Changing tack | PGG Wrightson

Back in the day, while managing cereal crops on a mixed farm, I worked with a Farm Consultant who was fond of saying, ‘If you always do what you've always done, you always get what you've always got.’ A colourful way of saying if you are not getting the desired results, then you need to change tack. We should always be evaluating our systems and looking for ways to fine tune them, particularly when it comes to weed control.

The overuse of one group of chemistry can potentially lead to resistance in weeds. So, if you are not getting results, it may be time to change it up. The weed spectrum changes with the seasons. Take chickweed, for example. Now is the time of year we see more chickweed in our new grass and clover. The traditional treatment is to use the active ingredient Flumetsulam (a group two herbicide), but over time the results become poorer and poorer. So, what can we do?

Changing your active ingredient is a good start. The active bentazone (a group six herbicide), found in several pasture herbicides, may be your first choice. While it is regarded as a weak active on it some weeds, like Californian and nodding thistle or even shepherd’s purse, it is very effective on other weeds like storksbill, chamomile, and stinking mayweed. Bentazone’s mode of action is as a photosynthesis inhibitor of weeds, burning the weeds off, making it effective against shallow rooting plants such as chickweed and spurrey. Mixing it with Tropotox and a surfactant, can strengthen its effectiveness across a wider spectrum of
weeds.

Available in a pre-mix with MCPB, Pulsar is effective against broadleaf weeds. The herbicide Dynamo, a mix of bentazone and flumetsulam, also targets broadleaf weeds. Using two different nodes of action to attack the same weed makes our weed control more effective and protects our chemistry from resistance. The withholding period for grazing stock is 14 days.

Dock is another troublesome weed and is becoming a real issue for dairy farms and cattle grazing blocks. Herbicides used to control dock do not enjoy being mixed with other herbicides which sees their efficacy drop away. However, mixing two litres of Dockstar with two kg of Baton or 700 mls of Sprinter can be very effective, especially when applied in the spring before the dock seed heads emerge, and two to three weeks post grazing when weeds are fresh. For best control, after application, leave them for a week or two before grazing again to allow toxic weeds to die down.

In addition to controlling dock, this mixture is also effective on seedling thistles and ragwort. Check the label for other weeds you may wish to control this spring.

For options to control weeds on your farm and prevent herbicide resistance, contact your local PGG Wrightson Technical Field Representative.