Hard to Control Weeds progress

 

As part of the regional project funding received from the Wine Australia, the Riverland Viticultural Technical Group is continuing research into better ways of controlling difficult weeds; especially Gazania, or African-daisy. This invasive weed can be a serious problem in vineyards, where it can reach levels that markedly restrict vine growth.

It can also be very hard to control, with increasing numbers of growers reporting poor control with normally reliable knockdown herbicides such as glyphosate. Different herbicides and adjuvants, applied at different rates have been used in order to find an effective, low cost program that growers may use as a reference for further control.

 

Early trial results have been promising, and have led to the following general rules about controlling Gazania:

  • Gazania is almost impossible to control when it is stressed. Uptake of herbicide into the plant is limited in these conditions. Spraying actively growing weeds (usually evident from the open flowers and healthy leaves) gives the best chance at control.
  • Where weeds have waxy leaf surfaces, adjuvants may be needed to penetrate this waxy layer and carry the herbicide into the leaf tissue. Organosilicon wetters and spikes can help.
  • ‘Double knock’ applications comprising systemic and desiccant herbicides have shown promise.For successful uptake it is important to ensure that herbicide droplet life on the leaf is extended.
    This includes:
    o Using higher than normal spray rates – typically 350-450 L/ha of herbicide may be needed;
    o Always spraying under favourable conditions; ideally when relative humidity is high, or delta T is between 2 and 8;
    o Adding adjuvants that reduce evaporation, such as oil or polymer-based adjuvants;
    o Some herbicides, such as glyphosate, work better in neutral or slightly acidic solution.Adding a suitable buffer (eg Agri-Buffa or similar) may improve efficacy.

The initial trial work has shown that a buffered solution of high strength glyphosate, with suitable adjuvants sprayed under favourable conditions can kill over 90% of a very dense Gazania population.

Adding a suitable buffer (eg Agri-Buffa or similar) may improve efficacy. The initial trial work has shown that a buffered solution of high strength glyphosate, with suitable adjuvants sprayed under favourable conditions can kill over 90% of a very dense Gazania population.

Double knock applications of glyphosate, followed by a Paraquat /Diquat (eg Sprayseed or similar) mix was also successful. Further work will be done this season to better understand and refine these treatments before a factsheet is developed. For more specific advice about herbicide applications consult a suitably qualified advisor.

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