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2010 is a medium dormancy year

2010 is a medium dormancy year

Results from HGCA-funded research (Project 3336) have shown that dormancy in black-grass seed samples this autumn is medium. Seeds for the project were collected by farmers, ADAS, AIC members, AICC and Rothamsted Research.

Based on 52 geographical samples from 2010 the actual mean figure was 37% germination. 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 2009 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 2010, during this period was cold during the first half and hot at the end, a similar pattern to 2009.

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.

What do these dormancy results mean? 
This is not a result we have seen before and so there is a degree of extrapolation in what we would expect. Based on our understanding the following management principles are likely to apply:

Black-grass emergence
• We do not expect either very rapid or very slow emergence of seed shed this year. It is possible it could be a couple of weeks later than a low dormancy year.
• Seed shed in previous years is likely to emerge early (given that most regions have had recent rain).
• Based on two years monitoring, high dormancy did not, in winter crops, lead to a spring flush of black-grass. Remember that late emerging plants are much less competitive, especially in a well established crop.

Before drilling
• Spray-off any black-grass that does emerge before drilling – there should be some opportunities this year, but ‘a little patience’ may be required. Adequate moisture will also be necessary.
• 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 and do not reduce crop seed rates where high populations of black-grass are expected.
• Avoid cloddy seedbeds to maximise herbicide performance and reduce risk of late emerging black-grass.

Herbicide strategies
• A robust pre-emergence herbicide, with a residual component, is an essential start for any programme and will help cover the period of emergence. 
  - Aim to apply within a week of drilling to a fine seedbed.
• Post-emergence sprays should be applied to small emerged plants in good conditions for activity. There might be a benefit from a residual element, especially if applying early, to control late emergers.
  - 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.

HGCA's guide ‘Managing weeds in the arable rotation’ (G50) which can be accessed from www.hgca.com/weedmanagement contains more information on managing weeds through a rotation including the latest Weed Resistance Action Group Guidelines.