SCENTLESS CHAMOMILE
OVER THE past three months you’ve read about the chamomile weeds, stinking mayweed and rayless chamomile, and now we tackle the last one, scentless chamomile.
I’ve always loved these weeds from a training sense – they form a bit of a graduation exam for the agronomists I train. The scenario is always to correctly identify the three weeds as seedlings as it’s very hard to do visually. But if they remember what they’ve been taught and use their sense of smell it becomes an easy test, and you can give it a go in your own garden – you might surprise yourself with your skills!
Scentless chamomile ( Tripleurospermum inodorum) is an annual (or a short-lived perennial in some situations) weed found all over New Zealand. It’s native to Europe, Asia and North Africa, but has moved most of the way around the world. In some parts (I’m looking at you North America) it is considered an invasive noxious species.
As with the other mayweeds and chamomiles, scentless chamomile is a member of the Asteraceae or sunflower family of weeds, but there’s a little bit of confusion over exactly where it fits in. For a long time it was thought to be a direct relation of rayless chamomile but genetic analysis has split this family in two with half of them forming the new genus of
Tripleurospermum.
Like the other mayweeds and chamomiles, scentless chamomile is very hard to visually identify from a small plant but super easy if you can crush it and smell it. They can also be differentiated by their very different flowers.
Scentless chamomile can germinate in soil all year round, so long as there is moisture, sunlight reaching the soil, and soil temperatures are above 3°C. Generally, most of them germinate in the spring and autumn in New Zealand. Following germination they produce small, dense rosettes of leaves which are very finely divided and kind-of resemble fern fronds. They soon produce a long stem (15cm to 1m), with a large number of branches covered in their fine leaves.
At the end of each branch the plant produces flowers with white petals and a brilliant yellow centre, kind-of like a giant daisy. These flowers produce a veritable horde of seeds – we are talking tonnes of seeds, like 10,000 to 200,000 seeds per plant! – which means they can effectively colonise large areas in only a couple of years. That can be a real pain in pasture as animals will not eat it.
How to control it
Controlling scentless chamomile is a cinch but only if you deal to it quickly – let it seed and you will be fighting the fight for years to come.
The best way to deal with it in a home garden is just to pull it out as it’s not too hard to weed out.
If you are dealing with a larger area you may want to spray it out. We are a little limited in what chemical will work here: 2,4D and MCPA are ok; Versatill works best but you need to be spraying small seedling plants to get any control.
If there is a flower, forget about spot spraying with chemical control as the plant will have finished its lifecycle and die off naturally after seeding, ready to reproduce next year.