What is it?
The Mexican daisy (Erigeron karvinskianus) is a common sight throughout New Zealand, often appearing in gardens, parks, on roadsides, and along the side of waterways.
It is also known as Erigeron mucronatus, Erigeron "Profusion", and seaside daisy.
It has daisy-like flowers that are familiar to most gardeners. They range from white to white-purple to pink, with a yellow to brownish-yellow central disc. The flowers typically appear throughout the year, and are followed by masses of fluffy seeds.
Mexican daisy is a sprawling perennial daisy that grows up to 40cm tall, with long thin stems. Its leaves are small and narrow, and give off a distinct fragrance when crushed.
It should not be confused with another garden daisy, Bellis perennis, which has nearly identical flowers but wider leaves arranged in a rosette at the base of the stems.
Why is it a problem?
Mexican daisy is considered a weed because of its ability to form dense mats of ground cover, particularly in the North Island and the upper South Island. These clumps smother native vegetation and, as they die off, pave the way for other invasive weed species, such as climbing vines.
In addition, it is able to survive and spread in a huge range of habitats, from intact stands of bush to riverbeds and herbfields, and can tolerate anything from moderate shade to full sun.
Unfortunately, while it is a plant that is easily removed from an area, it is also hard to keep out because it is such a prolific seeder. The seeds are able to spread long distances through wind dispersal and are also sometimes spread through contaminated topsoil and potting mix.
It is also sometimes still sold at markets and school fairs even though it is on the National Pest Plant Accord list.
Methods of control
Manual Control: Small areas of Mexican daisy can be pulled out by hand. To be successful, however, care needs to be taken to remove all roots and to avoid spreading the seeds as it is removed.
Chemical Control: A range of herbicides is suitable for controlling Mexican daisy, including Versatill, and glyphosate-based sprays.
Take care to spray only in still conditions to avoid wind drift to non-target plants, and don't spray when rain is expected. During spraying, non-target plants can be shielded with cardboard, plastic sheets or a large plastic container. Under the Biosecurity Act 1993, it is illegal to sell, propagate or distribute Mexican daisy. As with all spraying, you should read the instructions on the manufacturer's label closely and always wear protective clothing.
Contact any Department of Conservation office for further information on the identification and control of invasive weed species.
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