Fine tuning narrow windrow burning

It is that time of year again when a farmer’s thoughts turn to burning. Like most things there is more than one way to skin a cat. However I am going to talk about some of the dos and don’ts for narrow windrow burning.

Although at this point you cannot do anything about chaff windrows that have already been produced what you will see is that windrows from a well set up header will have withstood considerable amounts of rain over summer and still be ready to burn. The windrow you can see below has had over 100 mm of rain between harvest and burning.

Windrows that aren't over-threshed remain open and aerated like this one.

Chaff still on top of windrow despite 100 mm rain.Things to note are that the windrow appears prickly and this shows that during harvest the straw was not over threshed. This has allowed the chaff portion to remain high in the windrow which also aids drying after rain. The crop was harvested at a height of approximately 10 cm.

Another critical factor in burning windrows is the meteorological conditions when you start burning.

Starting the burn when the FDI is about 7 which in this case was about 18:00.The use of a fire danger index (FDI) has made stubble burning more of a science than a mystical art. The FDI is determined by temperature, humidity, wind speed and dryness of the fuel. These need to be measured and put into the fire index app to calculate FDI. This means that you need a weather meter, either hand-held or cab mounted, and your mobile phone with the app installed. A very useful app for both Android and Apple is Fire Tools by Mountain Pine Studios.

Doug Smith measuring wind speed, temperature and humidity to feed into the fire app. Also use the Bureau of Meteorology’s MetEye® site for monitoring local predicted changes to wind speed and direction so you can decide whether to press on or call it a night.

This is the sort of result you aim for.As a rule of thumb for the fire index:

Greater than 15 is too high

8 to 10 is ideal

Less than five is often too cool or damp

Starting when the fire index is too high means that the file will rarely stay in the windrow and the fire will burn significant portions of the paddock. See image below.
Too low and the windrows won’t burn as hot as needed to kill weed seeds in the row.

This paddock on another property was cut a little high and the burn started when the Fire index as too high. The fire didn't remain within the rows.Important pointers from Doug & Kerry Smith, Pingrup, WA

  • Always over-estimate the problem and under-estimate your ability when it comes to fire control
  • Your aim is to burn the rows not the farm
  • Buy a good fire lighter as it makes a big difference to the amount you can light per night
  • Conditions change by the hour so keep measuring conditions as well as knowing what is coming for the next couple of days before you light up.
  • Check for smouldering rows early the next day so they can be dealt with before the day heats up.
Southern Alberta Weed workshop - Transdisciplinary approaches to better weed research and management?

In June 2016 Sally Peltzer & I attended Andina III – a 5 day weed workshop in southern Alberta organised by a range of weedies including the notable Roger Cousens, University of Melbourne and Sonia Graham, a social scientist from the University of NSW.

The workshop was held at the Gladstone Ranch near Pincher Creek, in the eastern foothills of the Canadian Rockies and was attended by 32 ‘natural’ and 'social' scientists, agronomists and consultants, from seven countries. Australians and North Americans made up the bulk of the participants.

 Gladstone Ranch homestead

This was the third Andina workshop, with the first 2 taking place in Yellowstone National Park and Spain. Each conference has had a different theme. The theme for Andina III was “the transdisciplinary approach” to weed research and management and a few social scientists were thrown into the mix.

The general principle behind these get-togethers is to fill a perceived void left by traditional conferences by fostering international dialogue, collaboration and mentoring in a relaxed atmosphere. By spending 5 days together and doing a wide range of activities trust and relationships are built between the participants which will continue into the future once everyone has returned home to their normal lives and jobs.

So what is a "transdisciplinary approach"?

This was an interesting question because we asked “what is the difference between transdisciplinarity and a good research and extension program?” This was discussed at some length, for better or worse over the five days.

Integrative multidisciplinary research is thought to address complex real-world problems addressed systemically rather than as isolated problems.  It involves harnessing scholarly and practical knowledge across many stakeholder groups such as scientists from different disciplines, private sector players, farmers, and extensionists at a range of geographic and political levels e.g. local, regional, landscape-wide.

Some of the participants in a 'break-out' session.

Multiple parties bring:

  • a wide range of knowledge to address a complex problem.
  • AND a diverse and often conflicting range of interests and views

Normally what happens in research is that researchers concentrate on research directions and objectives and tack on some publicity, such as a dry press release, or ill-planned extension at the completion of the research. This is the old top-down approach to research - we know what’s good for you so you should use our research findings....... and be grateful while you’re at it.

We tried to test the multi-disciplinary approach in southern Alberta by doing a fair amount of pre-workshop communication between workshop members as well as reading up on the issues facing the diverse range of land users in southern Alberta.

For us the most interesting case study we investigated was the Waldron Grazing Cooperative which:

  • Is a collection of commercial cattle ranches  (over 16,000 ha) under a single progressive manager
  • It is a prime wildlife corridor for bears, cougars, elk, deer, coyote and moose
  • Accesses land management funds for projects from Alberta Province and Federal Government, private donors and the co-operative.
  • Has an agreement with the Nature Conservancy of Canada to protect the land in a state similar to that prior to white settlement, except running beef instead of bison.
  • Makes the Waldron Coop an outlier with other beef ranchers in the area because they are seen as different because of their size and the way they access a range of external funds. This is then seen as the major reason why they can run above district average numbers of beasts and obviously has nothing to do with the pasture and grazing management being practised.
  • Has leafy spurge (Euphorbia esula) as its major weed species. Leafy Spurge is a perennial with a spreading root system that isn’t eaten by cattle and has been spreading across North America since the early 1900s.

Mike the Walrond manager’s approach

Mike, manager of the Waldron Cooperative, outlining his approach to range management.

  • Manage the grass first and the cattle second because without the grass you can’t fatten the cattle. Mike tries to emulate the grazing patterns of the bison with rotational grazing and lets the perennial grasses seed before winter to maintain species diversity in his pastures. Like in Australia most cattle ranchers set stock their pastures over summer leading to an increased density of leafy spurge, and a decline in species diversity and cattle weight gain.
  • To manage the leafy spurge Mike uses a biocontrol agent that is a root-feeding beetle. Many other ranchers have also established this beetle on their leafy spurge infestations while others use an ‘unplanned’ herbicide program in an attempt to contain weed infestations.
  • What is different with the Waldron Co-op is that they graze  sheep (leased) on the spurge as well. We were told that the reason why the combination of biocontrol and grazing with sheep works so well was that the sheep disperse biocontrol agent. Interestingly no research has been conducted looking at the influence of defoliation in combination with the root feeding biocontrol. We thought that this is probably the reason why this combination works so well not the dispersal of the beetles. This is an excellent example where a multi-disciplinary approach to a problem would have paid off rather than leaving it to biocontrol specialists.

  • It is interesting to note that there also is a VERY negative attitude towards the grazing of sheep in the general ranching community going back to the time when homesteaders moved into the Canadian rangelands leading to ‘range wars’.  
  • We thought that if you hate sheep, why not try a combination of slashing and biocontrol?

Unfortunately we did not meet any other ranchers that would be considered “typical”. The ranchers we sat down and discussed a weed management with were all organic beef growers. What all ranchers do seem to like doing is sit on a horse.

Canada has also experienced contraction of provincial agriculture departments with a reduction in production research and extension being available to landholders.

So what did we take home from Andina III?

  • Andina is a great opportunity to meet a range of international researchers and get to know them having a great time while you’re at it.
  • Multi-disciplinary approaches (which are hard to define – just read the peer reviewed papers on the subject) have merit because a number of the researchers we met did not work with anyone from outside their technical silo. Hmmmm. Several researchers said that they would not look at multi-disciplinary cooperation because it would not progress their career objectives i.e. pump out papers.
  • Multidisciplinary teams seem an obvious approach for someone with an extension/research background but was a new concept for a number of the researchers.

If you get the opportunity to attend an Andina workshop it is well worth the effort. The next workshop is in Agentina in January 2018. This time the topic will be fundamental molecular biology through to mathematical modelling. For more information go to

Which herbicide caused that injury? We put some scientists to the test.

As part of the 20th Australian Weeds Conference Agronomy Field Tour in September 2016, the tour participants tested their ability to recognise herbicide damage symptoms across a range of crops and pasture species with the trial funded by Department of Agriculture & Food WA and Royalties for Regions™. To make it not too difficult, the guinea pigs (sorry, particpants) pre-downloaded the new GRDC Ute Guide herbicide Injury app to assist them in their quest. To sharpen their wits we also made it into a competition with extravagant prizes to be had. 

Herbicide injury demonstration at Muresk InstituteAfter saying I would never ever go on another Conference field tour, I had to put my money where my mouth was when Sally Peltzer and I were approached early in 2016 to organise the agronomy tour for the Weeds Conference to be held in Perth, WA.

We had to make the day interesting so decided to base it at or close to the Muresk Institute, just outside Northam, Western Australia. This is an easy 1.5 hour bus trip from Perth.

So back to the issue of herbicide injury of crops. We know herbicide damage is caused by herbicide drift, poor sprayer hygiene, adding the wrong product or spraying the wrong paddock. So how can growers and their advisers know what which herbicides are causing the problem? They can:

  • pinpoint the herbicide and therefore hopefully decipher how it happened
  • estimate a level of potential yield loss
  • determine harvest or grazing withholding periods that could affect marketing of produce through exceeding maximum residue levels

GRDC has recently released an app to enable growers and agronomists more easily identify which herbicides are damaging the crop. Sally and I decided to establish a herbicide injury demonstration to test the Agronomy tour participants’ brains, as well as evaluate the app.

The treatments in Table 1 were sprayed across 18 crop and pasture types 15 days before the field day. No tank-mixes were used as this would have “muddied the water”.

Table 1. Herbicides and rates used in the demonstration.

Trade name

Active Ingredient

MOA Group



MCPA ester


1 L/ha

Amitole® T



5 L/ha

Verdict® + Uptake™



100 mL/ha


metsulfuron methyl


5 g/ha


urea + ammonium nitrate


50 L/ha

Atrazine + Uptake



1.1 kg/ha




200 mL/ha




40 mL/ha




0.5 L/ha


paraquat (200 g/L)


500 mL/ha


So how did the competition go?

There were 8 ‘stations’ for the contest and we split the participants into groups of 3 or 4.  We wanted the modes of action causing crop damage at the 8 stations and those in the “herbicide business” also had to name the actual herbicide to help level the playing field.

As can be seen from the photos the groups were busy competing.

Various groups busy trying to identify the 8 herbicide modes of action

What this exercise highlighted was how difficult it can be to identify the herbicide causing crop damage. It is important to not just look at the crop, but the weeds and other species and observe how they are reacting. Knowing the time elapsed since herbicide application also makes a huge difference in assessing the symptoms as symptoms change with time and dose. For example with cool low light intensity conditions paraquat (Group L) damage to cereals can look like a number of other herbicides during the first 2 weeks before desiccation has properly commenced. Even some of the 'herbicide experts' were fooled.

 Catherine Borger, DAFWA, with Kerry Harrington, NZ, and two international visitors.

Besides the fun, some great feedback has also been supplied to the GRDC to improve the Herbicide Injury app.

Rest of the day

After the herbicide injury competition Peter Vella and Dave Rogers from Hardi Australia discussed how modern spray technology, as used on their Saritor 5500, improves spray efficiency and efficacy through lighter booms and accurate height control .

The group fascinated by the high tech Hardi Saritor 5500.

Next we inspected the exhibition model of the iHSD – integrated Harrington Seed Destructor – with Devon Gilmour, McIntosh & Son, along with Ray Harrington, the inventor.

 Inventor and farmer Ray Harrington explaining how the iHSD kills weed seeds.

After lunch Andrew Guzzomi, University of Western Australia, demonstrated his selective cultivating tine. The tines are activated when the sensors detect a weed, digging it out. This shows lots of promise for low density fallow weed control.

Andrew Guzzomi explaining the complicated path to developing a new concept in tillage.Then it was back on the bus to head out to Andrew Boultbee’s farm nearby to look at his approach to harvest seed management with chaff dumps. Andrew has a number of approaches to dealing with the dumps. He sows through them and may or may not burn them depending on the season and amount of rain received. Everyone was fascinated by Andrew’s adaptation of the dump and burn approach.

Farmer Andrew Boultbee explaining how he manages weed seed production in cereal crops.

After that it was back to Perth via York.

We are pleased to say that the feedback was all positive from the day and a great deal of thanks goes to:

  • Peter Vella and Dave Rogers at Hardi Australia
  • Devon Gilmour at McIntosh & Son
  • Ray Harrington
  • Andrew Boultbee
  • Andrew Guzzomi, UWA
  • the staff at Muresk Institute, Northam, Western Australia
  • Bridget & the team from Kalyx Australia
Paraquat resistance is gaining momentum in Australia

Another three weed species in Australia have just confirmed resistant to paraquat – Cudweed (Gamochaeta pensylvanica), blackberry nightshade (Solanum nigrum) and crowsfoot grass (Eleusine indica) taking the total number of species to 9 in Australia (Table 1).

Paraquat resistant crowsfoot grass regrowing following spraying. Image: P. Boutsalis & C. Preston

Overseas there are now 24 species resistant to paraquat, from the Middle East through to New Zealand, comprising of 6 grass and 18 broadleaf species.

Table 1 Species that have developed paraquat resistance in Australia
(Australian Glyphosate Sustainability Working Group)


Common name

Year first confirmed



Resistance to other herbicides / MOAs

Arctotheca calendula





Diquat (L)

Hordeum glaucum

Northern barley grass




Diquat (L)

Hordeum leporinum

Barley grass




Diquat (L)

Vulpia bromoides

Silver grass




Diquat (L)



Small square weed




Diquat (L)

Lolium rigidum

Annual ryegrass


South Australia

Pasture seed

A / M - 2 populations

Gamochaeta pensylvanica




Tomatoes, peanuts, sugar cane, avocados


Solanum nigrum

Blackberry nightshade



Tomatoes, peanuts, sugar cane, avocados


Eleusine indica

Crowsfoot grass



Tomatoes, peanuts, sugar cane, avocados



As can be seen from Table 1, paraquat resistance hasn’t developed in broadacre cropping yet and the listed rotations, or lack of them, were highly reliant on paraquat for weed control.  However the widespread adoption of paraquat either as a second knock or an alternative to glyphosate over the past 10 years we probably don’t have long to wait. There are rumours of a glyphosate-paraquat resistant population of annual ryegrass (L. rigidum) about to confirmed from southern Western Australia.

In 2013 we confirmed a ryegrass population from a Great Southern vineyard that is strongly resistant to both glyphosate and paraquat which was the result of a vineyard manager rotating between these two important herbicides. Rotating herbicide modes of action buys you time, but doesn’t prevent resistance.

The answer?

The only way to stop herbicide resistance in its tracks is ensure no survivors of a herbicide application are allowed to set fertile seed.

This means drive weed numbers down and use diverse crop rotations, which in turn gives you plenty of options to use a range of non herbicide weed tactics. Combined with competitive crops, good timing of operations and effective spray practices you are on the way to putting herbicide resistance well into the future.

While tank mixing solid rates of different modes of action can be effective, many growers will be too late for this tactic as they already have resistance to at least one of these modes of action. For tank-mixing to work as a resistance management strategy both herbicides MUST BE fully effective on the weeds in question.

Mixing glyphosate and paraquat is not a viable option because of antagonism (biological) in the plant. When mixed together these products are not complementary and the paraquat works too rapidly for the glyphosate to be effectively translocated. This is the reason the double knock is utilised. Both products can be utilised on the same weed population without antagonism of the mix.

But before you go, ask yourself the question, “How do I know which of my herbicides still work?”

Blackberry nightshade Image: AGRONOMO

Being aware of sensitive crops and (geographical) areas when spraying

There has been rain and that means it’s weeds and spraying time. This time of year also lends itself to extremely risky spray conditions. Beautiful autumn weather is when surface temperature inversions are most common. For more information on inversions read my previous blogs here and here.

Strong inversion conditions March 2016. Image: AGRONOMORemember that all pesticides drift, it is just that some, such as Group I herbicides like 2,4-D, have a recognisable odour and produce unique symptoms on sensitive vegetation.


So what is the problem with off-target movement of pesticide? The most obvious agricultural issue is damage to sensitive crops. For example in the 2007-08 cotton growing season it was estimated that 10 per cent of the Australian cotton crop has some level of herbicide damage costing $5 million.

The second agricultural issue is pesticide residues. Organic farmers certainly don’t want anyone else’s pesticides. Drift is a particular problem when a crop is getting close to harvest. Signing a vendor declaration that you haven’t used certain pesticides gets complicated when the purchaser tests the product and it is ‘contaminated’.

Some of our major trading partners also have zero tolerance for certain pesticides. Ship loads of grain have been turned around and sent back for such breeches. The wine grape industry is particularly aware of the potential effects of unwanted residues on their markets.

Contamination of the natural and human environments is also a major concern.

Sensitive areas

Other than showing a duty of care, reading and following the label, using buffer zones and using best practice application, we need to be aware of sensitive areas in the vicinity of the farm when spraying. Talk to your neighbours and find out what crops they will have in, particularly in paddocks along the boundary. Be aware of state restrictions on pesticide use and spraying.

Some Australian states have restrictions on spraying in or near ‘sensitive’ areas. Western Australia has listed most Group I herbicides as ‘Scheduled’ meaning they cannot be used within certain distances of sensitive crops and high volatile 2,4-D ester is banned within 5 km of a commercially sensitive crop (vineyards or tomatoes), within 19 km of the Geraldton post office and within the Swan Valley, or within 10 km of the Kununurra Post Office. High volatile ester is not registered any other state or territory.

Victoria has nine designated areas where the type of pesticide and its application is regulated.

Agricultural Chemical Control areas in Victoria. Source: Agriculture VictoriaThe cotton industry has led the way with on online mapping with 95% of cotton crops mapped.  There is no excuse to say you didn’t know there is cotton nearby.

Cotton field awareness map for the western Riverina. Source: Cotton Australia & Cotton CRDCWestern Australia also has a voluntary system of registering your pesticide sensitive crop with the Department of Agriculture & Food WA.

DAFWA sensitive areas map 2015The map highlights organic farms, vineyards, tree crops, vegetable, bee hives and aquaculture sites. Being voluntary not all WA sensitive crops are mapped and a quick comparison with Google Earth will show additional vineyards and orchards. Another problem is that most broadacre farmers I have spoken with are unaware that this map of sensitive crops exits.  This is ironic because much of the potential drift affecting these sensitive crops could come from cropping country.

When it is spray time, do some planning, look at the weather forecast and for any potential risks, talk to your neighbours, use the right gear and get that pesticide where it is meant to be.

Spraying at night - minimising the risks Part 2 - surface temperature inversions

In the past we were always told to worry about strong winds when spraying. We now know that low wind conditions can be as bad or worse. New and reviewed herbicide labels since 2008 state that you must not spray during a surface temperature inversion.

What is a surface temperature inversion?

At sunset the ground loses heat and under low wind conditions air close to the ground cools while air above it is warmer. The air doesn’t mix and is described as being stable. Air temperature increases with height compared with during the day when air temperature most often decreases with height.

When this occurs close to the ground it is called a surface temperature inversion.


Typical inversion profiles during night and day. In an inversion the air warms to the top of the inversion. Source: G Tepper

In a surface temperature inversion the point where the temperature stops increasing and begins to decrease is the top of the inversion layer. This is usually the top level of suspended particles such as dust, smoke and small spray droplets or vapour.

Note that these inversions can act as a barrier to regional winds which go over the top of the inversion preventing mixing of the air. This means that inversions can co-exist with higher wind speeds such as greater than 20 kph.

About 30 minutes after sunrise smoke from wood heaters not mixing and moving parallel to the ground due to a surface temperature inversion. Image: AGRONOMO

What is the big deal with surface temperature inversions?

In November-December 2015 large areas of sensitive crops in NSW and Queensland have been damaged by spray drift, largely through spraying during inversion conditions. See the APVMA press release saying they won’t take action at this point. Hmm.

Because inversions prevent the mixing of air, any suspended fine droplets and particles, including spray, can move off in any direction to be deposited up to 20 km away once the inversion breaks the next day.

Cold air drainage within the inversion will cause fine droplets and particles to accumulate in the low parts of the landscape.

Remember that spray drift creates a number of major issues including crop damage, damage to sensitive vegetation and contamination of water and produce. Have you signed a declaration saying that you haven’t applied certain chemicals? You might not have, however contamination could have occurred via drift and you could be paying the price through rejection of your product.

Visual clues to indicate the existence of an inversion

  • Formation of mist or fog
  • Smoke of dust hanging in the air and moving horizontally
  • Flattening of clouds as evening approaches

 As evening sets in fluffy (cumulus) clouds flattening is a sign of impending inversion formation. Don't mix another spray tank! Image:AGRONOMO

Rules of thumb – Conditions necessary for inversions to form Source: National Working Party on Pesticide Application  

  • A reduction in wind speed to below 11 kph is necessary for all seasons.
  • In summer, a fall of at least 4°C from maximum temperature recorded on the day promotes an inversion an hour after sunset.
  • In winter, a fall of at least 2°C from the maximum temperature recorded on the day promote an inversion even an hour before sunset.
  • If the difference between the observed maximum temperature and forecast minimum temperature is 10°C or more then there is a 90% risk of inversion conditions at sunrise.

Research funded by the GRDC is currently being conducted by Graeme Tepper and Warwick Grace to predict the formation of surface temperature inversions and assign risks for night spraying. The research is well advanced in Western Australia and will be continued in more complex terrain (i.e. not WA) over the next 12 months. Yes, WA is pretty flat.

Nufarm Spraywise Decisions™  and Syngenta’s Weather forecast are tools you should all be using for planning your spray program. 

Spraying at night - minimising the risks - Part 1

Most broadacre growers want the capacity to spray their whole farm within about a ten day period or less if possible. Generally the first way to get more spraying done in a limited time period is to spray at night. The widespread adoption of auto-steer and tram-tracking has meant that spraying at night is easier to do, thus giving more hours spraying per day.

Night spraying has also been promoted as giving better weed control because it is cooler with higher humidity so target weeds will be less stressed. This however is not always the case and anyone looking at meteorological data over a 24 hour period in summer will see that meteorological conditions may not necessarily differ much between night and day.

There is a lot of preparation for successful, low risk night spraying. Image:AGRONOMOThis first article on night spraying discusses the issues encountered if there isn’t a surface temperature inversion. The second part will discuss surface temperature inversions and why they are bad news for spraying.

No inversion, so you think you are covering the bases?

Despite trying to do all the right things such as using a coarser droplet spectrum with matching application volume and keeping within the ground speed limits of your sprayer significant drift can occur with night spraying. Night spraying can deposit 5 times the amout of spray into the air compared with spraying diring daylight hours.

To demonstrate what can happen I will discuss research conducted by Bill Gordon Consulting in northern NSW comparing drift from night versus day spraying.

A 55 ha paddock was sprayed at 2:30 am and again at 7:30 am using a 36 m boom travelling at 22 kph, with Teejet AIXR 11002 nozzles, 50 L/ha at 4 bar producing a coarse spray quality.

Herbicide drift was measured 80 m downwind of the paddock using a 20 m high collection tower.

The experiment showed that less than 0.5% of total spray applied to the paddock was collected at the tower during the daylight application compared with 1.5% from the night application. This means there was virtually one hectare’s worth of spray heading downwind from the sprayed paddock at night despite the “acceptable” spray conditions. Looking at the meteorological data below there was little difference between the two application times.

Table 1: Meteorological conditions at time of spraying

Wind Speed (km/hr)

Wind Direction (°)

Temperature (°C)

Relative Humidity (%)

Night (2:30 am)





Day (7:30 am)





Despite there being no surface temperature inversion there was still 3 times the spray in the air moving downwind at night. Higher daytime wind speed would have created more mixing of the air and forced droplets down to the target compared with night spraying. 

The other thing to consider is it isn’t just what you do, but the cumulative effects of other sprayers in the local area. Often neighbours will be spraying at night launching small amounts of spray into the air which can accumulate in downwind areas of the landscape and becomes a much bigger problem to sensitive vegetation in those areas.

How to reduce the problems with night spraying?

  • DO NOT spray during a surface temperature inversion.
  • Keep measuring meteorological conditions during spraying and stop spraying if conditions deteriorate. Have a pre-determined cut-off for when you will stop.
  • Use extremely coarse (XC) spray quality – in this experiment XC spray quality would have reduced drift to 0.5% for the same conditions. Keep in mind the suitability of these coarse droplets on the target and the product to be used and the need to go to increase application volume as spray quality becomes coarser.
  • Slow down and keep boom height to a minimum – higher speeds increase the volume of finer droplets being lifted behind the machine creating a plume of spray lifting 15 to 20 m into the air. Higher speeds usually means lifting the boom. Lifting boom height from 50 to 70 cm above the target increases drift potential 4 times while going from 50 to 100 cm increases it 10 times.
  • Only spray paddocks with good catch surfaces, such as stubble or dense vegetation.
  • Make sure you know if there are sensitive areas downwind.

Spraying paddocks with poor droplet catch surfaces like this will increase the likelihood of spray drift, especially with night spraying. Image: AGRONOMO

The next blog will explain surface temperature inversions and why most labels state that you are not to spray if an inversion has formed.

Why herbicide resistance tests don’t always reflect paddock experience

Some growers and agronomists feel the results from herbicide resistance testing services don’t accurately reflect what is happening in the paddock. Some samples are coming back susceptible to the tested herbicides while the farmers are finding poor control in the paddock.

Glyphosate resistant annual ryegrass in winter fallowThis phenomenon was investigated in northern NSW in 2008 where there were differences between in-paddock control of wild oats compared to the testing service results. What came back as susceptible in the “lab” tests were still not being well controlled in the field. So what is going on?

Differences occur due to:

  1. Sampling
    How were the samples taken? From one spot in the paddock, several dense patches or averaged over the whole paddock. Different sampling methods will give different test results. This needs to be known by whoever is interpreting the test. 90% resistance in one patch can be quite different to 5% resistance is a bulked sample from across the paddock. Results are only as good as the original sampling.
  2. Differences in herbicide coverage between field and lab
    Testing services spray the weeds in spray cabinets using 110° 01 twin jet nozzles. These nozzles produce a very fine to fine droplet spectrum and under the controlled conditions of a spray cabinet give excellent coverage. If a grower tried this at least half of the herbicide would not reach the target.
    Spray application by the grower has to contend with widely varying temperatures, humidity, wind, droplet interception by stubble and crop, much higher travel speeds, varying boom height and potential moisture and temperature stress of the target weeds.
    By necessity growers use coarser spray quality and often lower application volumes giving less than 15% coverage compare to the lab’s over 40% coverage. Add to this herbicide rate, adjuvant, water quality there is no wonder there are differences.
    Testing pre-emergent herbicides such as atrazine add another layer of complexity. Due to atrazine’s high water solubility the composition of the potting mix and level of watering by the testing service can make huge differences to the results. Too much watering can leach the herbicide from the pots. Add to this atrazine’s sensitivity to light, insufficient light means the herbicide doesn’t work, giving a false positive to resistance.

Blank pots were susceptible samplesBottom line

If an Australian testing service says you have resistance, you have resistance. No doubt about it. What that means to you as a grower or adviser is:

  • Make sure you take a representative sample.
    Seed from a harvest sample is more likely to be an average. Take some photos of the infestation and send them in with the samples so the service can give you some more accurate advice.
  • So you have resistance? But do you know which herbicides still work?
    Next time think more broadly and test for susceptibility.
  • Make sure you use the best spray application techniques available to you and don’t cut corners. Poor application will only make ALL of your weed problems worse!
Forget séances and reading animal entrails – your last chance to REALLY know which herbicides still work in the 2016 season

With so many farmers dry seeding crops to maximise potential yield, the loss of key post emergent herbicides through resistance makes it is even more important that weed control is planned before seeding.

Unfortunately many growers are unknowingly spending tens of thousands of dollars on ineffective herbicides. Gut-feelings and wishful thinking are no substitute for hard data and sound analysis. 

This is no way to develop a weed management plan!

To put this in perspective the 2010 pre-harvest survey in Western Australia by AHRI showed that over 80% of wild radish plants tested were resistant to Group B SU’s, 50% to Group B ‘imis’, 50% to Group F, and 70% to 2,4-D. Also Group B and Group A ‘fops’ were virtually useless on most annual ryegrass populations and clethodim was failing at an alarming rate. Five years later, the situation is much worse.

AGRONOMO and Peter Boutsalis at Plant Science Consulting offer you the chance to beat the resistance challenge in 2016 by conducting weed seed testing for which herbicides still work! Combined AGRONOMO and Plant Science Consulting have 50 years of weed and herbicide resistance expertise.

Seed testing requires the collection of weed seed samples before harvest and mailed to the lab. Once received dormancy of the seed is broken and seedlings grown before spraying with the herbicides determined as relevant to your farming system. Level of susceptibility for each herbicide tested is then measured. Results are normally available in early March.

Seed testing is an effective for both pre-emergent (trifluralin, Sakura®, Boxer® Gold) and post emergent herbicides.

A range of packages are available. Packages start with DIY seed collection and submitting samples for testing with report showing the effective herbicides.

Premium packages includes on-farm consultation, seed collection, advice on herbicide selection for testing, susceptibility testing, and a detailed report and management plan for the next three to five years.

For more information on Herbicide Susceptibility Testing go to /herbicide-suscept-testing/

Or phone on (Western Standard Time)

Andrew Storrie 0428 423 577

Testing for herbicide susceptibility is the way forward for growers

With herbicide resistance weeds are now driving the farming system in many areas, reducing crop yields and limiting enterprise options for growers AGRONOMO and Plant Science Consulting P/L are offering professional herbicide susceptibility testing using the Quick-test backed up with a professional management advice service.

No grower wants to be painted into a corner and forced to make management decisions that don’t suit your short term and medium term goals. The question is how can you be sure the herbicides you are using this season are going to work and are you spending thousands of dollars on herbicides that are giving poor levels of control?

Faba beans sprayed one month earlier with clethodim. Ryegrass happily growing. What to do now? Image:AGRONOMO

Alternatively, are you using expensive herbicides to tackle resistance when older and cheaper herbicides could still be working because you ruled them out thinking you have resistance to them already? This may not be the case.

The only sure way to be certain is to TEST!

For example many growers are now experiencing reduced levels of control from clethodim (e.g. Select®) due to herbicide resistance. Will butroxydim (Factor®) give better control of these problem grasses? Maybe yes or maybe no. The only way to be sure is to either spray the paddock with butroxydim or do a herbicide resistance test.

The service provided by AGRONOMO offers the Quick-test backed up by relevant personalised management advice.


What is the Quick-test?

The Quick-test can be conducted NOW by collecting live plants which are then expressed posted to the laboratory, trimmed, re-potted then sprayed with the herbicides of your choice following discussion of the relevant options.  Results are available in 3 to 4 weeks enabling effective management decisions to be made this season to prevent viable seed being produced by these resistant weeds. This is the ONLY way to manage herbicide resistance.


The Quick-test is ideal for pre-seeding or early post emergent herbicide survivors. Why didn’t those weeds die? What will you do about it?

Please note that the Quick-test is only suitable for post emergent herbicides such as glyphosate and paraquat or in-crop selective herbicides. To test for susceptibility to pre-emergent herbicides, particularly trifluralin, you must use the seed test later in the year.

For more information on this new service go here or phone AGRONOMO on 0428 423 577.