THE gap in pre-emergent herbicide options for growers to control broadleaf weeds, particularly in pulses, is set to be helped by a suite of new Group G herbicides.
University of Adelaide, South Australia, weed management professor Chris Preston said the new herbicides would help growers control brassica and thistle weeds and rotate away from the imi chemistry that had been heavily used in recent years.
"The new Group G herbicides will be of particular value in pulse crops," Dr Preston said.
"Until recently Group G products have only been used in small quantities, predominantly as a knockdown spike ahead of planting, but several of the new products have pre-emergent herbicide use patterns."
Group G mode of action inhibits part of the process for making chlorophyl, and the leaves die as a result.
Uptake of the herbicide is usually through the leaf surfaces, either through contact on emerging weeds or taken up from the soil as the weed seedlings break through the soil surface.
"The introduction of Terrain (flumioxazin) as a pre-emergent broadleaf herbicide in front of faba beans offered a new and helpful use pattern in the pulse phase," Dr Preston said.
"Terrain is also a good fenceline weed control option on heavier soils, provided all surface vegetation is removed prior to application."
Syngenta's Group G product Reflex, which is yet to be released, is expected to offer pulse growers pre-emergent control of broadleaf weeds that might be resistant to other mode of action groups.
The product can be used either pre-emergent incorporated by sowing (IBS) or post sowing, pre-emergent (PSPE) and will provide an alternative to imi herbicides for the control of weeds like sow thistle and prickly lettuce in pulse crops.
Lentils are less tolerant than other pulse crops, so Reflex can only be used IBS in lentils.
Dr Preston said growers and agronomists need to remember the importance of ensuring that herbicide product choice was always based on addressing the weeds present that are likely to cause economic loss or produce large quantities of seed.
"Mixing and rotating herbicide modes of action is one of the WeedSmart Big 6 tactics, but crop competition is just as important," he said.
"Pulses are particularly sensitive to competition from weeds in the early crop stages, so using these Group G herbicides in a tactical way to control early germinating broadleaf weeds could be a very good way to keep pulses profitable in our southern farming systems."
Mixing and rotating the new herbicides with existing products is an option, with the recommendation being to read the labels as they become available and look for opportunities to mix and rotate within and between seasons and crops.
"For example, Terrain offers broad spectrum weed control in tank mixes with TriflurX, Terbazine, Avadex Xtra, Kyte, Simagranz and Rifle, but Terrain has a narrow weed spectrum for the rate registered in-crop for faba beans," Dr Preston said.
"With some clever planning these products can help bring back some previously lost chemistry using the mix and rotate tactic, extending the effective life of a broader range of herbicide options.
"When coupled with some non-herbicide tactics the grower can regain control of herbicide resistance on their farm and operate in a low-weed situation."
Pre-emergent with IBS and knockdown options are the main new use patterns available with the new Group G herbicides.
Dr Preston said the first Group G with pre-emergent properties to hit the Australian market was Terrain (flumioxazin), from Nufarm with new use patterns registered for wheat and pulses.
"Other products with pre-emergent properties expected to come to market in the next year or two are Syngenta's Reflex (fomesafen) and BASF's Voraxor (saflufenacil + trifludomoxazin)," he said.
"Voraxor can be used pre-emergent in cereals and also as a knockdown spike.
"Terrador (tiafenacil) from Nufarm will have knockdown spike use and is safe for cereal or pulse planting just one hour after application."
Resistance to Group G products is not yet a problem in Australia, with no recorded cases of weeds resistant the group.
"Although the Group G mode of action has been commonly used for over 15 years, these products have generally been used in small quantities," Dr Preston said.
However, resistance to Group G is becoming widespread in North America.
