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Maximising the benefits of new pre-em chemistry

New pre-emergent herbicides on the market have increased growers’ options for mixing and rotating modes of action in cereal and broadleaf crops this winter.

Greg Condon, WeedSmart extension agronomist for southern NSW, said the wet conditions experienced last season gave some useful insights into the new chemistries under commercial field conditions.

“In central and southern NSW, the 2021 winter cropping season started dry and soon became very wet,” said Greg. “There was a lot for us to learn with five new pre-emergent herbicides either coming to market or in their final pre-release trials and two new pre-sowing options.”

“Last season, we observed the importance of matching the right herbicide to the soil type and soil moisture levels, and how critical it is to get the seed depth right and the furrow closed to ensure crop safety and effective weed control.”

Greg Condon, WeedSmart extension agronomist for southern NSW, said the five new pre-emergent herbicide products offer growers increased flexibility in application timing and bring new modes of action for rotational use in cereals and broadleaf crops.

Heading into the 2022 winter cropping season, Greg emphasises the need for growers and agronomists to familiarise themselves with how these new herbicides behave in the soil.

“These herbicides are all well-suited to minimum and no-till systems with significant stubble load,” he said. “Collectively, they are generally more mobile in the soil and wash off stubble easier than many of the older pre-emergent herbicides. Following the label directions carefully will provide the best protection of the crop from potential damage.”

“These new products offer growers increased flexibility in application timing and bring new modes of action for rotational use in cereals and broadleaf crops,” he said. “Having more diversity in any herbicide program will extend the effective ‘life’ of all the products used.”

Overwatch

– cereals and broadleaf crops – annual ryegrass and some broadleaf weeds

FMC Australia introduced Overwatch (bixlozone, Group 13 [Q]) for application in cereals and canola in 2021, with a new registration in 2022 that includes faba beans and field peas. Greg said that in the wet conditions experienced in southern NSW in 2021, Overwatch treated fields exhibited a characteristic bleaching effect on both the crop and the weeds. There were some early dry matter reductions in barley, whilst the effects were less noticeable in wheat and canola crops. In all cases, the herbicide provided effective ryegrass control and residual activity during a high pressure season.

“Particularly in southern NSW, Overwatch provided a viable pre-emergent alternative in canola, reducing the pressure on Group 3 [D] herbicides, such as trifluralin,” he said. “Overwatch is an exceptional rotation option for ryegrass and a number of broadleaf weeds across a diverse range of crop types.”

Knife point and press wheel systems are the safest seeding configurations when using Overwatch as this allows growers to achieve accurate seeding depth and mixing of the herbicide.

Mateno Complete

– cereal crops – grass and broadleaf weeds

Bayer Australia has launched Mateno Complete, which includes three active ingredients (aclinofen [Group 32], pyroxasulfone [Group 15 (K)] and diflufenican [Group 12 (F)]), for the 2022 season. It is registered for application in wheat and barley and offers the flexibility of both incorporated by sowing (IBS) or early post-emergence (EPE) application timing.

“Mateno Complete provided good control of grass and broadleaf weeds in the pre-release demonstration crops in southern NSW in 2021,” said Greg. “It performed particularly well when applied early post-emergence (EPE) in wheat. An effective strategy is to apply a lower cost pre-emergent before or at sowing, followed by Mateno Complete soon after crop emergence. This strategy provides long residual control, particularly of shallow germinating weeds, and is considered a herbicide ‘mix’ even though the products are applied separately.”

Callisto

– cereal crops – broadleaf weeds

Syngenta Australia’s Callisto (mesotrione, Group 27 [H]) provides pre-emergent control of broadleaf weeds in wheat and barley. Greg said the product was observed to provide 10 to 12 weeks of residual activity on sowthistle and volunteer Clearfield and Roundup-Ready canola.

“Callisto must be applied using a knifepoint press-wheel system only,” he said. “For crop safety, plant at a depth of 30 to 40 mm, and close the furrow. In 2021, weeds were observed in the furrow, and crops recovered well from any crop damage. Callisto is a relatively lower cost option for strategic use in a herbicide program.”

Ultro

– pulse crops – grass weeds

Ultro (carbetamide, Group 23 [E]) is new chemistry from Adama Australia to target ryegrass, brome and barley grass in pulses in 2022. Greg said care is required in sandy and low organic matter soils and high stubble load fields.

“In the wet seasonal conditions experienced in southern NSW in 2021, we saw Ultro provide excellent control of the target grass weeds and minimal crop safety problems in the pre-release demonstration crops,” he said.

Reflex

– pulse crops – broadleaf weeds

Reflex (fomesafen, Group 14 [G]) is another new product from Syngenta Australia, providing another option for pre-emergent control of broadleaf weeds in pulses.

“In 2021, Reflex did not have any crop safety issues, even in wet conditions,” said Greg. “It is important to check the label carefully and follow the directions for each pulse species. Depending on the rainfall outlook and weed spectrum, Reflex can be mixed with simazine, diuron or Terbyne.”

Voraxor

– pre-sowing knockdown with residual activity

BASF’s Voraxor (two Group 14 [G] actives, saflufenacil + trifludimoxazin) is a knockdown spike with residual activity. “This herbicide can be mixed with either glyphosate or paraquat, with paraquat being the preferred mix partner, as part of a double or triple knock program. This has been effective for treating sowthistle, fleabane or glyphosate-resistant annual ryegrass,” said Greg. “Take note of the plant back period when using this product as a spike, particularly when canola is planned for the field.” Voraxor also provides broadleaf weed control and some annual ryegrass control as a pre-emergent herbicide in wheat, durum and barley.

Terrad’or

– pre-sowing knockdown

Nufarm Australia’s Terrad’or (tiafenacil, Group 14 [G]) is another knockdown spike that can partner with glyphosate or mixed with paraquat for double knock applications. Terrad’or provided control on small broadleaf weeds, especially marshmallow and volunteer pulses. Terrad’or is also effective on ryegrass as part of a double paraquat program where glyphosate-resistant populations are present. Plant back is one hour for cereals and pulses, but 7 to 14 days for canola, depending on use rates.

“Pre-emergent chemistry is a key tactic in an integrated weed management program, and these new releases significantly expand the options for growers to mix and rotate modes of action throughout the crop sequence,” said Greg. “Obviously, the seasonal conditions will vary between seasons and regions, so it pays to be very familiar with the specific use patterns for these new products.”

“The WeedSmart Big 6 recommends stacking many tactics up against weeds. A combination of pre-emergent herbicide and strong crop competition is a very powerful way to suppress weed growth and weed seed production.”

Other resources

Will the new group G herbicides help control herbicide resistance in broadleaf weeds

New herbicide mode of action to help pulse growers tackle resistant grass weeds

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