Spray Topping Pasture

The very good autumn break and consistent follow up rain throughout winter has stimulated a huge growth of pastures. This prevented many paddocks from being winter-cleaned due to excessive biomass. As a result, many pastures will require spray topping in spring to prevent weed seed set.

Successful spray topping requires some planning and attention to detail, with the following being some things to keep in mind:

Paddock Preparation

• Paddocks should be heavily grazed 2-3 weeks prior to spraying to stimulate an even emergence of seed heads. This will be very challenging to achieve across numerous paddocks this season

Timing

• Paraquat should be applied when the majority of seed heads are at or just prior to the milky dough stage.

• Glyphosate should be applied slightly earlier, as it takes longer to translocate through the plant. The ideal timing is when the entire seed head has emerged until flowering.

Post Spraying

• Once grazing withhold periods have been met, the pasture should once again be heavily grazed to prevent regrowth of tillers and to prevent flowering of late seed heads. If grazing cannot control regrowth, an additional chemical application may be necessary.

The use of Glyphosate for spray topping should be carefully considered, particularly when used in perennial pastures. Incorrect timing or rates may damage the pasture or reduce seed set of pasture species.

When using Glyphosate, the resistant status of the ryegrass needs to be determined. If ryegrass is Glyphosate resistant, it will not sterilise the seed, thus increasing the proportion of resistant individuals in the weed population.

Given the prevalence of Glyphosate resistance and the pressure already on Glyphosate, it is best to avoid using it wherever an alternative exists.