South West: Oilseed rape canopies reduced

Following temperatures as low as -17C in January the rape crops in the area have a much reduced GAI compared to before Christmas, when some crops would have had a GAI of nearly 2. Those same crops are now supporting GAIs of between 0.6 and 0.8. This will have a profound effect on the top dressing regime with the canopies having to be re-built and the nitrogen that was tied up in the canopy largely lost to the present crop.

Nitrogen and sulphur applications will take place to most rape crops as soon as ground conditions allow. Total amounts of nitrogen for the rape crop are going to be significantly higher than we might have assumed just a few weeks ago, with many crops now needing between 200Kg/Ha and 230Kg/Ha instead of the 120Kg/Ha to 150Kg/Ha they would have received if canopies had been maintained.

Cereal crops have survived the freeze extremely well with the exception of a few barley crops where manganese deficiency has lead to a lack of winter hardiness and quite a bit of winter kill. Cereal growth stages are quite varied with early drilled crops now supporting a surplus tiller number. These crops will not be receiving any early N as to encourage further surplus tiller production can only be counter productive. 

Later drilled crops after maize and veg crops are however acompletely different case. Many of these crops have yet to start toproduce tillers and as such will receive nitrogen at the earliestchance. They will also get a bigger proportion of of their totalnitrogen earlier than the more forward crops.

Despite the cold many more forward wheat crops are already carryingsignificant Septoria Tritici infections. These will definitely bereceiving a T0 fungicide. Product choice will depend on the severity ofthe disease, the size of the crop and the varietal resistance.Varieties such as Lear, Gatsby and Sahara may only requireChlorothalonil at this time while more susceptible varieties willrequire the addition of a good septoria triazole (epoxyconazole).

TheT0 timing is also an ideal time to get the PGR programme started,particularly with varieties such as Lear and Deben. Deben still has asignificant following in the region despite its “weak” straw and thereason for this is that it quite simply consistantly out yields alot ofthe newer wheats.

We now desperately need the weather to dry up and warm up so that wecan get on with the spring workload and get the timing of fertiliserapplications right.

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