Just about now growers will be seeing areas in the field where the crop looks to be ripening prematurely, especially in recent warm conditions. This could be symptoms of Verticillium wilt, so it is well worth going out to inspect crops in detail any time now, says Neil Groom, Technical Director of Grainseed.

Plant pathologist Dr Caroline Young of ADAS says that ADAS has been involved in various projects on Verticillium for a number of years. “According to the Fera Crop Monitor, 22 per cent of winter oilseed rape crops were infected with Verticillium wilt last year. In 2013 it was 24 per cent, in 2012 it was 10 per cent and in 2011 18 per cent. It is found in all regions except the South West. Highest levels of disease were in the South East where 58 per cent of crops had infection and eight per cent of stems affected. So last year, one in five fields suffered from this soil-borne disease. The bad news this year is that there is still no chemical means of control. To control it sustainably, you need a long gap between rape crops or you need to use resistant varieties.”

She explains that Verticillium symptoms are usually seen later on as the crops starts to ripen. “Symptoms are yellowing leaves, premature ripening of branches and grey striping down stems, often on one side only but it can be the whole cross-section of a stem. Underneath the vertical stripes, if you peel off the outer stem layer you will see grey vascular tissue. If you use a hand lens, you can see tiny black microsclerotia in the grey stems. The microsclerotia can survive in the soil for many years to infect subsequent crops.”

Neil Groom says once you have identified Verticillium, a disease that has been spreading across the UK in recent years, you need to start thinking about how to handle it. “Unlike other diseases of rape, there is no proven chemical method of controlling it and so growers need to rely on cultural control measures – expanding the rotation and/or choosing varieties with known resistance.”

“Some seed breeders have been making a song and dance about Verticillium, but not actually having the means of helping growers with the management of this damaging disease. Many of the Grainseed oilseed rape varieties including Alegria and Alienor have proven resistance to Verticillium, following several years’ independent trials and commercial experience.”

Neil Groom advises growers to grow varieties with a good combined disease resistance. “And this means good known resistance to Verticillium and Phoma as well as to Light Leaf spot. Alienor has a 7 rating for Phoma stem canker and a 6 rating for Light Leaf Spot, giving it an excellent overall disease resistance package. Alegria has a 7 rating for Phoma and a 5 for Light Leaf Spot. Genetic resistance to Phoma in these varieties is multi-gene and so unlikely to break down.”

“Verticillium is best managed through growing resistant varieties and through better agronomy. It may also be the case that growing susceptible oilseed rape varieties in disease-affected area could lead to a build-up of microsclerotia in the soil. Alienor and Alegria show good resistance to Verticillium as well as exceptional vigour, helping them grow away from diseases and pests, increasingly important with no neonicotinoid seed treatments this year and the immense pressure of cabbage stem flea beetles at planting,” said Neil.

Dr Young says that ADAS will be conducting a three year project, led by Dr Faye Ritchie, starting this year, to look at different varieties and Verticillium resistance. “The idea is to develop a disease resistance rating that can be added to the AHDB cereals and oilseeds Listings.”