Abstract
SummaryThe spatial distribution of Elymus repens L. was mapped in five cereal fields during the 1994 season. Weed maps were created using a semi‐automated system mounted on a vehicle that travelled up the tramlines, centred on a 12‐m‐wide spray boom. Two operators detected weeds visually and recorded their presence and density by means of a simple push‐button system that recorded data from (2 × 1) m2 areas, or cells, across the boom section on a portable computer. The position of the vehicle along the tramline was monitored by integrating output from a wheel sensor. Eight tramlines of one field were mapped three times consecutively, to assess detection and navigational error. Pair‐wise comparisons of the three runs gave approximately 85% repeatability on presence/ absence data, 80% on zero/low‐ or high‐density data and 85% on low/high‐density data when weeds were definitely present. Simultaneous comparisons of all three runs gave 78%, 69% and 75% respectively. Repeated runs of tramlines up to 550 m long recorded mean differences of approximately 2 m with a maximum error of 14 m (2.5%). The spatial distribution of E. repens within the five fields was visibly patchy, but the size and morphology of patches varied both within and between fields. Thus, the potential reduction in herbicide usage as a result of patch spraying varied with patch morphology and infestation level. The effect of lowering the resolution from six (2 × 1) m2 cells to three (4 × 1) m2 cells across the 12‐m boom width showed little change in potential reduction in herbicide usage.
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