Gazanias are an increasing problem in several parts of the country, where they are spreading along roadside verges then into surrounding horticultural and farm land. They need virtually no water, are pretty well indestructible and germinate and proliferate readily.
There are two species, which appear to readily hybridise. They are best differentiated by their growth habits.
- Gazania linearis spreads short, mostly underground stems with glossy dark green leaves.
- Gazania rigens has stems spreading horizontally forming a mat-like ground cover, with the ends growing upwards and have lighter-coloured silvery or hairy leaves.
Both will readily reshoot from root and stem fragments after tillage and no simple, truly effective control method has yet to be found.
Experience in Riverland
Growers in the Riverland tried using normal chemicals registered for vineyard use but the gazanias kept bouncing back. The same happened with regular roadside spraying by councils. No matter how sick and sorry the gazanias looked initially, they returned stronger than ever.
Trials suggest the best treatment is a combination of of Glyphosate and Hammer® applied in winter and spring, particularly if there has been sufficient rain or irrigation to promote vigorous growth. It is also preferable to spray prior to or during early flowering, as the plants tend to harden up as flowering ends and become more difficult to treat. Frosts also invoke stress upon gazanias impeding the uptake of chemicals.
The effective use of Glyphosate is reliant on the gazania plants being in a healthy condition, preferably actively growing. Plants under stress or with fully matured leaves will not absorb the chemical as well and subsequently the treatment is likely to be less effective.