Catch the weeds flat, before spring sends them to flower

Walk a paddock around Whittlesea in early August and it can look deceptively clean. The grass is short, the ground is wet, and the weeds that will run riot in spring are still sitting flat and quiet against the soil. That flat, quiet stage is exactly the point. The broadleaf weeds worth spraying now are the ones you can barely pick out. Leave them another six weeks and they will announce themselves, by which time the cheap, clean fix has passed.

This is the late-winter spray window, and it is one of the most useful things to understand about your own block.

Rosettes now, flowers later

Most of the broadleaf weeds that trouble paddocks around here germinate after the autumn break and spend winter as a rosette: a flat, ground-hugging circle of leaves with no stem, sitting low out of the wind and the frost. Capeweed, spear and variegated thistles, and Paterson's curse (Salvation Jane) all do this. Right now they are storing energy and biding their time.

When the soil warms in spring, that stored energy goes straight up into a flowering stem. Capeweed carpets a paddock in yellow, thistles bolt waist-high and spiny, and Paterson's curse throws up its purple heads. Every one of those flowers is next year's seedbank being set. Once a weed has bolted and flowered, spraying it is far less effective and, in the case of thistles, you are killing a plant that has often already done its damage.

The weed you can barely see in August is the one you spray. The one you can see from the ute in October has already won that round.

A rosette is soft, actively growing, and has all its leaf surface flat to the sky. That is the ideal target for a selective broadleaf herbicide, the kind that knocks the weed and leaves the grass. The plant takes the chemical in through those open leaves and cannot outrun it. The same weed a month later, standing up and flowering, is tougher, waxier, and much harder to kill cleanly.

Learn to read the rosettes

You do not need to name every weed to know you have a problem. Get down and look at the ground between the grass plants. You are looking for flat circles of leaf that are not grass: broad, often lobed or hairy leaves radiating from a central point. A few things to notice:

• Capeweed sits as a flat rosette of grey-green, deeply lobed leaves, often with a pale, felty underside.
• Thistles show as rosettes of spiny-edged leaves. Run a hand near them and you will feel why stock leave them alone.
• Paterson's curse forms a coarse, dark green rosette of oval, bristly leaves, usually in the more run-down or bare patches.

If a good part of the paddock is these flat circles rather than grass, that is a paddock worth spraying now. If it is only a scatter, you may be better off spot-treating the patches and spending the rest of your effort on the pasture itself.

Reading the spray window

Timing the weeds is only half of it. The other half is timing the day. Herbicide only does its job if it lands on the target and stays there, which means the weather has to cooperate. The conditions that make for a clean, responsible spray are the same ones an experienced operator waits for:

• A calm, mild morning or evening, with a light breeze of roughly 3 to 15 km/h blowing away from anything sensitive, gardens, waterways, a neighbour's vegetables.
• No rain due for several hours, so the chemical has time to be taken up rather than washed off.
• Not the dead still of a cold, frosty dawn (which can trap spray and hold it low) and not the heat and gusts of the middle of the day.

Nobody worth their salt sprays in a howling wind or the heat of the afternoon. On a boom, the nozzles sit low, about half a metre above the weed canopy, and the tractor runs in straight, steady passes so the spray lands as an even, fine curtain right where it should. Get the day wrong and you either waste the pass or send it drifting where it is not wanted. This is a big part of why spraying rewards patience and a bit of judgment, and it is how we approach the job rather than just spraying because the diary said so.

Not everything is a winter job

Worth being clear: the late-winter window is for the soft, actively growing broadleaf weeds in pasture. The woody weeds are a different story. Blackberry, for instance, is best hit later, when it is in full leaf and actively growing through late spring and summer, and it is spot-sprayed to run-off rather than boomed. If your problem is a blackberry thicket down a gully, note it now and plan it for the warmer months instead.

Book the window, do not chase the flowers

The practical takeaway is simple. Get down and look at the ground now, while the weeds are flat. If the rosettes are there in numbers, that paddock wants spraying in the next few weeks, on the first suitable day, before spring warmth sends everything skyward. Chase it after it flowers and you are paying more for a worse result and a paddock already seeding itself for next year. If you want a straight read on whether your block is worth a boom pass, a spot job, or leaving well alone this season, that judgment is part of what we do around Whittlesea and the ranges.

Oak Ridge Agriculture

Tell us about your block