SCENTLESS CHAMOMILE

NZ Lifestyle Block - - Fasture Weed Watch -

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.

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