STINKING MAYWEED

WHEN IT COMES to training staff, farmers and junior agronomists, I really love to challenge and stretch people. I guess it’s because I come from a family of teachers (mum, dad and both sisters).

I have fond memories of my dad, a science teacher extraordinaire, quizzing me and my sisters on all things science, with the questions starting easy and getting progressively harder.

I follow the same principles when I’m teaching people weed ID. We start easy (a fathen here, a shepherd’s purse there), and then get progressively harder (like say the mayweeds or chamomiles, the names are interchangeable). There are three mayweeds and when vegetative they all look the same but there are some subtle tricks to differentiate them.

So begins your lessons on the mayweeds. Stinking mayweed ( Anthemis cotula) is a common annual weed of open pastures, waste areas, crops and roadsides all across New Zealand. It’s originally native to Europe and North Africa but has successfully migrated to North America, Southern Africa, Australia and New Zealand.

As you can see, it is a member of the Asteraceae or ‘daisy’ family and that’s exactly what it looks like when it’s flowering, but there’s one other distinctive feature. It stinks!

This is a very strong, very unpleasant odour which is so strong and so unpleasant that animals won’t even eat the grass around it, let alone the plant itself, which means it’s free to invade your pasture at its leisure.

While it does smell awful, it’s actually not toxic unless you are a cat, dog, horse or guinea pig, but you want to steer clear as it’s pretty nasty if you touch it (or eat it, which I don’t recommend). Symptoms can include dermatitis, vomiting, diarrhoea, anorexia, and other allergic reactions*.

It can be tricky to differentiate stinking mayweed from the other mayweeds as they look very similar when vegetative. It germinates in the spring, usually in areas where there is bare soil such as wastelands and open pugged pastures, and produces very slight, feathery, dark green leaves that emerge directly from the stem. It can reach a height of around 30-60cm before it begins flowering over the December to March period. The flowers resemble the classic daisy flower – 2-3 cm in diameter with a bright yellow centre surrounded by white petals.

One easy way to identify it is to crush some leaves and have a sniff, which will also help you figure out what is: - if it stinks, it’s stinking mayweed; - if there’s no smell you have scentless chamomile (the second mayweed);

- if it smells like pineapple you have rayless chamomile (the third mayweed).

How to control it

Controlling stinking mayweed can be really easy or really hard depending on the conditions. If your pasture or crop is competitive it will outcompete stinking mayweed which needs a bit of time to get going so good grass and clover will smother it out.

If it does get a toehold but you spot it when it’s about 2-3cm across, a spray with Reside or Headstart will control it (keep the rates up for best control).

If it’s bigger than that, you need the big guns like 2,4D or Versatill which will control plants right up to flowering but they will knock your clover so try to get to them early. ■