Verticillium stripe on oilseed rape
26 Jul 2019
In this blog, ADAS Plant Pathologist Dr Faye Ritchie discusses how Verticillium stripe has affected crops this season, and how to manage the disease.
Verticillium stripe (Verticillium longisporum), previously known as verticillium wilt, is a soil-borne disease of oilseed rape. The change in the common name brings us in line with other countries and reflects the fact that no wilting symptoms are observed in the crop. Symptoms are not normally observed until the crops are close to senescing or have been desiccated. In the early stages of symptoms expression in early to mid-June, verticillium causes characteristic yellow and brown stripes on individual plants (A). Browning/flaking of the outer surface of the stem and microsclerotia production (B) occurs from early to mid-July. Scraping the surface from green or yellowing stems can often reveal dark stripes that are not yet visible. Microsclerotia are survival structures and when returned to the soil have been shown to survive for over 10 years. Germination of the microsclerotia is stimulated by root exudates produced by subsequent oilseed rape crops, continuing the disease cycle.
Symptoms were relatively late in appearing in crops in 2019. Symptoms varied depending on the site. In some fields it was easy to find stem striping symptoms but the characteristic microsclerotia were not present. At other sites, microsclerotia were clearly visible. This is likely to have been caused by a range of factors including local weather, crop health and variety resistance. Crops grown on affected land that established poorly or are stressed are more likely to be affected.
Clear differences in the expression of stem symptoms and the relative susceptibility of different varieties have been observed in field trials. These effects have been consistent between sites and seasons. Information on the susceptibility of different varieties can be found in a recent AHDB project and from plant breeders. The inclusion of ‘old’ varieties with good resistance to verticillium in these trials, such as Catana, act as a baseline from which to compare the susceptibility of newer varieties. Information on the impact of verticillium on yield is limited, however, an inoculated trial conducted as part of the AHDB project suggests that the yield losses associated with verticillium in the soil could be between 10 to 15% when using a susceptible variety compared to 3% when using a variety with better resistance. The same trial also suggested that some susceptible varieties could ‘tolerate’ the disease; develop severe symptoms but yield is not affected. These yield effects are not always reported in trials, suggesting there are other factors influencing yields as well as verticillium at individual sites.
Decisions on managing verticillium need to be made prior to drilling. It is clear there are differences between sites, seasons and varieties and the associated impact on yield. There are no fungicides with control of verticillium on the label. The simplest strategy is to choose a variety with good resistance to use on fields and/or farms where the disease has been reported. Key points regarding management of the disease at affected sites are:
- Investigate any oilseed rape crops with premature ripening to determine the cause;
- Use a variety with good resistance to verticillium;
- Avoid using home saved seed;
- Good crop establishment.