A ‘time of cutting’ experiment at Wagga Wagga, NSW, showed a modest reduction in silver grass composition, compared to grazing, when the silver grass was cut early. However, later cutting times resulted in poor reduction due to large amounts of viable seed production and shedding prior to November cutting. Annual ryegrass was opposite and required later cutting (November) to affect viable seed maturity and set (Figure 2).

Figure 2. The percentage of silver grass or annual ryegrass in a mixed perennial ryegrass pasture in the third spring following either grazing with wethers (10 DSE/ha) or differing hay cutting times applied in the previous two springs. (Bowcher 2006)

There are several challenges in adopting this technique.

1. The most significant is the reduction in the quantity of fodder grown because of cutting. Reductions in hay production were recorded at Wagga Wagga, NSW, of 1t/ha, or 33%, from cutting early hay compared to hay cut as per normal district practice.

2. The second is the potential formation of new reproductive tillers from the cut plants if there is residual soil moisture or rain. New seed heads are produced with little leaf material.

3. Finally, the maturity times of weeds vary so it is difficult to impact multiple species.

Paddock cut for silage on 14 October showing barley grass forming new reproductive tillers (top and bottom) by late November.

Capturing viable seed

Hay will remain a re-infestation risk as seed may have matured sufficiently before cutting, enabling viable seed formation during curing. The baling process may not capture all the seed and often leaves mature heads due to shattering or not being picked up in the baling process. Seed contained in the hay remains more viable than if it was naturally shed in the paddock because of the reduced exposure to climatic conditions, ingestion by stock and predation from insects.

Animals consuming hay will render most ingested weed seeds unviable, however, the material that drops, is trampled or left uneaten will have seed that will germinate.

This has occurred in baled hay, where silver grass seed matured after cutting and subsequently resulted in silver grass regeneration when hay was returned to the paddock after storage over summer. (Dowling et al. 1996)

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