North: Mild winter brings early spring disease pressure

A relatively dry March and cooler weather has put the brakes on crop growth to a certain extent which is no bad thing. Crops still look excellent in the main and a lot of spring crops have been drilled into good seed-beds.

In winter wheat the main talking point is yellow rust, which is present in a wide range of varieties now. Thankfully the cool and dry weather has limited its speed of development, along with genetic suppression in more resistant varieties as plants move from the seedling to adult stage. However, in some areas the levels of yellow rust are particularly high in varieties such as Oakley, Beluga and Santiago. Pre-T0 fungicides have been applied in such situations and now it will be a case of using regular fungicides to try and keep on top of the rust and not letting spray intervals slip much past three weeks.

The dry weather has slowed Septoria tritici development, but there are extremely high levels in many crops that could increase rapidly should the weather turn wet and warm in April and May. Earliest crops are now at the GS30-31 and are receiving a plant growth regulator and T0 fungicide for yellow rust and/or Septoria tritici protection. The T0 fungicide is largely based on chlorothalonil with or without a triazole such as tebuconazole or cyproconazole.

Winter barley crops have turned increasingly yellow this month as older leaves die back, but this is also in part due to the high levels of disease present. The mild winter has allowed diseases such as brown rust a free run, with Rhynchosporium and net blotch not far behind. Where disease levels have been high then a T0 fungicide has been applied. A T0 spray is not a routine treatment in winter barley but has been necessary in some situations this year.  The earliest crops are at GS30 now and T1 fungicides will be due shortly, which can often be combined with a plant growth regulator. Very few spring germinating broad-leaved weeds have emerged so far so hopefully a competitive barley crop will prevent the need for a spring herbicide over spray.

Winter oilseed rape crops are looking good, although pigeons seem to have become more of a problem this month. The earliest crops are at yellow bud stage with most at stem extension to green bud stage. Many crops have required a fungicide with plant growth regulatory activity or Caryx to try and steady up the canopy, but delaying the first dose of nitrogen has had a more significant impact. Pollen beetle levels at the time of writing are extremely low so avoid the prophylactic use of insecticides.

Spring oilseed rape will need to be drilled into good warm seed-beds.  With no neonicotinoid seed treatments available it will be best to delay drilling for a few days and make sure the crop jumps out of the ground, rather than emerging slowly and becoming a sitting duck for merciless flea beetles. Use a good pre-emergence herbicide as post-emergence options are limited and polygynums in particular can be very competitive.

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