Read time: 6 minutes

Rhys Daniels, Capella Qld

Cultivation and grazing contribute to weed control

The Daniels’ family farming operation includes two cropping properties at Theresa Downs north of Emerald and a grazing property near Springsure. Rhys and his parents, Larry and Nancy, farm about 2500 ha of alluvial black soils, growing mainly sorghum and mungbeans in summer and wheat and chickpeas in winter.

“Large portions of Theresa Downs are very frost-prone, so we prefer summer crops,” says Rhys. “Sorghum is our crop of choice, partly because it also fits well with our cattle trading operation where we buy in cows and calves and fatten them on sorghum stubble. Mungbean also features in the summer program every three years or so as a good break crop that fulfils its nitrogen requirement.”

Having implemented a successful strategy to control feathertop Rhodes grass, sweet summer grass is now the main weed challenge in the summer fallow at Theresa Downs, and Rhys suspects that it is becoming resistant to glyphosate. In the winter crops, particularly chickpea, he finds Mexican poppy and parthenium hard to control with the available chemistry.

The Daniels are successfully implementing the WeedSmart Big 6 as a powerful way to drive down the weed seed bank using chemical and cultural tactics, which has helped in recent years where weed challenges have been ever-present.

Maximising crop and livestock diversity

The Daniels follow a set of guidelines to plan their crop rotation – ‘no more than three sorghum crops in a row, no wheat-on-wheat and no chickpea-on-chickpea’. They also factor in frost risk for their winter crops and use residual chemistry that doesn’t limit their ability to take advantage of favourable rainfall.

“Some years, we will have the whole farm sown to summer crops, mainly sorghum,” says Rhys. “Grazing the sorghum stubble works very well from a business perspective and as an additional weed control tactic. When other graziers are running low on grass in July and August, we can buy in cows and calves, and because we are putting them onto a rising plane of nutrition, we can turn them off with a good margin.”

The main benefit of the cattle grazing stubble from a weed perspective is the removal of fallen sorghum heads. If left in the field, multiple plants germinate from each sorghum head, and the young plants tend to shade each other and reduce the efficacy of sprays delivered with very coarse nozzles required for 2,4-D application.

Mixing and rotating herbicide modes of action (MOA)

Rhys is very mindful of the plantback conditions (time and rainfall) for the residual herbicides, and the potential impact on future crop choices.

In winter fallow blocks, Rhys applies residual chemicals such as s-metolachlor (e.g. Dual Gold, Group 15 [K]) and imazapic (e.g. Flame, Group 2 [B]) if intending to plant wheat the following winter crop season.

“After a dry spring in the winter fallow blocks, there are often some old weeds still in the field. One knockdown spray after the first rain is often not enough, so we double-knock with paraquat and atrazine to kill these hardened weeds,” he says. “Getting a good kill across the whole spectrum of weeds is difficult, so we also apply a post-plant spray mix to kill any survivors or newly emerged weeds – both grasses and broadleaf.”

The post-plant mix applied is usually paraquat (Group 22 [L]) plus the crop-appropriate residual, such as Glean (chlorsulfuron, Group 2 [B]) in wheat, isoxaflutole (e.g. Balance, Group 27 [H]) and or simazine (Group 5 [C]) in chickpea and atrazine (Group 5 [C]) in sorghum.

Double-knock to preserve susceptible chemistries

Rhys is doing his best to minimise glyphosate use across the rotation. He tries to apply no more than two applications of glyphosate in the fallow and has added a paraquat second-knock to the fallow weed control program to clean up any survivors of the glyphosate spray. The Daniels have seen first-hand on a newly-purchased block how hard it is to regain control of weeds where there has been an over-use of glyphosate in the past.

Haloxyfop (e.g. Verdict, Group 1 [A]) is another herbicide that Rhys is trying hard to protect using the double-knock tactic.

“Verdict is such a useful chemical that we need it to work well into the future,” he says. “We use it as required to control mainly summer grasses in fallow and prior to planting mungbean or chickpea crops. When Verdict is applied in fallow we apply paraquat as the second knock within ten days, ideally before it rains.”

In the last few years, a combination of dry winters, full-disturbance planting and narrow rows in chickpea and mungbean has reduced the need to apply haloxyfop, giving Rhys extra shots of this valuable chemistry for when he needs it.

Stop seed set

“We use glyphosate to desiccate our sorghum crops and have learned from experience not to skip desiccation, even in heavily frosted crops,” he says. “In addition to aiding harvest, this application also controls any weeds present in the crop.”

Desiccation is also used in mungbean, primarily to prepare the crop for harvest, but there is also some weed control benefit.

The Daniels do some patch management, but Rhys says they often wish they had just treated the whole paddock. He says they have had some success doing a blanket treatment of a problem paddock and then returning with a second treatment for high-pressure areas.

Crop competition

In the 1990s, the Daniels family adopted zero-till practices along with many others in the Central Highlands region of Queensland. Research at the time suggested that crop yield could be maintained at wider row spacing, saving growers money on the new zero-till planters. This saving came at the cost of reduced crop competition. The high efficacy of chemical control masked the impact of reduced crop competition for many years.

The Daniels settled on 50 cm row spacing for their wheat and legume crops and 1.5 m spacing for sorghum. With no crop competition in sorghum, in-crop weeds always require chemical control.

Having now moved to seedbed cultivation for their mungbean and wheat crops, the Daniels have noticed the benefits of narrower row spacing (now 23 cm) and are looking for ways to increase crop competition in their sorghum crops.

“Sorghum is currently our weakest link for crop competition,” says Rhys. “We plant sorghum with a precision planter, and it is expensive to go to narrower configurations. Ideally, we would look at 1 m or 75 cm next time we replace our precision planter.”

Harvest weed seed control

The Daniels have not used mechanical harvest weed seed control tactics on their farm to date. The systems they have in place are minimising the establishment of late germinating weeds, particularly in wheat and mungbeans.

“The cattle are providing a post-harvest weed seed control service, particularly in sorghum where volunteers would otherwise be a problem in future crops,” says Rhys. “The cattle also eat any grain left in the field, so we rarely have trouble with mice plagues.”

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