Good pre-emergent weed control vital for resistant ryegrass in Western District

SFS Chief Executive Officer Jon Midwood said the survey results surprised everybody.

“We passed the Mallee and the high intensity cropping areas in the Wimmera (in terms of resistant populations) within a 15-year period, so it was really pretty scary,’’ Jon said.

“Some growers even thought about taking paddocks out of cropping and returning to pastures.’’

SFS has about 500 grower members throughout the Western District, Gippsland and across to Tasmania.

Jon said the group had been conducting trials the past four years evaluating the effectiveness of pre-emergent annual ryegrass control in wheat as part of an Integrated Weed Management (IWM) project funded by GRDC.

The trials were initially coordinated at the group’s Lake Bolac site and have been continued at a site near Westmere the past two years.

“Post-emergent herbicide applications in the region are often affected by the weather. Growers are generally trying to put them out when it is cold and wet. It is part and parcel of why resistant annual ryegrass has taken-off,’’ Jon said.

“This places high importance on getting a good result with pre-emergent herbicides. Growers get little or no benefit from applying post-emergent herbicides with the high levels of ryegrass resistance, so good control has to come from pre-emergent herbicides. Growers must ensure they are getting bang for buck with pre-emergent products.’’

He said the trials confirmed that the Group K herbicide, Sakura® 850 WG, containing the active ingredient, pyroxasulfone, provided the highest level of ryegrass control.

The trials included stand alone and combination treatments of Sakura, TriflurX®, Avadex Xtra® and Boxer Gold® incorporated by sowing (IBS).

The treatments containing Sakura achieved excellent control long into the season. Sakura IBS alone at the recommended rate of 118 g per hectare, then applied with Avadex Xtra at 2 litres/ha and with Boxer Gold at 2.5 L/ha achieved 98 %, 98% and 92 % reduction in weed populations respectively relative to the control treatment.

The same three treatments maintained the greatest ryegrass control into the season, with an 85-97 % reduction in weed numbers 180 days after sowing.

Previously at the Lake Bolac site, Sakura and Avadex Xtra provided excellent control against high levels of resistant ryegrass. Other treatments performed poorly, particularly against later weed germinations.

Sakura controls annual ryegrass, barley grass, silver grass, annual phalaris and toad rush and provides suppression of wild oats and great brome in wheat (not durum wheat) and triticale crops.

Jon said its effectiveness in up to 50 % trash cover was especially important for the region.

“With high rainfall and, consequently, high stubble loads, we can have problems incorporating pre-emergent herbicides – getting them down into soils where they are active.’’

“With a 4-tonne (per hectare) wheat crop, the stubble can be double at 7-8 t/ha. With wetter years, we are now looking at 10 t/ha stubbles, so it is a real issue.

“This is where Sakura is a good fit for us because it doesn’t tie-up on straw like other products, such as trifluralin.’’

He said it was increasingly becoming part of growers’ resistance management strategies in the region.

“For so many growers, they have realised the huge resistance to Group A and B herbicides and the need for good pre-emergent control – and with the trash they are dealing with in their stubble retention systems, they are getting very good results with Sakura.’’

“It is an expense they have to wear and it is becoming widely adopted now because of the need for control and, particularly, good pre-emergent control.

“Sakura is a cornerstone for pre-emergent weed control, but the worst thing people could do now is to over-use it. Growers must try to have an integrated approach and use it in conjunction with other practices,’’ Jon said.