Celebrity gardeners aren’t joking when they describe gazanias as hardy plants suited to a range of tough environments. Unfortunately, that’s not such good news when you’re trying to get rid of them.
Gazanias have become such a problem to some grapegrowers in the Riverland that the Riverland Wine Viticulture Technical Group (RWVTG) organised a comprehensive two-year trial to work out how best to eradicate them.
‘They are virtually indestructible and don’t need any water so they are either a great plant or an awful weed’, said Riverland Wine’s Chris Bennett.
‘A couple of years of reasonable spring rains has allowed them to germinate and proliferate. After a year like we’ve just had, I hate to think what they’ll be like next year.’
A few growers found gazanias encroaching on their vineyards and tried to control them with the normal chemicals registered for vineyard use, but it was as if they were selected to encourage gazanias. ‘They were killing off everything else and the gazanias were saying thank you very much,’ Mr Bennett said.
The same happened with regular roadside spraying by councils. No matter how sick and sorry the gazanias looked initially, they invariably bounced back stronger than ever.
Spraying large areas also requires an awful lot of spray, and thus constant refilling, and there is the added problem that the leaves of the plants are quite hairy, so the droplets often stay suspended above the leaf surface.
When individual experimentation by growers failed to find an effective solution, the RWVTG decided to take a scientific approach, with funding from Wine Australia and support from the South Australian Government through Primary Industries and Regions SA (PIRSA).
‘First, we sat down and worked out all the possible combinations of available chemicals and the things that would improve efficacy, such as using wetters or slowing down the evaporation of droplets to give the chemicals more time to penetrate’, Mr Bennett said.
‘We also looked at a combination of treatments – coming in hard with an initial dose then following up while the plant was still recovering.
‘An initial round of trials gave direction to see if the first thoughts stood up to test. After that round we realised some were just a waste of time so we concentrated on those that showed more promise. That gave us the best results and a series of recommendations.’
The recommendations can be found in a factsheet available from the Wine Australia website and Mr Bennett says it is relevant to growers in any regions where gazanias are a problem.
‘The interesting thing is that the recommended solution wasn’t the best the first time around so it was fortunate that we could run the trial over a couple of years’, he said. ‘You’ve got to get the right conditions.’
Based on the trial results, it was concluded (as explained in the factsheet) that the best treatment is a combination of Glyphosate and Hammer®. Interestingly, this is most effective when the plants are healthy, and preferably actively growing.
‘Under dryland conditions, this means that there is a window of opportunity in winter and spring that must be taken advantage of’, the factsheet says. ‘In a dry year, this window can be very narrow. Plants under stress or with fully matured leaves will not absorb the Glyphosate as well and subsequently the treatment is likely to be less effective.’