Over the next four months we will be talking about the most common problems faced when undertaking a riparian planting or restoration project. To start it off this month we’re straight into the thick of it with weeds. In particular we’re going to focus our attention on Great Bindweed (also known as convolvulus).
All weeds compete for resources (light, water, nutrients). Weeds grow many times faster than native trees and it’s therefore important to eliminate them before planting to minimise their impact on native plants.
Perennials and summer annual weeds pose the greatest risk to native plantings because they disappear over winter when most restoration projects occur. Some harder to control weeds may require attention up to a year prior to planting to ensure they don’t pose a risk after planting.
Great Bindweed is a climbing, perennial weed that is common throughout New Zealand. It has recently received more attention because it is now becoming a significant weed in riparian plantings. What makes this weed so difficult to control is the extensive rhizome root system which can spread several meters underground.
Why is it a problem? Convolvulus competes for light. It smothers and strangles young plants and takes over entire riparian margins.
So what can be done? Non-herbicide control options for bindweed may include mowing, grazing, cultivation, flooding, hand removal, light deprivation with plastic covers, mulch or biological control. Unfortunately all these methods are both time consuming and impractical in riparian margins and may not actually control great bindweed effectively.
Chemical control is your best bet against this weed. In a study by Massey University on the effects of different herbicides on great bindweed this is what they found.
- No herbicide is known to control convolvulus 100%. Translocating herbicides are most effective
- Timing of spray applications is important. late/Autumn application when sugars are being transported down into the roots is most effective.
- Follow up sprays are needed. Ideally in early summer before sugar reserves are restored and once the plant starts to translocate sugars to the roots. Knock it while it’s down!
- Application of Triclopyr/picloram/aminopyralid (Brushkiller) and 2,4-D/Dicamba are most effective. When these chemicals were used in the trial regrowth didn’t occur until 22 weeks after spraying.
What else can be done? Plan and prepare! Planning is just as important as choosing the right herbicide to use and the timing of the application. Good preparation goes a long way to ensuring a successful planting project. If you are planning a planting project and there is convolvulus or other pest species present, now is a great time to spray them out.