Time it right for spot control

Getting the timing right for effective light leaf spot control is crucial, according to the latest fungicide performance information from HGCA.

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Getting the timing right for effective light leaf spot control is crucial, according to the latest fungicide performance information from HGCA.

Results show that controlling light leaf spot can be problematic so early detection and spraying before the disease becomes established are essential. “At high risk sites, growers should look to apply a protectant spray in autumn,” says Dr Paul Gosling of HGCA.

“The risk at specific sites depends on weather and the history of the disease in the vicinity. If light leaf spot was well established on stems and pods in crops before harvest in 2014, there is a high risk of continuing problems in 2015 as air-borne spores are produced on the previous year’s crop debris.”

To manage these risks, growers can use the light leaf spot forecast – www.rothamsted.ac.uk/light-leaf-spot-forecast (2014 update available soon) – to get an idea of the overall risk in their region. On specific farms with light leaf spot problems, varieties with a disease resistance rating of at least 6 (7 in Scotland and the far north of England) contributes to better control.

Following any autumn sprays, the new year is the next important period for light leaf spot control. “In January and February, monitor crops closely and deal with any light leaf spot symptoms promptly,” explains Dr Faye Ritchie of ADAS.

“The threshold of 25% of plants affected only applies at the early stem extension stage. If light leaf spot is found before this, there is no threshold and early treatment is recommended to prevent the disease spreading within the crop.

”Dose selection is very site and situation-specific and will depend on varietal rating, crop growth and disease pressure. Increased efficacy against light leaf spot can be achieved by higher doses, although the yield increases in response to product dose did vary depending on the site and season.“

The results showed that several products can achieve similar levels of control. Because of this, product choice will also depend on other factors including activity against phoma leaf spot and plant growth regulation. In smaller, stressed crops, some negative yield effects were noted at sites where fungicides with PGR activity were used at high doses, however, on advanced crops this year growth regulation is likely to be important.

For full details, read the fungicide performance report and other useful disease control information at hgca.com

 

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