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Crop Advice & Expertise

Scotland: Keep a lid on disease and weeds this April

Disease control in cereals and oilseed rape is the main focus of field activity this month. Grant Reid offers some advice on formulating fungicide programmes

This month’s key messages

  • Treat backward unprotected oilseed rape crops for light leaf spot now
  • Plan for a two-spray strategy for sclerotinia control at flowering
  • A robust T1 in barley is necessary to protect yield
  • Plan wheat fungicide applications based on disease risk
  • Tidy up weeds in late-sown wheats before herbicide cut-off dates

Crop progress

The last two weeks of March have provided some fine weather and some folk may be finished spring drilling by the first week in April. Seed-beds are fantastic and growers have managed to sow, roll and apply pre-emergence herbicides without any bother.

Potato planting is also in progress, with the larger farms with big acreages making an early start. There is plenty of moisture underneath and conditions will allow a good start for tatty growers.

Oilseed rape varies from rosette stage right up to yellow bud, but most are at least at stem extension. Some backward crops are still getting hammered by pigeons, but on the whole oilseed rape is looking good.

The dry winter means there has been plenty of residual nitrogen in the ground and after rain in early March, winter cereals have picked that up and look fantastic. Both wheat and barley crops range from tillering to GS30 heading into April. Pre-emergence herbicides have worked very well across the board.


Grant’s agronomy tips for April

1. Make sure late oilseed rape get a stem extension fungicide

There is still light leaf spot kicking about and where no stem extension spray has been applied, it needs to go on as soon as possible. Depending on the weather, some of the more forward crops will be in to flowering quickly so some growers will hold off in those cases. However, those that are only just starting to extend would definitely benefit from a dose of Proline (prothioconazole) to stop the disease infecting the upper canopy.

2. Protect OSR from sclerotinia with a two-spray fungicide programme

If it stays mild, the earliest oilseed rape crops will be flowering by the second to third week of April. The norm for Scottish growers is a two-spray strategy for sclerotinia control, particularly in high-risk areas. These would be where there is a history of the disease, short rotations of one in three or four, or where other sclerotinia hosts such as carrots, peas, potatoes or soft fruit are grown.

Prothioconazole is still performing well in AHDB trials and should be used for the more important first spray. Bear in mind the maximum total dose for Proline on oilseed rape is 1.26L/ha – if growers have used it in the autumn or at stem extension, they need to work out how much they have left. At mid-flowering use the 0.46L/ha rate and if within the limits, another application at 0.32L/ha three weeks later. Other products are available if Proline can’t be used at the second timing.

3. Monitor and treat pollen beetle where thresholds are reached

Pollen beetle is showing its face in places and needs monitoring. Treat only where AHDB thresholds are reached - it is important not to blanket treat. Where an insecticide is required, Biscaya (thiacloprid) is an effective option as pyrethroid resistance is widespread.

4. Plan robust T1 for good barley disease control

Some growers have applied a T0 fungicide to winter barley where mildew and Rhynchosporium were present. For most, the T1 timing in barley will arrive in the second week in April. A product like Siltra (bixafen + prothioconazole) at 0.6L/ha is a good option and Fandango (fluoxastrobin + prothioconazole) at 1L/ha provides an alternative.

Keeping rates up is important to keep on top of mildew, with SRUC trials showing prothioconazole still has good protectant activity on the disease. The jury is out on inclusion of chlorothalonil at T1 for ramularia control, as the disease comes in later and is more critical at T2.

5. Consider fungicide options in wheat

I’ve heard reports of yellow rust kicking about in parts of Scotland and it should be dealt with early using tebuconazole or a strobilurin at T0. Similarly, get rid of any active mildew at T0 with a specific product so protectant material such as prothioconazole is enough to keep on top of it through the rest of the programme.

The earliest crops are likely to reach T1 by Easter Weekend and there will be a choice between succinate dehydrogenase inhibitor (SDHI) and non-SDHI options. Look at crop potential, drill date and variety disease ratings to guide product choice. SDHI options include Ascra (bixafen + fluopyram + prothioconazole) and Aviator (bixafen + prothioconazole). Ascra is slightly stronger on Septoria on comparable dose rates. If risk is lower and growers opt for the non-SDHI option, a straight Proline (prothioconazole) plus multisite fits the bill.

6. Clear up weeds in late-sown wheat crops

There are a few wheat crops that went in late behind potatoes and never received a herbicide in the autumn. These will require a tidy up as soon as possible, with annual meadow grass and broad-leaved weeds the main targets. Othello (diflufenican + iodosulfuron + mesosulfuron) fits well but bear in mind growth stage cut-offs and don’t apply ahead of a frost.

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