Timing of post-emergence weed harrowing

The timing of post-emergence weed harrowing was evaluated for two years in spring barley with crop-weed selectivity and crop recovery as the key parameters measured. selectivity describes the relationship between weed control and crop soil cover immediately after harrowing, with crop soil cover as the percentage of the crop that has been covered by soil due to harrowing. Crop recovery describes the relationship between crop yield loss and crop soil cover in the absence of weeds. Neither selectivity nor crop recovery was affected by timing within a period of two weeks in the early growth stages of spring barley. Selectivity was unaffected by year and 80% weed control was associated with crop soil cover in the range of 23–33%, for all combinations of year and growth stage. Crop recovery was affected by year, with an average crop yield loss of 3.5% caused by 25% crop soil cover in 2007 and complete recovery in 2008. A detailed study of crop growth and weed density in the period just after harrowing, showed that the recovery processes of crop and weeds were influenced by timing of harrowing, but this had no impacts on crop yield. In conclusion, timing of post-emergence weed harrowing was not found to be crucial, given the condition that the aggressiveness of cultivation was adjusted to the growth stage