Weed control critical when water availability drives crop production

Weed control critical when water availability drives crop production

When you have a major focus on plant available water and related trigger points for crop production, you don’t want weeds drawing on your valuable resource.

This is a driving factor for Andrew McFadyen, Company Agronomist and Cropping Manager at Paspaley Rural Properties’ ‘Kurrajong Park’ group of farms near Coolah.

In his 15th season with the group, Andrew manages a 5500 ha continuous cropping program that includes summer and winter crops. He said, ideally, sorghum would account for about half of the program.

Rotations can include sorghum/sorghum/long fallow/wheat or barley, while canola or chickpeas can also come into the rotation before a return to sorghum.

‘Kurrajong Park’ comprises ironbark beach sand country through to rich, black vertisol soils.

The cropping program is managed on red clay loams through to the black vertisol soils.

Of the 675 mm average annual rainfall, Andrew said they factor in 250mm of in-crop rainfall and they start with 100-150mm of plant available moisture.

He said managing the different climates and ecosystems across the properties was a real challenge, as was weed control, including herbicide resistant weeds.

“We have mainly had to deal with glyphosate-resistant ryegrass. A huge reliance on glyphosate over the winter fallow period led to problems with resistance. Two out of every three winters was Roundup®, with no crop competition,’’ Andrew said.

“We also have a little bit of annual ryegrass with resistance to Topik® and black oats with resistance to Mataven®.

“Grasses are our biggest problem. If we lose plant available water, we lose sowing timeliness.’’

The crop rotation program has since been extended, double knockdowns occur across the board, strategic grazing effectively provides a triple knock and cultural practices, including windrow burning, are also employed. Residual herbicides and using pre-emergent herbicides with a fallow option are other considerations.

Andrew said trifluralin herbicide, good crop competition and Intervix® herbicide were keeping grasses under control in winter crops, while black oats were being killed in the fallow phase with glyphosate.

The range of broadleaf weeds they tackle includes wireweed, deadnettle, bindweed, sowthistle, turnip weed and other brassica weeds, as well as volunteer canola.

Andrew said the winter cropping program was becoming more heavily weighted to barley due to higher yields, quicker maturity and, hence, better frost tolerance, and, in conjunction with the use of the post-emergent herbicide, Velocity® from Bayer, it was proving to be highly effective against weeds.

“Velocity in barley, with good crop competition, leaves the country clean.’’

“As part of our broader herbicide management, it offers good chemistry, a different mode of action and we have no plantback problems – it is a good product.

“If we are coming out of canola, where there can be some Group B (herbicide) tolerance, having Groups H and C with Velocity is good. It also works well on any volunteer canola.’’

Velocity is based on the novel active ingredient, pyrasulfotole, and also includes bromoxynil and Bayer’s crop safener, mefenpyr-diethyl. The pyrasulfotole interrupts several biological processes crucial to weed growth, while the bromoxynil, which acts primarily as a contact foliar herbicide with virtually no soil residual activity, further disrupts the photosynthetic process, resulting in a unique action against weeds.

“We were previously using MCPA (Amine) and Ally® in a mix, but went to Velocity with Axial® for grasses in the one pass at the 3-4 leaf stage. The wireweed and bindweed can be a bit tougher if we don’t get in early,’’ Andrew said.

“The Axial is getting the black oats, phalaris and ryegrass. We still get ryegrass suppression and the crop competition is also taking them out, so they are getting a left/right jab.’’

The spray mix is applied through medium to coarse nozzles with water rates of around 75 L/ha.

“We also test our water here. It’s one of the biggest things to check. It’s also about nozzle selection, knowing your conditions and knowing your product,’’ Andrew said.

Local Agronomist with CRT store, Haynes Farm and Hardware, Ed Blackburn, who works closely with Andrew, said throughout the wider region, the Velocity and Axial spray mix in barley and wheat had been highly effective.

“It has left paddocks very clean,’’ Ed said.