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Preventing viable seed development

Three techniques can be used. These are:

1. Silage production

Cutting pasture for silage can be effective in reducing viable seed production, especially on early maturing weeds such as silver grass (Vulpia spp.). The process of ensiling fodder creates acetic and lactic acid, two products that disrupt viable seed formation (Blackshaw and Rode 1991).

NSW Department of Primary Industries research found silage reduced silver grass regeneration the following year by approximately 80% (Michalk and Dowling 1996) and barley grass was reduced by 49% in early cut silage (8 October), in comparison to a grazing-only treatment (Piltz et al. 2019). Silage production can also encourage sub-clover production as a result of getting more light to the plant while seed set is underway (Figure 1) (Piltz et al. 2019 & Bowcher 2006).

Figure 1. The percentage of sub-clover in a mixed perennial ryegrass pasture in the third spring following either grazing with wethers (10 DSE/ha) or silage production. Cut late October in the previous two springs (Bowcher 2006).

2. Spray-topping and hay production

This approach uses herbicides (glyphosate or paraquat) at rates to sterilise the seed while it is forming, followed by cutting after the withholding period is observed (usually two days). This allows the fodder to be cut later, enabling more quantity to be grown. Without the herbicide to sterilise the seed, the seed would remain viable. For more details on this method see the MLA fact sheet: How do I spray-top to reduce annual weeds in pastures?

3. Cutting plants in the early phase of maturity

This is a less commonly used method that aims to disrupt the formation of viable seed heads. Cutting in the early phase of maturity means the seed will not form adequately and there is insufficient time for the materials in the cut plant to translocate to the seed before the plant dries out. If cutting is delayed, seed heads mature and form viable seed even after being cut.

Stages of maturity in barley grass indicating seed viability.