Gettingthe timing right for effective light leaf spot control is crucial, according tothe latest fungicide performance information from HGCA.
Resultsshow that controlling light leaf spot can be problematic so early detection andspraying before the disease becomes established are essential. At high risksites, growers should look to apply a protectant spray in autumn, says Dr PaulGosling of HGCA.
Therisk at specific sites depends on weather and the history of the disease in thevicinity. If light leaf spot was well established on stems and pods in cropsbefore harvest in 2014, there is a high risk of continuing problems in 2015 asair-borne spores are produced on the previous years crop debris.
Tomanage 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 theirregion. On specific farms with light leaf spot problems, varieties with adisease resistance rating of at least 6 (7 in Scotland and the far north ofEngland) contributes to better control.
Followingany autumn sprays, the new year is the next important period for light leafspot control. In January and February, monitor crops closely and deal with anylight leaf spot symptoms promptly, explains Dr Faye Ritchie of ADAS.
Thethreshold of 25% of plants affected only applies at the early stem extensionstage. If light leaf spot is found before this, there is no threshold and earlytreatment is recommended to prevent the disease spreading within the crop.
Doseselection is very site and situation-specific and will depend on varietalrating, crop growth and disease pressure. Increased efficacy against light leafspot can be achieved by higher doses, although the yield increases in responseto product dose did vary depending on the site and season.
Theresults showed that several products can achieve similar levels of control.Because of this, product choice will also depend on other factors includingactivity against phoma leaf spot and plant growth regulation. In smaller,stressed crops, some negative yield effects were noted at sites wherefungicides with PGR activity were used at high doses, however, on advancedcrops this year growth regulation is likely to be important.