Zero Tolerance with Brome

February, 2004 - Modern, high intensity wheat systems are turning one of our biggest potential grass weed threats into a serious problem for many. And, warns Farmcare agronomist, Dr Bob Bulmer, these problems are set to mushroom if growers are not very careful indeed.

"We simply must treat brome with the utmost respect," insists the specialist responsible for the agronomy of the Co-op's 85,000 acre arable business. "Zero-tolerance is what we need if we are to avoid rapidly growing populations, swingeing yield penalties and serious harvesting difficulties.

"Unlike black-grass and wild oats, brome may occur only in patches or fields rather than across whole farms. And it may show no signs of herbicide resistance. But it is so well-adapted to modern wheat growing that it doesn't need to be resistant or widespread to cause headaches every bit as a severe.

"At the same time, the huge variations evident in dormancy and emergence across its many and varied forms mean the weed can adapt rapidly to take maximum advantage of every changing opportunity presented by our ever-more intensive wheat growing regimes."

While Dr Bulmer still sees barren brome as the biggest problem, he points out that a significant proportion of reported barren brome infestations are actually likely to be the more difficult-to-tackle great brome for which it is easily mistaken. He explains too that both meadow and soft bromes also appear to be becoming more widespread.

"Weeds don't stand still," he stressed. "All the time our changing systems are selecting for different populations better adapted to the opportunities they present; particularly with brome because its lifecycle and biochemistry are so similar to wheat.

"More wheat in the rotation, more winter drilling, earlier sowing, lower seed rates, less total inversion tillage, and autumn weed control regimes that selectively eliminate other grass weeds are all contributing to the growing challenge of brome."

Tackling the weed must be a priority for all those who have it, Dr Bulmer insists. While selective herbicides are available, he is adamant that growers must take an integrated approach to control, designed to stop the weed compromising yield and harvestability without totally eliminating it. That way they will avoid selecting for even more difficult-to-control populations.

He urges everyone to establish precisely what brome species they are dealing with through summer field recording then adapt their systems it exploit the weed's specific weaknesses.

Foremost amongst his management priorities where brome is a problem are:

• Combining infested fields last;
• Cleaning combines and field equipment thoroughly between fields;
• Burying barren brome seed with consistently even ploughing;
• Leaving meadow and soft brome on the surface for 4-6 weeks before cultivating;
• Achieving a good stale seedbed kill before drilling;
• Delaying drilling to achieve good out-of-crop control, wherever necessary;
• Avoiding low seed rates and initially open, less-competitive crops; and
• Introducing beans, peas or a spring crop into the rotation.