22 October 1999

Spray timing crucial to check blackgrass risk

APPLICATION timing is critical for good blackgrass control, especially where resistance is suspected or known to exist, warns Iain Hamilton of Novartis Crop Protection.

Speaking at a series of grower workshops organised by the firm last week, Mr Hamilton advised targeting the two-leaf stage of blackgrass and not be afraid to go early. "For many growers, that means changing the blackgrass product they use, not the timing. And it also means getting the sprayer out now."

For difficult blackgrass sites, early removal may be the only way to overcome weed resistance, he added. "For enhanced metabolism resistance, it is essential. You have to hit the blackgrass hard and early to have an effect. The longer you leave it, the more difficult it is to control."

He stressed that choice of blackgrass product can have a bearing on the consistency of results. "A minimum of 97% control is needed just to stand still. Products which are affected by environmental factors such as seed-bed condition and amount of rainfall will inevitably vary in performance.

"Many farms did not achieve the required levels of control last autumn," he said. "But it was very wet and control strategies went astray."

He illustrated this point with a six-season comparison of Hawk (trifluralin+clodinafop) and IPU. Hawk averaged 98% control while IPU managed 84%. "Hawk gives residual and contact weed control, so it has a further advantage."

Where resistance is known to be a problem, Mr Hamilton advises the use of Avadex pre-emergence. "That should be followed by 2.5l/ha of Hawk+oil at the two leaf stage. If no pre-emergence weed control product is used, then employ a Hawk/Lexus mix at the same stage."

A Hawk/IPU mix will extend the weed spectrum and extend activity through until the spring, he said. "But it wont give an improvement in blackgrass control." &#42