Dairy Exporter December 2021

Page 85

RESEARCH WRAP HERBICIDE ALTERNATIVES

That yellow pest Words by: Elaine Fisher GREEN THISTLE BEETLE: LIFE CYCLE

A beetle to beat the thistle Words by: Elaine Fisher

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gResearch is combining empirical and modelling work to understand and optimise the regulatory effects of nonchemical control methods on weed populations, including manual removal and natural enemies, under current and future climates. AgResearch’s Mike Cripps and Graeme Bourdôt are key researchers focusing on biocontrol of naturalised species of thistles (tribe Cardueae). This tribe contributes more species to New Zealand exotic pasture weed flora than any other taxonomic group. It contains some of the most economically damaging weeds and many ‘sleepers’. The tribe is uniquely amenable to biocontrol using agents imported from the plants’ native ranges overseas because there are no native NZ thistles and few economically valued species in the tribe, the researchers say. An example from this element of the research programme is the green thistle beetle, imported and released in NZ in 2007 for control of Californian thistle. The impact of the beetle on thistle shoot population density and spread was assessed over two years on a North Canterbury sheep and beef farm. Where there were high beetle densities of 10 or 20 beetle larvae per thistle shoot, the population of Californian thistle declined. At these high beetle densities, the spread of the weed in the paddock was also reduced. In comparison, where there were no beetle larvae, or only low densities of five larvae per shoot, the thistle population increased in density. The green thistle beetle can also attack other thistle weeds, however, its impact on other thistles that reproduce via seeds appears limited. • (Source: Cripps MG, Jackman SD, van Koten C 2019. Folivory impact of the biocontrol beetle, Cassida rubiginosa, on population growth of Cirsium arvense. BioControl 64: 91-101). Dairy Exporter | www.nzfarmlife.co.nz | December 2021

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n app to assist farmers to control the pasture weed species giant buttercup has been developed by AgResearch and is available free to use from the Dairy NZ

website. Dr Graeme Bourdȏt, AgResearch principal scientist, Weeds, Pests and Biosecurity Team, says the app enables the user to determine if the giant buttercup infestation in a paddock is economically worthwhile controlling (do the benefits outweigh the costs?). “It accounts for the loss of clovers from herbicide damage, enables herbicide options to be compared and herbicide resistance to be managed.” The tool requires estimates for: • % of the pasture covered by the buttercup prior to the intended control operation • pasture drymatter eaten or grown currently in the paddock • conversion rate for pasture drymatter to milksolids • pasture utilisation rate • clover content • milksolids payout • herbicide cost • N-fertiliser cost and % N content • herd lactation length • stocking rate Default values which can be edited are provided as examples for some of these input variables. The calculations used in the app utilise a unique data set comparing the efficacies of all herbicides available in New Zealand with a label claim for giant buttercup obtained from a three-year experiment on nine dairy farms in the Golden Bay district. The model used in the App is described in the peer-reviewed journal paper: https://www.dairynz.co.nz/feed/pasture/pestsand-weeds/giant-buttercup/. • (Source: Bourdôt GW, Lamoureaux SL, Jackman S, Noble A, Chapman DF 2021. Net economic benefit of Ranunculus acris control in dairy pasture - accounting for herbicide damage to clovers and evolved resistance. New Zealand Journal of Agricultural Research https://doi.org/10.1080/00288233.2021.19 81954) 85


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Articles inside

The Dairy Exporter in December 1971

3min
pages 90-92

Gen Z to make their mark

4min
page 89

Tracmap unit eases compliance pain

3min
page 88

Never too late to learn

5min
pages 86-87

A beetle to beat the thistle

2min
page 85

Plants waiting to be weeds

2min
page 84

The art of saying no

5min
pages 82-83

Variety from consulting to composting

7min
pages 78-81

Vet Voice: More to it than

4min
pages 74-75

Fast track to management

5min
pages 76-77

Reducing heat stress over summer

2min
page 73

M. Bovis: It had a head start

6min
pages 71-72

Restoring Horowhenua’s waters

6min
pages 65-67

And now, freshwater plans

3min
page 64

Sustainability: Gaining the knowledge

8min
pages 58-61

Open Country: Online tool for FEP

3min
pages 62-63

When will all this end?

5min
pages 54-55

Social media and anti-vax The dirty dozen

6min
pages 56-57

How to handle Covid-19 coming onfarm

3min
pages 50-51

No Jab, No Job in the milking shed

4min
page 48

It’s a health and safety issue

4min
pages 46-47

Dealing with vaccine reluctance

3min
page 49

Taranaki soft core

12min
pages 34-38

When the lights go red

5min
pages 44-45

Prepare for a virus attack

6min
pages 42-43

Ryegrass: Twelve years of torture

6min
pages 39-41

Benchmarking: Measure it to be sure

5min
pages 32-33

Ahuwhenua Trophy: Taking the leap to manager

5min
pages 26-27

Spending the payout: new kit or cutting debt?

8min
pages 14-17

Ahuwhenua Trophy: Quality on the coast

9min
pages 22-25

Frances Coles loves being an ambassador for Kiwi farming

3min
page 10

Future farming will need to give more than profit, writes George Moss

3min
page 12

What a payout, writes John Milne, but what prices

2min
page 13

Market View: Hedging bets on Singapore

3min
pages 20-21

Global Dairy: All change at FrieslandCampina

5min
pages 18-19
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