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What is winter cleaning?

Winter cleaning is a herbicide application technique to remove or ‘clean’ annual grasses, mainly silver grass, from established mixed grass/sub-clover pastures. It relies on a chemical (simazine) being absorbed through the roots when plants are actively growing. The cleaning effect is lifted further for mature plants by applying a second herbicide (paraquat) that damages the leaves.

Removal or suppression of the annual grasses creates bare ground for more desirable pasture species to populate.

Untreated pasture (left) compared to winter cleaned pasture (right) in mid-November

What plants does winter cleaning target?

Winter cleaning is highly effective on Vulpia species, such as silver grass, rat-tail fescue (Vulpia myuros), sand fescue (Vulpia fasciculata) and squirrel-tail fescue (Vulpia bromoides). It will also suppress barley grass (Hordeum leporinum) and soft brome grass (Bromus hordeaceus).

The technique is effective because it removes the grasses from the pasture before they have time to set seed. Silver, soft brome and barley grasses have short seed life (viability) and disrupting the seed set, even for one year, can dramatically reduce the seed available for germination the next year (see Figure 1).

Other annual grasses (annual ryegrass, wild oats) and some broadleaf weeds can also be suppressed by herbicide application, but the effect is not lasting. The growth of perennial grasses and sub-clover will temporarily slow, but they will go on to recover.

Figure 1. Longevity of seeds of annual grasses affected by winter cleaning. Longer cones indicate greater seed dormancy before germination.