Michael Shuldham of NPZ UK explains that, "Verticillium stem stripe (VSS) is a soil borne fungus which can cause yield reductions of 30% or even more. There are no fungicide treatments available and the key to managing VSS risk is crop hygiene, optimised establishment conditions and wider rotations. In addition, the RL table shows there are significant differences in the level of VSS resistance between varieties.  

 

 

"It is probably fair to say that VSS in less well known than phoma or light leaf spot as a threat to oilseed rape yields, but it is increasingly prevalent, so it is worth detailing the dynamics of the disease's progress through the season."  

The disease-infection cycle starts with microsclerotia. Infection of the roots usually takes place during the seedling stage at a relatively wide range of temperatures. The fungus colonises the vascular tissue and upper plant during stem extension. Leaf yellowing may occur from April onwards. Then yellow vertical stripes, followed by brown stripes, occur on stems towards the end of June and early July.

As ripening progresses, stripes extend along the full length of the plant from soil level into the upper branches. Usually whole plants are affected, but symptoms are occasionally limited to a few branches.

Scraping infected stem surfaces can reveal grey discolouration of the vascular tissue beneath the stripe. This becomes more obvious as outer fleshy tissues of the stem dehydrate during ripening. During this final phase, the stem begins to shred with masses of minute microsclerotia visible in the tissue. Affected roots are grey in colour.

Severely affected plants ripen prematurely with canopy collapse and seed shedding possible. Symptoms are also visible after harvest on stubbles and crop debris.

Micheal Shuldham adds, "Disease levels in our trials are increasing year on year, and this year we were seeing symptoms before the Cereals Event in June, which was a first.  Susceptible varieties were ripening up to two weeks early, reducing TGW and yield."