Teagasc is confirming that the area of winter oilseed rape sown out in Ireland has increased by an estimated 25% this season.

This is due to a combination of high forward prices and planting opportunities last August.

Crops are generally more forward than normal, due to above average temperatures in September, so monitoring for disease is important.

Phoma is common in the autumn and once the threshold of 10% of plants affected is reached, the crop should be treated. Light leaf spot is the main disease of rape in Ireland but identifying it in the autumn is difficult.

Preventing disease in oilseed rape

To prevent disease, all rape crops should get a fungicide for light leaf spot in November. This will also cover Phoma. Proline or Prosaro are rated the best for light leaf spot control.

Meanwhile, the Agriculture and Horticulture Development Board (AHDB) in the UK has confirmed that its newly improved light leaf spot forecast now reacts to rainfall during the winter, helping to focus crop monitoring, particularly in regions with higher predicted disease risk.

High winter rainfall encourages the development and spread of light leaf spot in infected oilseed rape, and movement to unaffected plants, even at temperatures lower than required for crop growth.

If long-term average levels of winter rainfall are assumed, the 2021/2022 forecast suggests that disease incidence will be high across many parts of the UK.

The forecast highlights the proportion of susceptible (disease rating of 5), fungicide untreated, oilseed rape crops predicted to have more than 25% of plants affected by the spring.

Robert Saville, who manages disease research at AHDB, said:

“As soon as the disease is observed, it is important to consider treating susceptible crops – with priority given to those sown relatively early.

“Since light leaf spot often occurs in distinct patches, whole-field monitoring is required to assess disease severity.

“Incubation of potentially infected leaf samples can help bring out symptoms. And some disease has already been detected this autumn, using this method,” he added.

Timing of forecast

Until this year, the forecast was issued twice. Firstly, in autumn, and secondly in spring, to account for the actual deviation in winter rainfall.

Saville continued: “Recent industry consultations confirmed the forecast is valued. However, one criticism was that the final forecast came too late to make a difference. As a result, we have replaced the static spring forecast with a live and dynamic winter forecast.

“Put simply, if the winter looks like it is going to be wetter than average at any given site, the risk will increase and vice versa.”

The improved tool now also features a scenario-planning function to help reveal the impact of both a relatively wet and relatively dry winter on the predicted disease incidence.