Alarm bells over poor black-grass control

POOR levels of black-grass control in some of this year’s cereal crops mean growers must make a determined effort to identify affected fields this summer.

The situation in many fields is so bad that any resulting increases in black-grass seed carryover must be dealt with properly in next season’s crops, a technical grass weed expert has warned.

“Although weed mapping of fields can be a time-consuming process, it could be a vital starting point for getting on top of the problem for next season,” said Simon Parker of Syngenta.

“While some fields have undoubtedly shown good levels of black-grass control, others have come off much worse. Whether this variability is due to resistance to some herbicides applied post-emergence of the black-grass, or whether it’s due to them being applied in less-than-ideal conditions, isn’t clear yet.

“But one thing’s for sure, with variable control, identifying worst-affected fields is likely to take on added significance for dealing with the problem for next season – because weed burdens could be proportionally higher.”

To tackle the issue, Mr Parker advises growers to earmark affected fields for special attention.

Additional cultural and chemical techniques may then be needed to deal with weed seed carryover into winter wheat and barley, he says, including ploughing it down and delaying drilling until after the first flushes have germinated.

Growers should also consider using more robust pre-emergence herbicide strategies and mixtures to reduce early weed competition. Tank-mixing the pre-emergence herbicide Defy with a flufenacet-containing treatment could boost control by around 10%, said Mr Parker.

“A single black-grass plant can produce 1000 seeds,” he added.

“When it comes to management, burial through ploughing can reduce black-grass by more than 60% compared to tine/disc cultivation. Similarly, sowing cereals in October rather than September has the potential to reduce black-grass plant densities by around 14%.

“Sowing crops at higher seed rates can also help suppress black-grass, as too can choosing competitive wheat and barley varieties, for example those that produce good ground cover.”