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Crop Advice & Expertise

Midlands: Target light leaf spot and grassweeds this March

Matt Garnett says disease control in oilseed rape and keeping a lid on grassweeds in winter wheat are priorities for growers as they head into the month of March

This month’s key messages

  • Use a protectant fungicide where light leaf spot risk is identified
  • Apply contact grassweed herbicides while targets are still small
  • Be aware of label restrictions when using herbicide Monolith
  • Assess foliar disease levels in wheat ahead of T0 fungicide applications
  • Save a date in the diary for October’s brassica veg demo day

Crop progress

After a relatively mild winter, everything on farm is about a month ahead of this time last year. In the last week of February, you could really notice oilseed rape crops standing up and starting to get going in unseasonably warm conditions.

We had a number of frosts over winter, but they have not been cold or prolonged enough to take out foliar disease. In winter wheat, winter barley and oilseed rape, disease symptoms are still easy to spot and growers will need to be mindful of this through March.

 

Matt’s agronomy tips for March

1. Consider a protectant fungicide spray in oilseed rape crops

There is light leaf spot present in oilseed rape crops and this will need managing as soon as possible, particularly if no fungicide has been applied through the autumn and winter period. Once the disease gets in the crop, it is very difficult to stop, so it pays to remain in a protectant situation.

Proline (prothioconazole) at between 0.32L/ha and 0.46L/ha will provide good protection, but take note of how much Proline has been used so far if planning to use the product at flowering for sclerotinia control. The maximum total dose is 1.26L/ha for the season.

If you are faced with forward oilseed rape crops, consider using prothioconazole-tebuconazole co-formulations for some plant growth regulator effect. Remember that you need 25g of tebuconazole active per leaf for canopy manipulation.

2. Build on good autumn grassweed control in wheat

The kind autumn and good seed-beds have seen residual herbicides work well on grassweeds, particularly where top-ups were applied post-emergence. Good growing conditions are now helping grass- and broad-leaved weeds to come through, so it’s advisable to get a mesosulfuron-based product on while weeds are still small. This will maintain the good results seen so far and reduce the need for complex tank mixtures at T0.

Monolith (mesosulfuron + propoxycarbazone) was new last year and is a strong option on black-grass (and brome) populations, but be aware it needs to be used before GS33.

All mesosulfuron products labels stipulate that you must plough ahead of planting broad-leaved crops, which is something to be aware of. Note that Pacifica and Atlantis WG (iodosulfuron + mesosulfuron) are on sale until 30 April and must be used by 30 April 2020.

3. Assess cereal disease and plan T0 fungicide applications

The winter frosts have knocked back, but not dried out, diseases such as mildew. Yellow rust and Septoria pressure is also there in winter wheat already this spring, despite the later drilling on farms where black-grass is a problem.

Now is the time to get out and assess disease development, which will help identify risk and inform any plans for T0 applications in late March or early April. In general, crops are showing good potential, which is worth protecting. We don’t have a crystal ball to see what the weather will bring later in the season, so a T0 to clear out rusts and provide some protection against Septoria will be worth the investment for a clean start. Where mildew remains a concern, a specific mildewicide may also be required to minimise crop stress.

4. Put brassica veg autumn demo day in the diary

 We are in the process of organising a new trials site for a brassica veg demo day in early October. It will focus on Brussels sprouts, cabbage, broccoli and cauliflower and showcase the latest varieties, plus fungicides and insecticides. Anyone interested in attending and looking at the latest technology should contact Bayer for more details.

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