6. Harvest weed seed control – the holy grail

Capture weed seed survivors at harvest using chaff lining, chaff tramlining, chaff carts, narrow windrow burning or integrated weed seed destructors.

Life is full of trade-offs. Do I buy the quality beer or go for volume? Should I take the high paid job or a job with lots of holidays? Harvest weed seed control (HWSC) is full of trade-offs. Some options are excellent but expensive. Others are cheap but require compromise. There are currently six HWSC tools being used by Australian grain growers. All remove weed seeds at harvest but they come at a different capital cost, running cost and cost of nutrient removal. To compare these tools we must first consider the running cost, and then add the nutrient cost to get a realistic comparison. You can view this AHRI insight for a proper breakdown of cost, but read on for a summary of the different tools available. You can also click through here for video tutorials on each technique.

Peter Newman has also put together a model on HWSC so you can calculate the cost of different HWSC options on your farm. You can download the model here. You can learn more about it in this AHRI insight too.

1. Narrow Windrow Burning Narrow windrow burning (NWB), is one of the most common HWSC methods chosen by farmers. It’s relatively easy to adopt and provides good results for weed management, but it does have its fair share of problems. It is time-consuming; comes with a high nutrient removal cost; removes much of the ground cover from the paddock; there is a risk of fire escapes, and it is difficult to achieve a good burn contained to the windrow over the entire farm. For these reasons, we are seeing many growers moving to some of the other tools that focus on the chaff fraction only. NWB is a bit of an art form and there are some core steps you need to take to get a job done well. Firstly, you have to harvest low. Secondly, you have to make sure you pick the right time to conduct your burn. This is when the grass fire index is between two and 10. A light crosswind is ideal, and ideally, light up every 200-400m. Click here for more detailed info.

2. Chaff Cart Chaff carts are towed behind harvesters during harvest with the aim of collecting the chaff fraction as it exits the harvester. So what do you do with the chaff? There are a few different options. Some people will opt for dumping their chaff and then perhaps grazing sheep on it. For others, burning the chaff in autumn is the preferred option. The benefits of grazing chaff dumps are that it’s beneficial for the sheep and your crop. Also, there may be no burning required. Click here for more detailed info.

3. Bale Direct The Bale Direct System developed by the Shields family at Wongan Hills (WA) consists of a large square baler directly attached to the harvester that constructs bales from the chaff and straw residues during harvest. This system serves to both capture weed seeds and bale harvest residues for livestock feed. AHRI studies have determined that 95% of annual ryegrass seeds that enter the front of the harvester are collected and removed from fields using this system. It’s a great system for those who have access to a market for the bales close to their farm. Click here for more detailed info.

4. Impact mills Most agree that the ultimate HWSC tool would complete the weed seed control in one pass at harvest, retain all stubble and nutrients and not require any follow-up work such as burning chaff. There are currently two machines that meet these requirements – the iHSD (Integrated Harrington Seed Destructor) and the Seed Terminator. Impact mills pulverise the entire chaff fraction, with both machines using similar technology to achieve the same outcome – destruction of over 95 per cent of the weed seed that enters the impact mill. The capital cost is high but residue/nutrient retention can help justify this cost. Click here for more detailed info about the development of the iHSD.

5. Chaff Tramlining A chaff deck is one of the main tools used for chaff tramlining and is used in controlled traffic systems to divert the chaff fraction (containing weed seeds) onto tramlines. This is left to rot/mulch while the straw residue can be chopped and spread to maintain ground cover. A chaff deck will cost $13,000 to $18,000, depending on your harvester. Click here for more detailed information.

‘Chaff deck on Case 8230’ – Hatty family, Matong NSW

‘Weedlining’ after chaff decks’ – Holding family, Yerong Creek NSW

6. Chaff Lining The chaff lining technique is clearly the cheapest. Chaff lining involves making a simple chute to divert the chaff fraction (containing weed seeds) into a narrow row in the centre of the harvester instead of onto tramlines. The chaff is then left to rot/mulch while the residue can be chopped and spread to maintain ground cover. Although suited to controlled traffic systems, chaff lining can work in non-CTF systems if the harvester operates along the same runs for consecutive years. Click here for video tutorials on setting up harvesters to capture weed seed in the chaff. ‘Chaff lining on Case 8230’ – Fox family, Marrar NSW