Successful weed control in forage brassicas Weed control is important in forage brassicas both to minimise crop competition and to reduce the soil weed seed burden in advance of subsequent crops or pasture. Forage brassicas are particularly susceptible to weed competition during establishment1. This is especially the case when sowing into scenarios with moderate to high weed seed loadings in the soil, such as previously cropped ground or run-out pastures with even just a low weed content. Cultivation can also bring long dormant weed seeds to the soil surface enabling germination within the crop. Three important weed control aspects worthy of focus in your forage brassica cropping plan include cultural control, spray out and seedbed preparation and the use of pre and post-emergent chemicals.
Cultural weed control Agronomic practices that contribute to the rapid development of a dense brassica leaf canopy have an important role to play in providing cost-effective weed control. Aside from enhancing weed control, the pay-off is increased yield and quality forage for your livestock. Areas to address include soil testing and correcting soil pH and fertility, preparing a quality seedbed, planting at appropriate soil temperatures and moisture, placing fertiliser down the spout at sowing (e.g. DAP), ensuring good seed to soil contact and monitoring early for pests to maintain plant population. These practices contribute to rapid germination, establishment and canopy cover ensuring the crop gets a head start on weeds and then shades them out.
Sprayout and seedbed preparation The principles involved here apply for both cultivated and direct drilling situations. An effective sprayout kills all existing vegetation including rhizomes and roots. This reduces seedbed trash and assists with preparation of good soil tilth for sowing and rapid germination2. The basis of this application, or applications, is typically glyphosate. A tank partner appropriate for any hard-to-kill broadleaf weeds present, with a residue profile appropriate for subsequent crops, may be warranted. Perennial weeds regrowing from root remnants e.g. dock, californian thistle or yarrow, can be difficult and more expensive to control selectively within the brassica crop, particularly under pre-emergence herbicide programmes and so are best dealt with at sprayout. Pre and post-emergence weed control Most brassica crops will still benefit from chemical weed control while the crop emerges and establishes. Effective control of weeds during brassica establishment relies on selecting a suitable approach for your scenario (pre or post-emergence programme) and then selecting herbicides that best fit the weed spectrum and crop rotation.
| Fathen at ideal time to spray.
50 | THE FARMLANDER
A pre-emergence herbicide programme may be suitable where you have a reliable understanding of the weed spectrum that will impact the crop, and can achieve the seedbed surface, incorporation or moisture activation requirements of the
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