Verticillium wilt has become a widespread disease problem in oilseed rape, particularly in the Eastern counties, the South and Midlands, and with no proven chemical cure, the only way to manage it is through cultural control methods including the use of resistant varieties.
Dr. Peter Gladders of ADAS advises that farms with this problem need to manage it through better agronomy and resistant varieties. “The initial approach is to grow crops as well as you can. Robust plants with stronger root systems are more resilient to infection. The second string to your bow is to grow resistant varieties. Widening the rotation is not a practical option as the pathogen can survive in the soil for over ten years. Verticillium also tends to be at higher incidence on lighter land and in crops established by minimal tillage, the most common way of establishing rape nowadays.”
He suggests that growers should be inspecting their own crops now and assessing their individual risk in order to decide whether to grow resistant varieties or call in other aspects of crop management. “Symptoms are just starting to appear in the field and are seen as premature ripening and pale green/yellowing pod colour. On the stem long vertical light brown stripes run the length of the stem and then develop into long vertical grey pin stripes with black microsclerotia on the stem surface. The disease impact is premature ripening and subsequent yield loss. Although yield loss in the UK has been found to be variable, in Sweden reports of up to 50% yield loss have been seen in some years.”
ADAS trials have indicated wide variation between varieties for resistance to Verticillium wilt. Dr Gladders thinks that the genetic resistance is multigene and that certain breeders including Grainseed have the necessary breeding stock that has this resistant capacity.
Neil Groom, Technical Director of Grainseed, confirms that the company do have a strong breeding portfolio of Verticillium resistant rape varieties including Es Agatha and Es Alienor. “Screening work in the UK and France has demonstrated significant differences between rape varieties grown under the same conditions. Alienor and Agatha appear to be able to resist Verticillium very well, much better than other varieties such as Castille and Excalibur that are very badly affected by this disease. Dr. Gladders has warned that growing susceptible varieties too widely can build up the pathogen in the soil for the future.”
Both Alienor and Agatha are particularly vigorous in the autumn and can be grown together on the farm, as Alienor is early maturing and Agatha a little later, so harvest can be spread, points out Neil.
With tighter rotations, more Verticillium being seen in oilseed rape crops and the main way of minimising this disease being the use of resistant varieties, growers should seriously consider planting Alienor and Agatha this autumn, particularly as we have no proven in-field chemical treatments to fall back on, he says.
“Alienor is already a popular variety because of its very early maturity and vigour. It matures 7-10 days earlier than Castille, allowing plenty of opportunity for seedbed preparation and stale seedbeds as well as for timely entry for autumn drilled crops. Its strong Verticillium wilt resistance, confirmed by Dr Peter Gladders trials, adds another important benefit. Alienor has a 7 rating for Phoma stem canker and a 6 rating for Light Leaf Spot, giving it a combined disease resistance package that is hard to beat.“
“New this year, the conventional variety Agatha is also a strong performer, with exceptional Verticillium wilt resistance combined with high yields and oil content. In fact Agatha was one of the best Verticillium resistant varieties in trials. It yields well at 106% and has consistently outperformed DK Cabernet and Sesame in a number of trials. It also delivers a high oil content of 45.1%” points out Neil Groom.