Two dates were employed, 21 September and 23 October with black-grass heads being assessed in June. The results showed a significant decrease in the mean black-grass head counts when drilling was delayed for by one month.
|Variety||Seed rate (numbers m2)||Plant Count m2 (21 September Drill)||Yield (t/ha)||Plant Count m2 (23 October Drill)||Yield (t/ha)||Yield Difference (late v early drilling)|
Table reproduced from Ward et al., (2012) – A demonstration on the effects of winter wheat variety choice, seed rate and sowing date upon control of black-grass (Alopecurus myosuroides).
Delaying drilling from September to October can have a significant effect on the number of black-grass plants, and consequently the number of seeds ready for germination in the subsequent autumn . The benefit from delayed drilling is most pronounced when soils are moist, stimulating relatively early germination of black-grass enabling one or more sprays of a non-selective residual herbicide such as glyphosate.
Taking a simplistic point of view – delayed drilling can reduce yield. However, the extent to which yield is reduced depends on a variety of factors including (but not limited to): black-grass pressure/competition, crop variety and speed of initial establishment. It is due to these combinations of factors that, if there is less black-grass pressure on the crop during establishment (which hopefully should be achieved through delayed drilling) then yield potential may not be reduced and there could even be an increase!