Over reliance on spring herbicides for grass weed control is causing congestion at the main fungicide and growth regulator spray timing and growers need to look to other methods of control, ProCam has advised.

According to the firm’s 4cast data, last year 70% of crops had their main grass weed control applied between February and April and this reliance on spring control causes several problems, technical director, David Ellerton said.

“This year is a classic example of fungicide programmes backing up because of cold wet weather in February and March stopping herbicide applications and due to a lack of tank mix options they are now holding up critical fungicide & PGR applications until they are done.”

Increasing weed resistance is another potential problem, he added. “We are now mainly reliant on just two main groups of chemicals – ACCase and ALS inhibitors, including fops, dims and sulfonylureas.

“Resistance to fops and dims is now so great that they are extremely unreliable particularly on large blackgrass plants. That leaves the sulfonylureas as the main means of late post emergence grass weed control.”

Dr Ellerton believes growers should make better use of cultural control methods, such as later drilling of difficult grass weed fields to allow control using stale seedbeds and avoid the main flush of germination occurring in the crop.

Focus should be given to pre-drilling and early autumn herbicides, with spring applications as a last resort, he noted.

“If we can do this, not only will we be able to keep on top of weeds, we’ll also get better disease control by relieving the spring log jam and allowing more timely applications of critical fungicides and PGR’s.”