Harvest weed seed control systems for the northern region

Take home message

Chaff tramlining is a simple, effective approach to harvest weed seed control (HWSC) that removes the need for residue burning for HWSC. This system is particularly suited to high residue situations with dedicated tramlines. The newly commercialised iHSD is a more sophisticated approach to HWSC where two hydraulically driven chaff processing mills are neatly fitted to the rear of the harvester. This highly effective system also reduces the need for residue burning but has the added advantage of retaining and redistributing all residues back across the paddock.

Background

There are now several commercially available HWSC methods that effectively target the weed seed bearing chaff fraction during crop harvest. Studies on the efficacy of these practices: narrow windrow burning, chaff carts, bale direct (BDS) and Harrington Seed destructor (HSD) have clearly demonstrated their efficacy in preventing inputs of viable inputs of seed into the seed bank (Walsh et al., 2014; Walsh et al., 2012; Walsh and Newman, 2007; Walsh et al., 2013). However, single system is suited for use across all of Australia’s crop production regions and situations. Therefore, there remains a need for the availability of multiple systems and the ongoing development and refinement of current HWSC options.  Two relatively new systems, chaff tramlining and the iHSD have recently been introduced and expectations are that their adoption will be high in the northern cropping region.

Chaff tramlining

The practice of concentrating chaff material on dedicated tramlines is termed chaff tramlining where weed seeds are placed in a hostile environment from which it is difficult for germination and emergence. As with all other HWSC systems chaff tramlining focuses on the weed seed bearing chaff fraction and therefore, depending on seed survival has the potential to be similarly effective.  In a trial at North Parkes, NSW, comparing narrow windrow burning and chaff lining with conventional harvest both HWSC systems resulted in a 60% reduction in annual ryegrass emergence. 

A study evaluating over summer annual ryegrass seed survival at Esperance, WA highlighted the hostile nature of the chaff tramline environment. There was very low seed survival for annual ryegrass seed placed under canola and barley (Table 1). Interestingly though survival was considerably greater for seed placed under wheat chaff. This is despite similar levels of chaff biomass for wheat and barley in particular. At the second time of assessment only annual ryegrass seed beneath the wheat chaff was surviving. At this stage it is not known why there are large differences in seed survival between the different chaff types but obviously this will have a significant effect on the efficacy of chaff tramlining.   

Table 1. Survival of annual ryegrass seed at seeding and crop anthesis following placement under a chaff tramline during the previous harvest.

Chaff type	Chaff (t/ha)	Survival (%)
		At seeding	Anthesis
Canola	31	2	0
Wheat	19	74	10
Barley	18	3	0

Integrated Harrington Seed Destructor (iHSD)

The iHSD is now commercially available as a retrofit system for harvesters in Australia. Testing of the weed seed destruction efficacy of this mill system over the last two seasons has determined that there was similarly high efficacy as the cagemill used in the trail behind HSD system (Table 2). Very high level s of seed destruction were recorded for the four dominant species of Australian cropping, annual ryegrass, wild radish, wild oats and brome grass. 

Table 2. Effect of iHSD mill processing of wheat chaff on the seed mortality of four weed species.

Weed species	Seed kill	SE
	(%)
Annual ryegrass	93	0.7
Wild radish	99	0.2
Wild oats	99	0.1
Brome grass	99	0.2

High weed seed destruction levels were recorded when the iHSD mill system was evaluated under commercial harvest conditions. During the harvest of canola and barley crops known numbers of annual ryegrass, wild radish, wild oat and brome grass seed were introduced to an iHSD mill fitted to a class 9 harvester. Processed chaff was collected and sieved and sorted to recover viable weed seeds. In all instances there was 99% kill of the introduced weed seed.