Oilseed rape growers who were hit by light leaf spot (LLS) last season face a high risk of further problems in 2013 and should be prepared to spray in the next few weeks, HGCA work has shown.

LLS has become more prevalent in England in recent years and this is set to continue. November is an important month for monitoring the disease and spraying if risk is high.

HGCA fungicide performance trials, which started in 2009, show that good control of light leaf spot is difficult to achieve. A report of the trials, now available from HGCA, shows azoles are the leading fungicides, but reduced sensitivity to these products may be affecting performance.

LLS decisions

• Spray in autumn at high-risk sites.
  
• After treatment inspect crops for light leaf spot regularly.
  
• If phoma sprays are being used, check crops in winter and early spring to determine if the sprays have given adequate control of light leaf spot.
  
• Apply fungicide before stem extension in spring as soon as light leaf spot is found.
  
• During early stem extension stage growers should spray when 15% of plants are affected.

Prothioconazole remains the leading active. Product choice will also be affected by the need for plant growth regulation and phoma treatment, according to the report.

Trials showed no improvement in control with more than half dose rate application. But better timing could boost control as many crops are treated when the disease is already well established.

Phoma

Further HGCA trials also highlight best practice control measures for phoma, which is appearing in crops and will soon require treatment. Fortunately early epidemics which can put 0.5 t/ha yield at risk have been avoided this season.

HGCA trials found that two sprays at half dose can give good control, though correct timing is key. The first spray should be made when 10-20 % of plants have phoma leaf spot, the second when there are visible signs of re-infection, says the report.

More on this topic

For full summary reports go to hgca.com

Full details of fungicide performance in oilseed rape, wheat and barley are being presented at the Agronomists’ Conference in Peterborough on 11 December. For more information visit hgca.com/events

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