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Crop Advice & Expertise

What’s happening in fields in Oxfordshire and Gloucestershire this March

Treat light leaf spot and check autumn vigour in OSR, says Jon Helliwell. He also offers some advice on disease and weed control in winter wheat

At a Glance

This month’s messages:

  • Treat for light leaf spot in OSR as soon as conditions allow
  • Assess OSR for spring vigour to help improve variety selection
  • Monitor mildew in lush or rapidly-growing cereal crops
  • Use a chlorothalonil-based T0 in wheat, adding rust-active products where present
  • Target grassweeds with a contact herbicide as soon as possible

Field conditions remain challenging across the area, although light land is beginning to offer travel opportunities. Still, I can’t foresee much happening for the next week or so, depending on the weather. Nitrogen applications will be top of the list and I’m seeing some manganese deficiency that will need addressing too.

Oilseed rape

Ahead of my last report OSR crops looked very good, with many were early drilled to try and negate flea beetle damage. However, high pest pressure didn’t materialise and many canopies were too thick and lush. A combination of a cold spell and relentless pigeon attack has now helped to knock these crops back.

Phoma was controlled well in the autumn, but ahead of the snow and cold, light leaf spot could be seen coming into crops and in the field I picked up first visible symptoms on 16 Jan.

Treatments should be prioritised based on what went on in the autumn. If no light leaf spot-active product was applied, a prothioconazole-based spray will be required as soon as possible, with any growth regulation dealt with later. Stronger varieties that had robust autumn fungicide programmes have more flexibility, and the first spring LLS-based spray can wait until stem extension. PGRs may still be required in a handful of crops, but many will look utilise tebuconazole now, rather than a specific PGR after the cold snap.

As crops grow away over the coming weeks, it is a good time to assess differences in spring vigour, to help with variety choice next season. Checking stem collar size and digging up plants to check rooting can give a good indication of a variety’s, and is complementary to above ground biomass observations.


If it warms up, cereal crops may grow away very quickly, particularly where nitrogen has been applied. Mildew could be an issue on this lush new growth and is worth keeping an eye on.

Where crops are being pushed with higher seed and nitrogen rates on the back of recent yield responses, this will inevitably lead to crops with higher biomass and disease pressure is increased. Growers need to bear this in mind when planning disease control strategies.

Septoria is there in the bottom of wheat crops and needs to be monitored closely. The cold weather has successfully checked yellow rust and I’m struggling to find active pustules in crops. My advice is to use a chlorothalonil as a base at T0 to give you flexibility if the T1 is delayed and where rust is active, include a strobilurin or secondary azole such as tebuconazole or cyproconazole for quick knock-down. Decisions on T1 chemistry should then be based on each variety’s susceptibility, drilling date and how quickly the farm can cover its acreage with the sprayer.


Generally, pre-emergence herbicides have worked well on black-grass for a second consecutive season, with growers leaning towards big stacks and sequences to get good levels of control. Where post-emergence applications were made in the autumn, black-grass activity remains low, but elsewhere we continue to see a few “spikes” emerging and these patches will need monitoring and treating with Monolith (mesosulfuron + propoxycarbazone) where broad-leaved weeds aren’t a concern.

If broad-leaved weeds are an issue, Atlantis OD (oil dispersion formulation) gives flexibility for broad-leaved weed tank-mix partners. If brome is also a target, Monolith gives best performance and Pacifica (iodosulfuron + mesosulfuron) remains a key option for all round grassweed and broad-leaved weed activity. Apply as a separate application where possible and particularly avoid mixing with chlorothalonil or tebuconazole to maximise herbicide efficacy.

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