Selective Weed Harrowing in Cereals

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Abstract
Selective harrowing is introduced as a new concept in weed harrowing. It is defined as inter-row harrowing in late growth stages of the crop. Selective harrowing is expected to operate with a high selectivity, which means that a high degree of weed control can be obtained without associated crop damage resulting in crop yield reductions. Two questions with respect to weed harrowing in cereals are emphasised: How can selective harrowing be complemented with other principles of weed harrowing in order to achieve efficient weed control with a low number of passes; and how can the selectivity between crop and weeds be improved? Experiments in spring barley and winter wheat showed that high degrees of weed control could be achieved with weed harrowing giving results comparable to herbicide spraying. An increase of the row distance from 12 to 20 cm improved the selectivity of harrowing carried out in early growth stages whereas the selectivity of selective harrowing was unaffected by row distance. The total number of passes could not be reduced by combining different weed harrowing principles. Crop damage due to selective harrowing could not be totally avoided with high intensities of harrowing in spring barley but there was no detectable crop damage due to selective harrowing in winter wheat. Tractor hoeing combined with selective harrowing gave very high degrees of weed control without associated crop damage.