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Crop Advice & Expertise

What’s happening in fields in the South West this March

The focus in the South West should be application of light leaf spot fungicides in OSR and completing grassweed control programmes in wheat, according to Tim Nicholson.

At a Glance

This month’s messages:

  • Prioritise a light leaf spot fungicide in OSR
  • Take every opportunity in March to apply contact herbicides when grassweeds are small
  • Plan a T0 fungicide in wheat based around chlorothalonil
  • Use a seed treatment to aid establishment in spring barley

We have had a wetter winter than usual in the South West and not much work has been done on the land. First early potato planting is behind schedule and crop protection schedules are behind too, with agronomists mostly confined to the office working out nutrient plans in recent weeks.

Oilseed rape

Oilseed rape crops have slowed in the cold and wet soils and crops that looked lush and vigorous before winter don’t look brilliant now. There are some small pockets now at early stem extension, but those crops look stressed too.

Light leaf spot is present and I have seen some visual symptoms over the past week or so. It is still a good idea to incubate leaves in a polythene bag to uncover latent infection and at the first sign of the disease, either in the field or incubated samples, you should bash on and treat crops with a fungicide.

Few, if any, crops in the area currently warrant a plant growth regulator (PGR), so the focus of immediate fungicide applications should be light leaf spot control. Prothioconazole-based products will protect new growth and help keep the disease off the reproductive parts later in the season. If you are finding low levels, use 0.32l/ha of Proline (prothioconazole) and increase this to 0.46l/ha where pressure is high.

Cereals

Where growers have black-grass land, many have been drilling winter wheat later and using residual stacks and sequences. As a result, we are seeing less blackgrass than expected this spring, but any surviving blackgrass plants will require a contact herbicide to complete the control programme.

Product choice will depend on target. Where there is more difficult blackgrass or bromes, Monolith (mesosulfuron + propoxycarbazone) or Pacifica (iodosulfuron + mesosulfuron) will give the best results.Where broad-leaved weeds are present, Pacifica has the broadest activity, but Monolith is a good option if broad-leaved weeds have been well controlled with previous residuals.

Growers should grab every opportunity through March to get these products on while weeds are small – particulary brome. Walk fields and check for active weed growth and apply to a dry leaf with at least two hours of dry forecast after.

Some good news is there will be no need for a pre-T0 spray to control yellow rust in wheat, with any latent mycelium significantly reduced by frost. This will also mean that where T0s are necessary, growers can hold off until early April, leaving a good window to get grassweed herbicides applied and an adequate gap to the first fungicide applications.

I would advise any variety below a septoria rating of 6.5 should have a T0 of chlorothalonil. There is then a debate on whether the more resistant varieties – particularly if they are late drilled – require a T0 CTL at all. In my opinion, erring on the side of caution is best where there is any doubt.

It has been too wet for spring barley drilling so far. The most important thing is to wait conditions to improve and drill into a good seed-bed, as good establishment will maximise yield potential. A Redigo Pro (prothioconazole + tebuconazole) seed treatment can aid good establishment, helping to achieve optimum ears/sq m and grains/ear at harvest.

For early weed control, there is an EAMU for Liberator (flufenacet + diflufenican) and unlike pendimethalin mixtures, it is very strong on annual meadow grass. Aim to apply it pre-emergence or early post-emergence at 0.3l/ha.

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