best applied for consistent success,” he concludes.
