The soil-borne oilseed rape disease, verticillium wilt, has been officially found in oilseed rape for the first time in the UK, David Slawson from DEFRA’s plant health unit has confirmed.
Two samples sent in from ADAS sites in Kent and Herefordshire were found to be infected with the fungus, Verticillium longosporum, following testing by the Central Science Laboratories in York, he said.
The disease produced long, grey streaks on stems leading up to swathing time, and as such could easily be confused with phoma and sclerotinia, which also cause root and stem blackening, according to ADAS plant pathologist Peter Gladders.
“The difference from phoma is that these streaks can run for long distances – maybe up to a metre – while phoma symptoms tend to be only a few inches in length.”
The fungus invaded the root system in the autumn, but usually remained symptomless until the spring, when it moved up through the plants vascular system once stem extension started, he explained.
Verticillium infections in oilseed rape crops had been suspected for two or three years in the UK, but this is the first time the disease had been officially recorded, he said. “I thought it was important there was an official UK record.”
Around 10-30% of plants were infected at the sites. “Quite a lot of the symptoms were on the lateral shoots.”
Yield loss from the disease was difficult to estimate, he suggested. “Researchers in Sweden, who have been battling with verticillium for 50 years, acknowledge it can be from very little to up to 50%. In these cases around 10-30% plants were infected, but only the odd one senesced early so I suspect the damage was very little in this case. It might be worse in very hot, dry summers.”
Control options were limited, according to Dr Gladders. “There’s not much else you can do other than extend rotations. It declines in soil over time, but observations in Germany suggest you need rotations of one in four or five years to reduce its impact.”
Plant breeders in Northern European countries where the fungus is found, such as Germany, Poland and Sweden, hadn’t had too much success in finding resistant genes, he said. “And nobody is claiming any control from fungicides, although in theory there might be a chance to have a go at it in the autumn and the spring.”