Weeds – April 2020

Residuals that weren’t applied in the autumn can be applied in early spring, but generally not beyond the end of March, and weeds needed to be very small. So, we now need to focus on post-emergence treatments.

As we move into April with temperatures rising slowly, the spring post-emergence treatment options can control larger weeds, but there are limitations on which crops they can be used in. For grass weed control there are no herbicides in oats and very limited options in winter barley. There are a number of herbicides for wheat, although resistance issues and restrictions on sequences limit what can be done. Only one ALS grass weed herbicide is allowed per crop, so if an ALS treatment such as iodosulfuron, mesosulfuron, or pyroxsulam was applied in the autumn, there are very limited options in the spring.

Grass weed herbicides work best with good spray coverage on actively growing weeds. It is counter-productive to treat stressed crops too early in cold weather. However, for problem weeds such as black-grass and brome, they need to be treated when small.

At the time of writing most agronomists are still able to offer a crop walking service.  If you notice problems with emerging weeds you are advised to contact your local agricultural adviser or agronomist to draw up a treatment plan appropriate for your cropping situation.