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VINE TALK: Late weed growth needs a plan of attack

Vine Talk with Scott Mathew
Vine Talk with Dave Antrobus

One of the most talked about topics this year has been weed management. In many cases, it’s due to growing concern about herbicide resistance in the vineyard. Significant rain events over the recent summer has stimulated this discussion. It has germinated weeds that are creating a problem at an already busy time of year. If you don’t start planning weed control until after harvest then by the time you action the plan, it might be too late.

There is still time to plan your strategy! That way, when vintage is finished you can take quick action to ensure weeds don’t have chance to set seed. After all, stopping weeds multiply is at the heart of every good weed control program.

Non-selective knockdown herbicides provide an effective kill of established weeds. If the vineyard has a history of glyphosate use, then rotating to another herbicide group, such as GRAMOXONE® or SPRAY.SEED®, under vines is a sensible option. Both are non-selective contact bipyridyl herbicides that belong to the Group L herbicide group.

The choice of product depends on the weed species present. GRAMOXONE is an annual grass specialist, whereas SPRAY.SEED, a mix of paraquat (GRAMOXONE) and diquat which does the ‘heavy lifting’ on broadleaved weeds, is more suited to where more annual broadleaved weeds are present.

Being contact herbicides, water volumes and spray coverage are very important as better coverage of the plant with these herbicides gives a higher level of control. Match the water volume to the size and density of the weeds you are targeting. Both GRAMOXONE and SPRAY.SEED should be applied at higher water volumes than systemic herbicides like glyphosate.

The effectiveness of bipyridyls can be improved when they are applied in lower light conditions, such as in the evening. Bipyridyls are rapidly absorbed into leaves, destroying green plant tissue quickly on contact, and the speed of cell destruction can be influenced by the intensity of light. The greater the light intensity, the faster the reaction.

Applying GRAMOXONE or SPRAY.SEED in the evening slows the speed of cell damage and extends the drying time of the droplet on the leaf. The longer drying time allows more time for the active ingredient to be absorbed into the leaf and a slower speed of cell damage can enable better movement of the active ingredient within the leaf. So spray at the end of the day or at night if you can.

An effective weed control strategy to manage herbicide resistance is the ‘double knock’, which utilises two different herbicide modes of action. Generally, it involves applying glyphosate followed by either GRAMOXONE or SPRAY.SEED five to ten days later. It can be a very useful tool, when done correctly. In theory, if any weeds survive or are resistant to the first glyphosate application, they will be controlled by the second herbicide application or ‘double-knock’. Both herbicide applications should be at a full lethal dose rate to control the weeds. To ensure a really good result on difficult to control weeds such as marshmallow, stinging nettle or erodium, the addition of a Group G herbicide spike mixed with the SPRAY.SEED is very effective.

And finally, while they may give perennials like couch and kikuyu a really good knock, GRAMOXONE and SPRAY.SEED will not fully control these grass weeds. FUSILADE FORTE® or glyphosate should be used in these circumstances.