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Northern Herbicide Resistance Updates Tamworth - 4 September 2007 Toowoomba - 6 September 2007

Compiled by Dr Michael Widderick Email: [email protected]

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Northern Herbicide Resistance Updates

HERBICIDE RESISTANCE IN WILD OATS- THE POTENTIAL FOR MORE THAN ONE MODE OF ACTION

Dr Peter Boutsalis, The University of Adelaide & Plant Science Consulting Introduction Wild oat resistance to Group A herbicides was first identified in a population collected from York in Western Australia in 1985. This population was confirmed resistant to diclofop-methyl in pot trials in 1989 (Boutsalis, 1989). Since this time over 500 cases of wild oat (Avena fatua & A. sterilis) resistance have been reported in Australia (Crop Life register). The most common resistance is to the Group A FOP herbicides diclofop (Hoegrass etc.), fenoxaprop (Wildcat) and clodinafop (Topik). With increasing resistance to Group A FOP herbicides, farmers have increased their reliance on herbicides from other chemical families such as Group A DIM (Achieve, Select, Aramo etc.), Group A DEN (Axial), Group B (Atlantis, Hussar) and Group K (Mataven) herbicides. In many cases DIM, DEN, Group B and Group K herbicides are effective in controlling FOP-resistant wild oats. However cases of resistance to DIM, DEN, Group B and Group K herbicides have been confirmed. It is the purpose of this paper to summarise the current status of resistance in wild oats in order to raise awareness and enable new strategies to be implemented to delay the onset of resistance. Results & Discussion Level of resistance from random surveys in Victoria and Western Australia In 2006 a random survey was conducted in north-east and north-central Victoria (Boutsalis and Preston). Paddocks were chosen at random, and surveyed for weed seeds including wild oats. Of 120 paddocks that were visited, 96 contained wild oats. The following winter, a pot trial was conducted and wild oats were treated with 750 g ai/ha of diclofop-methyl, 15g ai/ha pinoxaden (Axial) and 99g ai/ha mesosulfuron (Atlantis). 8% of wild oat samples were found to be resistant (R) to diclofop-methyl with a further 4% developing resistance (DR) (Table 1). As expected, improved control with Axial and Atlantis was observed (Table 1). A random survey of this region in 1995 identified 6% resistance to diclofop-methyl (Walsh 1995). However, with the increased reliance on herbicides for weed control, resistance in wild oats is expected to escalate at a faster rate. A random survey of 677 paddocks across the WA cropping zone in 2005 identified 22% of paddocks containing wild oats (Owen and Powles 2007). 16% of these paddocks contained diclofop-methyl resistant (‘R’) wild oats and a further 61% of wild oat samples were classified as ‘DR’ (Table 1). Similar to the Victorian study, 2% of wild oat populations showed resistance to Axial. Atlantis was not tested in the WA study.


Table 1 Wild oat resistance detected in two random surveys. Samples classified as resistant (R) if survival was ≥ 20% and developing resistance (DR) if survival was between 1-19%. WA data from (Owen and Powles, 2007). State and year conducted

Wild oat samples tested

Hoegrass R (DR)

(%)

Axial R (DR)

(%)

Atlantis R (DR)

(%) Victoria- 2006

96 8 (4) 2 (3) 0 (3)

WA-2005 150 16 (61) 2 (2) Not tested Information from Resistance Testing Services Confirmation of resistance: Since 2004, 80 wild oat samples suspected of being resistant have been sent to Plant Science Consulting for testing. In 25% of cases no resistance was detected suggesting that, factors other than herbicide resistance were responsible for poor herbicide efficacy. Such factors include stressed weeds and poor herbicide application. In contrast, over 95% of ryegrass samples that are received for testing have been confirmed resistant. Cross-resistance in FOP-resistant wild oats: A trial was conducted to determine the level of cross-resistance of 23 FOP-resistant wild oat samples. These samples had been received from consultants or farmers across WA, SA, NSW and Qld as paddock failures requiring herbicide resistance confirmation. All these samples were confirmed as resistant to FOP herbicides. In a subsequent trial, the 23 populations were tested with Wildcat, Topik, Axial, Atlantis and Mataven (Table 2). Axial and Atlantis: The findings from this study confirm cross-resistance to modern herbicides, represented by Axial and Atlantis. Continued selection with these herbicides will probably lead to elevated levels of resistance. Axial has only been available for a limited time and it is not likely that this period has been sufficient to select for resistance but that FOP herbicides have resulted in cross-resistance. The cause of resistance to Atlantis can be due to cross-resistance by FOP herbicides and/ or independent selection with Group B herbicides. Mataven: Mataven is a Group K product registered for the selective control of wild oats by post emergence treatment in wheat and triticale and selective spray topping of wild oats in wheat only. It is used as an alternative to Group A and B herbicides to reduce the selection pressure imposed by these herbicides. Investigation of resistance to Mataven revealed that 43% of the FOP-resistant wild oats (both A. sterilis & A. fatua) also showed significant levels of resistance to Mataven (Table 2). Paddock histories were obtained for most of the samples which revealed that in the majority of cases Mataven use was minimal. Thus, the study revealed that resistance to Mataven was unpredictable in FOP-resistant wild oats. An independent study of wild oats


in Canada reported a similar link between FOP and Mataven resistance (Karlowsky et al 2006). Table 2 Survival (%) of selected FOP-resistant wild oat populations to Wildcat, Topik, Axial, Atlantis and Mataven, 4 weeks after treatment. Plants were sprayed at the 3-4 leaf stage in an outdoor pot trial during winter. Data recorded as % survival (percentage of plants surviving) as compared to control plants unsprayed. A sample was classed as ‘resistant’ if ≥ 20% of plants survived the herbicide application. As references, a known sensitive and a FOP-resistant biotype were included.

Wildcat

300 ml/ha + 0.25%

BS1000

Topik 75 ml/ha + 1% Hasten

Axial 200

ml/ha + 0.5%

Adigor

Atlantis 330 ml/ha

+ 0.25%

BS1000

Mataven 2.5 L/ha

Resistant samples

(%) 83 63 21* 4* 42

*Survivors to Axial and Atlantis were classed as possessing weak resistance- survivors exhibited heavy herbicide damage but recovered by the production of new tillers). Random surveys in southern NSW in 1991 and 1994 did not detect any resistance to Mataven (Broster, 2004). In 2001 a sample of wild oats that survived a field application of Mataven was sent to Charles Sturt University for resistance testing. At the recommended rate of Mataven, greater than 80% survival was recorded. In addition, prior to the 2001 field application of Mataven, this paddock had never been treated with this herbicide. This result has implications for resistance management, where Mataven is chosen to control a wild oat failure to a Group A FOP herbicide. The complexity and unpredictability of herbicide resistance in wild oats highlights the importance of herbicide resistance testing prior to the selection of a herbicide. References

Boutsalis P (1989) Diclofop-methyl resistance in a biotype of Avena fatua L. Honours Thesis

Broster JC (2004) A population of wild oats (Avena ludoviciana Durieu) resistance to flamprop-m-methyl. Fourteenth Australian Weeds Conference. pp. 432-433.

Crop Life register: http://www.croplifeaustralia.org.au List of herbicide resistant weeds in Australia

Karlowsky JD, Brule-Babel AL, Friesen LF, Van Acker RC and Crow GH (2006) Inheritance of multiple herbicide resistance in wild oat. Canadian Journal of Plant Science. pp. 316-328.

Owen M and Powles S (2007) Frequency of herbicide resistance in wild oat (Avena fatua) across the Western Australian wheat belt. In Weeds Updates, Agribusiness Crop Updates 2007, Department of Agriculture & Food, Western Australia pp. 31-34

Walsh MJ (1995) Biology and control of herbicide resistant wild oats. Final Report- GRDC, Project DAV54.

http://www.croplifeaustralia.org.au/


TO EVALUATE THE EFFICACY OF SPRAY SEED® ON THE NARROW TARGET LOLIUM RIGIDUM (ANNUAL RYEGRASS) WHEN APPLIED WITH A RANGE OF NOZZLE TYPES AND WATER VOLUMES Jason Sabeeney, Syngenta Crop Protection Australia Pty. Ltd. Key Messages The results from these two trials indicate that the efficacy of Spray Seed on annual ryegrass was not compromised when applied with a coarse spray quality from a HARDI INJET or AI TeeJet® nozzle compared with a standard XR nozzle generating a fine spray quality or a Turbo TeeJet nozzle producing a medium spray quality. If using air induction (AI) nozzles make sure the pressure is adequate for the nozzle (especially if using high pressure AI type nozzles) and the water volume sufficient to compensate for the lower number of droplets produced from these types of nozzles, especially if targeting grasses. Below is a guide to pressure and water volume by nozzle type. For high pressure air induced nozzles (eg TeeJet AI, HARDI INJET, Agrotop Turbo Drop®, Lechler ID) Must use high pressures > 4 bar generally 4-8 bar If targeting grass weeds use > 75L/ha For low pressure air induced nozzles (eg TeeJet AIXR, HARDI MINIDRIFT, Agrotop Airmix®, Lechler IDK) Must use pressures > 2 bar generally 3-5 bar If targeting grass weeds use > 75L/ha Introduction & Aims Interest in using air induction type nozzles for broadacre spraying has increased dramatically in recent years due to a number of factors. It has been well established that the larger droplet size generated from air induction type nozzles can significantly reduce drift and losses due to evaporation. There is increased pressure from the public and regulators to reduce drift and the use of these types of nozzles will help manage drift issues. It has also been shown that AI nozzles can provide good levels of weed control when targeting certain weeds with systemic herbicides. However there has been very little data generated in Australia to show that these nozzles provide adequate efficacy under some of the most challenging scenarios eg when using contact type herbicides like Spray Seed on difficult to target and control weeds like annual ryegrass. The aim of these trials is to evaluate the efficacy of Spray Seed on annual ryegrass when applied with a fine, medium and coarse spray quality from a range of nozzles including air induction type nozzles at three water volumes. Method Two replicated field trials were established at Mingenew in WA and Roseworthy in SA in winter 2006 to evaluate the efficacy of Spray Seed on annual ryegrass. Both trials were a RCB design consisting of 3 replicates each. The rates of Spray Seed chosen were

targeted to give 80 – 90 % control so that differences between treatments became more evident. The treatments consisted of an untreated and three nozzle types were chosen representing three spray qualities. 1. TeeJet extended range XR (fine) , 2. Turbo TeeJet TT (medium), 3. TeeJet Air Induction AI (coarse). All nozzles were trialed at 50, 75 and 100L/ha respectively. The HARDI INJET nozzle was chosen for the 50L/ha rate only instead of the TeeJet AI as it was an 01 size more suited to the speed & volume & pressure combination chosen. In the WA trial Spray Seed was applied at 2 pm on 28/7/06. Spray Seed was applied at 1.2L/ha for all treatments to 2 leaf – early tillering annual ryegrass. Weather conditions at spraying were as follows, Temp. 16 deg. C, Delta T 2.5 deg. C, wind calm. Speed of travel was kept constant at 15 km/h. Assessments were conducted at 10 and 28 days after application. In the SA trial Spray Seed was applied at 2.30 pm on 31/8/06 at 1.4L/ha to early tillering annual ryegrass. Weather conditions at spraying were as follows, Temp. 23 deg. C, Delta T 7.0 deg. C, wind calm. Speed of travel was kept constant at 15 km/h. Assessments were conducted at 7 days after application. Unfortunately due to error in the SA trial a Lechler IDK low pressure AI nozzle was used instead of the HARDI INJET at 50L/ha. Results (Figure 1) shows the % control of annual ryegrass from using Spray Seed applied via a range of nozzles and water volumes from the field trial in WA. Statistics were conducted on the results from this trial including ANOVA and factorial analysis, but no significant differences were found between treatments or between factors of spray quality or water volume. However in this trial there was a trend towards improved control where water rate was increased eg 50L/ha (ave. 92% control), 75L/ha (ave. 93% control) and 100L/ha (ave. 97% control). The efficacy of the air induction nozzle producing a coarse spray quality (average 93% control) in this trial was equivalent to the TT nozzle a medium spray quality (average 94% control) and the standard XR nozzle a fine spray quality (average 95% control).

Figure 1: Spray Seed efficacy on Annual Ryegrass 28 DAA, WA, 2006

93 93 95 969998889191

020406080

100

INJ 018bar

50L C

TT 0154bar

50L M

XR 0154bar

50L F

AI 0158bar

75L C

TT 024bar

75L M

XR 024bar75L F

AI 028bar

100L C

TT 033.5bar100L M

XR 033.5bar100L F

% C

ontro

l

Codes Used Spray Quality: Fine (F), Medium (M), & Coarse (C). Nozzle Type: HARDI INJET (INJ), Turbo TeeJet (TT), TeeJet XR (XR) & TeeJet AI (AI) Nozzle Size: 01, 015, 02, 03 Spray Volume: 50L/ha (50L), 75L/ha (75L), 100L/ha (100L)


Figure 2: Spray Seed efficacy on Annual Ryegrass 7 DAA, SA, 2006

93 8783888790878588

020406080

100

IDK 018bar

50L M

TT 0154bar

50L M

XR 0154bar

50L F

AI 0158bar

75L C

TT 024bar

75L M

XR 024bar75L F

AI 028bar

100L C

TT 033.5bar100L M

XR 033.5bar100L F

% C

ontro

l

(Figure 2) shows the % control of annual ryegrass from using Spray Seed applied via a range of nozzles and water volumes from the field trial in SA. (Table 1) shows the results of the factorial analysis looking at 2 factors, spray quality and water volume. In this trial the optimal water rate was found to be 75L/ha which was significantly better than either 50L/ha or 100L/ha. The efficacy of the air induction nozzles producing a coarse spray quality in this trial was better and statistically significant compared with the standard XR or TT nozzle delivering a fine and medium spray quality respectively. Table 1 Factorial Analysis for Spray Quality and Water Volume Level Means for Factor Spray Quality Untrans Letters

Fine Treatments: 6 11 16 86.67 B Medium Treatments: 3 8 13 86.11 B Coarse Treatments: 2 7 12 90.00 A F-test Probability 3.20% 5% LSD 3.04 Level Means for Factor Water Volume Untrans Letters50L Treatments: 2 3 6 86.67 B 75L Treatments: 7 8 11 90.00 A 100L Treatments: 12 13 16 86.11 B F-test Probability 3.20% 5% LSD 3.04

Conclusions The results from these two trials indicate that Spray Seed efficacy on annual ryegrass when applied with a TeeJet AI or a HARDI INJET producing a coarse spray quality is equivalent or better than standard nozzles (XR) or TT producing a fine or medium spray quality. Given these trials were designed to represent one of the most challenging of situations, there may be scope for these air induction type nozzles producing a coarse spray quality to be used with many other herbicides on a range of other weeds.



More trial work needs to be conducted to confirm these findings so that product recommendations can be refined and changes to product labels can be made. Key Words Spray Seed, Annual Ryegrass, Efficacy, Air Induction, Nozzle, Spray Quality, Water Volume Acknowledgements The author would like to acknowledge Serve-Ag SA for spraying the trial in South Australia and Agritech Crop Research in WA for spraying the trial in Western Australia. Also Lester Snooke, Simon Kerin and Brian Staines from Syngenta for conducting weed control assessments for the trial in WA. I would also like to acknowledge the assistance given by Garth Wickson and Charissa Rixon from Syngenta, Graeme Betts from ASK GB, Peter Alexander and Jake Lanyon from TeeJet Australasia. References

Betts, G. (2005) ASK GB spray application handbook 13 edition August 2005, pp 38-39.

TeeJet Catalog 50-M (2007) pp 1-192. Wolf, TM. (2006) Meeting variable application goals with new application

technology. Proceedings of the 2006 South Australian GRDC Grains Research Update, pp 157-176. Jason Sabeeney Technical Services Manager, Syngenta Crop Protection Ph. 0408 082 894 Email. [email protected]


MANAGING GROUP B HERBICIDE RESISTANCE IN WILD OATS

Craige Lang – Bayer CropScience, Market Development Manager-NSW

Take home messages • Herbicide resistance is real! • Group B resistance already exists – act sooner rather than later • Make resistance testing a normal part of the service you offer • Keep good paddock records • Group A’s are the only post-em option in barley, cereal rye, canola and pulse crops, we

need to preserve their effectiveness • Limit Group A use in wheat? • Summer crop rotation key component of seed bank management and chemistry

rotation • Think long-term impact, not short-term cost Background information Evolution of herbicide resistance One of the key drivers of herbicide resistance is the intensive use of herbicides. In any weed population there are likely to be a small number of plants that are naturally resistant to herbicides, even before the herbicides are used. These naturally resistant weeds survive the herbicide application and set seed whilst the susceptible plants are killed. Continuous use of a herbicide or a particular herbicide group will eventually result in a dominant population of resistant weeds. Factors that influence the evolution of resistance There are a number of factors that can influence the evolution of herbicide resistance. These factors include: • The intensity of selection pressure. • The frequency of use a particular herbicide group • The frequency of resistance present in untreated populations. Herbicide resistance will

develop more quickly in populations that have a high frequency of natural resistance as opposed to that of a population where the frequency is low.

• The biology and density of the weed. Generally weed species that produce large numbers of seed and with a short seed bank life will evolve resistance quicker than those with long seed bank lives. Species that exhibit a greater genetic diversity are more likely to develop resistance and generally speaking resistance is more likely to occur in larger populations.

Herbicide resistance has developed because of repeated and uninterrupted use of herbicides with the same mode of action. If a failure is suspected do not use the same product or product from the same mode of action group. To prolong chemistry effectiveness rotate to another mode of action the following year. Rotational options The integration of crop and chemical rotational options into a farm management plan can provide an effective means of delaying the onset of herbicide resistance. In the Northern NSW and Southern Qld cropping areas there are a number of winter and summer crops that can be utilised as part of a rotational programme. (Table 1).

Table 1 Winter and summer crop options Winter crops Summer crops

Wheat Cotton Barley Sorghum Oats Maize Triticale Sunflowers Cereal rye Mungbeans Canola Chickpeas Faba beans In regards to delaying the onset of herbicide resistance it is essential that when the crop rotational programme is being developed that consideration be given to avoiding the consecutive use of the same herbicide group, regardless of crop grown. The following table, (Table2), outlines the current winter crop wild oat herbicide options available. Table 2 Winter crop wild oat herbicide options. Crop Knockdown Pre-emergent Post-emergent Wheat Group L, M Group B*,D, E Group A, B, K Barley Group L, M Group D, E Group A Oats Group L, M Nil Nil Triticale Group L, M Group E Group A, K Cereal rye Group L, M Nil Group A Canola Group L, M Group D, E Group A TT Canola Group L, M Group C, D, E Group A Chickpea Group L, M Group D, E Group A Faba bean Group L, M Group D, E Group A
*Pre-plant knockdown label claim It should be obvious from the above table, (Table 2), that there is a strong reliance on Group A herbicide chemistry. Losing the Group A herbicide option from a rotational programme due to increasing levels of resistance will not only put increasing pressure on Group B herbicide products such as Atlantis® and Hussar® but it will also impact upon the crop rotation options that can be included. Of all the winter growing crops, wheat offers the greatest flexibility in regards to the chemical options available to manage in-crop populations of wild oats. In areas where there are increasing levels of Group A herbicide resistance it is important to avoid the temptation to grow back-to-back wheat crops so that the Group B herbicide options can be utilised. Not only does this have the potential to increase the speed at which Group B resistance develops, it also has the potential to result in increased levels of inoculum of various diseases of wheat. So in the interest of preserving the effectiveness of Group B herbicides such as Atlantis and Hussar, it is important that they are used strategically as part of a total management programme, not just as a short term fix. Other factors to consider when developing a crop rotational programme should include, but not be limited to, the following: • Resistance status of the field/farm
o Know the status of the field in question prior to the commencement of the cropping programme. This will involve having samples tested prior to a problem being suspected. The cost associated will be much less than a failed spray.

• Competitive nature of crop



o Utilise crops/varieties that have rapid growth, reconsider sowing rates and row spacings as these will assist in the crop effectively shading out the weed competition.

• Disease management o Use good management practise in regards to disease management that inhibits

the build up of disease inoculum. • Plantback considerations for varying herbicides

o Be aware of the recropping intervals required for herbicides used as part of the management programme.

• Fallow management o Use the fallow component of the cropping rotation to introduce additional

chemistry groups that could not otherwise be used. Devise a fallow management programme, this will assist greatly by helping to reduce the seed bank size and weed competition in crops following the fallow phase of the rotation.

Ideally the rotational programme developed will not focus purely on just one aspect, but provide a balanced approach to total field management. Conclusions One of the key driving factors behind the development of herbicide resistance is overuse or repeated use of a single herbicide group. Crop rotations are a management option that can assist in delaying the development of resistance and managing the size of the weed seed bank. We have options other than chemical to manage resistance and these options should be included in the development of any rotational programme. Whilst it may prove difficult to find a rotation that works for you, it will prove decidedly more difficult to continue to produce high yielding crops in the face of increasing levels of herbicide resistant weeds that constantly compete with the crop for vital soil moisture and nutrition. Atlantis® and Hussar® are registered trademarks of Bayer. Contact details Craige Lang Bayer CropScience Phone: 0409 870 663 Email: [email protected]


THE MECHANISMS, EVOLUTION AND DISTRIBUTION OF GLYPHOSATE RESISTANCE IN GRASSES AND BROADLEAF SPECIES Christopher Preston and Angela Wakelin CRC for Australian Weed Management and School of Agriculture, Food & Wine, University of Adelaide, PMB 1, Glen Osmond SA 5064 Evolution of glyphosate resistance in weeds populations Glyphosate resistance was first reported from annual ryegrass (Lolium rigidum) in Australia in 1996. Since then resistance has appeared in 5 grass species and 8 broadleaf species (Table 1). Table 1 Glyphosate resistant weeds around the world. From Heap (2007). Weed species Countries Year first

reported System

Lolium rigidum (annual ryegrass)

Australia USA South Africa France

1996 1998 2001 2003

Various Orchards Vineyards Orchards/Vineyards

Eleusine indica (goosegrass)

Malaysia 1997 Plantation

Conyza canadensis (horseweed)

USA Brazil China

2000 2005 2006

RR crops/Roadside Orchards/RR soybean Orchards

Lolium multiflorum (Italian ryegrass)

Chile Brazil USA

2001 2003 2004

Orchards Orchards/RR soybean Orchards/RR crops

Conyza bonariensis (fleabane)

South Africa Spain Brazil Colombia

2003 2004 2005 2006

Vineyards Orchards Various crops Various crops

Plantago lanceolata (plantain)

South Africa 2003 Vineyards

Ambrosia artemisiifolia (common ragweed)

USA 2004 RR soybean

Ambrosia trifida (giant ragweed)

USA 2004 RR soybean

Amaranthus palmeri (Palmer amaranth)

USA 2005 RR cotton

Amaranthus rudis (waterhemp)

USA 2005 RR soybean

Euphorbia heterophylla (wild poinsettia)

Brazil 2005 RR soybean

Sorghum halepense (Johnsongrass)

Argentina 2005 RR soybean

Echinochloa colona (barnyard grass)

Australia 2007 Fallow

In Australia, there are 64 populations of annual ryegrass with resistance to glyphosate (Table 2). There is also one population of barnyard grass with confirmed resistance to glyphosate. The main situations with resistance are chemical fallows, horticultural


systems and non-cropped areas around the farm. Resistant populations are known from all states of Australia except Queensland and Tasmania. Table 2 Occurrence of glyphosate resistant annual ryegrass in Australia (Preston 2007) Situation Number of

sites States

Broadacre cropping

Chemical fallow 21 NSW

No-till winter grains

8 NSW, Vic, SA, WA

Horticulture Tree crops 3 NSW Vine crops 13 SA, WA Other Driveway 1 NSW Fenceline 9 NSW, SA, Vic Firebreak 1 SA Irrigation channel 6 NSW Airstrip 1 SA Railway 1 WA In Australia, and elsewhere in the world, glyphosate resistance occurs in situations where glyphosate is intensively used, no other effective herbicides are used and there is no tillage. In many situations, glyphosate was used continuously for 15 years or more before resistance evolved. However, in other circumstances where glyphosate was used many times in a season, resistance has evolved more quickly. Resistance has evolved in both grass and broadleaf weed species and in both outcrossing and self-pollinated weed species. Mechanisms of glyphosate resistance There are two known mechanisms of resistance to glyphosate that have been identified in resistant weed populations. There may be additional mechanisms that we have not yet discovered. One mechanism of glyphosate resistance is a mutation within the target enzyme EPSP synthase that reduces the ability of glyphosate to inhibit the enzyme. So far, there is only one known site within EPSP synthase where mutations giving resistance have occurred, but several different mutations at this site have been found. Target site resistance to glyphosate has typically provided weak resistance to glyphosate, usually about 3 to 5-fold compared to susceptible individuals. Target site resistance is inherited as a single gene. The other known type of resistance is the result of a change in the way that glyphosate is moved around the plant. Resistant plants accumulate glyphosate in the leaf tips; whereas susceptible plants have a more even distribution of herbicide. In particular, resistant plants have less than half the amount of glyphosate in the meristematic zone compared to susceptible plants. This difference in translocation of glyphosate results in resistant plants being initially stunted, but then growing away from the damage. This mechanism typically provides 5 to 11-fold resistance. Like target site resistance, translocation-based resistance is inherited as a single gene. Typically, translocation-based resistance provides a higher level of resistance than target site resistance. The two mechanisms of resistance together will result in higher levels of resistance than each mechanism alone. Both mechanisms of resistance have occurred in annual ryegrass and Italian ryegrass. Target site resistance has been observed in goosegrass. Translocation-based resistance only has been found in horseweed. Overall,

translocation-based resistance has been more common than target site resistance, probably because it provides a higher level of resistance in the field and is therefore more easily selected. Consequences of glyphosate resistance in weeds Some studies have suggested that glyphosate resistance carries a fitness penalty reducing the productivity of plants when the herbicide is not used. These studies have indicated the frequency of resistant individuals may decline if the herbicide is not used (Figure 1). However, only populations with the translocation-based resistance mechanism have been examined in these experiments. It is not known what the effect on populations with target site resistance might be, nor on those with both mechanisms.

2002 2003 20040

10

20

30

40

50

60 NLR 70NLR 71NLR 72SLR 76

Year

Surv

ival

(%)

Figure 1 Percentage survival of four glyphosate-resistant annual ryegrass populations grown in competition with a crop in the absence of glyphosate. The line is the average survival of all populations. From Wakelin and Preston (2006) A large fitness penalty for glyphosate resistance helps explain why glyphosate resistance proved so difficult to select and why resistance is occurring more rapidly with the advent of glyphosate resistant crops. A large fitness penalty will tend to keep resistance alleles at low frequencies in populations in the absence of selection by the herbicide. It will also mean that susceptible escapes, due to timing or placement of herbicide application, may dilute resistance more effectively, requiring more intensive selection for resistance to evolve. It is possible to exploit a large fitness penalty in the management of glyphosate resistant populations. Management strategies, such as rotation of herbicides, crop competition and seed set control of escapes, will have more impact on reducing the selection for resistance if there is a large fitness penalty. Therefore, more integrated management approaches to weed management, rather than relying on glyphosate alone, may significantly delay the onset of resistance. In this context, it is significant that glyphosate resistance does not readily evolve in situations where glyphosate was not relied virtually exclusively for weed management. To the future Current understanding of the evolution of glyphosate resistance suggests that glyphosate resistance will continue to occur in situations where glyphosate is used almost exclusively for weed control. These will include situations with glyphosate-based chemical fallows, in tree and vine horticulture and in uncropped areas around the farm. The major weeds at Northern Herbicide Resistance Updates


risk are those that are widespread, occur in large populations, are more susceptible to glyphosate and which have short-lived seed banks. However, it is possible for glyphosate resistance to evolve in most weedy species. If the present heavy reliance on exclusive use of glyphosate for weed control in some systems continues, glyphosate resistant populations will continue to evolve. Glyphosate resistance does not readily evolve in situations where glyphosate is not almost exclusively used for weed control. This property is quite different to our experience with resistance to the Group A and Group B herbicides. Two related factors appear to be important: glyphosate resistance alleles are a lot less common in weed populations and carry a significant fitness penalty. Therefore, any system that has diversity in weed control would appear to be significantly less at risk from glyphosate resistance evolution than those that rely heavily on glyphosate. Introducing diversity into weed manangement systems will reduce the risk of glyphosate resistance, possibly dramatically so. References Heap, I. (2007). The International Survey of Herbicide Resistant Weeds. Online.

Available www.weedscience.com Preston, C. (2007) Australian Glyphosate Resistance Register. National Glyphosate

Sustainability Working Group. Online. Available www.weeds.crc.org.au/glyphosate Wakelin, A.M. and Preston, C. (2006). The cost of glyphosate resistance: is there a

fitness penalty associated with glyphosate resistance in annual ryegrass? In: C. Preston, J.H. Watts and N.D. Crossman, eds. Proceedings of the 15th Australian Weeds Conference. Weed Management Society of South Australia, Inc., Adelaide, pp. 515-518.


MANAGING AWNLESS BARNYARD GRASS (Echinochloa colona (L.) Link) IN NORTHERN NSW Andrew Storrie, Technical Specialist (Weeds), NSW Department of Primary Industries. Tamworth Agricultural Institute, 4 Marsden Park Rd., Calala. 2340

Key words herbicide resistance, glyphosate, awnless barnyard grass, tolerance, monitoring, control survivors, mode-of-action, double knock, water quality

Summary • One population of glyphosate resistant awnless barnyard grass is confirmed • Several other populations are suspected • The key to preventing/managing herbicide resistance is to prevent seed set of weeds

that survive a glyphosate application • Spray weeds when small • Residual herbicides will have to play a greater role in fallow weed management • Introduction of the ‘double knock’ concept will increase weed control costs ($23-

30/ha/germination), but by preventing herbicide resistance, will maintain farm management flexibility

• A range of herbicide modes-of-action are available to use with competitive crops as part of an integrated weed management program

Current situation The decline in the price of glyphosate has seen widespread adoption of reduced-tillage farming systems and a near total reliance on glyphosate for fallow weed control. Glyphosate-based fallows have many advantages over other forms of fallow weed control which include: • Low cost - fewer labour units required to manage the same area of fallow • Better weed control – initially anyway • Maintenance of crop residues reducing erosion risk and increasing efficiency of storing

soil water • When combined with controlled traffic, reduced soil compaction and associated

benefits accrued from improved soil condition A survey of fallow management practices by the author in 1999 showed that tank-mixing herbicides with different modes-of-action (MOA’s) had declined in favour of increasing the glyphosate rate due to convenience, cost and no issues with herbicide residues affecting crop planting. The past few years has seen an increase in tank-mixing glyphosate with 2,4-D or metsulfuron. The latter is more common in the lower rainfall areas. Both these additions are aimed at improving broadleaf weed control. However a quick look at what happens with a single-solution approach to weed management in the USA should sound alarm bells and encourage farmers to re-assess current fallow management practices. The rapid and widespread adoption of Roundup Ready™ crops has seen the development of 4 glyphosate-resistant broadleaf weed species and numerous glyphosate-tolerant weed species becoming new weed problems. Currently there are at least 3 properties with suspected glyphosate-resistant awnless barnyard grass (Echinochloa colona) populations in the Moree-Narrabri area. One population has been confirmed in field and glasshouse experiments.


Common factors between these properties include a long history of winter cropping with summer fallow control entirely with glyphosate, a high incidence of summer storms and lighter textured soil favouring establishment of large barnyard grass populations.

Summer fallows and summer weeds – some tough issues Control of summer weeds with herbicides poses 4 major problems: 1. Rapid weed growth - A control opportunity is missed, or weeds survive due to

resistance or tolerance, decreases the options available while increasing costs to successfully control the weeds due to their increased size. The confirmed resistant barnyard grass population also becomes more resistant as plant size (age?) increases. Therefore SPRAY SMALL WEEDS!!!!

2. Weeds are often heat and/or moisture stressed, reducing herbicide absorption, translocation and effectiveness within the plant. Watch tank-mixes that reduce the efficacy of one of the partners. Glyphosate + 2,4-D may reduce level of barnyard grass control, especially if the weeds are stressed or in high densities, which limits herbicide coverage.

3. A small (read ‘tiny’) “window” when meteorological conditions are favourable for herbicide application – high Delta T’s and temperatures, too windy or too still. Use the best herbicide application technology available, such as low drift nozzles with higher application volumes.

4. Poor water quality – As water supplies decline, the temptation to use poor quality water increases. Muddy water ‘ties-up’ glyphosate and paraquat/diquat. However, by far the biggest problem is hard water, usually from bores. The calcium, magnesium and bicarbonate ions attach to amine (weak acid) herbicides reducing their solubility and level of control. Glyphosate is the main example here, and the problem is exacerbated in the higher water volumes recommended with many air-induction nozzles. If better quality water is not available add 1-2% ammonium sulphate to the tank and agitate before adding glyphosate. This reduces the effect of the hard water. The pH of the water is a minor problem by comparison, and only affects some herbicides when over 8.5 and when left in the spray tank for extended periods. Marginal improvements in efficacy can be achieved by lowering the pH of the spray solution to around 6.0.

To prevent or manage (the more likely scenario) herbicide resistance/species shift growers must:

1. Keep weed numbers low 2. Monitor levels of control 3. Stop any survivors setting seed

Growers must change their weed control mind-set from one of economics to that of seed-bank management. Without stopping survivors of the first weed control method, usually an application of glyphosate, the current spread of herbicide resistance and species shift will only worsen. Point 3 is ‘the bottom line’.

The ‘Double Knock’ – the key to sustainable farming The widespread adoption of the concept of ‘double knock’ MUST occur for farming to continue in the NGR. ‘Double knock’ is the use of a second weed control tactic to eliminate the survivors of the first tactic. The original ‘double knock’ was Spray.Seed® pre-sowing followed by a full


disturbance sowing operation with a combine. The development and widespread adoption of the minimum disturbance planter has seen the end of the ‘double knock’ being practiced on most farms. The practice of using 2 knockdown herbicides is close succession has been shown to give excellent control of both resistant BYG (Table 1). Table 1 Control of 1-2 leaf glyphosate resistant awnless barnyard grass (E. colona) using knockdown herbicides, Bellata, March, 2007.

Herbicide Time 1 Time 2

(5 days later)

Rate L ha-1

Control %

glyphosate (450 g L-1) 1.5 90 glyphosate (450 g L-1) 2 95 glyphosate (450 g L-1) paraquat (250 g

L-1) 1.5 + 2.4 100

glyphosate (450 g L-1) Spray.Seed® 1.5 + 2.4 100 paraquat (250 g

L-1) 2.4 99

Two Scenarios Early - low numbers of resistant/tolerant weeds – prevention still an option Glyphosate resistance and to a lesser extent glyphosate tolerance, is relatively rare compared with resistance to other MOA’s. Therefore when it does appear it will be as low numbers of survivors. Farm hygiene is very important. Cleaning up weeds around shed and fences, sowing clean seed, ensuring machinery and plant are free of weed seeds are all important tactics to prevent the development of glyphosate resistance. Glyphosate will still be used as the primary weed control method. A “double knock” needs to be introduced to control survivors. As weed numbers are being kept low, to boom spray the whole field (Note that high risk paddocks are those that have received >15 glyphosate applications as the sole means of controlling the target species), with 2-3 L ha-1 of a bipyridil herbicide will be wasteful and expensive. Applying the herbicide with a Weedseeker™ or Green target sprayer (GTS) would be the best option. Don’t however rule out scouting the paddock for survivors and either hand pulling or chipping the weeds. Substituting a high label rate (>2 L ha-1) of bipyridil herbicide for a glyphosate application on small weeds once every 3 or 4 fallow sprays will significantly reduce the risk of glyphosate resistance developing. The horse has bolted – weed numbers (& seedbank) out of control Once a glyphosate resistant weed population has established in a paddock the control options available decline rapidly. Double knockdown – glyphosate followed by high rates of paraquat or Spray.seed® 2-3 days later will be mandatory. BYG will grow and set seed very quickly, so the time between the first and second sprays must be short.


Using top rates of paraquat or Spray.seed® alone could be an option if the weeds are small. A second application might be required depending on the size of the plants being sprayed. By including a soil-active herbicide with a bipyridil knockdown such as paraquat + Flame®, 3 glyphosate applications can be saved. Issues with using residual (soil-active) herbicides include a lower level of control under dry conditions and limiting cropping options through herbicide residues. Cultivation will bury weed seed increasing the life of seed in the soil. Fields should not be grazed as stock will spread resistant seed to new areas, and grazing intensities are rarely high enough to effectively control the weeds.

“Double knock” - insurance against glyphosate resistance The increased weed control costs from adopting the “double knock” (seed set management) should be seen as an insurance premium. Most farmers insure their crops for hail damage, fire, and other calamities, so why not insure against glyphosate resistance? Table 2 shows there is a significant increased cost from introducing paraquat or Spray.Seed® however this would be used on high risk paddocks and substituted every third or fourth glyphosate application. However once glyphosate resistance is established in the field glyphosate will have to be followed by a bipyridil increasing control costs by $23-30 for each germination event. Barnyard grass might germinate five or six times a season and if it required the double knockdown treatment it could increase costs by $180 ha-1. Using a residual herbicide like Flame® with paraquat has the potential to save 3 glyphosate applications. Table 3 shows that this is effectively an increase cost of $2.10. This would limit following crops to wheat, barley or chickpeas. Table 2 Costs of introducing different MOA’s to fallow weed control

Herbicide Rate ha-1 Cost ha-1

($)

Additional cost over glyphosate

alone /ha Glyphosate (450 g L-1) + BS1000 + Boost®

1.5 + 0.2 + 2 L 13.50

Paraquat (250 g L-1) + BS1000

2.5 + 0.2 L 22.60 9.10

Spray.Seed® + BS1000 2.5 + 0.2 L 30.35 16.85 Glyphosate f.b. paraquat 1.5 L f.b. 2.5 L 36.10 22.60 3 sprays glyphosate + 2 extra application costs @ $6 ea.

3 X 1.5 + 0.2 + 2 L 52.50

Paraquat (250 g L-1) + Flame® + BS1000

2.5 + 0.2 + 0.2 54.60 2.10

Other herbicide options combined with crop competition Herbicides alone are not the answer to herbicide resistance, however recent research in NSW has shown that a range of MOA’s are still effective on glyphosate-resistant barnyard grass.


A range of selective herbicides were found to highly effective on glyphosate-resistant barnyard grass, including A, B, C, D, E + K and K . Other MOA’s, particularly high risk groups like A and B, should be part of a rotation and only used in-crop. Selective post emergent herbicides should never be used in a fallow. Growing a competitive broadleaf summer crop such as narrow-row mung beans with a pre emergent herbicide, followed by post emergent grass herbicide and then diquat pre harvest will optimise seed set control over summer.

Conclusions At least two control tactics should be used for each weed germination to prevent seed set, otherwise the development of herbicide resistance is inevitable. The concept of ‘double knock’ will increase weed control costs, but nothing like the additional costs and ‘opportunity costs’ of having herbicide resistance determine weed management tactic and enterprise. Weed control must be optimised by spraying small weeds and maximising the amount of herbicide getting to the target by using robust rates and the best application technology available.

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