Understanding glyphosate resistance in ryegrass

Plant ScienceConsulting

Glyphosate resistance

Winter weeds

Year

Num

ber o

f pop

ulat

ions

1996 2000 2004 2008 20120

100

200

300

400

500

600Annual ryegrassWild radishRed bromeGreat brome

Summer weeds

Year

Num

ber o

f pop

ulat

ions

2006 2008 2010 2012 20140

20

40

60

80

100 Barnyard grassLiverseed grassFleabaneWindmill grassSowthistle

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

Points indicate fields surveyed by the University of Adelaide GRDC funded random weed surveys.

Incidence of Glyphosate resistant fields in red

16%(2012)

1% (2013)

3% (2015)

9% (2015)

1% (2014)

4% (2014)

0% (2012)

2015 random weed survey- WimmeraIncidence of glyphosate resistance=9%

Facts about glyphosate resistant weeds

• All growth stages are resistant- seedlings, pollen etc. • Younger growth stages usually more sensitive.• Resistance transferred by pollen & seed• Progeny from survivors usually more resistant

(accumulation of mechanisms)• From fencelines glyphosate resistance detected out to

at least 50m• Some glyphosate-resistant populations have reduced

fitness (less competitive than susceptible ryegrass in the absence of glyphosate). Produce less seed.

Increasing the level of glyphosate resistance: mechanisms are additive

Surv

ival

(%)

TS

S

Translocation

Cross: Translocation + TS

Reduced glyphosate efficacy

1. Herbicide resistance (weak or strong)

– Depends on type of resistance mechanism

1. Translocation/ sequestration (to leaf tips)- ryegrass

2. Target-site resistance: weak R detected in ryegrass

– Pro106 (S) to Ser/Thr at target site (EPSPS gene)

3. Both 1 & 2 in ryegrass

4. Increased expression of EPSP (brome) (Amaranthus spp in

USA (waterhemp, palmer amaranth)

Reduced glyphosate efficacy

2. Other factors:– Treating older/ larger plants eg. fencelines in spring!!– Poor coverage sub-lethal rate

• Nozzles, water rates, calibration, correct boom height– 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 reduced effect

2016 Quick-Test Glyphosate resistance results• Received April-June, 2016

• 20 ryegrass plant samples from knockdowns for Glyphosate

testing

• 14 = not resistant

• 6 = resistant

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

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 sometimes improve control of resistant individuals.

– Test for glyphosate resistance (several rates) to determine resistance level (Quick-Test or Seed test).

– 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).

Elmore Vic

Some 2016 farmer results from 2016 Quick-Tests from Victoria

Lake Bolac , Vic

Some 2016 farmer results from 2016 Quick-Tests from Victoria

Some 2016 farmer results from 2016 Quick-Tests from SA

Bordertown, SA

Some 2016 farmer results from 2016 Quick-Tests from SA

Cummins, SA

Some 2016 farmer results from 2016 Quick-Tests from WA

Mukinbudin, WA

Some 2016 farmer results from 2016 Quick-Tests from WA

Esperance, WA

Glyphosate resistance in ryegrass. Results from 2015 Plant Science Consulting Quick-Test

and Seed testing of farmer samples

Glyphosate 540 rate (L/ha)

Ryegrass Samples Tested % resistant

1.0 200 291.5 300 252.0 100 153.0 125 10

Increasing rates can improve control of plants resistant to lower rates.

Increasing the level of glyphosate resistance: mechanisms are additive

Surv

ival

(%)

TS

S

Translocation

Cross: Translocation + TS

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

Slight increase in control from 1L to 3L glyphosate

Weak and strong glyphosate survivor from same paddock

Weak glyphosate survivor

Crop Margins- Fenceline control?

Paraquat mixtures, bromacil (Uragan)

2L/ha Glyphosate

Use residuals along fencelines early in the season starting from pre-sowing

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

2013Fenceline was sprayed in late winter, 2013

Rather than treating fencelines (large plants) in spring:

- Use knockdown+residuals before sowing starts or once sowing finished

- Sow as close as possible to fenceline with crop-residuals crop competition

along fenceline = fewer ryegrass seeds

- When sowing outer laps, use outer nozzle to apply residuals along fenceline.

- Mowing is used in some cases

Life Impact The University of Adelaide

Life Impact The University of Adelaide

Life Impact The University of Adelaide

www.plantscienceconsulting.com.au

PLANT SCIENCE CONSULTING

RESISTANCE TESTING

Testing: www.plantscienceconsulting.com.au

Testing Plants Testing Seed

- Even plants with 50+ tillers can be tested!!

- May be interested in a couple of survivors only, eg 5 plants.

Results using Seed Testing

Herbicide Product Rate

Herbicide Group Farmer paddock

(g or ml/ha) Survival(%) Rating

Verdict + 1% Hasten 85 A-FOP 70 RR

Select + 1% Hasten 250 A-DIM 20 R

Select + 1% Hasten 500 A-DIM 0 S

Hussar + 1% Hasten 200 B-SU 90 RRR

Glyphosate 540 1500 M 0 S

Triflur X 1000 D 0 S

The End

Plant ScienceConsulting