Keeping a lid on light leaf spot and tackling problem grassweeds in cereal crops are priorites in Southern Scotland this month for James Howatt
Oilseed rape in the region was 100% drilled by the second week in September. On the whole, crops went in well and moving in to October, growth stages are anywhere between just emerging and four true leaves.
Winter barley is almost 100% drilled and some crops have emerged. Winter wheat planting is about 25-30% complete, but progress has been checked by recent wet weather. Growers are also holding off with rolling after the drill to avoid capping of seed-beds in heavy rain.
The Rothamsted Research light leaf spot forecast, based on last season’s pod incidence and summer temperature and rainfall, gives a good indication of disease risk to oilseed rape crops. Growers can also utilise the Bayer and ADAS SpotCheck service to test leaf samples for latent infection. Where risk or latent infection is identified, an autumn spray to protect crops from light leaf spot is recommended before winter sets in. Proline (prothioconazole) at 0.46L/ha is the most effective treatment for light leaf spot and will also provide additional activity on phoma.
Annual meadowgrass is still adequately controlled by low herbicide doses, such as 0.3L/ha of Liberator (flufenacet + diflufenican). However, grassweeds such as bromes, ryegrass and rat’s tail fescue are becoming more prevalent across Southern Scotland and they are all tougher to control.
This means pre-emergence herbicide stacks in wheat need to be better tailored to grassweeds are present and may mean more robust rates, more modes of action and ultimately more cost to achieve adequate control.
Liberator should be the foundation of wheat pre-emergence programmes, but dose inceased to a full rate of 0.6L/ha, along with 2L/ha prosulfocarb. Pendimethalin and tri-allate are also options to add to the stack and can help achieve the best levels of control.
With no contact-acting herbicide options to control grassweeds in winter barley post-emergence, growers should focus attention on applying a robust pre-emergence spray to the crop. This will give you the best chance of controlling key grass- and broad-leaved weeds early. Liberator is fully approved on winter barley up to growth stage 22, although it is best applied pre-emergence. It can be used in combination with pendimethalin or tri-allate, which will improve control of problem grassweeds such as the various brome species.
Liberator can also be used for grassweed control in winter oats under an extension of authorisation for minor use (EAMU). The EAMU allows a rate up to 0.6L/ha before the fifth tiller stage, or before 31 December in the year of planting. We would recommend that it is applied pre-emergence. Using rates above 0.3L/ha can cause yellowing of the oats, so it is at the grower’s own risk. However, experience shows this has little long-term impact on crop yield.
With no Deter (clothianidin) to provide early protection against aphids carrying barley yellow dwarf virus (BYDV), crops will be vulnerable this autumn. Temperature drives the aphid’s lifecycle and a T-Sum system can be used to calculate accumulated day degrees above 3C from emergence. When the T-Sum reaches 170, crops should be checked for colonising aphids and treated with a pyrethroid where present to minimise secondary BYDV spread.