Verticillium seen in OSR Trials
As harvest approaches and the hot weather hopefully returns, growers may start to see areas in the field where the crop looks to be ripening prematurely. This could be symptoms of Verticillium wilt, so it is worth going out to inspect crops and see if this disease is found, says Neil Groom, Technical Director of Grainseed.. “If you have Verticillium in your soils, the only way to live with it is to grow a variety which has good Verticillium wilt resistance or tolerance. You have no other choice. Using crop intervals or rotations is impractical, since the disease remains viable in the soil for over 20 years. Nor are there any approved chemical answers. In the East, Midlands and the West 8% of crops had this disease last year according to Crop Monitor. If you don’t grow a resistant variety, you will have to suffer the consequences. We suggest that those who are seeing Verticillium wilt now or in the past few years, make a proactive decision to grow a resistant variety this autumn.”
Plant pathologist Dr Faye Ritchie of ADAS points out that Verticillium symptoms are usually seen as the crops starts to ripen. “We have already seen the first symptoms this year. What to look out for 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 dots or microsclerotia. The microsclerotia survive in the soil for over 20 years to infect subsequent crops, hence the impractical nature of crop intervals in its control.”
“To control it sustainably, you have to use resistant varieties,” says Neil. “Theoretically growing particularly susceptible oilseed rape varieties in disease-affected area could lead to a build-up of microsclerotia in the soil.
Logically the opposite could also apply, so by growing a resistant variety you could minimise build up in the soil.”
Neil Groom says once you have identified Verticillium, you need to start thinking seriously about how to handle it. “Unlike other diseases of rape, there is no proven or approved fungicide to control it and so growers must rely on cultural control measures – and the only one you really have open to you is to choose varieties with known resistance. Grainseed oilseed rape varieties including Es Mambo have proven resistance to Verticillium, following several years’ independent trials and commercial experience.”
Neil advises growers to grow rape varieties with a good overall combined disease resistance. “In cereals you don’t think twice about studying disease resistance ratings in detail before choosing your variety. This needs to be the same for rape varieties now. A good variety needs to have resistance to Verticillium, Phoma as well as to Light Leaf spot. Es Mambo has a 7.8 rating for Phoma stem canker and a 6.4 for Light Leaf spot plus it is the Number 1 performing variety in AICC Verticillium trials. Out of all the varieties tested in a trial in Sussex in 2016, Mambo had just 2% Verticillium plus a yield of 5.5 t/ha, compared with all other varieties where the level of Verticillium went right up to 60% and yields were between 4.1 and 5.6 t/ha. Mambo had the lowest level of Verticillium and the second highest yield at this site. At another site in Norfolk Mambo had 8% Verticillium which was the lowest level of all varieties and it yielded 5.1 t/ha, which was again the second highest yield. Genetic resistance to Phoma in all Grainseed varieties is multi-gene and so unlikely to break down.”
When growers are looking more closely at their growing costs, choosing a variety such as Mambo where you can be sure of its strong disease resistance across the board can save you money, says Neil.
“Mambo also shows exceptional autumn vigour, helping the crop grow away from diseases and pests, increasingly important with the pressure of cabbage stem flea beetles at planting,” says Neil. ”It also has good oil levels of 46% and a high Agronomic Merit rating of 41.2. As a variety it gives growers peace of mind with its strong broad disease resistance, its low biomass and its vigour characteristics.”
Dr. Ritchie says that in the future the AHDB is looking to assess and rate susceptibility of a range of varieties to Verticillium. “The idea is to develop a disease resistance rating that can be added to the AHDB oilseeds Listings, probably in 2020,” she says.