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Why keep vineyards weed free?

grapes hanging down towards the ground

​Late summer and early autumn rain can mean weeds germinate or are primed, ready to go.

But why should you tackle these weeds?

The main reason to control weeds is to conserve soil moisture and reduce their competition with the vine for sunlight and nutrients. Waiting for further germinations to occur and doing one big clean up, or hoping that weeds die from lack of follow-up rain can work against this principal reason.

There are other reasons to keep the vineyard clean at this time of year as well. These include:
• Reducing the feed source and shelter for vermin (particularly mice)
• Keeping air circulating in the vineyard to reduce the incidence of disease;
• And making it easier for pruning and general management leading into autumn and winter.

If you are planning to use residual herbicides over winter, the argument for an early autumn spray is even more compelling. Residual products are significantly more effective when applied to bare soil. Large weeds, a dense mat of weeds or a thick carpet of decaying weed matter often leads to poor results from residual herbicides that would otherwise offer good extended control.

If you decide to spray with a knockdown now, the key thing to remember is that your spray should always target weeds when they are small. Big weeds are harder and more costly to control.

At this time of year, use herbicide rates towards the higher end of the label recommendations to help control any larger or more difficult-to-control weeds and use plenty of water for good coverage.

Looking longer term, using only knockdown herbicides to control weeds can lead to the development of herbicide resistance. It can also change the composition of your weed population.

If you have identified that your vineyard contains glyphosate-resistant weeds, or if it has received a lot of glyphosate applications over the years, introduce herbicides with different modes of action.

Other knockdown options include SPRAY.SEED®, REGLONE®, glufosinate ammonium or a tank-mix of amitrole/GRAMOXONE® 360 PRO.

A double-knock strategy is a good option, especially for dense and large stands of weeds including Annual Ryegrass. A double-knock is when two sprays with different mode of action (such as glyphosate and SPRAY.SEED) are sprayed in succession, 5-7 days apart.

The application of pre-emergent residual herbicides in winter and spring is a good follow-up strategy that will complement any program if set up well. Good pre-emergents include ZOLIAR (norflurazon), pendimethrin or oryzalin.

A mixture of different herbicide modes of action, along with non-chemical weed management practices, should be incorporated into your program. And finally, always remember to seek professional advice for your specific situation.