Cereals 2009: Cultural controls to play increasing role in blackgrass strategy

Growers with blackgrass problems will increasingly have to consider non-chemical methods as part of an overall control strategy, experts suggested at Cereals 2009.

Rothamsted Research‘s Stephen Moss said there was now a grudging acceptance from growers that cultural controls were necessary, largely as a consequence of increasing resistance to key chemicals. “The truth is that Atlantis, although it is still working well in general, it is not working as well as it used to.”

Pre-emergence herbicides would continue to play an important role, but were not the whole answer, he said.

There were several cultural control measures, including ploughing, spring cropping and improving in-crop competition using varieties or high seed rates, growers could consider.

By themselves levels of control weren’t high, he admitted. “If you came to market with a new chemical control means of controlling blackgrass that gave 22% control, like using Oakley rather than Hereward in our plots, growers would just laugh,” he pointed out.

“By itself each non-chemical method gives a pathetic level of control, but taken together three pathetic levels of control can give something useful.”

Seed rates

The impact of seed rates and varieties were also demonstrated by Velcourt. Where a seed rate of 350 seeds/sq m had been used, final blackgrass head numbers were half that of where just 100 seeds/sq m had been sown, the firm’s Keith Norman explained, which was a hugely worthwhile contribution. “It is similar to what you’d expect from a pre-emergence treatment.”

Varietal competitiveness could also play a part in reducing blackgrass populations, but it appeared that the best effects were in combination with high seed rates.

For example, there was very little difference in the numbers of blackgrass heads in the low seed rate plots of Robigus, a leafy, profuse tillering variety, and Cordiale, which is a much less competitive variety.

But in the higher seed rate plots the extra competitiveness of Robigus’s growth habit had made more of a difference in reducing the blackgrass population, Mr Norman said.

Higher seed rates would probably cost the same as Atlantis for trifluralin levels of control, Dr Moss said. “That seems ridiculous, but we haven’t got trifluralin any more, and if Atlantis is not working well, what other options do you have?

“In fact growers should be considering cultural controls before they have problems with Atlantis. If you leave it until then, it is really too late.”

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