Buttercup survives in pasture because cattle find it genuinely unpalatable, so it's left standing while everything around it gets grazed down. Flumetsulam-based herbicides such as Decision control both annual and giant (perennial) buttercup while leaving clover largely untouched, unlike older broadleaf sprays that knock clover around too. Spring, before flowering, is the window to act.

  • ✓Why buttercup gets away on you even in well-grazed pasture
  • ✓What the research actually shows about flumetsulam and clover safety
  • ✓How and when to spray for the best result with the least clover damage
  • ✓The mistakes that mean farmers end up spraying the same paddock every year

If there's one weed that gets a free pass through winter, it's buttercup. Cows work their way through everything else in the paddock and leave it standing, which is exactly how it gets the jump on spring. Rainbow & Brown, a New Zealand agricultural chemicals and soil health supplier, put this guide together to explain why buttercup behaves the way it does and what's actually worked in NZ pasture trials to bring it back under control, without hammering your clover in the process.

What is buttercup, and why does it spread?

Buttercup spreads because stock simply won't eat it. It tastes bad enough to cattle that they graze everything around it right down to the ground while the buttercup itself stands untouched, flowering and setting next season's seed while it's at it.

That's why late winter is when you actually notice it. Pasture growth slows, cows work the paddock hard, and there in the short grazed-down gaps stands buttercup, taller than everything else and clearly winning. There are two forms worth knowing apart: annual buttercup, which regrows from seed each year, and giant (also called perennial) buttercup, which persists from an established root crown and is harder to shift. Both spread through New Zealand pasture, and both are covered by flumetsulam-based control.

Why it matters in New Zealand

Buttercup isn't a minor annoyance on New Zealand farms. It's been enough of a problem for long enough that it's been the subject of dedicated research here, not just overseas literature.

  • It's a recognised dairy pasture problem. An AgResearch review commissioned by DairyNZ identified flumetsulam as one of the most useful tools available for buttercup control in established pasture, specifically because it controls both annual and giant buttercup without damaging clover.
  • Field trials back it up. Research published in NZ Plant Protection (Harris & Husband, 1997) found that repeat spring applications delivered good ongoing suppression of giant buttercup, with white clover showing very low impact compared with older options like MCPA, where clover suppression was considerably higher.
  • Winter grazing patterns make it worse here. New Zealand's pasture-based, rotational grazing systems mean buttercup gets exactly the conditions it needs: short, hard-grazed pasture in the cooler months with little competition left standing around it.

How to approach control

The short version: spray in spring, before flowering, with a product that targets buttercup without taking your clover down with it. Here's how flumetsulam-based control (Decision) stacks up against the older broadleaf option many farmers grew up using.

Flumetsulam (Decision) Older broadleaf sprays (e.g. MCPA)
Clover impact. NZ trial data shows very low impact on white clover with repeat spring use. Clover impact. Clover suppression considerably higher in the same trials.
Weed range. Annual and giant buttercup, plus chickweed, cleavers, mallow, sorrel and other broadleafs. Weed range. Broad general broadleaf control, less specifically suited to giant buttercup.
Application. Water dispersible granule, needs a spraying oil to perform. Application. Liquid concentrate, no oil adjuvant required.

The practical process looks like this:

  1. Identify actively growing buttercup before flowering. Spring, while the plant is putting on leaf and before it sets seed, is the window that gives you the best result.
  2. Add a spraying oil. Flumetsulam needs a spraying oil to perform properly. BioWet, a food-grade rapeseed oil adjuvant, added at 500ml per 100 litres of water, helps the active spread across the leaf and get taken up, while reducing spray drift.
  3. Spray at label rate. Apply Decision in spring before flowering, when both annual and giant buttercup are actively growing.
  4. Plan on repeating. Giant buttercup in particular regrows from an established root crown, so ongoing suppression relies on repeat spring applications rather than a single pass.

Always follow product label and local regulations.

Buttercup Pack. Decision and BioWet are also available bundled as a Buttercup Enforcer Pack in Lifestyle and Farm sizes, so you've got the herbicide and the oil adjuvant sorted in one order. Pricing changes from time to time, so check the pack page for what's current.

Practical tips

Tip: Spray before flowering, not after. Once buttercup is flowering it's already thinking about next season's seed, and you've missed the best window for suppression.

Tip: Don't skip the spraying oil. Decision needs it to perform, and BioWet is also the go-to oil-based adjuvant whenever a label calls for a crop oil, including with MSF600 or glyphosate.

Tip: Walk paddocks in August. That's when short winter pasture makes buttercup stand out clearly against everything cattle have grazed down around it.

Tip: Treat giant buttercup as a multi-year job. A root crown doesn't give up after one spray, so budget for repeat spring applications rather than expecting a single pass to finish it.

Tip: Check your clover status before spraying. Flumetsulam is clover-friendly in NZ trial data, but timing and rate still matter, so always read the label first.

Common mistakes

Mistake: Waiting until buttercup is already flowering to spray. By then it's visually obvious, but you've lost the best control window. Get onto it while it's actively growing in spring, before flowers appear.

Mistake: Spraying without an oil adjuvant. Flumetsulam won't perform to its potential without a spraying oil like BioWet helping it spread and get taken up across the leaf.

Mistake: Treating it as a one-and-done job. Giant buttercup regrows from an established root system, so one good spray doesn't mean you're finished. Plan for repeat spring applications.

Mistake: Assuming all broadleaf sprays are equal on clover. Older options like MCPA can suppress clover considerably more than flumetsulam does in NZ trial comparisons, which matters if clover content is part of your pasture goals.

Quick checklist

  • Walk paddocks in August/September and mark where buttercup is standing above grazed pasture
  • Confirm whether you're dealing with annual or giant (perennial) buttercup
  • Plan spraying for spring, before flowering starts
  • Have a flumetsulam-based product (Decision) and a spraying oil (BioWet) on hand together
  • Apply at label rate, oil included
  • Note the paddock for a follow-up spray next spring if giant buttercup is present
  • Check current product and pack pricing at rainbowbrown.co.nz before you order

Next step: walk your worst paddock this week and mark where buttercup is standing clear of the grazed pasture, that's your spray list for spring.

FAQs

Why won't my cows just eat the buttercup?

Buttercup is genuinely unpalatable to cattle, not just mildly unappealing. That's exactly why it gets left behind while stock graze everything else around it down, giving it the clear run it needs to flower and spread.

What's the difference between annual and giant buttercup?

Annual buttercup regrows from seed each season. Giant (perennial) buttercup persists from an established root crown, which is why it tends to come back in the same spots year after year and needs repeat treatment rather than a single spray.

Will spraying for buttercup damage my clover?

NZ field trial data on flumetsulam (the active in Decision) shows very low impact on white clover with repeat spring applications, notably lower than older broadleaf options like MCPA. Timing and rate still matter, so always follow the label.

Do I need a spraying oil with Decision?

Yes. Flumetsulam needs a spraying oil to perform properly. BioWet, a food-grade rapeseed oil adjuvant, is added at 500ml per 100 litres of water to help the active spread across the leaf, get taken up, and reduce spray drift.

Further reading