OILSEED RAPE growers must beware of increased risk from sclerotinia where flowering periods are protracted, experts have warned.

The main flush of sclerotinia spore production is not anticipated until late April, so protecting crops throughout flowering and petal fall over the next two to three weeks will be crucial, said Syngenta.

Rotting petals stuck to the leaf surface act as a food source for spore germination and crops with the longest flowering will be at greatest infection risk, added Caroline Young from ADAS.

“In very dry years, when petals fall straight to the ground, we have had high spore levels, but relatively low plant infection. But if leaf surfaces are wet, petals can stick incredibly tightly,” she said.

“The worst incidence is frequent light rainfall or heavy dew that wets the leaf surface, but doesn‘t wash fallen petals off.”

There is no curative solution for controlling sclerotinia, so growers must apply a fungicide to protect leaves before petal fall, said Syngenta‘s technical manager, Iain Hamilton.

Mr Hamilton recommends using Amistar (azoxystrobin) before mid-flowering and the onset of petal fall, which is likely to be over the next fortnight in many areas, he said.

Farms with a history of the disease, or a short rotation between susceptible crops (including peas, potatoes and carrots) should pay close attention to the risk, he noted.