Verticillium wilt hits yield
The impact of Verticillium wilt on the yield performance of oilseed rape has been highlighted in variety trials performed by ADAS.
The trial provides a graphic illustration of the different tolerance levels between varieties while varying yield levels demonstrate that the impact on performance is complicated.
The effects of Verticillium wilt are typically more pronounced in a difficult year because it is a disease that thrives when the plant is already in a weakened state. Despite a reasonably low disease pressure season, the effects of Verticillium wilt had on yields in 2017 is clear.† This is highlighted in chart 1 and table 1.
Chart 1: 2017 ADAS Verticillium wilt field trial
Source: ADAS, 2017
The effects of Verticillium wilt are also evident in plant vigour. This can exacerbate the effect of poor seedbed conditions or attack from cabbage stem flea beetle.
In a low pressure season its effects are not always obvious. The crop is able to tolerate infection when conditions are good and the plant has access to sufficient moisture and nutrients, but under stress, and we have seen plenty of that with light leaf spot and flea beetle, then the crop can suffer greatly.†
The generally accepted view is that Verticillium wilt makes the plant less physiologically robust. Principal symptoms are grey striping on the plant stems, while maturity occurs several weeks earlier than normal on affected side branches. Come harvest the plant is clearly dead while the stems of uninfected plants would still be green.
Chart 2: The effect on plant vigour following inoculation
Source: ADAS, 2017
Yield results from official trials in 2017 also highlight the effect of Verticillium wilt. At Cowlinge, Suffolk, a site considered to be heavily infested with Verticillium wilt inoculum, some varieties yielded almost a tonne per hectare less their mean for 2017. The 2015 season was also good for Verticillium wilt with yield reductions of up to 20% recorded.
This is summarised in table 1 below.
Table 1: Variety performance under known Verticillium wilt infestation
Source: RL trials, 2017
For some time growers have been advised against sowing varieties found to display more than 30% infection in the weeks before harvest.
We still have much to learn about this disease, but while its impact maybe at its most severe in a difficult season, it has the potential to reduce performance even in an a relatively low-pressure year.† It is also clear that variety choice will be increasingly important to managing its impact.