Optimising the impact of glyphosate

- Glyphosate resistance- Factors affecting glyphosate performance- Improving glyphosate performance

Plant ScienceConsulting

Glyphosate resistance

Winter weeds

Year

Nu

mb

er o

f p

op

ula

tio

ns

1996 2000 2004 2008 20120

100

200

300

400

500

600

Annual ryegrass

Wild radish

Red brome

Great brome

Summer weeds

Year

Nu

mb

er o

f p

op

ula

tio

ns

2006 2008 2010 2012 20140

20

40

60

80

100 Barnyard grass

Liverseed grass

Fleabane

Windmill grass

Sowthistle

1996-2014 2007-2014

Confirmed cases in Australia

Where & why has glyphosate resistant ryegrass evolved?

Intensive use of glyphosate >15yr with little alternative weed control practices

Uni of Adelaide random weed surveys between 2004-2014(Glyphosate resistance)

16%(2012)

1%(2013)

Facts about glyphosate resistant weeds

• All growth stages are resistant- seedlings, pollen etc.

• Younger growth stages can be more sensitive.• Resistance transferred by pollen & seed• Progeny from survivors can be more resistant

(accumulation of mechanisms)

Increasing the level of glyphosate resistance: mechanisms are additive

Surv

ival

(%)

TS

S

Translocation

Cross: Translocation + TS

Reduced glyphosate efficacy

– Herbicide resistance (weak or strong)– Depends on type of resistance mechanism

• Target-site resistance: weak to strong (not common)• Increased expression of EPSP (brome)• Uptake and translocation/ sequestration (common)

– Depends on the nr of resistance mechanisms present in individuals

Percent survival (%) of a selection of grower resistance tests from 2013 and 2014 treated with Glyphosate (540g ai/L). Data ranked according to percent survival at 1000ml/ha.

Different resistance profiles! Data courtesy of P. Boutsalis, Plant Science Consulting

Reduced glyphosate efficacy

• The below factors are not independent of each other:– Treating older/ larger plants– Poor coverage sub-lethal rate

• Nozzles, water rates, calibration

– Stressed plants • temperature extremes, moisture, nutrition, pest damage

etc. affect translocation etc.• Reduced efficacy at high temperatures (better effect

spraying high 20oC’s than 30oC’s)

– Dust covering leaves sub-lethal effect

Improving glyphosate efficacy

– Increased glyphosate rates can aid in buffering the effect of:• Treating older plants

• stressed plants

• high temperatures

• Poor coverage

• Dust covering leaves

– Increased glyphosate rates can improve control of HR individuals.

– Avoid using higher rates unless a resistance test confirms effective.

– Do not let glyphosate resistant individuals set seed to avoid

accumulation of resistance mechanisms.

– Rotate from glyphosate even if no resistance (paraquat products/

residuals eg. bromacil along fencelines/ non-cropped areas).

– Test for glyphosate resistance (several rates) important.

Quick-Test: Survivors resistant ??

Glyphosate resistance testing

• Seed Testing from 2014:– 275 ryegrass samples & 251 Glyphosate testing

requests (91%)– Data not available on % resistant samples

• Seed Testing from 2013:– 305 ryegrass samples & 232 Glyphosate testing

requests (76%)– 71% exhibited glyphosate resistance

Plant ScienceConsulting

1000ml/ha 1500ml/ha

Glyphosate 540g ai/L

1000ml/ha 1500ml/ha

Survivors to 1000ml/ha indicates low-level glyphosate resistance

which is becoming common

Are survivors always Glyphosate resistant?

Paraquat mixtures, bromacil

2L/ha Glyphosate

Control of Glyphosate -R ryegrass on a fence line in Kapunda SA with herbicide mixtures-

2013Fenceline was sprayed in late winter, 2013

Kapunda SA, 2013

At sprayingUntreated

Uragan 3kg/ha + Basta 5 L/haUragan 3kg/ha + Paraquat 2 L/ha

Life Impact The University of Adelaide

Life Impact The University of Adelaide

Life Impact The University of Adelaide

Life Impact The University of Adelaide

Life Impact The University of Adelaide

Life Impact The University of Adelaide

The End

Plant ScienceConsulting