Aerial spraying of herbicide in native vegetation

• The effect on native vegetation of spraying with a low rate of Ally™ has been monitored for three years.
• To date there is no decline in the long-lived plants due to herbicide damage.
• The variety of annual plants varies with the season.
• Two daisies are affected but they still flower after spraying.

The Group B herbicides (acetolactate synthase inhibitors) are very effective for the control of branched broomrape in agricultural regions in the Murray Mallee of South Australia and are currently the only viable option for branched broomrape control in infested native vegetation. Current practice for many of the larger areas of native vegetation in the region, is to aerially apply the Group B herbicide, Ally™, at a rate of 3g/ha.  Due to the translocation of the herbicide from host foliage into branched broomrape attached to host roots, control can be achieved at very low application rates with minimal detrimental effects on the host plant.  The program is monitoring a site with native mallee and grassland vegetation at Tailem Bend to assess the effects of aerial herbicide application on native perennial and annual plant species. Plants and plots have been sampled twice annually since 2007, prior to, and following spraying.

We visually inspect the condition of five plants of each of the seven perennial plants listed below. None have showed any decline in condition following spraying in the 3 years of monitoring.

• Mallee - Eucalyptus gracilis
• Murray Pine - Callitris gracilis
• Native Apricot  - Pittosporum phyllaerioides
• Dryland Teatree - Melaleuca lanceolata
• Old Man’s Beard - Clematis microphylla
• Ruby Saltbush - Enchylaena tomentosa
• Small-leaved Bluebush - Maireana brevifolia

Condition scores for Old Man’s Beard have declined across the three years of monitoring and Ruby Saltbush condition has declined from 2007/8 to 2009. Plants have shown no visible symptoms of herbicide toxicity so the decline may be due to seasonal conditions, grazing or natural aging processes.

Native annual species are counted in ten, 1 X 1 m plots in winter before spraying and in spring after spraying. There have been changes in the abundance and variety of the annual species following spraying but the analysis is able to show this is largely driven by seasonal effects.

The native annual daisies, Variable Groundsel (Senecio pinnatifolius) and Podolepis rugata showed signs of herbicide damage with some plants dying off.  However, both species were observed in flower after spraying and there has been no long-term decline in the abundance of these species after three years of monitoring.

Group B herbicide residues can persist in soils that are repeatedly sprayed. However, no herbicide residues were detected in a bioassay of soils collected from the site.

Dr Jane Prider
Research Officer
Branched Broomrape Eradication Program