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Talking agronomy with Maddy Vaughan: Watch for disease in high biomass OSR

Agronomist, Maddy Vaughan says mixing multi-sites could be more effective than a comparable increase in dose of the actives applied alone, according to new trials.

The 2019 season got off to an unexpected early start with some very warm and dry weather. We saw the driest January we have experienced for 13 years and had the hottest February day on record.

 

March entered like a lamb, before Storm Gareth blew in and brought some more seasonable wet and windy weather. The mild autumn and winter has meant winter cereals raced away in February and some oilseed rape plants even started to flower in early March, surprising everyone out of their winter sedentary state and into action.


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Drilling

 

With conditions so favourable early on, many growers took the opportunity to start their spring drilling. For those with grass-weed problems the use of pre-emergence chemistry has been widely employed and, with adequate moisture, hopefully to good effect.

 

For those that held off with the aim of grass-weed control, conditions look set to return to favourable drilling conditions next week, so it looks like most spring drilling should be completed by the end of March this year; a welcome relief after last year’s late season!

 

Residual

 

Fertiliser applications were generally applied early to winter crops, with growers taking advantage of ideal travelling conditions. However, due to the relatively dry and warm winter, any residual nitrogen from last year that is usually washed away is still in the soil, leading to some high soil mineral nitrogen levels.

 

Autumn drilled crops have also developed good rooting structures in the dry winter conditions enabling them to better scavenge for nitrogen, and so most crops are in a luxury nitrogen uptake situation.

 

Growth

 

As a result, many crops are quite leggy and thoughts are turning to T0 applications and the robust use of PGRs early on.

 

It should be remembered that high nitrogen uptake from soil reserves and top dressings, together with the favourable growing conditions, are accumulating high biomasses which are also producing perfect microclimates for disease development.

Disease

 

I have therefore been closely monitoring disease pressure out on farm. Yellow rust has been relatively active this season, particularly in the more susceptible varieties like Crusoe.

 

On varieties which score a five or less for yellow rust on the AHDB Recommended List, a rust active azole or strobe should be included at the T0 timing.

 

This chemistry will also have good efficacy on brown rust, and while not seen as much this season so far, brown rust does enjoy warm winters and early springs and so its development over the next few weeks might be expected.

 

Septoria is easy to find on the older winter wheat leaves, particularly on earlier drilled crops or in the more susceptible varieties. Control of septoria at T0 is not usually associated with yield benefits in winter wheat and ultimately weather conditions at stem extension will have the greatest impact on septoria pressure.

 

However if you have a susceptible variety, the application of a multi-site fungicide such as chlorothalonil can help lower infection levels early on and so reduce the risk of septoria becoming problematic on upper leaves. It would also help to insure against the spread of septoria if the timing of the second spray is delayed.

In trials, chlorothalonil still remains the most active multi-site fungicide on septoria compared to folpet and mancozeb. However, work is being done to see if mixing multi-sites provides better control. Trials are ongoing, but early indications suggest this may be more effective than a comparable increase in dose of the actives applied alone.

 

Pests

 

The mild start to the year is also causing concern that aphids will be more active earlier than usual this year, causing a potential threat to our spring crops.

 

The AHDB are predicting that aphids will start to fly around two weeks earlier than average due to the unseasonably mild temperatures experienced in January and February. Monitoring forecasts should be watched to see how pressure is mounting this spring.

 

Other pests have also taken advantage of the mild weather, with adult cabbage stem flea beetles still being found in oilseed rape crops in February and the beginning of pollen beetle migration into green buds beginning in early March.

 

While the windy, wet weather of late has stopped these pests from reaching thresholds, it will be crucial this season to regularly consult pest forecasts and monitor pest threats in field to help determine threats and facilitate decision-making when it comes to the use of insecticides.

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