In a response to member concerns, for the last two seasons Riverland Wine Viticultural Technical Group (RVTG) has been trialling a wide range of treatments in an attempt to find an economical and effective control for gazanias – an increasingly problematic weed.
The initial trial aimed at casting a ‘very wide net’ by trying every conceivable potentially effective alternative. These early results gave the trial team a good idea of where to concentrate efforts in the project’s second stage, focusing on the most promising treatments. Also included were a number of suggestions from growers who had also tried chemical control on their properties.
A number of important lessons learnt over those two years. Anyone who has tried to control it well knows gazanias are tough; almost bulletproof. While easy to ‘burn-off’ initially and get growers excited, it has the ability to readily regrow and will usually reappear within a month or so. Young plants are easy to control; the older established ones are the challenge. Give them a good season with enough rain (or irrigation) to get established and they soon put down a very deep root system. They are then very hard to kill under commercial conditions.
It is most important to kill any new infestations before they become established to avoid the repeated treatments necessary to control the older plants.
In general, all treatments, which had a strong dose of glyphosate 450 at 8 litres/ha worked fairly well, as long as this was spiked with Agribuffa, AGDirect and Pulse. The trick is to get as much of the glypho as possible through the tough cuticle and into the plant. The limitation with this treatment is that with 8 litres of glypho/hectare, it is expensive. The rate of water used was 342l/ha.
An equally good, or slightly more effective performer was to combine 4l/ha of the glypho, Agribuffa and Pulse with Hammer 400EC at 45ml/ha. This is also a cheaper option.
All other treatments tried (and 25 were tried in all) were either more complex or less effective.
There was no ‘magic bullet’ and all known treatments will require timely follow-ups to deal with the weakened survivors.
It is most important to spray when the plants are actively growing. Stressed plants mean limited uptake. It is also better to spray when the weather is more conducive to effective uptake, such as when it is cooler; to slow down the evaporation rate. Higher water rates do assist, but have obvious practical limitations if the area to be sprayed is large.
A fact sheet fully summarising the trial results will be available on the Riverland Wine website shortly and copies will be distributed at the breakfast meetings.