Farmers Weekly Interactive

East: Cold spell will help clean up brassica weeds in OSR

As this is being written, three inches of snow cover the ground and there have been at least three decent frosts. All this, is to my mind, is a very good thing. Many crops are just too lush and forward especially since the Christmas period, with them greening up and appearing to be taking up mineralising nitrogen. It’s just not right for this time of year.

Disease levels in wheat which had calmed down during late November were being reported as increasing again, particularly yellow rust with some brown rust as well. Many people had resisted the urge to apply fungicide up to this point on the advice of most experts, but if the mild weather had continued, rethinks were on the cards.

However, this spell will certainly put a brake on things and may bring things back to where they should be disease wise anyway, time will tell.

Management of these forward crops is, however, going to be a perplexing issue, particularly in fertilising and plant growth regulation. This also applies to oilseed rape.

Cereal herbicide effectiveness has been very varied due to the dry conditions in the autumn with some follow-up sprays also not working to their best. This is going to be very problematical, especially in relation to blackgrass. Quite a few wild oats are also showing up though these will be easier to deal with.

The one thing that must not happen where blackgrass is to be treated is a reduction in the rate of the iodosulfuron/mesosulfuron products from the recommended one. At the moment there is nothing on the horizon to control blackgrass even remotely effectively post-emergence so the loss of these materials to continued resistance must be avoided. Short term gains will lead to long-term pain!

One other benefit of this cold period is the obvious discomfort of the large amounts of brassica weeds that have dogged many rape crops. Many crops have been treated to a greater or lesser effect, but the combination is now working on these bigger weeds.

The few crops of herbicide tolerant oilseed rape are, however, clean from these brassica weeds showing the effectiveness of this technique.

Brian Ross

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