Top tips for autumn undersowing

by Hamish Mulcock, Portfolio Manager, PGG Wrightson Seeds

As the season gets underway, some paddocks will be thinning or ‘opening up’ and requiring attention this autumn. To prioritise and plan for autumn undersowing, pasture condition scoring is recommended as a method of identifying and prioritising paddocks.

Pasture condition scoring is a process of visually evaluating paddocks and assigning a score (1-5) based on plant density, insect damage and weed presence. The ascribed pasture condition score (PCS) will help with implementation of an undersowing or pasture renovation program.

Generally, paddocks scoring a PCS of 2 (severe damage in parts, many weeds and bare ground) or 3 (large sections of low-level damage, some weeds and less vigorous grasses) are targeted for undersowing. Refer to the diagram below for a visual reference of PCS pasture, ranging from lowest (1) to highest (5).

Paddocks with a PCS of 3 are often selected for undersowing with perennial ryegrass (e.g. Platform AR37) to provide another two to three years of productivity. For paddocks with a PCS of 2, short term Italian ryegrasses, such as Lush AR37, are recommended to provide another 18- 24 months of productive growth.

Undersowing on paddocks with severe pasture damage across the entire paddock and significant weed presence (PCS 1) is not recommended. Instead these paddocks should be sprayed out with glyphosate and appropriate partner herbicides, before planting in Winter Star II annual ryegrass. This option will provide good weed control and provide 6-9 months of winter and early spring production, before allowing the paddock to be planted in a spring crop such as chicory, turnips or maize.

Timing is crucial when it comes to undersowing; in late summer/ early autumn while soil temperatures are still high, perennial ryegrass is a good option for undersowing. As the days shorten and soil temperatures drop below 12°C, it is recommended to switch to Italian and annual ryegrasses (e.g. Lush AR37) as these are much faster to establish and have better cool season activity.

Early undersowing allows seedling establishment to occur in more favourable conditions, which in turn maximises establishment, tillering and early dry matter production. In comparison, late undersowing may result in missing favourable growing conditions and the opportunity to produce valuable winter feed, while increasing the risk of invasive grasses and weeds establishing.

Choosing the right endophyte and utilising seed treatment is also important to a successful undersowing operation. In areas with high Black Beetle and Argentine Stem Weevil pressure, it is recommended to undersow with a ryegrass that contains AR37 endophyte that provides protection to established plants in future seasons. Superstrike® seed treatment is also recommended, as this will provide insect protection until endophyte protection is established within seedlings.

Following undersowing remember to monitor for autumn establishing broadleaf weeds and apply an appropriate herbicide if required. Early grazing management is also important to ensure seedlings can tiller and are not shaded out by the existing pasture. As with all new pastures the first grazing should happen when seedlings pass the ‘pull test’ - leaf blades tear when ‘plucked’ while roots remain anchored in the ground.

Find your pasture condition score