New infections of phoma leaf lesions have already been widely spotted with repeated heavy rainfall and there is a serious risk of rapid infection spread in susceptible plants this season, warned Syngenta's technical manager, Georgina Wood.

She said the key application timing is to stop development of leaf surface lesions and the invisible spread of infection down to petioles and stems, aiming to prevent the later formation of yield limiting stem cankers.

“Plants currently with small leaves are more susceptible and a priority for early fungicide treatment such as Plover, since it takes less time for the infection to move to the stem, compared plants with larger leaves,” she advocated. Disease development is also faster in warmer conditions, which typically makes early season infections more damaging.

Syngenta iOSR growers have reported crops at widely varying growth stages this season. Those planted before rainfall in early August had largely grown away well, whilst those drilled later were generally slow to emerge in dry conditions with many also significantly impacted by cabbage stem flea beetle damage.

The treatment threshold is normally considered around 10% of plants showing visible signs of leaf lesions. However, factoring in the size of plants, along with pressure of repeated rainfall events and windy conditions triggering spore spread this season, would indicate small crops may require earlier protection – on the presumption that you can travel on the land!

The Borders area in Scotland has fared worse than most, with 47 days rain since mid-July and 34 since the start of August and some crops now face prolonged and serious disease pressure, she added.

The early onset of phoma lesions require initial treatment now, and is likely to require a two spray-programme to cover the autumn infection period. A second application is typically applied where new infection and leaf lesions are identified four to six weeks after the first treatment, or when light leaf spot is seen.