Parkinsonia control at the Gulf Field Day

Tahnee Thompson (foreground left) and Kit Jolly (centre right) at the Guld Field Day

NT Government Weed Management Branch officers Tahnee Thompson and Brad Sauer and Dow Agro’s Kit Jolley provided some advice on Parkinsonia control at the recent Gulf Field Day.

Parky is a Weed of National Significance. Tahnee said that there are several control methods, and integrating these methods can increase success rates. Maintaining a competitive grass layer is one aspect because Parky responds well to disturbed or bare soil. Once established it can outcompete grasses and reduce carrying capacity.

Kit demonstrated graslan application using a dispenser that he donated to each property present. The product label states that you should estimate the area within 30cm beyond the drip zone of each plant and apply at 1 to 1.5g/m² to that area (the root zone). The dispenser releases 7g at a time which is enough to treat about 5m². Treatments become effective after sufficient rainfall has occurred to move the chemical into the root zone, though in some cases the plant may defoliate more than once before dying. Residual action may be impaired if fire occurs before pellets are dissolved. One application can be effective for several years. Success can be limited on clayey or organic soils. Applying more than 2g/m² may results in the death of grasses if actively growing.

The most common method of control is basal barking with access and diesel at 1:60. Kit’s rule for applying access is to wet the base of the stem from one foot in height for every inch of stem diameter. Spray all the way down to the soil and all around the stem with a narrow nozzle setting to avoid waste. Stem injection into an axe cut can also be effective. If the plant has seeded its worth applying graslan to control seedlings.

There have been several pathogens used to control parky, including a dieback that occurs naturally in the soil. The dieback reduces seed production and is useful for containing larger infestations until other methods can be applied. The pathogen is contained in a capsule and is applied by drilling a hole, inserting the capsule and sealing with silicon. The dieback spreads through denser infestations where roots from one plant touch another. Tahnee hopes that capsules will soon be commercially available.

Another biocontrol agent, Eueupithecia cisplatensis, a defoliating caterpillar, was recommended for release in July 2012 and should be arriving in the NT soon.