Germination figures for blackgrass give concern

Mean germination figures for blackgrass seed tested as part of the annual dormancy testing service are the lowest since the recording started in 2001, making control even more challenging this autumn.

The germination of 10% compares with last year’s 23% and the 37% in 2010, where many growers successfully reduced populations with stale seed-beds. It means there will be a delay of six to eight weeks before 2012 blackgrass seed will germinate, although there will be a range as germination is also dependent on soil moisture, cultivation type and timing.

ADAS’s Sarah Cook advises growers to spray off any blackgrass that does emerge before drilling. “Although this is likely to be less than in a low dormancy year, there could be still quite high numbers where seed return was high. Also, seed from previous seasons will germinate after cultivation.

“For example, 280 heads/sq m could lead to a seed return of 28,000 seeds/sq m – of which 10% is 2,800 seeds/sq m.”

Where there are high blackgrass populations, consider burying weed problems by ploughing. However, care is needed to avoid ploughing up more seed than you bury, particularly where high levels of control were achieved in the current crop.

If land was ploughed in 2011, shallow cultivation will lead to most blackgrass seed germinating over a protracted period, while ploughing again will bury this year’s seed and bring up old seed that will germinate quickly if moisture is present.

However, where land was shallow- cultivated in 2011, there will be old seed near the surface, so shallow cultivation this year will stimulate old seed to emerge quickly and freshly shed seed will germinate over a protracted period. Ploughing may be a better option, burying 2012 seeds, with older seed brought to the surface, which will germinate rapidly.

At drilling, she advises establishing a competitive crop by preparing a good seed-bed or using a higher seed rate. “Avoid cloddy seed-beds to maximise herbicide performance.”

A robust pre-emergence with a residual component will be needed to cover the protracted emergence. Richard Peake of Harlow Agricultural Merchants believes the core to a successful programme should be pendimethalin + flufenacet + diflufenican (DFF).

“In two years of trials, we have counted emerging blackgrass plants that have come through the various treatments on a monthly basis from October through to March. We found that, on average, 75% of those that made it through will die by March, but they do not start to die until after Christmas.”

He believes that is due in part to the longevity of pendimethalin slowly killing the plants. “Similar treatments without pendimethalin show only a 50% plant loss. So look at the emerging blackgrass and see whether the 25% that will remain are likely to be a problem. If so another spray needs to be made.

“By far the best performing programme was Avadex (tri-allate) granules, followed by Crystal (flufenacet + pendimethalin) + DFF. It was head and shoulders above the other stacks of actives and this combination also helps control wild oats and rye grass.”

Testing is carried out by ADAS and funded by BASF.

Blackgrass heads north

Contractors and climate change are being blamed for the northwards spread of blackgrass in the UK.

Dan Finch, an agronomist with DKB Crop Protection, has seen a marked rise in the weed in north-east England, while Mark Ballingall of the SAC highlights increased ingress in the Borders and the Lothians.

Both put the rise down to seed being carried on contractors’ vehicles and Mr Ballingall suggests that climate change could be playing its part.

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