Controlling weed recruitment in isolated areas

of Cape York Peninsula

Melissa Setter Biosecurity Queensland

Stephen Setter Biosecurity Queensland

Darryn Higgins Cook Shire Council

Simon Brooks Biosecurity Queensland

Wayne Vogler Biosecurity Queensland

• Sicklepod

• Bellyache Bush

• Gamba Grass

• Grader Grass

• Giant Rats Tail Grass

Cape York Peninsula’s worst weeds include:

• Rubber vine

• Pond Apple

• Lantana

Sicklepod is the example species used in this study.

Sicklepod (Senna obtusifolia) description

• Competitively vigorous woody shrub

• 1.5-2.5m tall x 1m wide

• 3 opposite pairs of leaves

• Small yellow flowers

• Sickle shaped pods

• Pods 10-15cm long, 3-5mm wide

• 24-28 seeds per pod

Sicklepod lifecycle

• Short lifecycle

• Usually annual, can perreniate

• Seeds produced during dry season

• Dispersal by dehiscence, water,

mud adhering to vehicles, stock,

people etc

Sicklepod flowering at very small size (May)

Sicklepod can produce seeds

within 6-10 months of

emergence

Sicklepod in flower (May)

After seedfall (Aug)

Up to

8000 seeds

per

plant

annually

How

long

does

seed

last?

At least 2 years

Some say 10+ years

Checking in Qld: wet & dry

Sicklepod distribution from https://avh.ala.org.au

• Local gov’s

• Beef industry

• Sugar industry

• Parks and Forestry

• Indigenous land use

• Environmental

Sicklepod impacts- loss of production, management costs and environmental impact

Cape York Peninsula

averages approximately

1305 mm annually

Wet season

inaccessibility

Wet season inaccessibility

Controlling “remote”

infestations becomes

impossible

Sicklepod

in May

While infestations are inaccessible, the plant continues to flourish

• Slashing to control flowering can cause some mortality

• Foliar herbicides are quite effective

• Both methods can work, but only on accessible plants

• Current post-emergent herbicide control is effective,

but inaccessible plants are able to reproduce

• Biocontrol has been investigated, but not currently used

Sicklepod current control methods

Sicklepod Herbicide control

recommendations from DAF factsheet

To try to help break the life-cycle,

we investigated the use of herbicides that

could be applied when plants are accessible,

to kill emerging seedlings when access is

impossible, i.e. pre-emergent herbicides.

Pre-emergent herbicides

We conducted a pot trial to test

16 herbicides

at 3 rates each

for their potential

pre-emergent effects on Sicklepod seeds

Pot trial methods

Herbicides and rates were chosen on their known and potential pre-emergent effect.

We made sure to include the herbicides and rates registered and commonly used already on sicklepod.

Herbicides tested

Herbicides and application rates used in the trial.Group Trade name Active Ingredient Low Med High

B Mako sulfometuron methyl 750g/Kg 0.4 kg/Ha 0.6 kg/Ha 0.8 kg/Ha

B Arsenal imazapyr 250g/L as isopropylamine salt 1 L/Ha 1.5 L/Ha 2 L/Ha

C Bobcat hexazinone 250g/L 3 L/Ha 9 L/Ha 15 L/Ha

C Metribuzin 750 WG metribuzin 750g/Kg 0.5 kg/Ha 1.25 kg/Ha 2 kg/Ha

C Graslan tebuthiuron 200g/Kg 5 kg/Ha 7.5 kg/Ha 10 kg/Ha

D Treflan trifluralin 480 g/L 1 L/Ha 2 L/Ha 3 L/Ha

G Valor WG flumioxazin 500g/kg 0.4 kg/Ha 0.7 kg/Ha 1 kg/Ha

I Stuka flexi picloram 240 g/L as potassium salt 0.93 L/Ha 1.25 L/Ha 1.57 L/Ha

I Grazon extra triclopyr 300g/L + picloram 100g/L as hexyloxypropylamine salt+ aminopyralid 8 g/L 2.25 L/Ha 3 L/Ha 3.75 L/Ha

I Conqueror triclopyr 300g/L + picloram 100g/L as hexyloxyproplamine salt 2.25 L/Ha 3 L/Ha 3.75 L/Ha

I Tordon 75-D 2,4-D 300g/L + picloram 75 g/L as triisopropanolamine salt 3 L/Ha 4 L/Ha 5 L/Ha

B Brushoff metsulfuron -methyl 600 g/kg 0.03 kg/Ha 0.075 kg/Ha 0.12 kg/Ha

H Balance isoxaflutole 750 g/Kg 0.1 kg/Ha 0.2 kg/Ha 0.3 kg/Ha

I+B Stinger aminopyralid 375 g/kg + metsulfuron-methyl 300 g/kg 0.06 kg/Ha 0.15 kg/Ha 0.24 kg/Ha

G Goal Tender oxyfluorfen 480 g/L 1 L/Ha 2 L/Ha 3 L/Ha

I Tordan regrowth master triclopyr 200g/L + picloram 100g/L as triisopropanolamine salt+ aminopyralid 25 g/L 2.25 L/Ha 3 L/Ha 3.75 L/Ha

The average number of live sicklepod seedlings in each treatment approximately four months after treatment. The Least significant difference between treatments is 4.569 at P<0.05)

• There were significant treatment effects at four months after treatment

• Herbicides containing Picloram caused high levels of control, including Conqueror®, Grazon Extra®, Stuka flexi®, Tordon 75-D® and Tordon Regrowth Master®.

• The herbicide Pledge® was also effective at the “high” application rate.

Some good results:

Sicklepod example pots at 3 MAT

We were able to identify several effective herbicides in

a pot situation, and rule out many others.

We now plan to apply the successful herbicides in field

conditions.

Sicklepod (Senna obtusifolia)

Two of the successful herbicides (Conqueror® and Grazon Extra®) and rates are those already listed on PER82158 for the post-emergent control of sicklepod.

There may need to be variations in applied volumes and possibly methodology of application to get best pre-emergent results.

Sicklepod (Senna obtusifolia)

As an example, Grazon

extra® could be applied

in the dry season at

relatively low volume to

the bare soil between

senesced plants.

Field use of pre-emergent: bare soil

Or as a higher volume application to younger, greener plants to run off leaves and reach the soil surface. This would have the dual effect of killing both existing plants and their potential progeny.

Field use of pre-emergent:

plant cover

Future work

Use of pre-emergent herbicides may be adapted to many other species in many other situations where weeds are inaccessible at important lifecycle stages.