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Achieving good weed control with glyphosate

Vine Talk columnist and Syngenta Technical Services Lead Dr Brandy (Belinda) Rawnsley.
Have you heard the latest tips, tricks and industry advice? Vine Talk author, Dr Brandy (Belinda) Rawnsley takes a look at the issues facing grape growers.

By Brandy Rawnsley 

Glyphosate is arguably one of the most popular and effective herbicides used under-vine. With widespread public interest it’s important to use glyphosate wisely.

Glyphosate is a broad-spectrum systemic herbicide and is more effective on actively growing young weeds. Inconsistent rain events at this time of the year can cause a staggered germination of annual weeds with larger and smaller weeds all together under the vines. For this reason, it is important to select a robust label rate that will control the largest weeds present. Herbicide efficacy is lowest when weeds are mature.

Glyphosate works best on annual weeds, including grasses and broad-leaf weeds. Poor control is achieved on weeds such as fleabane, marshmallow or Erodium. In these instances, glyphosate can be used in a tank mix with another knockdown herbicide. Knowing your weeds before you decide to spray assists herbicide selection.

Often overlooked is the application of glyphosate on stressed weeds when this will give poor control. Avoid spraying weeds under moisture stress, in low temperatures (<12°C) or water-logged conditions.

Continued reliance and overuse of glyphosate can promote resistant weeds, such as annual ryegrass.  To identify if you have resistance developing, look for weeds that survive after a glyphosate application. Often individual plants will survive but these will multiply forming clumps of resistant weeds in the vineyard. After a few more applications of glyphosate, these weeds will dominate the weed population.

There are a number of strategies to improve the efficacy of glyphosate and reduce the risk of resistant weeds. Firstly, don’t rely solely on herbicides for weed control. Use other alternative methods such as undervine mowing and mulching, which also improves soil health.

Rotate or tank mix glyphosate (Group M) with herbicides of a different mode of action. This can extend the period of weed control and reduce the need for glyphosate.

The ‘double knockdown’ technique utilises two different herbicide modes of action used in succession, such as glyphosate followed 5 to 10 days later by SPRAY.SEED®. The second herbicide kills any weeds that survive after the first application and controls newly emerged weeds.

Grape growers can contact their local Syngenta representative for more information.

Dr Belinda (Brandy) Rawnsley is a Syngenta Technical Services Lead for Viticulture and Horticulture