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Keeping the farm clean using tactics

Case study: Graham Clapham

A diversified cropping system requires great attention to detail and offers many opportunities to implement several tactics in an integrated weed management strategy.

Spray application technology like these multiple-nozzle fittings make it quick and easy for the operator to change the nozzle type if environmental conditions change during the spray operation. The Claphams have placed the nozzles on their spray rig close together (250 mm apart) to maximise coverage and minimise drift.

Spray application technology like these multiple-nozzle fittings make it quick and easy for the operator to change the nozzle type if environmental conditions change during the spray operation. The Claphams have placed the nozzles on their spray rig close together (250 mm apart) to maximise coverage and minimise drift.

Graham Clapham started his farming career straight out of school at 15 years of age. Even then he was clear about his desire to own a black soil farm on the Darling Downs. Graham grew up on his parent’s 200 ha mixed cropping farm, growing irrigated and dryland crops including corn, soybean, wheat, sorghum, onions and pumpkin.

With help from his parents, Graham realised his first goal when he was 18, purchasing a farm of his own at Norwin, west of Toowoomba. He now grows mostly irrigated cotton, corn and wheat and dryland cotton, wheat and sorghum on the family’s 1840 ha aggregation in the Brookstead–Norwin district.

On the 700 ha that is usually irrigated each year Graham has two main rotations—irrigated cotton or corn followed with irrigated wheat then a long fallow before returning to cotton or corn. In the corn–wheat rotation there is no cultivation but Graham has different herbicide options available and an opportunity to provide a disease break to combat fusarium wilt.

Rainfall dictates the dryland crop rotation on the rest of the cropping area. Minimum till is practiced to conserve soil moisture with occasional cultivation only to renovate the tramtracks.

Graham is aware of the risk of herbicide resistance, particularly in weeds like flaxleaf fleabane and feathertop Rhodes grass, which have always been hard to kill with glyphosate, and milk thistle is a new concern for the business.

Since the introduction of genetically modified cotton in 1996, the Claphams have practiced pupae-busting cultivations to manage resistance in helicoverpa. This has had the spin-off benefit of keeping hard to control weeds like flaxleaf fleabane and feather-top Rhodes grass under control.

“Pupae busting is a robust cultivation to a depth of 100 mm and is required to remove all large soil clods,” he says. “It must be done before the end of July following the cotton harvest in April–May.”

The deep cultivation after cotton buries weed seeds deep in the profile where they can’t germinate. Unfortunately flaxleaf fleabane seeds remain viable for longer when they are buried than when they are close to the soil surface. This means cultivation in subsequent years can bring viable seed back to the surface where it can germinate so it is not a complete solution but another useful tactic in the farming system.

The cultivation leaves the soil dry and prone to erosion so the Claphams aim to sow a wheat crop after cotton to provide ground cover over winter and stubble for the following summer.

Soil moisture and irrigation water availability govern the sowing rates used although the Claphams have two options when it comes to row width in their dryland crops. When sowing wheat into cultivated soil after cotton they can use an air seeder to plant rows 150 mm apart rather than the single disc planter used in minimum till planting to sow 500 mm rows.

Sowing in narrow rows has several benefits for weed control in the dryland system. To begin with sowing is a full tillage operation that removes any weeds present at the start of the season. The increased shading of the inter-rows suppresses weed germination and after harvest there is more stubble left on the ground, again suppressing weed germination.

Infrastructure such as channels and pump sites are kept clean throughout the year to avoid the risk of weeds spreading throughout the farm in irrigation water.

Infrastructure such as channels and pump sites are kept clean throughout the year to avoid the risk of weeds spreading throughout the farm in irrigation water.

Graham has not noticed a yield difference between crops sown at the narrow and wider spacing although the air seeder does dry the soil out more than the single disc planter.

“The wheat crop is often not great, especially if winter rain is scarce,” he says. “But it provides good cover and we can use different chemistry to control weeds, especially to achieve a residual effect on flaxleaf fleabane.”

Graham says the chemistry available for use in wheat is very effective, keeping the wheat crops quite clean. Corn can experience some late grass germinations, which they have previously treated with glyphosate at harvest and then burnt the stubble.

When there is additional water available for irrigation early in the year the Claphams often take the opportunity to plant soybeans. Having this as an option they are conscious of the residual action of the herbicides used in the previous wheat crop. “We use herbicides with no residual effect to control broadleaf weeds such as thistles and turnip in the wheat so we don’t need to worry about the plant back period for soybean,” says Graham.

So far the Claphams have not experienced any spray failures that have raised concern about herbicide resistance. Graham is very conscious of the potential risk and is mindful of the experience in the USA with widespread glyphosate resistance in their cotton industry.

“Glyphosate-ready cotton has been a positive innovation for the industry, making it more sustainable and ending the use of environmentally-harmful herbicides,” says Graham. “However, glyphosate does not give 100 per cent control of weeds in cotton. Vines particularly can survive a spray and so we use inter-row cultivation and hand chipping to remove vines as needed.”

Inter-row cultivation in cotton, corn and sorghum also helps maintain the furrow profile and to conserve moisture before the canopy closes. Graham occasionally uses an inter-row shielded sprayer to apply glyphosate in corn and sorghum crops.

The Claphams recently purchased a neighbouring farm with a very heavy weed burden. They have used cultivation and herbicides to drive down the weed seed bank and to treat weeds they have never seen in the area before.

The Claphams do all their own spray operations, mainly so they can control when they spray. “The Darling Downs region is closely settled and there are not many trees across the cropping area. It can be very difficult to find suitable times to spray without the risk of off-field impacts. Having our own gear and labour available means we can spray as soon as suitable conditions prevail.”

Spot spraying larger weeds that have escaped earlier treatment is the last operation before plating clean seed into clean paddocks with clean borders (#8 in the 10 Point Plan).

Spot spraying larger weeds that have escaped earlier treatment is the last operation before plating clean seed into clean paddocks with clean borders (#8 in the 10 Point Plan).

Graham’s son-in-law, Jonathon Mengel, is responsible for the spraying operations across the farms. They have found that having a person with the designated responsibility to have the chemicals in stock and be looking for spray opportunities has been very beneficial to their operation.

“We have very few weed escapes after a herbicide spray,” says Graham. “On the rare occasion that it does happen we prevent seeding using tillage or a follow-up application of a knockdown like paraquat.”

“In the fallow we look for opportunities to do a double-knock treatment but it can be very difficult to get favourable conditions for two sprays close together,” he says. “Glyphosate, Starane®™ and MCPA®™ are relatively easy to apply using air induction nozzles to splash the product on with minimal risk of spray drift. The second application of paraquat 10 days later is more difficult, especially given the need to apply a fine droplet size.”

The Clapham’s Case Patriot sprayer, with its 36 m boom and 4 m wheel base, fits perfectly into their on-farm control traffic system. They have doubled the number of nozzles on the boom, placing a set of nozzles every 250 mm instead of the traditional 500 mm, allowing greater coverage and helping to extend the tight spraying window.

“This gives us a double overlap so we can consistently use coarse droplet nozzles and still get coverage, and it also enables us to operate lower to the ground,” he says.

When necessary Graham will spot spray or hand rouge weeds prior to planting the next crop to ensure the paddocks are as clean as possible going into the season.

The Claphams are also careful to keep irrigation infrastructure such as head ditches, supply channels and tail drains weed free. They use residual herbicides at high rates to effectively sterilise the soil in these non-cropping areas. “The risk of distributing weeds throughout the farm is of great concern and maintaining weed-free infrastructure is a year-round priority for us,” says Graham. “We also pay attention to planting clean seed each year, buying in cotton, sorghum and corn seed, and grading the wheat seed we keep the next season.”

“Black oats has been a bad problem in the winter cropping program but we seem to have won the battle with a consistent approach to planting clean seed.”

Throughout the crop rotation the Claphams are looking for ways to manage weeds to achieve the best possible productivity and profitability in the long term from their cropping operation.

Watch Graham’s video below!

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Never cut the herbicide application rate

Scientific studies have demonstrated that resistance can rapidly evolve in weeds subjected to low doses of herbicide. Some weeds can develop resistance within a few generations. Full rates when mixing herbicides too! When mixing herbicides it is important that each product is still applied at the full label rate to ensure high mortality. Applying different chemicals in one mix can provide an additive advantage. It is important to understand the mode of action of each herbicide on the plant when preparing a herbicide mix. This is just as important for pre-emergent grass weed mixes as it is for post-emergent mixes aimed at broadleaf weed control. ALWAYS READ THE LABEL. Surrounding weed seeds with a combination of pre-emergent herbicides with different modes of action can give a high level of control and help extend the useful life of all the chemicals used. The high level of control must be supported with additional control measures for all survivors. All products with different modes of action must be applied at full label rates for this to be an effective strategy.   Mixing two chemicals with the same mode of action can achieve some additional efficacy, however, the mix should deliver the combined full rate to ensure a lethal dose. The amount of stubble present and crop safety are all important considerations when mixing chemicals. For example, when using a tank mix of Avadex® and trifluralin to control ryegrass in wheat, the rates used will vary depending on the sowing system and level of stubble retention. Be sure to get good advice. Many herbicides on the market are a combination of two or more modes of action within the one product. These products must be applied at the full label rate to be effective. Having dual action does not negate the need to change herbicide products and rotate modes of action. Repeated use of any single strategy will reduce the effectiveness of that strategy over time.  

Spray well – correct nozzles, adjuvants and water rates

Spray application is a technical field and growers need to make sure their equipment and application techniques are spot-on. The GRDC Spray Application GrowNote provides detailed information and about 80 videos to demonstrate key skills. Prevent spray-drift The focus of spraying herbicide needs to be on doing the job right so the weeds receive the correct dose and die, and this includes reducing the air borne fraction to a bare minimum. Bill Gordon’s 10 Tips for Reducing Spray Drift Choose all products in the tank mix carefully. Understand the product mode of action and coverage requirements. Select (and check) the coarsest spray quality that will provide effective control. Expect that surface temperature inversions will form as sunset approaches and will likely persist overnight and even beyond sunrise on many occasions. DO NOT SPRAY. Use weather forecasts to inform your spray decisions. Only start spraying when the sun is about 20 degrees above the horizon and when the wind speed has been above 4–5 km/hr for more than 20–30 minutes, and clearly blowing away from any adjacent sensitive crops or areas. Set the boom height to achieve a double overlap of the spray patterns. Avoid higher spraying speeds. Leave buffers unsprayed if necessary and come back. Continue to monitor conditions, particularly wind speed, at the site during the spray operation High water rates don’t have to slow you down Some growers are concerned that increasing the water rate when applying herbicide will slow down their spray operation and cost them money. However, the biggest financial loss during spraying usually comes from a failed spray job. To keep your spray operation as time efficient as possible when using more effective and reliable application volumes, you can: Use nurse tanks around the farm to reduce the time spent travelling back to a central re-fill point. Use a larger pump, e.g. 2.5 inch, to make re-filling quicker. Pre-mix the batch while the sprayer is operating. Many mixes can be held in the mixing tank for up to 6 hours. However, wettable granules and suspension concentrates will need agitation to keep them in solution. For pre-emergent herbicides in high stubble situations, carrier volume has a large effect on the level of control achieved. Across four trial sites Dr Borger’s research demonstrated that ryegrass control with trifluralin or Sakura® increased from 53% control when the carrier volume was 30 L/ha to 78% control when the carrier volume was increased to 150 L water/ha in high Water quality and mixing order Water quality is often overlooked as a possible contributor to herbicide failure and can lead to confusion over the herbicide resistance status of weeds on a property. Water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source. Getting the mixing order right is essential for effective spray results. Don’t start mixing until the water quality is right Podcast – Mixing herbicides Adjuvants Sometimes adding an adjuvant is beneficial and sometimes it is detrimental; and there is an art to knowing how to best deploy these additives. When weeds are susceptible to the applied herbicides, the effectiveness of adjuvants generally goes un-noticed. Correctly applied adjuvants can reduce the impact of low level herbicide resistance by helping to maximise the amount of herbicide taken up by the plant.

Clean borders – avoid evolving resistance on the fence line

About one-quarter of glyphosate-resistant populations within broadacre cropping situations across Australia come from fencelines and other non-cropping areas of the farm. Along paddock borders, where there is no crop competition, weeds can flourish and, if not controlled, set lots of seed. The traditional approach has been to treat these weeds with glyphosate to keep borders clean but after 20-odd years this option is now failing and paddock borders are becoming a significant source of glyphosate-resistant weed seed. Weed researcher Eric Koetz said the limited options for managing weeds along irrigation infrastructure and other non-crop areas is a problem and is putting additional pressure on knock-down herbicides in irrigated systems. In some situations, cultivation can be used to kill the weeds and provide a firebreak, but on light soils this may pose an erosion risk and mowing or slashing may be safer options. Another possible tactic is to continue using herbicides but to ensure that a clean-up operation is carried out before any survivors can set seed. Some growers are choosing to increase the heat on weeds along the borders by planting the crop right to the fence and then baling the outside lap and spraying with a knockdown herbicide to kill any weeds and provide a firebreak. Another good option in some situations is to maintain a healthy border of vegetation using non-invasive grasses. In Queensland, buffel grass is a good example of a grass that can outcompete other weeds while not invading crop lands. If only herbicides are used on fencelines, resistance is inevitable. Surviving weeds on fencelines have no competition and access to plenty of soil moisture, so they set a lot of seed and resistance can easily flow into neighbouring paddocks. Other resources It’s time for a glyphosate intervention Farm hygiene cottons on – Cleave Rogan, St George What’s new in management of herbicide resistant weeds on fencelines? Keeping the farm clean – Graham Clapham, Norwin Don’t jeopardise glyphosate for clean fencelines Keeping fencelines clean Resistance risk to knock-down herbicides on irrigated cotton farms

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