Tillage management: When is the best time to spray oilseed rape?

From now on is the ideal time to spray oilseed rape crops for weeds and disease, according to Dr. Tom McCabe, Crop Science lecturer in University College Dublin.

McCabe stated that weed control is important in terms of the current crop. He also said it is important in terms of the rotation and controlling weeds for future crops.

AstroKerb will control broad leaved weeds; grass weeds; and volunteers.

“Astrokerb is still the most important and widely used herbicide on oilseed rape. There’s a very good chance you will do a field once and you’ll be done with it. Sow thistles would be an exception and can be controlled in the spring time,” he said.

With Astrokerb, farmers need to be patient and wait for the cold weather – which we are getting now. It is ideally used from mid-November onwards.

“It’s good to spray for weeds now and get on a fungicide at the same time.”

Oilseed rape crops are getting strong and should be monitored for disease at this stage.

“It’s difficult to know what the disease risk is, but you’re trying to protect against Phoma and light leaf spot. They’re the two main diseases. Varieties will differ a little. Phoma is a bit sporadic in Ireland. It’s hard to know what the risk is year-to-year.”

Proline is an excellent fungicide option because it covers all of the main diseases and has performed very well in trials.

“Spray in November rather than December for disease, as you’re more likely to get better control with an earlier timing,” he stated. Light leaf spot is difficult to spot in the autumn – spraying should be carried out as a preventative measure.

Proline should be applied at 0.4-0.5L/ha. Prosaro is another good option and should be applied at 0.8L/ha.

Prosaro can also have a plant growth regulator (PGR) effect, which is useful on crops with large canopies. Many crops of oilseed rape are strong this year – the PGR effect may be useful. However, McCabe stated that: “For normal crops, the PGR doesn’t come into play.”

Light leaf spot is difficult to see in crops but Phoma is easier to find – an example can be seen in the picture below.

Phoma (Stem Canker)

November is a month to watch out for ‘Phoma’ in oilseed rape. The disease has already been spotted in some crops.

If left untreated the disease can lead to Phoma stem canker later on. Phoma can be controlled with the fungicide application used to control light leaf spot.

oilseed rape
A Phoma leaf spot

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