The earliest phoma attack on oilseed rape since 1999 merits a two-spray control programme, according to Syngenta.

The last time the disease hit this early in the season, crops responded very well to a two-spray Plover (difenoconazole) programme, says the firm’s Iain Hamilton.

With the high risk and rapidly spreading incidence of leaf spotting he urges growers not to worry about growth regulation now.

“Last year some growers opted to use metconazole in the autumn to check lush growth, but suffered from a reduced level of phoma control.

“Autumn disease must be the priority to protect yield potential; with any growth regulation reserved for the spring, when the effects of winter die back and pigeon damage can be realistically assessed.”

Most growers cut seed rates this season, and although crops are growing strongly, canopies can be better managed in spring, he maintains.
 
With southern England receiving significant recent rain, spore release has been almost continuous. Crops close to last year’s rape fields are most at risk, especially if stubbles were not ploughed in, he warns.

“Wet and warm conditions mean the spread of phoma within the leaf will be rapid, particularly on any small-leaved crops and low resistance varieties.

“Plover should be applied well before infection reaches the stem, for the best curative activity and to prevent disease developing further.”

Fast growing crops are expected to benefit from a follow-up application after about six weeks. But growers should be ready to treat if spotting reaches the threshold of 10% of plants infected if the weather stays showery and warm, advises Mr Hamilton.