Herbicides and weeds regional issues trials and developments

GRDC codes: UQ00062, UA00124, GOA0002

Regional issues trials and developments


Tony Cook and Greg Brooke, NSW DPI; Michael Widderick, Qld DAFF; Maurie Street, GOA

Take home messages

  • There are many weed related problems facing growers in the northern grain region.
  • Herbicide resistance is the major issue, affecting many species and making many herbicide options redundant.
  • Most farmers will be dealing with some or many of the topics covered in this paper, making effective management difficult.
  • Research has found solutions for many of these issues, however there are some research needs for a good range of problems.
  • A great proportion of the solutions to our problems are still herbicide based and in the future will lead to other herbicide resistance problems.

Multiple resistant wild oats

Resistance to one mode of action herbicide is very common in most parts of the northern grain region, specifically for post-emergence herbicides. Farmers overcome this issue by selecting another post-emergence herbicide from a different mode of action. However, the steady increase in multiple resistant wild oats has forced farmers to make substantial changes.

The most recent wild oat survey for the northern region was completed in 2007 so getting a more precise understanding of the situation is difficult. Furthermore, this survey was focused on the SE Qld and N NSW regions. With this in mind, The Grain Orana Alliance has conducted a wild oat resistance survey in 2013. It was solely focused on the resistance issues of central western NSW and the results from this study will be eagerly sought when reported in 2014.

There are many cases of multiple or cross resistance occurring. In some cases the resistance can be to three herbicide groups (A, B and Z). However, in extremely serious cases of multiple resistance there is still a good chance that a few post-emergence herbicides will work. One example is a population of wild oats from Edgeroi that was confirmed resistant to Group A, B and Z herbicides, but was still susceptible to Verdict and high rates of Select.

The mechanisms controlling resistance within wild oat plants are complex. Unless a resistance test is used, you will remain in the dark as to which herbicides are likely to still work and which won’t. 

Growers with wild oats that have resistance to one or two herbicides groups (either, A, B, Z,   A and B or A and Z), could use a pre-emergence herbicide followed by the remaining useful post-emergence option and get excellent levels of control. Table 1 below best summarises this strategy.

Table 1. Controlling group A resistant wild oats, North Star
Herbicide Rate of product/ha Herbicide group(s) Wild oat seeds per m2
control N/A N/A 90.7
Achieve® (post-em) 380g A 43.8
Topik® (post-em) 65mL A 180.9
Wildcat® (post-em) 300mL A 123.3
Avadex® Xtra (pre-em) 1.6L J 9.4
Trifluralin® 480 (pre-em) 1.5L D 47.8
Mataven® 90 (SST) 1.875L Z 0.4
Hussar® (post-em)  200g B 2.3
Atlantis® (post-em) 330mL B 4.2
Crusader® (post-em) 500mL B 0.0
Avadex® Xtra (pre-em) + Hussar® (post-em) 1.6L + 200g J + B 0.3
Avadex® Xtra (pre-em) + Atlantis® (post-em) 1.6L + 330mL J + B 0.0
Avadex® Xtra (pre-em) + Mataven® 90 (SST) 1.6L + 1.875L J + Z 0.0
Atlantis® (post-em) + Mataven® 90 (SST) 330mL + 1.875L B + Z 0.0
Hussar® (post-em) + Mataven® 90 (SST) 200g + 1.875L B + Z 0.0

SST = Selective Spray Topping – late post-emergence to prevent seed production.

However, there are some cases of multiple resistance to all three post-emergence herbicide groups. In this case, data in Table 1 would be irrelevant as no post-emergence option would be effective (refer to Table 2 instead). Reliance solely on pre-emergence herbicides would result in populations of wild oats increasing. Surviving plants from trifluralin and Avadex Xtra treatments tend to be large and produce more seed than what is lost from the germination process.

The radical step of changing crops may open the door to the use of other herbicides (Table 2). Although this wild oat population can be well managed in wheat with pre-emergence herbicides + Atlantis®, alternative crops can be grown with better weed control outcomes. Chickpeas grown on conventional row spacing or wide rows resulted in excellent control and utilised herbicides that have probably never been used for many years. The inter-row spraying of Gramoxone® in wide row chickpeas was successful and the inclusion of simazine, trifluralin and Avadex Xtra as a pre-emergent option was useful.

Table 2. Controlling multiple resistant (Groups A, B and Z) wild oats.
Crop Treatments Herbicide group(s) Wild oat seed production per m2 Yield (t/ha)
TT Canola trifluralin +  Avadex Xtra + atrazine + Sertin® D + J + C + A 0.5 0.82
Canola trifluralin +  Avadex Xtra + Dual® Gold + Sertin® D + J + K + A 15 0.82
Clearfield® canola Intervix® B 469 0.41
Chickpea 35 cm row trifluralin +  Avadex Xtra + Simazine  + Sertin® D + J + C + A 1 1.24
Chickpea 75 cm row trifluralin +  Avadex Xtra + Simazine + Gramoxone D + J  + C + L 11 0.87
Wheat trifluralin +  Avadex Xtra + Atlantis D + J + B 14 0.94
Wheat Sakura® K 35 1.08
long fallow Flame® + glyphosate B + M 5 N/A

Note: This population had confirmed complex resistance to groups A, B and Z, however it was shown in previous trials that it was partly susceptible to Atlantis and Sertin hence their inclusion

The same principle applied when growing canola with the inclusion of atrazine, trifluralin, Avadex Xtra and Dual Gold.

Long fallowing paddocks is another alternative. It is important to note that the Flame treatment did not control wild oats well and a follow-up application of glyphosate was required to prevent seed set.

Poor wild oat control was reported in Clearfield canola after using Intervix. This population may exhibit some resistance to this herbicide without prior history of its strong levels of Hussarresistance (Group B) may infer other Group B herbicide resistance. This is a likely reason why Flame did not work well in the fallow. Despite the failure of Clearfield canola, Roundup Ready Canola should work since the population seems susceptible to glyphosate.

Another option is the use of Roundup Ready Canola. This provides excellent control of wild oats. In one experiment at Edgeroi that was infested with A, B and Z resistant wild oats, wild oat seed production was almost 100% prevented with one application of glyphosate. The flip side of this choice is increased risk of glyphosate resistant annual ryegrass not being controlled. 

One crop in the north-west that is under more threat due to herbicide resistant wild oats is chickpeas. Although a wide range of post-emergence selective grass herbicides are registered, all are Group A herbicides. Unlike wheat, herbicides like Hussar, Atlantis and Mataven are not registered for use. The pre-emergence herbicides trifluralin and Avadex Xtra are options worthy of consideration and the inclusion of simazine could improve the control. However, if Group A resistance is present, chickpea growing would be totally reliant upon pre-emergence herbicides with in-crop options limited to inter-row tillage or wick wiping. There are two issues with relying solely on pre-emergence herbicides in chickpeas. These are;

  1. pre-emergence herbicides usually result in only 60-80% control under favourable conditions (not as effective as post-emergence herbicides – 85 to 95% control) and
  2. that chickpeas do not compete well with weeds allowing the survivors of pre-emergence treatments to develop into large plants capable of large seed production.

There are numerous tactics that can be used to reduce the impact of wild oats. These are summarised in Table 3 and could be used in combination as an integrated weed management approach to maintain the usefulness of effective herbicides.

Table 3. List of tactics that could be used to manage wild oats
Tactic Wild oats to Likely control % (range) Ability to incorporate into farming system (easy, mod, hard)
Crop choice and sequence 95 (30-99 Easy to moderate
Improving crop competition 70 (20-99) Easy to moderate
Herbicide tolerant crops 90 (80-99) Easy
Burning crop residues 40 (0-80)# Moderate to hard
Inversion ploughing 50 (40-60)# Moderate to hard
Autumn tickle 40 (30-60) Easy to moderate
Fallow and pre-sowing cultivation 40 (0-80)# Easy to moderate
Knockdown herbicides for fallow & pre-sowing control 80 (70-90) Easy
Double knockdown (doubleknock) 99 (99-100)# Easy to moderate
Pre-emergence herbicides 80 (70-90) Easy to moderate
Selective post-em herbicides 80 (70-90) Easy
Spray-topping with selective herbicides 90 (60-99) Easy
Crop-topping with non-selective herbicides 30 (10-50)# Easy
Pasture spray-topping 80 (70-90) Moderate
Silage and hay – crops and pastures 97 (95-99) Moderate to hard
Renovation crops – green or brown manuring, mulching etc. 95 (85-99)# Moderate
Grazing – actively managing weeds in pastures 75 (60-80) Moderate to hard
Weed seed collection at harvest 70 (20-80) Hard
Sow weed-free seed 85 (50-99)# Moderate
Source: Integrated Weed Management in Australian Cropping Systems (A training resource for farm advisors), Section 6-Weeds, weed 1 annual ryegrass (p151) and weed 18 wild oats (p200). Eds. McGillion, T. and Storrie, A.
# - no reference in IWM manual, so estimate was made by author of this paper.

Some of these tactics will be rather easy to incorporate into the farming system, as little or no adjustments to equipment are required. A few examples are changing to herbicide tolerant crops or crop topping with a non-selective herbicide. However, some new tactics may involve introduction of pastures or new machinery, therefore the costs to implement these changes could be prohibitive. This table of tactics includes 19 different options. Many of these may not be applicable to your farm, but there are likely to be at least 6 to 8 that should be considered.

It is important to note that most of the tactics that involved a change in spray/herbicide strategy had an easier inclusion into the cropping system. In northern NSW we are fortunate to have a majority of our ARG and wild oat populations susceptible to most herbicides. Therefore, changes in weed management are likely to involve a change in herbicide selection (e.g. doubleknock, herbicide tolerant crops, crop-topping, using pre-emergence herbicides, etc.) as these relatively easy transitional options. As the level of herbicide resistance worsens, for instance multiple resistance to most pre- and post-emergence herbicides, the tactics required to manage the problem become increasingly harder to implement. This is what is happening in winter dominant rainfall areas in Australia.

Although it is easy to combat herbicide resistance with other herbicides from a different mode of action (herbicide group), it will place resistance selection pressure on these alternate herbicide groups. Some non-chemical options should be implemented to take the reliance off herbicides. The two most suitable options would include using adequate crop competition and the use of strategic cultivation that minimises soil moisture losses and structural damage.

Glyphosate resistant windmill grass

Due to the extended period of dry weather in the central west region of NSW in the past 18 months, no new research findings are available. Plans were to investigate to re-confirm the excellent control achieved with a paraquat + Group H herbicide. Discussions with many weed scientists and agronomists had also identified the research need into the potential of pre-emergence herbicides. The rationale behind this approach is to aim for better control when weeds are more susceptible to herbicides, emerging after rainfall, then to try control to larger plants that may be under some moisture stress. Therefore, a few more years of research are required before the possibility of a few more treatments is available to growers.

Current herbicide registrations for control of Windmill grass in summer fallow are limited to Touchdown® Hi Tech. No other formulations of glyphosate are registered to control this weed.

There are only two other products registered for selective control of this weed in various situations as listed in the table below.

Table 4. List of registered products to control windmill grass
Product Name Active Ingredient Use situation
Factor® Butoxydim Various summer crops e.g. mungbeans, cotton, sunflowers.
Dacthal 900® Chlorthal-Dimethyl Various brassica and vegetable crops e.g. cotton, lucerne and lawns.

As of June 2012, the Grain Orana Alliance (GOA) successfully obtained a Pesticide Permit (number 13460) that allows the use of quizalofop based products at a rate of 0.5 to 1.0L/ha (10% active products) or 250 to 500mL/ha (20% active products). An application of paraquat must be made 7 days after application to ensure better control and to minimise the chance of Group A resistance developing. There are application directions that allow for consistently high levels of control; applying to 3 leaf to early tillering plants and to avoid spraying under moisture stress. GOA has shown that waiting more than 11 days after rain to apply herbicides will result in diminishing levels of control.

As of March 2013, there are 9 confirmed cases of glyphosate resistant windmill grass in Australia, three are located in NSW. Two of these infestations were located in summer fallows and the other on a roadside. It is highly likely that the number of cases of glyphosate resistance is far worse as seed is easily moved by wind and continued use of glyphosate solely will ensure its gradual spread over the central west region of NSW.

Group I resistant wild radish

Late in 2013 a population of wild radish from the central west was confirmed resistant to phenoxy herbicides (Group I), reported as 50% resistant. This discovery has now placed many farmers around the central west district on ‘resistance alert’.  The area of concern is approximately a 250km square region south of Nyngan. This region was subject to a long and frequent history of phenoxy use. Common farm practices have included the use of few pre-emergent herbicides and low rates of 2,4-D, MCPA and MCPA LVE formulations in the cereal dominant rotation, sometimes with the addition of a group B herbicide.

It is not uncommon for this weed to be sprayed several times in a summer fallow leading up to sowing of the winter crop, then often more than once in crop due to successive germinations. It is not uncommon that a population of radish in this area will receive 4 applications per year of a group I product.

Traditional rotations included lucerne phases however lucerne paddocks and paddocks being “spelled” from cropping are frequently dominated by wild radish as it is largely unpalatable and control options are more limited and expensive than in a cereal crop.

Paddock screening trials done by DPI, at a known resistance site, showed poor efficacy from group B products but very good results from those products containing group H (Precept® and Velocity®).

Approximately 15 samples of wild radish from around this region are going to be tested for group I resistance.  From these results it will give a better snapshot of the distribution of this problem and should trigger more detailed resistance screening to determine other effective modes of action available to growers.

There is much to learn from the Western Australia wild radish experience. In the Geraldton region farmers have been dealing with Group I resistant wild radish for at least 5 years along with resistance to many other modes of action. A great deal of their weed management is based on weed seed collection or windrow burning with some assistance from glyphosate (within Roundup® Ready canola). 

Competition trials

A few experiments have been completed in the past three years. One investigated the row spacing of wheat and its effects on fleabane numbers and the other studying the effects of wheat density on wild radish. Dry conditions at the end of the 2013 winter cereal season meant that drought effects dominated the experiment with most wild radish plants dying from extreme moisture stress regardless of crop density.

Crop competition is known to be a factor that reduces the germination and growth of fleabane. This was highlighted in a trial at Trangie Agricultural Research Centre (TARC), where increasing the row space of Crusader wheat from 33 cm to 66 cm resulted in a 120% increase in fleabane plants in the stubble immediately after harvest (Figure 1). The trial showed that the effect of row space is real and measurable, and can add significantly to other weed control practices. The trial showed no significant effect of seed rate on fleabane population post-harvest. Based on past trial results and the practicalities of row spacing, the ideal set up seems to be about 25 cm for disc seeders and about 30 cm for tine seeders for western areas, and potentially narrower for eastern regions.

Figure 1. Wide rows reduce crop competition with fleabane. This was shown at TARC with 66 cm row space resulting in 120 % more fleabane in fallow than the 33 cm row space (sow time l.s.d. p < 0.05 = 0.34) , with no significant effect of seed rate on subsequent fleabane population. 

  Barchart showing fleabane seed rate and row spacing (text description follows image)

Figure 1 text description: Seed rate and row spacing per metres squared (m2) of Fleabane. At 33cm: for 50 ppm2, Fleabane was just over 1.5m2; for 100ppm2, just under 1.5m2; for 150ppm2 approx 1.25m2, for 200ppm2 just over 1.25m2. At 66cm: for 50ppm2 and 150ppm2 Fleabane levels were just over 3.0m2 for 100ppm2 and 200ppm2 Fleabane levels were just under 3.0m2.

Resistance in fleabane and sowthistle


Glyphosate resistant fleabane is common in regions between the Liverpool Plains and the Darling Downs. Isolated infestations have been located in the central west parts of NSW and the national register of confirmed cases totals 57. All of these cases were discovered between 2010 and 2012. Knowing that fleabane has large seed production capacity and the seed is easily spread by wind, the potential for widespread glyphosate resistant fleabane throughout the northern grain region is possible.

There are concerns that the frequent use of 2,4-D and other group I herbicides may lead to resistance to this class of herbicide. In light of this, a comprehensive survey completed in summer of 2012/3 attempted to find Group I resistance.  Approximately 50 fleabane samples were tested for susceptibility/resistance to 2,4-D amine.  All samples were found to be susceptible to 2,4-D amine.


The same survey mentioned above also determined the extent of Group I resistance in sowthistle. Seed was collected from sowthistle growing in winter cereals and summer fallows from 2012 and all were found to be susceptible to Group I chemistry.

In the past few years there was unease about survival of sowthistle following glyphosate applications. Recently screening work has identified two populations from the Liverpool Plains with elevated levels of tolerance to glyphosate. Table 5 shows that the “yellow” and the “CRK”  biotypes to have reasonable survival rates and reproductive capability 42 days after the standard label rate of glyphosate (1.6L/ha or 720 g active ingredient per hectare).

The discovery of two populations of sowthistle with elevated survival rates following glyphosate may indicate a world’s first case of glyphosate resistant Sonchus species. Further research is underway to determine if a panel of glyphosate resistance experts deem this as glyphosate resistance.

This experiment was split into two separate growth stages. Results presented within are those following application to large rosette/early stem elongating plants. Anecdotal evidence suggests the recovery and reproduction of confirmed resistant biotypes following label rates of glyphosate to larger flowering plants is more pronounced and faster than those treated earlier. This could be due to greater expression of glyphosate resistance as plants develop and/or biological dilution of herbicide due to greater plant volume per unit area.

Table 5. Final assessments on sowthistle for plant survival, biomass control / production and reproductive capacity, made 42 days after treatment. Note: growth stage at treatment was large rosette to early elongating stage.
Glyphosate rate g a.i./ha rate Live plants (max = 1 plant per pot) Green biomass as g/plant
(% control)
Viable flower buds per plant
Susceptible biotype
0 1 32.56    (0) 26.6
360 0.8 3.46    (89) 0
720 0.4 1.12    (97) 0
1000 0.4 0.56    (98) 0
“CRK” biotype
0 1 49.94    (0) 21.8
360 1 18.36   (63) 0.4
720 1 10.38   (79) 0
1000 1 19.06   (62) 0
“Yellow” biotype
0 1 59.26     (0) 16.8
360 1 32.84    (45) 6
720 1 18.92    (68) 0.2
1000 0.8 19.08    (68) 0

Implications to grains and cotton industries

Fallows, glyphosate tolerant crops and non-cropping areas are under threat of another glyphosate resistant species.

Group B resistance is already present within the QLD/NSW border region. It is likely that plants will develop multiple resistance to Groups B and M.

With the partial loss of effectiveness of glyphosate and Group B resistance in other parts of the northern grain region, there will be more selection pressure on Group I chemistry. Further to this, herbicide Groups C, G, H and L could be used more to take selection pressure off Groups B, I and M.

Due to its wind borne seed, glyphosate resistant sowthistle populations will spread rapidly, similar to fleabane. Surveys are presently underway to gauge the spread of resistance in the northern grain region. In time, southern regions should be surveyed to determine the extent of resistance to glyphosate.

Interim results from the survey work indicate that another two populations have similar tolerances to glyphosate as those discussed above. The location of these plants was within the Liverpool Plains. Sowthistle samples were collected further north and into the Darling Downs regions. The extended dry period in the central western parts of NSW has made it difficult to find samples to test.

Latest research to combat the glyphosate resistant threats (sowthistle)

With recent cases of suspected glyphosate resistance in common sowthistle, effective glyphosate alternatives are required. A field trial evaluated alternatives to glyphosate for fallow control of common sowthistle and the impact of weed size. Treatments included alternative single and double knocks.

Located near Cecil Plains on the eastern Darling Downs, the field site had a dense (6-10 plants/m2) population of common sowthistle plants at two different growth stages (small <10cm diameter, and large >10cm diameter to elongating).

Summary of results

The most effective fallow treatments were the double knocks which were as equally effective on both small (97-100% control) and large (95-100% control) sowthistle plants (Table 6). Most double knock treatments provided 100% control, thereby stopping any weed seed production. Our results show that the double knock treatment is essential for the effective control of small and especially large sowthistle plants.

Antagonism between glyphosate and any tankmix partner was apparent. With reference to the data presented in Table 6, weed control from a single application of glyphosate (Roundup Attack® 1.23L/ha) ranged from 93 to 100% regardless of growth stage, whereas the levels of control when mixed with Amicide Advanced® 700, Tordon 75-D® and Starane Advance® were 2-43%, 12-62% and 40-64%, respectively. This phenomenon is not uncommon throughout the northern region, as agronomists constantly raise this issue with researchers. It is thought that the cause of this antagonism is the stress that glyphosate imposes on the plant which contradicts the conditions needed for effective hormonal activity.

Even though glyphosate was shown to be effective on this population of sowthistle, continued over-reliance on this herbicide is likely to lead to glyphosate resistance in this species. Growers with glyphosate susceptible populations should be using the double knock tactic to stop seed set on survivors. This is of particular importance in reducing weed density and herbicide resistance risk for the future.

While not tested on a glyphosate resistant population, it is likely the double knock tactic would also be effective. If a population of glyphosate resistant sowthistle is confirmed as part of our project, a pot study exploring the effectiveness of the double knock will take place.

Table 6. Visual biomass reduction of common sowthistle (Sonchus oleraceus) assessed 31 days after treatment where 0 - no control and 100% - total control. For double knock treatments, the second knock was applied 7 days after the first. LSD on transformed data = 29.24. Numbers in parentheses are transformed and should be used when comparing treatments using the LSD.
Treatment Herbicide rate/s
(<10cm diameter)
(>10cm diameter to elongating)
control (%)
transformed (%)
control (%)
Roundup Attack® 1.23 100† (90) 93† (81)
Sprayseed® 2 80 (69) 43 (39)
*Roundup Attack® fb Sprayseed® 1.23 fb 2.0 100   100  
Amicide Advanced® 700
+ Roundup Attack®
0.65 + 1.23 43 (40) 2 (4)
*Amicide Advanced® 700
+ Roundup Attack® fb Sprayseed®
0.65 + 1.23 fb 2.0 100   100  
Tordon 75D® + Roundup Attack® 0.7 + 1.23 62 (52) 12 (19)
*Tordon 75D®
+ Roundup Attack® fb Sprayseed®
0.7 + 1.23 fb 2.0 100   100  
Starane Advance® + Roundup Attack® 0.6 + 1.23 64 (58) 40 (39)
*Starane Advance®
+ Roundup Attack® fb Sprayseed®
0.6 + 1.23 fb 2.0 100   100  
Sharpen® + Roundup Attack® 17g + 1.23 57 (49) 38 (38)
+ Roundup Attack® fb Sprayseed®
17g + 1.23 fb 2.0 97† (81) 95† (80)
Alliance® 2 70 (59) 18 (19)
Sprayseed® 2.4 92† (73) 57/td> (49)
*Roundup Attack® fb Sprayseed® 1.23 fb 2.4 100   100  
Amicide Advanced® 700
+ Roundup Attack®
1.1 + 1.23 67 (60) 30 (31)
*Amicide Advanced® 700
+ Roundup Attack® fb Sprayseed®
1.1 + 1.23 fb 2.4 100   99  
Tordon 75D® + Roundup Attack® 1.0 + 1.23 88† (78) 58 (49)
*Tordon 75D®
+ Roundup Attack® fb Sprayseed®
1.0 + 1.23 fb 2.4 100   98  
Starane Advance® + Roundup Attack® 0.9 + 1.23 97† (84) 67 (55)
*Starane Advance®
+ Roundup Attack® fb Sprayseed®
0.9 + 1.23 fb 2.4 100   100  
Sharpen® + Roundup Attack® 34g + 1.23 82 (66) 60 (52)
+ Roundup Attack® fb Sprayseed®
34g + 1.23 fb 2.4 100† (90) 99† (87)
Alliance® 2.8 90† (75) 50 (50)

fb - followed by, as part of a double knock                      * - excluded from analysis as most values = 100
† - not significantly different to 100. To compare with treatments excluded from analysis.

Latest findings: residual herbicides on summer grasses

Residual herbicides will play an important role in the control of summer grass weed species barnyard, feathertop Rhodes and windmill grass. Little is known about the efficacy of some new and some existing residual herbicides on these weed species. Consequently, a pot trial was established to evaluate the efficacy, over time, of different residual herbicides on the control of grass weed species barnyard, feathertop Rhodes and windmill grass. Due to the confidentiality of unregistered treatments and GRDC policy, treatments presented for this experiment are expressed in broad herbicide mode of action groups.

For barnyard grass, Group D, Group G and Group G + K treatments have provided the best control for 0 and 4 week plantings. No treatments provided any control of barnyard grass for the 8 week planting.

The best treatments for feathertop Rhodes grass are from herbicide Groups D and K. Both treatments have provided sustained control with 53 and 68% control at the 8 week planting. Other treatments which provided good short-term control are from Group G, K, G + K and B(imi) + K.

The best treatment for windmill grass has been from a Group D herbicide which has provided long term control with 77% control for the 8 week planting. Other treatments which have provided good short-term control (0 and 4 week plantings) are from Group G, K, K + G and B + K.

This experiment will be repeated in 2014/15 with the aim to have many of these herbicides registered. Plant-back considerations are important and thus some research needs to be focused to determine if these new treatments are not too restrictive for the various cropping regimes of the northern grain region.

Clethodim damage in canola – impact and avoidance

The application of clethodim at rates of product of 500mL/ha have been reported to cause the following symptoms on canola:

  • Delayed flowering
  • Distorted flower buds
  • Possible yield suppression

The current label states that if applications of herbicide above 250mL/ha are made, canola can not be greater than the large rosette stage (GS 29). Other warnings such as not applying twice in the crop, not applying to stressed canola or avoid adding crop oil are aimed to minimise this damage.

Recent research in the central west parts of NSW by GOA had resulted in variable results.  Overall damage seemed to be light and it was difficult to ascertain whether some damage was attributed to frost or other abnormal conditions.  Yield effects were negligible for most sites. It was concluded that more field experiments could be completed over several sites and years, or some of this work could be achieved under controlled climate conditions, but loses the realistic conditions of field based research.

Clearly growers need to be aware of the main factor driving such drop damage. There may also be varietal differences, about which little is known, however, farmers can control the timing and rate of herbicide and should be able to avoid such issues. As for controlling the conditions of canola at the time of application, spraying earlier may avoid moisture stress issues particularly in seasons when rainfall is light. Spraying early means late emerging grass weeds will not be controlled with in-crop sprays but these plants are likely to be suppressed by a rapidly closing canola canopy. Seed production from these weed could still be managed with non-chemical options such a wind-row burning. 

Barley grass on the increase in the central west

It is common to see farming systems involving continuous cropping without fallow or delayed sowing.  The practices of dry-sowing and cereal dominance in the crop rotation are leading to increasing problems with barley grass.

Extremely high populations of barley grass 40,000 seedlings per square metre are sometimes targeted in a cereal crop after dry sowing and spray failures are common on these high weed densities.  This is usually with group B or C products and results in very poor control. It is also far in excess of label constraints which target a maximum of 100 seedlings per square metre (as per metribuzin label).

There are some things to be learnt from other farmers in Australia that have been battling this weed for many years.

  • There is resistance to herbicide Groups A, B and L.
  • Delayed sowing could allow the use of glyphosate but research has indicated doing this continuously may select for populations with delay emergence patterns.
  • Barley grass is a surface germinating species and may not emerge after some soil inversion.
  • Break crops (e.g. lupins or TT canola) in a rotation provide different herbicide options such as simazine and clethodim.
  • Burning residues may result in 50% (0-75%) control of barley grass.
  • Avoid totally relying upon post-emergence herbicides, herbicide such as trifluralin and Boxer Gold® can achieve reasonably good control.
  • Barley grass can be strategically managed in pasture phase prior to sowing cereals. If timed correctly, pasture spray-topping can control 60% (50-90%) of barley grass. Stock grazing can also reduce barley grass by approximately 30%.

Contact details

Tony Cook
Mobile: 0447 651 6070447 651 6070447 651 6070447 651 607
Fax: 02 6763 1222
Email: tony.cook@dpi.nsw.gov.au

Greg Brooke
Mobile: 0437 140 5770437 140 5770437 140 5770437 140 577
Fax: 02 6888 7201
Email: greg.brooke@dpi.nsw.gov.au

Maurie Street
Mobile: 0400 066 2010400 066 2010400 066 2010400 066 201
Email: maurie.street@grainorana.com.au

Michael Widderick
Phone: 07 4639 885607 4639 885607 4639 885607 4639 8856
Fax: 07 4639 8800
Email: michael.widderick@daff.qld.gov.au

GRDC Project Code: UQ00062, UA00124, GOA0002,