Keeping disease at bay in winter oilseed rape

Farmers with winter oilseed rape crops should be keeping an eye out for disease on plants at present.

Light leaf spot (LLS) and phoma leaf spot are the main concerns at this time of the year and those with forward crops may also be thinking about growth regulation.

If light leaf spot is not visible in crops then preventative action should be taken to keep the disease at bay. Light leaf spot is difficult to find in the autumn so preventative action can reduce problems later on.

Light leaf spot can take time to become visible on plants, whereas phoma is easier to spot. Teagasc recommends that farmers spray a fungicide if 10% of plants have been affected by phoma.

Where crops do not need a growth regulator, prothioconazole is an option. However, forward crops will most likely need some growth regulation and should receive fungicide products based on either metconazole or tebuconazole.

At this time of the year a half rate of the fungicide is often sufficient. Those who can travel in fields in November should do so as better control can be achieved with an earlier spray timing.

Identifying light leaf spot

For those who want to see if light leaf spot is present in their crop, Teagasc has previously advised growers that they can collect 30-40 leaf samples from different areas of the crop.

The leaf samples should then be placed in a plastic bag and left at a temperature of 10-15° for four to five days. This will help the sporulation of light leaf spot if it is present in the crop.

However, prevention is still recommended and control of phoma will also be necessary.

Herbicide

Those who have not yet applied a herbicide may consider it at this time of the year. If field conditions are suitable, herbicide and fungicide applications, along with growth regulation, should all be considered in the coming weeks.