Dormancy in black-grass this autumn is high.

To minimise risks of black-grass

• Leave high populations from previous years buried;
• Establish a competitive crop;
• Ensure good herbicide timing and choice.

Results from BASF-funded research have shown that dormancy in black-grass seed samples this autumn is high. Seeds for the project were collected by farmers, ADAS, AIC members, AICC and Rothamsted Research.

Based on 52 geographical samples from 2011, the actual mean figure was 23% germination.

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This compares with the results for at least 20 samples tested in each of the years 2001 to 2005 as part of a LINK project (LK 0923) and from tests in 2006 to 2010 funded by HGCA.  In all years samples were collected from across the country.  All these years’ results are summarised in the table below. 

Weather conditions during maturation influence the dormancy level of black-grass; this period generally occurs during the second half of June through to early July.  The weather in 2011 was average for temperature but slightly wetter.

As in previous years, some samples tested showed lower levels of dormancy indicating that local conditions were still important, but there were no obvious regional differences.

High dormancy is likely to mean a more protracted germination period for black-grass.

What do these dormancy results mean?

The prediction this year is that black-grass germination will be slow, even with adequate seedbed moisture.

The results of 2011 are most similar to 2002, 2004, 2007, and 2008. They are unlike 2005 and 2006, where seeds had a lower dormancy and germinated readily when moisture was available.

Key action points are:

Before drilling

• Spray off any black-grass that does emerge before drilling – although this is likely to be less than in a low dormancy year.
• Where there are high black-grass populations, consider burying weed problems by ploughing.  However, after high levels of control in the current crop, avoid ploughing-up more seeds than you bury.

At drilling

• Aim to get a competitive crop, perhaps by early drilling.
• Avoid cloddy seedbeds to maximise herbicide performance and reduce risk of late emerging black-grass.
• Do not be tempted to reduce crop seed rates where high populations of black-grass are expected.

Herbicide strategies

• Use a robust herbicide with a residual component to cover the protracted period of emergence. Crystal (flufenacet + pendimethalin) containing pendimethalin is especially suited to these conditions due to its longer residual activity.

pre-emergence

• sprays could need a residual element to cover some late emergers.  Based on previous years monitoring, high dormancy does not, in winter crops, lead to a spring flush of black-grass.  It is also worth remembering that late emerging plants are much less competitive, especially in a well established and competitive crop.

Post-emergence

• Consider the following important aspects in determining the optimum post-emergence timing: 

-       Apply herbicides in conditions most suited to their activity

-       Small black-grass plants are easier to control.  This is especially the case where enhanced metabolism resistance is, or may be, present.