Over-sowing and weed control demonstration – ‘Marenda’

Over-sowing and weed control demonstration – ‘Marenda’

Wayne Burton and Caterina Vecchio farm at Mount Dryden, near Ararat. They purchased their initial block in 2003 and since then, the family have invested time renovating the farm and improving the fertility, infrastructure and the pasture species. Wayne also works off-farm as a canola breeder.

Wayne and Caterina have been involved in the Perennial Pasture Systems (PPS) group since it began 2007. PPS is an independent farmer group that conducts pasture research across central Victoria and the Southern Wimmera and provides information on productive pasture management to members. Wayne sits on the management board and was group president from 2015 to 2017.

Producer demonstration project

Wayne and Caterina are host producers for the Enhanced Producer Demonstration Site (EPDS) run by PPS and Agriculture Victoria and co-funded by Meat and Livestock Australia (MLA).

The aim of the demonstration is to investigate methods of controlling barely grass in perennial pastures. It has been evaluating three main strategies, which include:

• Early season competition using grazing cereal, annual ryegrass and clover
• Conventional and emerging chemical control options
• Physical removal of seed heads including hay, silage and grazing.

Barley grass (Horduem leporinum) has a significant impact on the ability to turn off seed-free meat and wool. Despite providing useful early-season feed, it produces prolific seed numbers and competes with perennial species, especially after dry periods which the PPS group and many other producers encountered in 2014–15.

Site history and treatments

The ‘Marenda’ demonstration site is a 24-ha paddock that was sown to a phalaris and sub clover mix in 2006. The paddock was selected for the trial because of its heavy infestation of barley grass and other weeds.

The demonstration was set up in May 2020 with the intention of controlling barley grass and, at the same time, bulking up feed and extending the productive life of the paddock. The three-treatment trial (detailed in Table 1) included:

• Full Treatment: Over sowing, weed control and nitrogen
• Partial Treatment 1: Over sowing and nitrogen (no weed control)
• Partial Treatment 2: Weed control and nitrogen (no over sowing).

Table 1: Treatment details

The 2020 growing season had below average rainfall at Mount Dryden (563mm). However, most of this rainfall (462mm) occurred in April to October, which was great for spring growth.

Pasture cages were placed in the paddock, and dry matter measurements and feed tests were taken approximately monthly through the growing season (August 30, October 1, November 9, and December 19).

Key results

Dry matter

Dry matter production across the across the paddock was highest under the Full Treatment of spray topping with over sowing and nitrogen (Figure 1, Table 2), followed by Partial Treatment 1 (over sowing and nitrogen).

Table 2: Total dry matter production (1 Aug – 1 Dec 2020) for each treatment

Pasture quality

Feed tests were undertaken on 9 September and 9 November 2020 (Table 3). Full Treatment plots had a slightly higher Metabolisable Energy (ME) and Crude Protein (CP) in September. However, the CP had reduced late in the season, measured again in November, as the soil profile dried.

Table 3: Feedtest results from each of the treatments in September and October 2020

Barley grass control

The effectiveness of controlling barley grass was measured five months after the treatments in May 2020 through seed head counts for the three treatments. The results showed that weed control was very effective on this site with both the Full Treatment and Partial Treatment 1. However, seed counts were high in Partial Treatment 2 (no weed control). Over-sowing without weed control did little to reduce the amount of barley grass present.

Cost-benefit

A cost-benefit analysis was undertaken to compare the three treatments (Table 4). The analysis included an estimate of the operational cost of treatments, inputs (including chemical and seed), hours of labour and the relative cost of the equipment. The cost of barley grass seed head contamination was beyond the scope of the project and was not included in the cost-benefit analysis.

Feed test values were used to calculate a market value of the feed based on Metabolisable Energy.

Partial Treatment 2 (no over sowing) was used as the basis of comparison for the benefit-cost. The cost of weed control was $27/ha which is shown as an ‘avoided cost’ for Partial Treatment 1 and not included as an additional cost in the Full Treatment as Partial Treatment 2 also had an application of herbicide.

The analysis shows a clear benefit to using both weed control and over sowing and a reduced benefit when over sowing was completed without weed control. This highlights that the minimal cost of weed control was justified by the additional benefits it gives to production.

Table 4: Cost-benefit analysis of the Full Treatment and Partial Treatment. Costs and benefits measured above the control.

The benefits of the Full Treatment (over sowing, weed control and Nitrogen) is summarised in Table 5. The Full Treatment increased dry matter production throughout the season leading to the highest return per hectare. It also incurred the lowest seed numbers, reducing the likelihood of barley grass seeds impacting on animal health and germinating in the following year.

Table 5: Summary of treatment benefits

Over-sowing with annual species was a highly valuable tool and extends the life of perennial pastures while continuing to produce highly valuable feed throughout the growing season.

Producer feedback

Wayne is happy with the results and the comparative feedback from the different treatments.

'Absolutely, I will do this again. The early break in 2020 meant the clover was big enough to spray, which contributed to the good success.

'I did over-sow a couple of paddocks this year (2021) but due to the late break, I was unable to spray prior to sowing, so the results weren't as good. I was still able to grow a good amount of quality feed, but I haven't had the weed control benefits from spraying. I was also unable to get fertiliser on this year as paddocks were too wet.

'The 2021 trial sites are still looking good and the barley grass control is evident 12 months later. I’m looking forward to seeing the seed head counts this month (October 2021). There is still some barley grass, but it’s certainly not a carpet. Ultimately, I would have liked to treat the paddock again this year with propaquizafop but it was too wet in winter to get on, so I will have to follow up and possibly look at topping again in late this spring.'