Cold soils raise rhizoctonia risk

Cold soils and delayed emergence could increase the risk of rhizoctonia infection in potato crops, growers have been warned.

“The quicker stems grow through the ground the better,” said United Agri Products’ Barrie Florendine.

“But with cold soils (many typically around 6C) slowing early growth, seed or soil-borne rhizoctonia infection will take advantage of young shoots before they are strong enough to grow away.”

The British Potato Council’s Rob Clayton agreed. “Rhizoctonia is most infective shortly after planting. Plants are better able to defend themselves once green tissue has formed, but very cold soils can slow emergence and give the disease more time to attack.”

Its effects can also be exacerbated in dry soils, he noted.

He urged growers who have already planted crops to keep an eye on emerging plants and sample them frequently for signs of pruning. Those who are yet to begin planting should wait for warmer soils and assess seed for any seed-borne symptoms.

Infection during the stem canker phase can result in the loss of emerging stolons and will impact on crop viability and growth rate, with colonisation of daughter tubers ultimately resulting in black scurf blemishes on the skin surface, added Mr Florendine.

Vulnerability to the disease appears to increase where nematacides have been applied, possibly due to plant stress, he added.

Mr Florendine recommended using a seed treatment, such as the planter-applied RhiNo DS (flutolanil), which is available for the first time this season.