OILSEED RAPE and bean growers should consider delaying the application of residual herbicides until conditions are more suitable, Interfarm has advised.

Warm, dry soils and rapid crop canopy growth all mean it may be worth waiting one to two weeks or longer before applying residual products such as propyzamide, said the firm’s technical manager, David Stormonth.

“So far, this autumn is not playing into our hands when it comes to residual herbicide performance.”

Below average rainfall in the past nine out of 11 months has left soil moisture deficits in many areas and products like propyzamide need good soil moisture to penetrate into the weed rooting zone, he explained.

With more rain forecast, it may be worth waiting a week or two before treating crops, he suggested.

Soil temperatures are also too high for maximum residual performance at present, so it may be worth holding off sprays until conditions turn cooler, he said. “Growers have from now to the end of January to use propyzamide.”

Dr Stormonth also pointed out that rapid crop canopy development may reduce spray ground coverage. “It may be worth taking a rain check to see if frosts and rainfall will reduce canopy ground cover in very forward crops.