Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free...

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Toni Withers, Michelle Watson and Mike Watt April 2013 Buddleia leaf weevil: 7 years in New Zealand

Transcript of Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free...

Page 1: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Toni Withers, Michelle Watson and Mike Watt

April 2013

Buddleia leaf weevil: 7 years in New Zealand

Page 2: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

The weed

Buddleia in forestry

Buddleia in native forests

The insect

Field releases

Where?

What impact to date?

What benefits for forestry?

How to collect and redistribute the agent

Overview

Page 3: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Woody shrub from China

Rapidly colonises disturbed sites

Fine, wind-dispersed seed

Able to flower 1st yr, attain 4m height in 2 yrs!

Weed of plantation forests and natural areas

Potential distribution most of NZ

buddleia summer flowers

Buddleia (Buddleja davidii)

Page 4: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Buddleja davidii New Zealand

predicted vs actual distribution

Page 5: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Reduces growth of plantation species

Was no. 1 weed of central Nth Island

Can’t be controlled with FSC approved

herbicides

Cost forestry industry ~$2.9 million/yr

control & lost production

Buddleia control vital 3-5yrs after planting

Buddleia in forestry

Pine growth with,

and without

buddleia shading

Page 6: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

1 yr old

uncontrolled

stand

Buddleia in forestry – light and nutrient competition

Page 7: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Colonises disturbed sites = stream beds & slip sites, out-

competing native colonisers like tutu, rewarewa

Alters plant communities, blocks access, shades rivers

e.g. Te Urewera, Kaikoura

Difficult to control due limited access, rapid growth

Buddleia in native forests

Page 8: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Leaf feeding weevil from China

Larvae and adults both damaging plant

Weevils overwinter as adults

Weevils have a spring and 2 autumn generations

Weevils readily fly to new sites

First released in NZ 2006 by Scion (Forest Research Inst)

4mm

adult weevil larvae pupa

Buddleia leaf weevil (Cleopus japonicus)

Page 9: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Initial releases and monitoring in 5 north is sites

Revealed an initial slow spread of 65 m/ year

Established at all release sites

Adults stop mating & laying eggs at high temps

no larvae in January-February

Field releases - where

Page 10: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Councils, forestry

companies, trusts,

community groups etc

200-500 weevils per

release

Almost 100%

establishment rate

Still room for more

spreading/ releases

Further releases

Page 11: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa
Page 12: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Predicted distribution of buddleia leaf weevil by

climate

• CLIMEX modelling

predicted the following

distribution of weevil

• Should see a wider

geographic range in the

future as weevil spreads

Page 13: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Some damage visible in spring-time

Massive damage & defoliation in autumn

Must reduce plants’ ability to sequester energy in roots

Delays in re-foliation/ re-sprouting in following spring

(instead of September, leaves appear later)

BEFORE: February 2007 AFTER: March 2008

What impact to date?

Page 14: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Number of Cleopus japonicus larvae (no. plant-1

)

0 5 10 15 20 25 30

Perc

en

tage

defo

liation (

%)

0

10

20

30

40

50

*Treatment level averages, by distance, for all days after release.

y = 10.62 x 0.33

R2 of 0.810

Number larvae correlated with damage

Page 15: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Time after planting (days)

0 100 200 300 400 500

Bu

ddle

ja d

avid

ii heig

ht (c

m)

0

10

20

30

40

50

60

70

Treated plants

Untreated plants

Values - least square

means & standard

errors

Buddleia height is reduced

End year 2 = significant reduction in growth

compared to insecticide-treated (control) plants

Page 16: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Faster rate of dispersal than initially observed

• Mass-migration of

weevils observed

following exhaustion

of local resource

Page 17: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Spectacular defoliation, but quantified impacts from

insecticide exclusion trials marginal to date

Only most potent insecticides kept plants weevil-free

Difficult maintaining high weevil levels in plots

Can we quantify the impact?

Page 18: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Kaingaroa Forest herbicide & exclusion 3 yr trial

Page 19: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Significant reduction in weed height, but not

pine tree height (yet)

Time since first measurement (days)

0 200 400 600 800 1000 1200 1400

Tre

e h

eig

ht

(cm

)

0

100

200

300

400

500 Spot

Weedy

Operational

Page 20: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

C. japonicus will only be an economically

successful buddleia control option in forestry if:

disperses rapidly

reduces growth of buddleia over entire stands

effective within the first 3-5 yrs

However, benefits suggested from buddleia

control > 3yrs

easier for pruning & thinning

roadside buddleia less vigorous

reduced seed production?

What benefits for forestry?

Page 21: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Microclimate

Preference for gullies

Sunny, open areas

Often exhaust their resource

– new adults forced to seek new

host plants to survive winter

BUT, doesn’t appear to colonise newly planted

forests quickly enough, to benefit forestry

What we know about the agent

Page 22: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Results indicate C. japonicus

has the ability to suppress

growth of buddleia seedlings

At first this is close to the

source population

Repeated defoliation between

& within years can be expected

What we know about the agent cont.

Page 23: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

To date forestry companies have

NOT been able to reduce pre and

post-plant herbicide treatments

Mainly due to other weeds still need

to be controlled

If buddleia can be reduced to very

low densities, then FSC-approved

herbicides can be used for

remaining weeds

To date some companies have been

able to reduce road-side sprays,

and speed up thinning operations

Summary – no $ benefits yet

Page 24: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Adults most robust life stage

Best collected in spring and autumn when easy

Collect by beating buddleia whilst holding

a beat sheet, tarp, or upside-down umbrella underneath

Keep adults out of the sun in a ventilated container with

buddleia stems

Release ~20-50 adults on a clump of plants

Contact Scion for advice on collection sites and to help us

track releases made

Help spread this agent

Page 25: Buddleia leaf weevil: 7 years in New Zealand...Only most potent insecticides kept plants weevil-free Difficult maintaining high weevil levels in plots Can we quantify the impact? Kaingaroa

Funding by FRST & Better Border Biosecurity (B3)

program

Forestry companies:

Rayonier, Hancock F.M., Timberlands, Pan Pac, Lake Taupo

Forest Trust /NZ Forest Managers, Tempest & Associates

Forestry, PF Olsen, et al.

The Conservation Company

Other forestry companies and Councils

with releases

Scion Forest Protection group

Big thanks to …