POTENTXAL OF PHYSICAL BARRIERS FOR ROOT WEEVIL MANAGEMENT IN NURSERIES

Michael K. Bomford

B. Sc.(&.), University of British Columbia, 1995

THESIS SUBMITTED IN PARTIAL FULFILLMENT OF

THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF PEST MANAGEMENT

in the Department of

Biological Sciences

Michael Bomford

SIMON FRASER UNIVERSITY

Apri.19, 1998

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Aîthough physical exclusion shows some potential as a novel root weevil control

strategy, it has received iittle research attention. Several studies were undertaken in

1997 to assess the potentiai of two physical barriers, alumirium fences and extruded

plastic trenches, for root weevil management in local nursery crops. In laboratory

tests, fluon and powdered talc both reduced the climbing ability of adult root weevils.

In field studies, trenches and fences with Teflon added reduced pooled root weevil immigration into plots of strawbemes by up to 67%. Immigration of the two most commody captured weevils, Nemocestes incomptus (Hom) and Barypeithes pellucidus

(Boh.),was reduced by up to 84 and 7396, respectively. Concurrent increases in strawberry plant mass and suxvival were observed. Adding diatomaceous earth to trenches did not increase their efficacy, and fences without Teflon were not effective bamiers. Immigration of carabids < 1 and > 1 cm long, respectively, was reduced by up to 84 and 54% by trenches, and 58 and 99% by fences. Adding diatomaceous earth to trenches or Teflon to fences had no effect on carabid immigration. Field trials with pardel trenches revealed up to 100% weevil escape rates, yet trenches proved a more reliable method of monitoring weevils than pitfall traps, catching larger numbers and a wider variety of curculionid species. Smaii-sale field and laboratoxy trials suggested that surfaces which root weevils cannot climb when dry are made climbable by condensation. Fences weathered field conditions well adare made of comxnerciaUy available components, but their practical potential is limited by their height and considerable labor requirements. Trenches have many disadvantages, includùlg a tendency to trap beneficial insects, shallow soii penetration, and a tendency to crack, bend, and twist under UV exposure and temperature variation. However, most of these problems could be overcome through simple design modifications, their low profile makes them compatible with wheeled farm machinery, and they could potentially kiU root weevils, instead of just excluding them. Both barriers wodd be lesexpensive than chernical controls if used to protect large areas for several years.

iii Acknowledgements

1 th&: Jeff Hicks, Pickett's Nurseries and John Traas, Traas Rootstock Nursery, for providing field space and advice; Murray Isman for providing laboratory and field space and computer access; Lynne GLli.net for ofFehg her yard as a weevil collection site,

and helping to coiiect specimens; John Borden for advice, assistance, and review of this manuscript; Mark Bomford, Sharon Coliman, Natasha Bassagnova, Richard

Cowles, Adony Melathopolous, Linda Gilkeson, Hanna Mathers and Dave Raworth for advice and encouragement.

Bob Vernon deserves especidy heartfelt thanks for the enthusiasm, encouragement, knowledge, and support he offered throughout the course of this work. He struck a careful balance between being always available for help, yet offering me enough independence to create my own project and make my own mistakes. His confidence in me gave me confidence in myself.

Thanks to my partner, Ga Ching Kong, for listening to me say far more about weevils than she ever wanted to know, and still continuhg to offer support and encouragement. 1 would also like to thank my parents, for supporting me throughout my Me-long education, and continuhg to do so with this project. Their loan of a vehicle when mine broke down proved especially invaluable.

This work was supported in paxt by the BC Nursery Trades Association,

Agriculture and Agri-Foods Canada, three SFU Graduate Fellowships, the H.R.

MacCarthy Graduate Bursary, the Thelma Finlayson Graduate Fellowship, and the BC

Councii of Garden Clubs Pxize. Table of Contents

APPROVAL ...... i

ABSTRACT ...... ii

ACKNOWLEDGEMENTS...... iv

TABLE OF C0NTENTSaeo.o...... b.~*b.~wm.~....w...... ~...*...... ~~* *.**v

LIST OF TABLES ...... W

LIST OF FIGURES ...... m...... ix

1.0 INTRODUCTION ...... 1

1.1 Rom WEEWLS ...... 1

1.1.1 Black vine weeuil ...... 1

1.1.2 Strawberry root weevil, rough strawbeny roof weeuil. and clay colored weevil .... 4 1.1.3 Woods weevil ...... 7

1.1.4 Ban/peieithespellucidus ...... 8

1.1.5 Increasing impact ...... 8 L 1.1.6 Control Options ...... 9

1.1 . 7 Examples of p hysical crintrols...... 12

1.1.8 Potential for root weevil management using physid control ...... 14

1.2 OWECTNES...... 15

2.0 MATERIALS AND MJ3THODS ...... 17

2.1 EFFECTOF POWDER AND FLUON ON WEEVIL CLIMBING ABILiTY ...... 17

2.2 TEST OF PHYSICAL BARRIERS SURROUNDINC) SMALL PLOTS OF RHODODENDRONS AND AZALEAS 18

2.3 PHYSICALBARRIERS SURROUNDINO SMALL PLOTS OF STRAWBERRIES ...... 2 1

2.4 ESCAPEFROM PARALLEL TRENCHES ...... 23 2.5 BLACKVINE WEEVIL CONTAINMENT IN SMALL ENCLOSURES ...... 24

2.6 EFFECTOF CONDENSATION ON BLACK VINE WEEVIL ESCAPES ...... 28

3.0 RESULTS ...... 29

3.1 EFFECT OF POWDER AND FLUON ON WEEVIL CLIMBINO ABILITY ...... 29

3.2 PHYSICALBARRIERS SURROUNDING SMALL PLOTS OF RHODODENDRONS AND AZALEAS ...... -29

3.3 TEST OF PHYSICAL BARRIERS SURROUNDING SMALL PLOTS OF STRAWBERRIES ...... 34

3.3.1 Weevil catches ...... 34

3.3.2 Ground beetle catches ...... 39

3.3.3 Plant health ...... 42

3.3.4 Bam'er tueuthering ...... 42

3.4 ESCAPERATE FROM PARALLEL TRENCHES ...... 45

3.4.1 Pitfall trap catches ...... 45

3.4.2 nench catches ...... 49

3.4.3 Trench weathering ...... 49

3.5 BLACKVINE WEEVIL CONTAINMENT WiTHIN SMALL ENCLOSURES ...... 54

3.6 EFFECTOF CONDENSATION ON BLACK VINE WEEWL ABILITY TO ESCAPE SMALL CANNISTERS ....-55

4.0 DISCUSSION ...... *.*57

4.1 EFFEC~OF POWDER AND FLUON ON WEEVIL CLIMBING ABILITY ...... 57

4.2 WEEVILEXCLUSION BY PHYSlCAL BARRIERS ...... 57

4.2.1 Small enclosures ...... 57

4.2.2 Parallel trenches...... 58

4.3 GROUNDBEETLE EXCLUSION BY PHYSICAL BARRIERS ...... -...... 59 4.3.1 Small enclosures ...... 59

4.3.2 Parallel trenches ...... 60

4.4 EFFECTOF CONDENSATION ON BARRIER EFFICACY ...... 61

4.5 FENCESETUP AND DURABILITY...... 61 CONCLUSION ...... 67

REFERENCES ...... 69

PERSONAL COMMUNICATIONS...... o...... o...... 74

APPENDIX 1 CALCULATION OF ANGLE OF SLIPPAGE IN A SEMI-SPHERICAL

BOWL ...... *...... 75

APPENDIX 2 CALCULATION OF PARALLEL TRENCH ESCAPE RATES ...... 80

APPENDIX 3 BARRIER COST ANALYSIS ...... 85

vii List of Tables

1. EVALUATIONOF ATTEMPTS TO ESCAPE BY BLACK VINE WEEVILS AND ROUOH STRAWBERRY ROOT

WEEVILS, FROM A CLEAN WAX BOWL, A WAX BOWL COATED WlTH FLUON, AND A WAX BOWL

COATED WITH POWDERED TALC...... 32

2. PREDATORYBEETLE CATCHES AT PICKETT'S NURSERY, JULY10 THROUGH AUOUST22, 1997. 33

3. LEAF NOTCHINQ AND SURVTVALOF STRAWBERRY PLANTS IN FNE UNPROTECTED PLOTS AND FIVE

PLOTS EACH SURROUNDED BY ALUMINUM FENCES WITH AND WITHOUT TEFLONTAPE, AND

PLASTIC TRENCHES WITH AND WITHOUT DIATOMACEOUS EARTH...... -...43

4. INDICATORS(X f S.E.,~~5) OF STRAWBERRY PLANT OROWTH IN FIVE UNPROTECTED PLOTS AND

FNE PLOTS EACH SURROUNDED BY ALUMINUM FENCES wmAND WITWOUTTEFLON TAPE, AND

PLASTIC TRENCHES WITH AND WITHOUT DMTOMACEOUS EARTH. TENSEEDLINGS PER PLOT

PLANTED ON MAY2...... 44

5. TOTAL CATCHES OF BEETLES AND ISOPODS IN PITFALL TRAPS AND TRENCHES FOR TWO TRAPPING

SESSIONS AT AN APPLE ROOTSTOCK NURSERY IN LANGLEY,BC...... 46

6. ESCAPESBY BLACK VINE WEEVILS FROM CANISTERS (2 WEEVILS IN EACH OF 10 CANISTERS) IN AN

UNSEALED CONTAINER, AND A SEALED, HUMID CONTAINER OVER A 3 H PERIOD. TWO BUCK VINE

WEEVILS WERE PLACE0 IN EACH CANISTER. CANISTERSWERE LEFT CLEAN (CONTROL), OR

COATED WITH POWDERED TALC, FLUON, OR WHITE LITHIUM GREASE...... 56

7. MEANINGAND DERNATION OF VARIABLES USED IN APPENDIX1...... 78

8. CALCULATIONOF ROUT WEEVIL CONTROL COSTS IN A 10 X 28 M CONTAINER NURSERY BED USING

REGULAR INSECTICIDE DRENCHES WITH A BACKPACK SPRAYER, PHYSICAL EXCLUSION WITH A

PLASTICTRENCH, OR PHYSICAL EXCLUSION WITH AN ALUMINUM FENCE AND ANNUAL TEFLON

APPLICATIONS...... 86

viii List of Figures

1. BLACKVINE WEEVIL ADULT (A), EGO (8),LARVA (C,D), AND NOTCHING ON RWODODENDRON

LEAVES CHARACTERISTIC OF ADULT FEEDING (E).COMPARATIVE SUES OF STRAWBERRY ROOT

WEEVIL (F), ROUGH STRAWBERRY ROOT WEEVIL (G),AND BLACK VINE WEEVIL (H)...... 2

2. BLACKVINE WEEVIL LIFE CYCLE, AND PERIODS OF VISIBLE AND ECONOMIC DAMAGE IN BC OVER

TWO YEARS ...... 5

3. &CENT GROWTH IN THE AREA GROWING NURSERY CROPS IN BRITISHCOLUMBIA...... 10

4. CONTROL(A), FENCED (B)AND TRENCHED (C)PUYI'S OF RHODODENDRONS AND AZELEAS AT AN

ORNAMENTAL NURSERY ...... 19

5. CROSSSECTION OF AN EDQE OF THE CONTROL ENCLOSURE WITH PERIMETER OUTTER CONTAINING

DORMANT OIL EMULSION TO TRAP DEPARTINO WEEVILS (A), AND TREATMENT ENCLOSURES

TEsTING WHETHER A FENCE (B)OR A PLASTIC TRENCH CONTAINING A DORMANT OIL EMULSION

(C)WILL PREVENT DEPARTING WEEVILS FROM REACHING THE GUTTER...... 26

6. MEANANGLE ACHIEVED BEFORE SLIPPING BY BLACK VINE WEEVIL AND ROUOH STRAWBERRY ROOT

WEEVIL ADULTS ON BARE WAX, OR WAX COVERED BY DRY FLUON, OR POWDERED TALC...... 30

7.SEASONAL TREND OF WEEVIL CATCHES IN A WINDBREAK NEAR ABBOTSFORD,BC...... 35

8. P~~FALLTRAP CATCHES OF WEEVILS, IN A WINDBREAK NEAR AEIBOTSFORD, BC, IN UNPROTECTED

CONTROL PLOTS (NO BARRIER), AND PLOTS SURROUNDED BY AN ALUMINUM FENCE (FENCE); AN

ALUMINUM FENCE WITH TEFLONTAPE ATTACHED (FENCE + TEFLON);A PLASTIC TRENCH

(TRENCH); AND A TRENCH WlTH DIATOMACEOUS EARTH ADDED (TRENCH + D.E.). BARSWITHIN

SUB-FIGURE WITH THE SAME LmER ARE NOT SIGNIFICANTLY DIFFERENT, TUKEY'S TEST,

P0.05...... 37

9. ~FALLTRAP CATCHES OF CARABID BEETLES IN A WiNDBREAK NEAR ~BOTSFORD,BC IN

UNPROTECTED CONTROL PLOTS (NO BARRIER) AND PLOTS SURROUNDED BY A PLASTIC TRENCH

(TRENCH), A TRENCH Wïi'H DIATOMACEOUS EARTH ADDED (TRENCH + D.E.), AN ALUMINUM FENCE

(FENCE), AND AN ALUMMUM FENCE WWTEFLON TAPE ATïACHED (FENCE TEFLON). CATCHES FOR ALL SPECIES POOLED FOR ENTIRE SEASON (MAY 14 - OCTOBER2). CATCHESFOR LARGE

AND SMALL CARABIDS FROM JUNE25 UNTIL THE END OF THE STUDY. BARS WITH THE SAME

LFTMCR ARE NOT SIONIFICANTLY DIFFERENT, WY'STEST, -0.05...... 40

10. A COMPARISON OF PITFALL TRAP CATCHES ON THE BRUSH AND THE FIELD SIDES OF PLOTS

BETWEEN AN AFTLE ROOTSTOCK NURSERY AND A WINDBREAK. PLOTS WERE EITHER LEFI' OPEN

(CONTROL) OR HAD THREE PARALLEL TRENCHES RUNNINQ THEIR ENTIRE LEN(M.H, BETWEEN

PïïFALL TRAPS ON THE BRUSH AND FIELD SIDES (TREATMENT). ASTERISKS MARK CASES WHERE

TRAP CATCHES ON THE FOREST AND FIELD SIDES ARE SIONIFICANTLY DIFFERENT, TuKEY's TEST,

R0.05. TREATMENTAND CONTROL BARS ON FOREST AND FIELD SIDES WPTH THE SAME CAPiTAL

OR LOWER CASE LETTER, RESPECTIVELY, ARE NOT SIQNlFICANTLY DIFFERENT, T-TEST, F<0.05.48

1 1. COMPARATIVECATCHES OF ARTHROPODS IN THHEE PARALLEL TRENCHES BETWEEN AN APPLE

ROOTSTOCK NURSERY AND A WINDBREAK NEAR LANGLEY,BC. BARS WRHIN A SUBFIGURE WïïH

THE SAME LEITER ARE NOT SIGNIFICANTLY DIFFERENT, TUKEY'STEST, -0.05...... 50

12. ESCAPERATES (APPENDIX 2) FROM EXCLUSION TRENCHES PLACED BETWEEN AN APPLE

ROOTSTOCK NURSERY AND A WINDBREAK NEAR LANQLEY, BC. ESCAPERATES COMBINED FOR

TRAPF'ING SESSIONS ENDINQ MAY15 AND JUNE19. ASTERISKSINDICATE ESCAPE RATES

SIaNXFICANTLY LESS THAN 100%, T-TEST, (R0.05)...... 52

13. CROSSSECTION OF THE TRENCH CURRENTLY USED EXPERIMENTALLY (A), AND THREE PROPOSED

DESIGNS (B-D) ...... 65

14. KEY DISTANCES USED IN THE CALCULATION OF THE SURFACE ANGLE OF A BOWL AT ANY POINT

FROM THE APPARANT DISI'ANCE OF THAT POINT TO THE CENTRE OF A CIRCLE DRAWN ON A

PLEXIGLASLID ABOVE THE BOWL...... 76

15. A MODEL OF INSECT MOVEMENT BETWEEN THREE PARALLEL TRENCHES...... 8 1

16. THE CALCULATED ESCAPE RATE (X) REACHES AN EQUILIBRIUM WITW PASSING TIME (A). THIS

EQUILIBRIUM IS A FUNCTION OF THE ACTUAL ESCAPE RATE (4AND THE ACTUAL MORTALITY RATE

(M) (B).IN FIGURE A, VALUES FOR X AND MARESET ARBITRARILY AT 0.5. THIS EQUILIBRIUM IS 17. PHYSICAL BARRIER COST AS A FUNCTION OF LIFESPAN AND AREA ENCLOSED. ALTHOUGHTOTAL

COST (A) RISES AS THE ENCLOSED AREA INCREASES, COST PER UNIT AREA (B)FALLS...... 87 1.0 Introduction

Weevils (Coleoptera. Curculionidae)which eat plant roots as larvae are

collective1y termed root weevîls. At least six species of root weevil are considered pests

in southem BC: the black vine weevil, Od'orhynchus sulcatus (F.); the strawberry root

weevil, 0. ovatus (L.); the rough strawberry root weevil, 0. mgosfnatus (Goeze);the

clay colored weevil, 0.szSZngu2a~s {L.); the woods weevii, Nemocestes incamptus (Horn); and Barypeifhes peltucidus (Boh.).

1.1.1 Black vine weevil

Considerable economic damage is caused by black vine weevil larvae feeding on plant

roots. 0. sulcatus was identifieci as the most important insect pest problem by the

Fraser Vdey Strawberry Growers Association (1997), and is among the most

important pests iisted by the BC Nursery Trades Association (1997).The biology and

control of this weevil was reviewed by Moorhouse et al. (1992).

Aduits (Fig. 1) are about 10 mm long, and have duIl black elytra marked with

smail, pale yellow spots (Fig. 1).The elytra are fused, and there are no mesothoracic wings, so flight is impossible (Cowles 1995). Larvae are C-shaped, soft, white, legless grubs with pale brown heads (Fig. 1).

Teneral adults emerge Çom pupal cells around June and begin nocturnal feeding on foliage. In daylight they hide at the base of plants under soil, in leaf litter, or beneath loose bark. Of 108 plant species tested, only seven were resistant to black vine weevil feeding (Masaki et al. 1983).The parthenogenetic adults feed for 3-4 weeks before oviposition begins (Fig. 2) (Feytaud 19 18, Philips 1989, Moorhouse et ai. 1992).

Oviposition continues until about October. Adults overwinter in a state of Figure 1. Black vine weevil adult (A), egg (B), lama (C,D), and notching on rhododendron leaves characteristic of aduft feeding (E)(Drawùlg ikom the Center for

Integrated Pest Management, North Carolina State University). Comparative sizes of strawberry root weevil (F), rough strawbemy root weevil (G),and black vine weevil (H)

(Photo from Washington State University Extension Bulletin EB0965, 199 1). temperature-induced quiescence (Cram 1965),and resume activity and ovipostion in

Apd or May (Garth 86 Shanfrs 1978).Adults rarely live 2 years in the field, but can survive >2 years in the laboratoxy (Moorhouse et al. 1992).

Eggs hatch after 8 days at 27°C and 56 days at 9°C (Stenseth 1979). The larva burrows into the soil, begins feeding on heplant roots, and progresses through six or seven instars, consuming ever larger roots, and eventually cotms, rhizomes, and stem bases of some plants (Moorhouse et al. 1992). In one test, larvae fed on all but 13 of 65 test plant species (Masaki et al. 1984). Most black vine weevils overvpinter as late instar larvae, between 2-20 cm beneath the soi1 surface. They are unable to survive prolonged periods <-6"C,but there is little mortality if soil temperatures remain above

2°C (Stenseth 1979). They resume feeding in spring, and pupate in May or June

(Moorhouse et al., 1992). Depending on temperature, pupal development takes 10-50 days (Stenseth 1979).

1.1.2 Strawbeny root weevil, rough strawbeny roof weed, and clay colored weeuil

These Otiorhynchus spp. ali appear to be capable of crop damage.

The strawberry root weevil (Fig. IF) was once considered a primarily agricultural pest, feeding on crops such as strawbeny, cranberry, currant, alfalfa, and clover (Treherne 19 14, Blatchiey & Leng 19 16, Alberta Agriculture 1988) , but is now more commonly recognized as damaging seedlings of conifers, including Abies, Picea,

Thuja and Tsuga spp. (Brandt et al. 1995). It often invades houses in late summer or faii, resulting in cornplaints from home owners (AIberta Agriculture 1988). Figure 2. Black vine weevil iifé cycle, and periods of visible and economic damage in

BC over two years (Cram 1965). Width of life lines indicates approximate abundance.

Open arrows indicate oviposition leading to a new generation.

The rough strawbeny root weevil (Fig. 1G) and clay colored weevils are considered mirior pests in the lower mainland of BC (Tanigoshi, pers. comm.). The rough strawberry root weevil was the most fiequently collected weevil in the faii in

Vancouver (pers. obs.) , and is commonly coiiected in Northern Washington

(Bassagnova, pers. comm.). Both are common in nurseries, nursery poly-houses, and smaii fimit farms (Shetler 1995; Bassagnova, pers. cormn.; Coilaan, pers. comm.).

The life cycles of these weeviis are similar to, but asynchronous with, that of the black vine weevii. Strawberry root weevii adults tend to emerge earlier than black vine weeviis, have a shorter preoviposition feeding period, and do not continue oviposition as late into the fa11 (Gerber et al, 1984). My observations of the rough strawberxy root weevil suggest that adults emerge and enter diapause later than the black vine weevil. Clay colored weevil adults are active in northern Washington state as early as late February or early March (Coiiman, pers. comm.) and can no longer be found by mid August (Bassagnova, pers. comm.). Peak oviposition usuaiiy occurs in

May so that insecticides applied to control clay colored weevils must be applied in early spring, at a time of regular rainfd (Tanigoshi, pers. comm.). Because most clay coloured weeviis can survive local winters, lifespans of 2-3 years are common

(Tanigoshi, pers. comm.).

1.1.3 Woods weevil

Collman (pers. corn.) suggests that the woods weevii is an important pest of woody ornamentals in Pacific Northwest nurseries. Adults emerge in mid August, and continue feeding and ovipositing through the whter and into the early summer, when one would not normaiiy look for active weeviis. 1.1.4 Baqpeithes pellucidus

This tiny weevil (ca 3 mm) was reported only on strawbemy untiî Galford ( 1986) noted it as a major cause of mortality in a red O&, Gercus mbra (L.), plantation in Ohio.

Subsequentiy it was found to feed on at least 18 other species, with heavy feeding on

Aster divaricatus (L.) and A. lowrieanus (Porter.), and American eh, üïrnus ~rne~cuna

(L.) (Gaiford 1987). It was recently reported as a nuisance pest in lakeshore cottages 21

Minnesota and Montana (Baisbaugh 1988). In a Colorado blue spruce, A'cea pungens

(Engelm.),plantation in Ontario, 56% of the weevil larvae feeding on the roots were B. pellucidus (Brandt et al 1996). Despite several clairns that B. pelluadus was imported from Europe (Blatchley & Leng 19 16, Lindroth 1957, O'Brian 86 Wibmer 1982), fossils fkom lake sediments deposited 9,000 to 11,000 years ago in southwestern Ontario confïrm its prehistoric existence in North America (Schwert et al. 1985).

In Ohio, adults began to appear in April, populations peaked in May, and addts disappeared by June (Galford 1987).

1.1.5Increasing impact

Root weevil damage is an increasing problem, probably due to the loss of effective insecticides because of environmental concerns and insect resistance, disruption of the balance between weevils and their natural enemies, changing grower practices, and increasing production of susceptible crops (Masaki et al. 1984, Moorhouse et al.

1992).

A single aldrin treatment on a strawbeny field could k3.l ali black vine weevil larvae, and increase yield by 270% (Cram & Andison 1959). Both aldrin and heptachlor effectively controlied larvae 5 years after application (Breakey 1959). Even if these insecticides had not been banned, they might have become less effective; populations resistant to diel& were reported in Ohio by 1975 (Nielson et ai. 1975). The natural enemies of root weevils include carabid and staphylinid beetles, which are very sensitive to many insecticides (Kirk 1971), and are less abundant in the

homogeneous fields associated with conventional agriculture than in organic

agroecosystems (Kromp 1989). Other natural enemies include birds, reptiles and

amphibians, and entomogenous fungi (Feytaud 19 18; Moorhouse et al. 1992), aii of which might be discouraged by current ag;ricultural practices. Peat-based potting mixes and black polythene mulches have ais0 been blamed for msiking the

environment more amenable to root weevils (Moorhouse et al. 1992).

In BC, crops susceptible to root weevils (e.g. bemes, nursery crops, and flowers) are becoming more common (Statistics Canada 1992, BCMAFF 1995%

BCMAFF 1995b).The area planted to grapes and berries in British Columbia almost doubled between 1971 and 199 1 (Statistics Canada 1992).The area in nursery production more than tripled between 1988 and 1994 (Fig.3). The British Columbia floriculture industry has grown rapidly since the 1%'Os, and continues to expand at a rate of about 5% per year (BCMAFF 1995b).

1.1.6 Control Options

Since the advent of organochlorine insecticides in the 1940s, growers have reiied primarily on chemical controls for root weevils (Moorhouse et al. 1992).The loss of some chernicals has prompted a search for new, efficacious means of control.

Feytaud ( 19 18) documented the destruction of black vine weevils by a diverse array of organisms, including hedgehogs, moles, shrews, chickens, lizards, toads, fkogs, carabid beetles, and fungi. A few other biological controls have since been noted, includllig spiders and mites (Wilcox et al. l934), nematodes (Gaugler & Kaya IWO), and bacteria (Marchai 1977). Entomogenous nematodes are now commerciaiiy available for root weevil control (Daar et ai. 1994).Current research is focusing on improving the efficacy of nematodes (Webster,pers. comm), and adapting the Figure 3. Recent growth in the area growhg nursery crops in British Columbia

(BCMAFF, 199Sa). entomogenous fungus, Beauvana bassiana (Bais.)to commercial production

(Moorhouse et al. 1990).

Some workers are attempting to change farming practices to promote carabid abundance (AUan 1979, Kromp 1989, Raworth, pers. comm.). Other cultural control practices aim to minimize the importation of root weevii infested stock, and to plant clean crops far enough away from infested crops to prevent infestation (Moorehouse et al. 1992). Flooding can be used in local cranbeny bogs to drown root weevils (Hayes

1994). A third, but generdy ignored, option is to develop physical control strategies and tactics.

1.1.7 Examples of p hysicaî controls

There are two broad strategies implicit in physical controls: to "prevent pests fiom reaching [theix hosts] or remove them if they do" (Bradley & Ellis, 1992). Physical controls are so common, and have been used for so long, that they often go wnnoticed.

Animals build houses, dens, nests and burrows not just to protect themselves from the elements, but also to bar the entrance of predators. Humans design houses to do these jobs while also preventing the entry of some parasites, such as mosquitoes or blackflies, through the use of screens. Greenhouses offer similar advantages to plants by both modifying the environment so that it is not conducive to pest problems

(cultural control) and excluding many pests f?om entering at aU (physical control). The physical control potential of greenhouses is attracting increasing attention, as more pests develop resistance to pesticides (Bethke & Paine, 199 1).

A less expensive option than houses and greenhouses is the protection of outdoor crops with screens or row covers. This tactic was widely used around 1900, when growers protected vegetable crops with cheesecloth on frames (Matthews-

Gehringer 86 Hough-Goldstein 1988). It is again being recommended for vegetable crops, employing spunbonded polyester and polypropylene fabrics for row covers (Miliar 8s Isman 1988, BCMAFF 1993). Many fhit growers cover individual trees, or even entire plantations, with plastic netting to protect theh crops fiom bird damage

(BCMAFF 1996a).

Fences can effectively exclude pests which stay on or near the ground. Woven wire fences are recommended as "the most reliable protection from deer damage"

(BCMAFF, l996b). Some gardeners use strips of copper (Bradley & Ellis 1992), or salt- impregnated plastic, to bar slugs from their plots. Mesh fences have been used experimentally to reduce the movement of adult cabbage maggots, Delia radicum (L.), and several species of plant bug (Hemiptera: Miridae), both of which fly close to the ground (Wipfli et al. 1991, Vernon 86 MacKenzie 1998). Plastic trenches surrounding fields have prevented a signincant proportion of Colorado potato beetles, Leptinotarsa decemh'neata (Say.), from entering experimental plots of potatoes (Boiteau et ai. 19941, leading to the development of an extruded plastic trap designed to catch and kill any

Colorado potato beetles attempting to wa& into a field (Vernon & Hunt patent

#08/616,627).

Some physical controls are designed to protect individual plants. For example, sticky bands wrapped around the trunks of valuable urban trees can protect their crowns fkom crawling lepidopteran larvae (Collman 1990). Cardboard tubes are placed around transplants to protect them ikom cutwonn damage (Bradley 86 Ellis, 1992).

Taxpaper discs can be used at the base of cmciferous plants to discourage cabbage fly oviposition (Finch 1993).

Traps are also a type of physical control, whether they lure pests to their death, as with light or pheromone traps, or simply catch pests unfortunate enough to pass by, as with fly strips or pitfaZ1 traps.

A small proportion of physical controls do not target pest movement, but exploit the strategy of actively removing pests from contact with their hosts. These active physical control tactics include hand picking of highly visible lepidopteran larvae or slugs (Stylommatophora: Limacidae); vacuuming of whitefiies, leafhoppers and aphids

in vegetable crops (Weintraub et ai. 1996) and greenhouses (Bradley & Ellis, 1992);

and water sprays, which injure aphids or knock them off their host plants (Bradley &

Ellis, 1992).

Passive physical controls interfere with a pest life cycle by impeding the movement necessary to complete that life cycle, e.g.:

pests such as the cabbage maggot, which feeds on roots as a lama and on

nectar as an adult;

@ pests such as the Colorado potato beetle, which ovenvinters in wooded areas

and must kdsolanaceous crops in the spring;

pests such as root weevils, which feed on plant foliage at night but hide in soi1

and leaf litter during the day; and

pests such as the carrot rust fly, Psila rosae (F.), which has a single host and no

extended dormancy, and thus must move to a new canot field after harvest.

1.1.8 Potential for root weevil management using physicul control

Hand-picking of root weevils was occasionaily attempted to reduce root weevil populations around 1900 (Feytaud 1918). Even today, some local raspberry growers, instruct their workers to destroy any weevils knocked off canes by harvesting equipment. Experimental sticky bands on shrubs have reduced adult feeding on leaves

(Antoneu 86 Campbell 1981), and aluminum fences with a strip of grease near the upper edge have reduced root weevil invasion of nursery plots (Cowles 1995).

The inability of root weevils to fly makes them particularly susceptible to the strategy of preventing them f?om reaching their hosts. This led Cowles (1995) to praise unclimbable barriers as "probably the most underutilized, most common-sense tool to combat root weevils." Others dismissed the strategy as 'unonginal and simplistic" (Anon.,pers. comm.), or 'academic hoky-ne& (Peters, pers. comm.). In replicated trials in 1993, most black vine weevils were incapable of climbing over aluminum bamers, with a 5-8 cm wide strip of white lithium grease dong the upper edge, which had been exposed to regular irrigation under field conditions for up to four weeks (Cowles, pers. comm.). Occasional instances in which weevils climbed over these barriers were attributed to soi1 or vegetation 'bridges" over the unclimbable lubricant (Cowles, pers. comm.). Simiîar bamiers, constnicted of polythene without a grease strip, substantially reduced carabid abundance inside enclosures (Wolopainen

& Varis, 1986).

Field trials in 1995 and 1996 showed that extruded plastic trenches (Vernon &

Hunt, patent # 08/616,627) excluded a signüïcant proportion of Colorado potato beetles fkom plots of potatoes, resulting in damage reductions (Vernon, pers. comm, pers. obs.). The trenches incorporated a curved lip to xeduce beetle escape, and were most effective when coated with a thin layer of ~IYdust (Boiteau et al. 1994, Vernon, pers. comm., pers. obs.). A commerciaily available Tefion-coated aluminum tape (EnviroSafe Teflon Crawling Insect Barrier, Professional Ecological Services, 98-B

Burnside Rd. W., Victoria, BC, V9A 1B5) claims to create a surface which crawling insects cannot climb.

1.2 Objectives

My objectives were to assess the potentiai of physical bamiers for root weevil exclusion under field conditions, specitlcaiiy to:

1. determine the angle at which abhesive (no-stick) surfaces become unclimbable to

root weevils;

2. determine the effectiveness of trenches and alum.inum fences in preventing

weevir movement into smdplots;

3. determine whether Teflon tape added to aluminum baniers or diatomaceous

earth added to trenches could increase bamer effectiveness; 4. determine weevil escape rate fkom trenches;

5. assess the effect of trenches and aluminum fences on non-target organisms, such

as predaceous carabid beetles;

6. evaluate the ability of these physical controls to withstand field conditions; and

7. develop hypotheses to explain any weevil successes in evading or defeating

barriers. 2.0 Materials and Methods

2.1 Effect of powder and Juun on weevil ch'mbing ability

Black vine weevii and rough strawberxy xoot weevil adults were coîlected after dark

Çom foliage and buildings in a private garden in Vancouver. Weevils of each species were held at 20°C and 16L:8D photoregime in two Plexiglas cages, each with two potted strawberry plants, w-atered every 2-3 days, as a food source.

A semi-spherical wax bowl was constructed by dipping a plastic ball, 2 14 mm diam., half wyinto a container of molten paxaffin, aiiowing the wax to harden, and then removing the bail. The lowest point on the bowl was marked. At the beginning of each test, a root weevii was placed in the bowl, which was thsn covered with a

Plexiglas lid marked with a 2 14 mm diam. circle exactly fitting the outer edges of the wax bowl, and with the centre of the circle and the low point mark on the bowl verticaiiy aligned. The distance from the Plexiglas to the observer's eye was measured, and held constant over the centre point. The weevil's path was foilowed by tracing a line on the Plexiglas, keeping the nib of the pen above the weevil's thorax. Any point at which the weevil slipped backwards while tr-ying to climb was marked on the Plexiglas.

The distance Çom the centre of the circle to each marked point was measured. The angle of the wax surface at the point of slippage was calculated using an equation derived fiom magoras' theorem (Hardy 86 Wright, 1995) (Appendix 1).

Three surfaces were tested: the bare wax bowl, the bowl coated with powdered talc, and the bowl coated with fluon. A fine, even coat was achieved by Suirling the surface coatings in the bowl to cover aii surfaces, then inverting the bowl to drain any excess material. Each replicate weevil was foilowed for approximately 0.5 h, and the mea.angle attained before slipping on al1 attempts to climb was calculated. The control and fluon treatments were replicated 9 and 4 times, respectively for each species. The taîc treatment was replicated 7 times for black vine weevils and 14 times for rough strawbeny root weevils.

Data were analyzed using a GLM mode1 dapted for unequal numbers of replicates, and means were separated ushgTukey's test (SAS Institute 1988).A mUiimum significance level of a=O.OS was maintained throughout al1 trials.

2.2 Test of physical barnmerssurrounding srnail plots of rhododendrons and azaleas

A commercial container nursery with a history of root weevil problems was selected in

Pitt Meadows, BC. A 100 m2 triangular section was cleared of plants, leaving only black woven landscape fabric on top of cedar chips. Fifteen square plots (1x 1 m, 1 m apart) were staked out. The landscape fabric was removed f?om a 15 cm border around each plot, leaving exposed cedar chips.

Plots were assigned to one of three treatments in a completely randomized layout. Five control plots were unaltered (Fig. 4). Five plots were surrounded by a black plastic exclusion trench, dug approximately 3 cm into the cedar chips on the outside, but sitting on top of the landscape fabric on the inside (Fig. 4). A fine coating of diatomaceous earth was deposited on the inside of ali trench components before instaliation. A final five plots were surrounded by a 30 cm wide piece of aluminum fîashing (fence),dug 10 cm into the ground. Teflon-coated alumirium tape (EnviroSafe tape, Professional Ecological Services Ltd., Victoria, BC) was fastened to the outside of the aluminum flashing, near the upper edge. The landscape fabnc inside the fenced plots was ikdy secured between the fence base and the cedar chips (Fig. 4). Figure 4. Control (A), fenced (B) and trenched (C) plots of rhododendrons and azaleas at an ornamental nursery.

On April 17, 1997,23 plastic plant pots (20 cm diam.), fiiîed with the pottulg

mix used at the nursery, were amanged touching one another according to commercial

practice, with a trap board (30 x 30 cm) placed on the empty centre space of each plot

(Fig. 4). Pitfall traps were placed in the four corner pots, fiush with the soi1 surface.

The remaining pots were planted with rhododendron (var. Chikor) (10 pots per plot)

and azalea (var. Blue Danube) (9 pots per plot) which had been root washed to remove

aii weevil larvae. AU plants were watered daily by overhead sprinkler, accordhg to the

normal nursery regime.

AU pitfd trap contents were transferred to vials, then fiozen, on April24 and

30, and on May 7. On May 7 the pots in the southeast and northwest corners of each

plot were replaced with pitfd traps installed flush with the landscape fabric. Traps

were again checked and emptied on May 15 and 23, June 7 and 25, July 10, and

August 22. The experiment was terminated on August 22 and the largest and smallest

rhododendron and azalea fkom each plot (4 plants) were removed and the soii and

roots checked for root weevil lantae or damage.

Captured root weevils were identified to species. No analysis of weevil catches

was done because only two root weevils were caught in this experiment. Carabid

beetles were identifïed to genus, and any other captured insects to order. Carabid

beetle catches from July 10-Au~ust22 were pooled, transformed by square root (X +

0.5) to correct for heterogeneity of variance (Zar 1984), and subjected to ANOVA and

Tukey test (a=O.OS) (SAS Institute 1988).Trapping sessions before July 10 were not

included in the andysis due to very low carabid catches.

2.3 Physical banfers surrounding smdl plots of strawbemks

The undergrowth was removed nom five 22 x 5 m strips in a windbreak consisting of two rows of mature conif'er trees between a raspberry farm and a kiwi fitplantation in Abbotsford, BC. The end of each strip was 2 10 m fkom the start of the next strip. Five plots (1x 2 m) were staked out in each strip, so that plots were 2 m apart and the fïrst and last plots were 2 rn from the ends of the strip. A trench (2 x 0.2 x 0.2 m) was dug down the centre of each plot. A piece of black woven landscape fabric was used to cover each plot, including the sides and bottom of each trench. Trenches were nIled with a commercial potting soil mix, and 10 strawberry plants, fkee of root weevil larvae, were planted in each trench. Four pitfall traps were evenly spaced dong the centre of each trench, flush with the soi1 surface.

Plots within each stxip were randody assigned to one of five treatments, using a randomized complete block design. Control plots were left unprotected. Black plastic exclusion trenches were erected around plots for the second and third treatments, with the inner edge on top of the landscape fabric and the outer edge buried in soil outside of the area covered by landscape fabric. The inside of one exclusion trench was coated with a fine layer of diatomaceous earth, and the other was left bare. The fourth and fifth (fenced) plots were smounded by a 30 cm wide strip of alumirium flashing, dug 10 cm into the soi1 swrface. The edge of the landscape fabric was tucked between the soil and the alumirium to prevent any hsects emerging beneath the fabric from entering the enclosure. Teflon-coated aluminum tape (EnviroSafe tape, Professional

Ecologicai Services Ltd., Victoria, BC) was attached to the outside of the top outer edge of the first aluminum fence; the second was left bare.

Aluminum fence setup took ca 10 min per m, mostly digging the trench to bury the bottom section. Addition of Teflon tape took another 1.5 min per m. Exclusion trench setup took ca 2.5 min per m, or 3 min per m if diatomaceous earth was added.

Trapping began on May 6, and traps were checked on May 14, and 27, June 5,

12, and 25, and July 18, and September 5 and 17. Very few weeviis were captured in

August. Most traps were destroyed by animais before a ka1trap check on October 2.

Ali weevils caught were identined to species and counted. Ail ground beetles caught on or before June 25 were counted. Tbereafter they were identiەed as Amarini, Bembidini, Notiophilus directus., Pterostichini, Trechus spp. or other spp., before

enumeration, and divided into groups of beetles larger, or smaller, than 1 cm. On June

12 and September 17, the notches on ali leaves were counted. Plant survival was noted at these dates and on October 10, when all plants were removed, and the ro~ts

checked for root weevil lmae and darnage. Roots were excised, and the roots and shoots weighed.

Trap counts were transforrned by square root (X + 0.5) to correct for heterogeneity of variance (Zar 1984) and subjected to a three-way ANOVA, using the

GLM procedure (SAS Institute 1988) to test for effects of treatment, repücate and trapping session. A two-way ANOVA was used to test for effects of treatment and replicate on plant mass, survival, and leaf notching. Means were compared using

Tukey's honestly significant ciifference test (a=0.05)(SAS Institute 1988).

2.4 Escape fiom paraIlel trenches

A bare soil roadway in Langley, BC, running north-south between an apple rootstock nursery and a strip of mixed brush, was divided into 5 strips 18 m long and 1 m wide, separated end to end by 24 m. Two plots, 8 x 1 m, separated by 2 m, were staked out in each sep. Pitfall traps were inserted flush with the soil surface on each edge of each plot, 2 m fkom either end (4 per plot).

Plots in each strip were randody assigned as bare controls or treatment plots with one plastic exclusion trench dug ca 3 cm into the soil ninnlng the entire mid-line of the plot, and two other trenches dug in 15 cm to either side of the centre trench.

The inside of each trench was dusted with diatomaceous earth. A strip of aluminum flashing (1 m x 5 cm) was dug into the soil to block the trench ends.

Trapping began on April22, 1997. On April29, and May 7 and 15, ksects were removed frorn traps, and swept fkom trenches ushg a toilet cleaning brush

(Rubbermaid),bent to fU the width of the trench. Insects were swept fiom the midpoint of the trenches into a specially constructed altiminum collecthg device at each end. Collected insects were preserved by fkeezing.

A backpack sprayer was used to apply herbicide (Roundup, 1.0% ai.

Glyphosate) to the experimental site on May 8 to suppress plant growth which might have provided a bridge across the trenches. Cardboard strips coated with Stiky Stuff

(Olson Products, Medina, OH) were placed between the aluminum end pieces and the trenches on June 9, and secured using elastic bands attached to screws in the trench materiai. Traps and trenches were emptied again on June 19, and cardboard strips replaced.

AU curculicnids, carabids, elaterids, and isopods collected on May 15 and June

19 were counted. All root weevils were identified to species. Catches in pitfail traps nearest ,the windbreali and nearest the field in treatment and control strips were transformed by square root (X + 0.5) to correct for heterogeneity of variance (Zar 1984), and compared by t-tests (u=0.05)(SAS Institute 1988). Trench catches were analyzed by ANOVA and Tukey's honestly significant difference test (SAS Institute 1988). Pitfdi trap catches in control and treatment plots were compared by t-test (a=0.05).Escape rates were calculated using the equation derived in Appendix 2, and a t-test (a=0.05) was used to determine whether escape rates were less than 100%. Correlation coefficients were calculated for the relationship between catches in pitfdl traps and trenches (SAS Institute 1988).

2.5 BZack vine weevil containment in small enclosures

Three squaxe enclosures were built using 7.5 cm aluJPinum gutter (Revy Home

Hardware, Vancouver, BC). Segments of straight gutter 1 m long were joined by corner pieces to make squares meashg lx 1 m on the inner edge. Seams were sealed water-tight with hot glue. The squares were sunk into the soi1 in an open field at the University of British

Columbia, in Vancouver, BC, so that the soil swface was even with the upper lip. The

soii inside each enclosure was covered with a landscape fabric square folded into the

gutter and attached with screws so that the edge of the fabric extended haif way down

the inner waii of the gutter. One iitre of 1: 1 \~ater:dorrnantoii emulsion was poured

into each gutter.

Three treatments were randoniiy assigned. The control enclosure had a 10 cm

strip of aluminum flashing placed dong the inner wall of the gutter, covering the

margin of the landscape fabric and screws, and secured to the landscape fabric by a

contuluous strip of duct tape (Fig. 5). The second enclosure had a 30 cm strip of

aluminum flashing with Teflon tape attached to the upper inner edge (Fig. 5).The third

enclosure had a sealed plastic trench perimetex, containing 11 of 1: 1 water:dormant oii

emulsion. Aluminum flashing was screwed to the trench Çom below, and a second

layer of landscape fabric was attached to the inside of the trench square with screws,

and the seams were seded with duct tape (Fig. 5).

In late July and August, 1997, adult black vine weevils hiding beneath smd

trees in an apple rootstock nursery in Langley, BC, were collected during dayiight

hours. Weevils were housed at room temperature and naturd photoregime in a

covered plastic container (Rubberrnaid)with apple or blackberry leaves, replaced weekly, as a food source.

The experiment was replicated three times on August 13, 18, and 20. During each replication, 20 black vine weevil adults, individuaiiy marked with iiquid paper, were released in the centre of each enclosure at 2 130 h PDT. Their location was recorded at 5 min. intervals for 20 min., and at 10 min. intervals for the next 40 min.

Their ha1location, and the number of survivors, was recorded the foliowing morning at 1000 h. Figure 5. Cross section of an edge of the control enclosure with perimeter gutter containing dormant oil emulsion to trap departing weevils (A), and treatment enclosures testing whether a fence (B) or a plastic trench containing a dormant oit emulsion (C) will prevent departing weeviis from reaching the gutter. Key: - PVC Plastic - Alum inum ~crew ...... 1.1. Landscape Fabric Soil

Teflon Tape **+é Duct Tape 2.6 Effed of condensation on black vine weeoil escapes

Forty black plastic nIm canisters were washed, dried, and divided kt0 four groups of

10. Ten canisters were left clean (control canisters); 10 were fUed with powdered talc, then shaken empty, leaving a film of talc on the inside; 10 were filied with iiquid fluon, then emptied and air dried, leaving a coating of dry fiuon inside; and 10 had a layer of white lithium grease spread on the top 2 cm of the inner surface.

The next day five canisters fkom each group were fïiied with water, then emptied, leaving water droplets inside. These were placed in a seaied plastic container, with an open source of warm (ca 80°C)water to provide hurnidity. The dry canisters were placed in an identical container, left open to ailow air circulation, with no water source. The canister order was randomized within each plastic container.

Two adult black vine weevils, çom among those collected in Langley for the previous experiment, were placed on the bottom of each canister. Every 0.5 h, for 3.5 h, the number of weevils remaining in the canisters was recorded, and escapees were removed from the containers. During this procedure the sealed container was opened for ca 2 min. For each canister treatment, the numbers of escaped weevils in open and seaied containers at the end of 3.5 h were compared by t-test (a=0.05). 3.0 Results

3.1 Effect of powder and mon on weed ch'mbing abiiity

Both black vine weevils and rough strawbeny root weevils were able to climb significantly steeper angles on a clean wax suface than on a wax surface coated with nuon or talc (Fig. 6). The mean angles attained on fluon and talc were not sigdicantly different. Black vine weevils were able to climb signincantly steeper angles than rough strawberry root weevils (P20.73, R0.000 1).

For black vine weevils and rough strawberry root weevils, respectively, 75 and

28% of attempts to escape on clean wax were successful (Table 1). No successful escapes by either species were observed when the bowl was coated with talc, but one black vine weevil escaped kom the fluon-coated bowl (Table 1).

3.2 Physical bam'ers surrounding small plots of rhododendrons and azaleas

Black vine weevils were observed on rhododendrons within 20 m of the experimental site during June and Juiy, however none were caught in the experiment, no leaf notching or weevils were observed on any experimental plants, and no weevils or damage were found on the roots of 60 plants examined at the end of the experiment.

Catches of carabid beetles were also low during most collection periods. Of the

6 1 carabids caught from July 10 to August 22, 39 were Amara spp., 12 were

Pterostichus spp., 7 were Omus spp. and 3 were not idenaed. AU but two were caught in the pitfdl traps at ground level rather than in the elevated pots. When catches were pooled, sigdicantly more carabids wexe caught in the control plots than in the plats surrounded by trenches, which in turn had signincantly more beetles caught than in plots swrounded by fences (Table 2). This trend was reflected in catches of Pterostichus spp. and Amam spp., but not Ornus spp. Catches were evenly divided between the Figure 6. Mean angie achieved before slipping by black vine weevil and rough strawberry root weevil adults on bare wax, or wax covered by âry fiuon, or powdered talc. For each species, bars with the same letter are not significantly different, Tukey's test, P<0.05. Rough strawberry Black vine root weevil weevil

Clean Wax+ Wax+ Clean Wax+ Wax+ wax fluon talc wax fluon talc n=9 n=4 n=14 n=9 n=4 n=7 Table 1. Evaluation of attempts to escape by black vine weevils and rough stsawberry root weevils, from a clean wax bowl, a wax bowl coated with fluon, and a wax bowl coated with powdered taic.

Black vine weevil Rough strawberry root weevil

No. Y0 No. Oh Treatment No. tested escape successfÛl No. tested escape successful attempts attempts Clean wax 9 32 75 9 29 28 Fluon 4 18 6 4 21 O Talc Table 2. Carabid catches at a nursery near Pitt Meadows, BC, July 10 through August

22, 1997.

Number of beeties per plot (2f S.E.) AU species Treatment Amara spp. Pterostichus spp. Omus spp. pooled Control 6.4 f 1.5 a 1.8 i 0.4 a 1.2 f 0.6 a 9.4 I 1.0 a Trench 1.2 i 0.5 bc 0.6 f 0.3 bc 0.2 f 0.2 a 2.0 f 0.5 b Fence 0.2 f 0.2 c 0.0 f 0.0 c 0.0 f 0.0 a 0.2 f 0.2 c a Means within a col- followed by the same letter are not significantly different, Tukey's test, R0.05. north-west and south-east corners of the plots. No beetles were caught under the trap

boards.

By the end of the experiment the alumGium fences were in excellent condition,

and the Teflon tape remained secure and clean. The trenches were also in good

condition, except for some openings at the seams in the corner connector pieces, and

between the corner pieces and the main trench pieces. No spaces had opened up

beneath any baniers to dowinsect passage. Both the a1-m fences and the

plastic trenches were clean and fkee fkom caked mud.

3.3 Test of physicd barnoerssurounding small plots of strawbern'es

3.3.1 Weevil catches

Of the 864 root weevils caught, 43% were B. pellucidus, 43% were woods weevils, N.

inmmptus, 10% were obscure root weevils, Sciopithes obsnrms Horn., and 3% were

other species, including the strawbeny root weevil, 0. ovatus, the rough strawbemy

root weevil, 0. rugostriatus, and the clay coloured weevil, 0. singularis. Barypeithes

pellucidus and woods weevils were dominant until late July, and other species were

more prevalent in September (Fig.7).

Treatment, replicate, and trapping session d had significant (P < 0.000 1)

effects on total root weevil catches. Catches of al1 species cornbined were significantly

lower in plots surrounded by trenches (with or without diatomaceous earth) and by

aluminum fences with Teflon than in control plots (Fig. 8). Aliiminum fences without

Teflon did not exclude enough weevils to signincantly reduce catches compared to

control plots. Diatomaceous earth did not improve trapping efficacy of the plastic

trenches. Figure 7. Seasonal trend of weevil catches in a windbreak near Abbotsford, BC. Woods weevil

I Barypeithes pe//ucidus

Other spp.

Collection Date Figure 8. Pitfall trap catches of weevils, in a windbreak near Abbotsford, BC, in unprotected control plots (no banier), and plots surrounded by an aluminum fence

(fence);an alumirium fence with Tefion tape attached (fence + Teflon); a plastic trench

(trench);and a trench with diatomaceous earth added (trench + d.e.). Bars within sub- figure with the same letter are not signincantiy diaerent, Tukey's test, R0.05. 1.2 Al1 Species a Woods weevil Pooled T

d 0.08 - Barypeithes a Other spp. T pellucidus 0.07 -- a T

Control Fence Trench + Trench Fence + Control Fence Trench + french Fence + d.e Teflon d.e Teflon Similar trends were apparent for woods weevils and B. pellucidus, with trenches

and the aluminum fence with Teflon exhibithg a general superionty over other types

of barriers (Fig. 8). No treatment effect was observed for other weevil species. Fewer weevils were caught in the two southernmost replicates than in the remainder of the

experiment site.

3.3.2 Ground beetle catches

Of the 865 ground beeties caught over the course of the season, 70% belonged to the

Pterostichini subfamily, the most common species being Pterostichus melanarius

(Iiiiger). Representatives of the subfamilies Amarini and Bembidini each comprised

2% of the catch, Notiophilus directus (Casey) and hechus obtusus (Erichson) respectively comprised 3% and 9% of the catch, and 13% of the carabids were not identiîïed.

There were si@cant effects on catches by treatment and trapping date

(R0.0001) and replicate (P0.04). Catches increased to a peak on September 5, before decluling slightly in the final two collections. The order of trapping efficacy for carabids

(Fig. 9) was very different from that for weevils (Fig.8). Pitfall traps in the control plots caught more total carabids than traps in plots surrounded by fences or trenches with diatomaceous earth added (Fig. 9). Traps in plots protected by aluminum fences caught the fewest carabids, but the addition of Teflon to the fences had no signüicant effect.

Catches of large carabids (Amara spp., Carabus nemoralus, and Rerostichus

(Poecilis) spp.) Çom June 2 5 onwards (Fig. 9),were very similar to those for al1 species pooled, except that catches in plots surrounded by fences were strikingly low. Catches of smail carabids (Bembidion spp., Notiophilus diredus., Trechus spp.) were signif5cantly lower than the controls only in plots surrounded by trenches with or without diatomaceous earth (Fig. 9). Figure 9. Pitfall trap catches of carabid beettes in a windbreak near Abbotsford, BC in unprotected control plots (no b&er) and plots surrounded by a plastic trench

(trench), a trench with diatomaceous earth added (trench + d.e.), an alurninum fence

(fence), and an alumirium fence with Teflon tape attached (fence + Tcflon). Catches for ail species pooled for entire season (May 14 - October 2). Catches for large and smail carabids from June 25 until the end of the study. Bars with the same letter are not significantly different, Tukey 's test, R0.Os. All species pooled

Large species 2 1 .O cm long

Small species < 1 .O cm long

Control Trench Trench + Fence + Fenœ d.e. Teflon

Table 3. Leaf notching and survival of strawberry plants in five unprotected plots and

five plots each surrounded by alumirium fences with or without Teflon tape, or plastic

trenches with or without diatomaceous earth.

Natches per lcaf, n-5 (2 f s.E.)~ Surviving phts, n-5 6 I s.E.)~

Treatment June 12 Sept. 17 June 12 Sept. 17 Oct. 10

Control 1.6f 0.4 a 1.1 f 0.2 a 9.6 f 0.2 a 4.8f 1.0a 4.0f 1.0 a

Fence 0.8fO.labc 1.3fO.la 9.6f0.2a 8.0I0.8ab 7.4fl.lb

Trench + d.e. 1.0 f 0.2 ab 1.2 f 0.2 a 9.6 * 0.2 a 8.4 f 0.4 b 8.2 f 0.6 b Trench 0.6fO.lbc 0.9fO.la 9.8f0.2a 9.0kO.Ob 8.6I0.4b

Fence + Teflon 0.1f0.0~ 1.4I0.3a 10.0fO.Oa 9.2f0.8b 9.2f0.8b aMeans within a column followed by the same letter are not significantly different,

Tukey's test, -0.05. Table 4. Indicators (? f S.E., n=5) of strawberry plant growth in five unprotected plots and five plots each swounded by aluminum fences with and without Teflon tape, and plastic trenches with and without diatomaceous earth. Ten seedlings per plot planted on May 2.

~ootmass Total plant 1shoot Plant mass per

Treatment June 12 Sept 17 Oct 10 Oct 10 Oct 10

Control 6.8 f 1.5a 10.1 f 1.5a 1.9 f 0.3a 10.1 f 1.2a 42.8 f l2.2a

Fence 7.8 f 0.4a 12.5 f 1.4a 1.4 f O.lab 11.6 f l.6a 91.4 f 23.4ab

Trench + d.e. 8.1f0.5a 12.2f 1.3a 1.3fO.lab 10.4f 1.2a 87.6f 13.4ab

Trench 7.6 f 0.4a 13.3 f 1.4a 1.4 f O.lab 9.7 f 1.la 84.0 f 11.3ab

Fence + Teflon 8.2 f 0.4a 14.4 f 1.2a 1.0 f O.1b 14.3 f 1.6a 130.2 f 17.0b aMeans within a column followed by the same letter are not signincantly different,

Tukey's test, R0.05. corner pieces over the season. Gaps also appeared between the outer trench pieces

and the trench inserts. The single riveted corner on ail the fenced enclosures remained

tight enough to prevent any insect passage. Over the season the dumUium fences

became increasingly muddy, due to rain splash. The problem was worst near the base,

but some soii accumulated on the upper sections of the fences, even on the Teflon

tape. The inner face of the fences rernained clean because the landscape fabric inside

the plots prevented splashing.

3.4 Escape rate fiom parailel trenches

A total of 6,575 beetles and 5,150 isopods were collected in two trapping sessions at

the Langley site (Table 5). Curculionids, carabids, elaterids and staphylinids made up

80%, 1796, 2% and 196, respectively. Most (>70%)arthropods were caught in pitfall

traps. The carabid Trechus obtusus was an exception to this rule, as were ail

curculionids except Barypeithes pellucidus. More than hice as many arthropods were

coîiected on June 25 as on May 15, largely due to the higher isopod and B. pellucidus

catch in the second session.

3.4.1 Pîtjàll trap catches

Generaiiy, more arthropods were caught in pitfall traps closest to the brush than the

field, whether or not trenches were positioned between the traps (Fig. 10). Most of this

trend was accounted for by carabids in the subfamily Bembidini, and by isopods.

These differences were significant regardless of whether trenches were positioned between the brush and field pitfall traps.

Although there was no ciifference in total catches of B. pellucidus between the bru& and field sides of the plots, signlnlcantly more B. pellucidus were captured on the brush side of treatment plots (199.0 f 21.7 vs. 63.8 f 24.6) (t=6.01, P =O.OOgS) on June

19, when 9 1% of the individuals of this species were captured. Table 5. Total catches of beetles and isopods in pitfall traps and trenches for two trapping sessions at an apple rootstock nursery in Langiey, BC.

% Capture by trapping device % Caphue by date Total Pitfd Taxonomie category catch traps Trenches May 15 June 25 Coleoptera Curcuiionidae Bqpeithes pellucidus Siruphosorna rnellanograrnmzim Otiorhynchus sulcatus Trachyphoeus bifo veolahts Other Curcuiionidae Carabidae Bembidini Notiophilus directus nechus obtusus Pterostichini Amarini Unidentined carabids Elateridae Staphylinidae Isopods Total 11725 72.0 28.0 3 1.2 68.8 Figure 10. A cornparison of pitfall trap catches on the windbrealc (black bar) and the field (white bar) sides of plots between an apple rootstock nursery and a windbreak.

Plots were either left open (control)or had three parallel trenches running their entire length, between pitfall traps on the brush and field sides (treatment). Asterisks mark cases where trap catches on the windbreak and field sides are signincantly different,

Tukey's test, -0.05. Treatment and control bars on windbreak and field sides with the same capital or lower case letter, respectively, are not significantly different, t-te st,

RO.05. Total Carabids A Bembidini (Carabidae; -- a -- T

Staphylinids

lsopods Elaterids

A

Control Treatment Control Treatment 3.4.2 lYench catches

Of the 3279 arthropods coliected fiom the trenches, 7 1% were B. pellucidus (Table 5).

There was no signincant difference between catches in midde or latexal trenches for B. pelZucidus or for other curculionids (Fig. 11).The overall trench escape rate was 54% for B. pellucidus, and 78% for the other curculionids caught (Fig. 12).

More carabids were caught in trenches nearest the field than in the other trenches, there were no significant ciifferences in catches of elaterids between the three trenches, and more isopods were caught in trenches nearest the forest than in the middle trenches. The escape rates for carabids, elatends and isopods were 57,90, and 4594, respectively (Fig. 12).

Significant correlations were observed between pitfall trap and trench catches of both carabids and isopods, on both the windbreak and field sides (carabids: windbreak side, 1-0.9945, R0.00 1; field side, ~0.8303,P-0.006)(isopods: windbreak side, ~0.9577,B0.001; field side, ~0.9133,P4.001). Correlations were observed on the forest side only for weevils other than B. pellucidus (~0.8891, P0.00 1).In no other case was there a signincant correlation between catches in pitfall traps and trenches.

3.4.3 Trench weathering

Within two months of installation the tsenches were beginning to bend upwards at their ends, leaving spaces underneath large enough for most insects to pass thxough.

The width of the gap at the top of the trench sometimes grew and sometimes narrowed.

011 several rainy days B. pellucIdus adults were observed escaping from the ends of the trenches and the points where trenches joined. These joints spread apart as the trenches weathered. The alunilnu strips, which were initidy secured with soil against the end of the trenches parted from the trenches due to the constant expansion and contraction of the trench. When these were secured with elastic bands attached to screws in the trench plastic, most of the elastics snapped dera few Figure 11. Comparative catches of arthropods in three pardel trenches between an apple rootstock nursery and a wuidbreak near Langiey, BC. Bars within a subfigure with the same letter are not si&nincantly different, Tukey's test, B0.05. Other a Curculionids T i

Carabids Elaterids a

Field Middle Windbrea k slde side

Trench

Field Middle Wndbrea k slde side Trench

Betypeffhespellucldus

Other Curculionids

Carabids

Elaterids

Isopods

50 100 Escape Rate (%) (E+S.E.) (n=5) weeks. Twine used to replace the elastic bands did not provide a satisfactory seal.

Within a week cardboard pahted with Stilq Stuff was so thoroughly covered with soi1 that most insects could crawl over it.

3.5 Black vine weevil containment un'thin srnall enclosures

In the fist two replicates of the expehent, during which there was no precipitation, no black vine weevils were able to cross the aluminum fences with Tefion, or the trenches with dormant oil, during the 55 min. of observation, or by the followuig morning. In the same period, ca 80% of the weevils released in the control plot escaped, and entered the gutter. Observations for the thhd replicate were taken during a light rah shower. Again, ca 80% of the observed weevils in the control plot escaped, but 20% of the weeviis in the fenced plot were able to cross the Teflon barrier, and one

(5%)of the weevils released in the trenched plot escaped to the outer edge of the trench. By the follovrring morning ail 20 of the weevils had escaped the control plot,

65% (13)had escaped the fenced plot, and 15% (3)had escaped the trenched plot.

In al replicates, weevils were able to crawl unimpeded up the bare aluminum fence. In the fist two replicates, weeviis clustered at the lower edge of the Tenon, unable to crawl further. In the Wdreplicate, some weevfis were able to crawl over the

Teflon banier; the fkst weevii to accomplish this was observed on the Teflon tape 5 min after it was released in the plot centre. Weevils which fell into the oil-covered gutter or trench in the other two treatments during the f%sttwo replicates attempted, unsuccessfully, to climb the alumirium walls of the gutter and the plastic walls of the trench. Dormant 02 could be seen on their tarsae, because it stuck to dust particles, giving weeviis the appearance of wearing muddy boots. Many weevils which feu into gutters or trenches coated with dormant oil during the &st two xeplicates died. None died during the observation period of the third replicate, although 69% had died by the following morning. In aii replicates weevils in the trenched plots crawled upside down dong the curved lip of the trench, and then exited the trench without falling to the bottom.

3.6 Effect of condensation on black vine weed ability to escape srnall canisters

AU escapes occurred within the first 2 h of the 3 h observation period. Significantly more weevils escaped fiom the canisters coated with powdered tdc in the sealed container, than in the open container (Table 6). No weevils escaped fiom grease-coated canisters, and one escaped fYom a fluon-coated canister. Fluon exposed to water did not retain its structure, like Teflon, but re-iiquined, cau&g 70% mortality among the weevils in the sealed container. Table 6. Escapes by black vine weevils fkom canisters (2 weevils in each of 10 canisters) in an unsealed container, and a sealed, humid container over a 3 h period.

'i'wo black vine weevils were placed in each canister. Canisters were left clean (control), or coated with powdered talc, fluon, or white lithium grease.

P that open

Number of escaped weevils per canister (z f S.E.) and sealed

Treatment Open container Sealed container are equal (t-test))

Control 2.0 I0.0 1.8 f 0.2 0.3739 Talc 0.0 * 0.0 1.4 f 0.4 0.0249 Fluon 0.0 * 0.0 0.2 i0.2 0.3739 Grease 0.0 f 0.0 0.0 * 0.0 - 4.0 Discussion

4.1 Effect of powde~and fiuon on weevil dimbing ability

The data show that surface coverings of dry fiuon or powdered taic affect the angle that root weevil adults can climb (Fig. 6). Fluon can prevent granq weevils Çom climbing glass (Radinovsky 8& Krantz, 19621, and is commonly used to prevent the escape of crawiing insects Çorn open containers in the laboratory. The effectiveness of a coating of powdered talc reflects the observation that Colorado potato beeties are less able to climb dust-covered than clean plastic-lined trenches (Boiteau et al. 1994).

Fluon creates a super-smooth surface without tarsal holds for traction

(Radinovs& & Krantz 1962). Electron micrographs show that dust is caught in tarsal pads of Colorado potato beetles, perhaps contributing to their reduced ability to chb dusty surfaces (Boiteau et al. 1994). 1 observed powdered talc caught in the tarsal pads of root weevils which had walked on dusted surfaces. Like fluon, the fine powder accurnulated in cracks or crevices in the wax, probably reducing the number of potential tarsal holds, preventing direct tard contact with the fhn wax surface, and dislodging when weevils attempted to gain a hold on them.

The abiîity of dust to limit weevil climbing ability can be exploited in the field by cnrmbiing soi1 into a smooth dry container, such as a plastic bucket, to make an open collection container which weevils cannot escape (pers. obs.). The same technique can be used for Colorado potato beetles.

4.2 Weevil exclusion by physical barriers

4.2.1 SmaZl enclosures

My results show that B. pellucidus has little difficulty climbing bare aluminum, and that a bamer is likely to be ineffective without some unclimbable portion incorporated (Fig. 8).The poor exclusion offered by the trenches with diatomaceous earth added was not expected, since it would be expected to have similar properties as talc. The poor performance of the diatomaceous earth was probably due to the fact that it quickiy caked to the insides of the trench when condensation fonned, providing an easy surface for weevils to climb. The superiority of the aluminuxn fence plus Teflon in excluding the woods weevil suggests that the larger N. incompfus adults were less able to scale the Teflon surface than the tiny B. pellucidus aduits (Fig. 8).

Weevils other than B. pellucidus or N. incomptus made up a larger proportion of the weevils caught inside the alruninum fences with Teflon than those caught in the control plots, perhaps because B. pellucidus and N. incompfus were present early in the season, before the Teiion was worn or dirty.

The low weevil catches at the Pitt Meadows site, despite the presence of black vine weevils within 20 m, emphasizes the limited dispersal of black vine weevil adults during the summer months when food is plentifül. Nielson 86 Dunlap (1981) noted that black vine weevil oviposition tended to occur near the site of ernergence, and Maier

(1978)found that the majority of marked adults released in an urban area remained within 10 m of the release site after 57 days.

4.2.2 ParaIlel trenches

AZthough the parallel trenches captured more black vine weevils and other cuxculionids than the pitfâii traps (except for the very smdB. pellucidus), the calculated escape rates were very high (Fig. 12).This suggests that the weevils were having little problem crossing or escaping from the trenches. The trenches used at the

Langley site wouid have to be improved before they could be used operationally as an effectivephysical control for root weevils.

The absence of a signincant Merence between the root weevil catch in trenches closest to the ulitdbreak and the field (Fig. 11) is probably because weevils were approaching the trenches from both directions, rather than invading the field from the forest. In support of this conclusion root weevil densities were uniforrnly high throughout the field, with no noticeable concentration near the windbreak edge.

4.3 Ground beetie exclusion by physicd barnaers

4.3.1 Small enclosures

Both the fence and the trench tended to exclude carabid beetles Çom smd enclosures, although more were able to cross the trench than the fence (Fig. 9). The ability to escape the trench was likely enhanced by cracks which opened at the trench corners, providing a good tarsal hold to assist in escape by chbing. Some srnail carabids might also have escaped through the drainage openings at the bottom of the trench.

There have been several reports of the effectiveness of barriers for carabid beetfes (Edwards et al. 1979, Holopainen 86 Varis 1986).These observations suggest that predatory beetles would have to be added to any areas enclosed by barriers in order for them to have any population regulating effect. Once inside an enclosure, barriers would limit their dispersal, increasing their efficacy.

Predatory carabids may not be very effective in reducing pest populations in potted plants. None of the three most fiequently occurring genera caught at the Pitt

Meadows site was represented in the pitfall trap captures at plant level. The inability of these beetles to evade the barriers probably also means they are unable to climb into the pots, where they are most needed Xthey are to be effective biological control agents in a container nursery.

Ground beetles have been credited with helping to maintain naturd control of root weevils (Feytaud 19 18, Evenhuis 1983). In particular, Pterostichus melanarius

(Iiüger) can attack and consume many root weevil adults (pers. obs.). In the laboratoxy, two Pterostichinid species, P. melanarius and P. lucub2andus (Say) consumed all He stages of the carrot weevil, Lisb-orrotus oregonds (Leconte), destroying about 10 weeviis per carabid per day (Baines et ai, 1990). Because no barrier appears to be

100% effectiveagainst root weevils, exc1udin.g them with barriers without introducing predators into the enclosure might allow weevii populations to increase to damaging levels.

My results suggest that fences exclude most large ground beetles, such as P. melananus, but not smaU ground beetles, such as Bembidion spp., or Trechus obtusus

(Fig. 9). This hding reflects the observation of Holopainen &iVaris (1986) that enclosing areas with a polyethylene barrier has a much stronger effect on large and medium shed than on small carabids, possibly because many smali species are strong fiers, and can fly over barriers. The barriers then protect smaii carabids inside enclosures Fom predation by larger carabids (Holopainen & Varis 1986).

4.3.2 Parallel trenches

The observation that fewer carabids were caught in the trenches at the Langley site than in the pitfall traps positioned beside them (Table 5) suggests that the trench design somehow selected against carabids, without selecting against root weevils.

Perhaps carabids actively avoided the trenches, were less active near the trenches (as suggested by the lower pitfall trap catches on both sides of plots with trenches than plots without), or were disinclineci to climb the 45" angle of the outer trench walls.

The high carabid catches in trenches closest to the field and the high pitfall catches closest to the windbreak reflect the merence in carabid species caught in the two types of trstps. Mainly bembidinids were caught in the piffd traps, apparently approaching fiom the windbreak. Carabids most common in the trenches, such as

Ikechus obtusus, might have been approaching fkom the field. Isopod and elatend catches at the Langley site were more predictable than those of root weevils or carabids. The strong correlation between isopod catches in trenches and in the corresponding pitfall traps, suggests that either could be used as a monitoring tool. Both trench catches and pitfall catches led to the conclusion that isopods were most abundant nearest the windbreak.

4.4 Effect of condensation on bam'er efJicacy

My results indicate the need for more research to cietenmine the efkcts of condensation on powders, lubricants, and other substances used to make physical barriers unclimbable. Weevils were apparently able to climb wet surfaces which were unclimbable when dry, possibly explaining some of the weevii success in defeatllig

Teflon barriers in the field. Repeated casual observations suggest that condensation is a key to weevil escapes over unclimbable barriers. For example, weevils placed in a dusted bowl were unable to escape for several days, but escaped within hours of the bowl being placed in a covered cooler with free water in the bottom. Several weevils escaped fkom wax cups with a ring of white lithium grease around the edge when the cups were placed in a sealed container, but no escapes were observed from identical cups in the open air. Any effects of condensation on physical bamer egectiveness could have important implications for future barrier design.

4.5 Fence setup and durabitity

The combination of landscape fabxic on top of wood chips provided an excellent foundation for testing bamers. They remained firmly fixed in the wood chips, and fkee fi-om mud, whkh might have reduced their effectiveness.

Erecfing aluminum fences around plots took approximately four times as long as erecting trenches, a major consideration in any economic anaiysis (Appendix 3). The alufniflum bamers proved more durable than the extnxded plastic trenches under cool, moist conditions. The extra subsurface depth prevented riVUIets forming under

the aluIl3inum barriers, and the single, flexible barrier needed only one seam to form

an enclosure. In contrast, each square trench enclosure had 12 separate pieces,

resulting in 12 seams at which cracks or notches frequently developed, probably

facilitating weevil escapes.

Under field conditions, with long borders, fewer seams would be necessary for

both typas of barrier, which might result in a less marked difference in durability. If an

dumin- fence were erected dong a long border, without corners to irllpart strength,

there might be some danger of the fence folding over at the soil surface.

The extra 14 cm height of the fences proved useful in two ways. It removed the

Tefion from the splash zone irnmediately above the soil, and it meant that most faiien

twigs or leaves could not bridge the distance between the soil surface and the fence

top. The advantage of the low profile of the trench is the ease with which ramps could

be placed above it, or wheel chocks placed on either side of it, to ailow the passage of

carts and machinery.

4.6 Future physical bam'er design considerations

1 have shown that physical barriers can reduce the number of weevils able to cross a

boundaxy by up ta 84%. Future bârrier designs must maximize efficacy even mer

wide minimizing costs. Before physical barriers will be adopted for root weevil control,

they must be shown to offer sorne advantage over conventiond strategies, in terms of

efficacy, cost, environmental impact, or any other criterion.

One advantage of the plastic trench is its potential to kill pests. It is double

sided, trapping pests which enter fkom either side, and could contain lethai

substances, e.g. dormant oil, which would increase efficacy. Increasing morkdity of insects which encounter a barrier has a stronger effect on preventing successful barrier crossings than reducing escape rates (Appendix 2), because repeated attempts

to cross a barrier are minimized.

The plastic trench had numerous disadvantages. These include: trapping

beneficials insects; lack of durability; development of gaps due to expansion,

contraction, and twisting; brittleness under UV exposure; inability to match curved

field boundaries; shdow mil penetration that allows rivulets to fonn underneath;

fiequent bridging of the top gap by field debris, aliowing insects to cross; lack of

visibility and vulnerability to crushing by farm machinery; escape by weevils despite

the curved upper lip; and admission of min, necessitating drainage holes which dow

smaii insects to escape.

The aluminum fence offers several advantages. It is easily bent, allowing

seamless corners and curves; it can exclude insects coming fiom either side; the high

profle prevents easy bridging; its deep soi1 penetration prevents insect passage

beneath the trench; it weathers well; and it is easily constructed of inexpensive,

commercially available material. There are also disadvantages to the aluminum fence.

The high profile makes it difficult for farm machinery, wheeled carts, and pedestxians to cross; long straight sections could bend over at soi1 level; setup takes longer than trench setup, because at least 10 cm of aluminum must be buried to support the fence; and additives, such as grease or Teflon, must be repeatedly applied to make it unclimbable. It can only exclude insects; it is not lethal, and could not contain insecticides.

Neither trenches nor fences should be under plants, so a buffer zone must be established between barriers and the crop, and weeds must be carefully controlled.

The designer of the plastic trench, Dr. R.S. Vernon, has proposed a new trench design incorporating some of these considerations. The proposed trench would be similar to the current trench (Fig. 13A), but one side would be extended, so that the opening would no longer be at the top (Fig. 138). This trench would exclude insects fiom oniy one direction. However, it would prevent entry of rainwater; would reduce

the likelihood of bridging by leaves or debris; would not need drainage holes; and

could contain insecticides, such as dormant oil, which would not be released into the

surrounding environment. Two new lamellae would be added which would penetrate

the soi1 surface more deeply than the current trench, and would provide more

structure, preventing the base of the trench nom falling in the centre, and keeping the

trench walls at their intended angle.

The current and proposed trenches have a rough outer surface to allow

Colorado potato beetles to scale the outer wall (Fig. 13A,B). For weevil management, 1

propose a non-textured adaptation of the modifïed trench, with verticai walls (Fig.

13C). Removing texture, or increasing the wall angle would not discourage weevils

Çom entering the trench, as illustrated by the inability of an aluminum barrier without

Teflon to exclude weevils. This design could be moued to restore the bi-directional

aspect of the original trench (Fig. 13D).

There is considerable potential for cost effectiveness for large enclosures with durable bamers (Appendix 3). In certain circumstances, bamers might be used as an alternative to commody used insecticides, e.g. for organic production, or if insecticides are lost to resistance or de-registration. More likely, bartiers could compliment insecticide use, reducing the number of sprays necessary for root weevil control.

Barrier cost would then be compared to the cost of insecticide applications saved, rather than the total cost of root weevil control with insecticides. Barriers should be used when the cost of insecticides saved exceeds the cost of a barrier. Figure 13. Cross section of the trench currently used experimentally (A), and three proposed designs (B-D). Outside of Inside of field field 5.0 Conclusion

Physical baders show some potential for root weevil management in nursery crops.

Laboratory studies showed that surfaces which root weevils can normally clirnb, can be made unclimbable by the addition of substances such as fluon, powdered talc, or white lithium grease. Field studies showed that aluminm bamiers with Teflon added, and an experimental extruded plastic trench both reduced the number of weevils able to enter enclosed plots of strawbeny. This reduction was equated with increased plant mass and plant survival, and reduced leaf notching early in the season.

More work is required before physicai bamers can be recommended to nursery growers as a reiiable form of root weevil management. Of particular concern is an apparent loss of efficacy of unclimbable surface additives in the presence of moisture.

The reasons for this loss of efficacyneed to be detennined before potential solutions can be devised. Potentidy superior trench designs discussed in this paper should be field tested to evaluate their effectiveness.

The effect of barriers on non-target organisrns must be appreciated. Both types of bamer excluded large carabid beetles, and trenches are potentially lethal to carabids. This PYght not be a concern in container nurseries, where carabid beetles do not climb up into containers and act as biological control agents, but their population regulating impact could be lost in field nurseries if carabids are excluded. Future trench designs should be modified so that carabids cannot enter, thereby preserving carabids already within plots. Carabids added to enclosed plots could be contained with physical barriers, which might simultaneously prevent root weevil immigration and carabid emigration.

Practical considerations such as barrier cost, durability and compatibility with grower practices will ultimately determine their success. The plastic trenches used experimentaily showed adequate durability over one season in a container nursery, but did not hold up under field conditions. Future trench designs should attempt to improve durabiiity. Alumirium fences showed good durability in aii situations tested.

Tests did not determine the necessaxy fiequency of Teflon re-application, but this factor will contribute to the cost and useful life of fences, because Teflon was essential for fence effectiveness. The cost of barriers fdswith increasing enclosure size and durability. More work is needed to examine how these factors aiiect bamier efficacy. 6.0 References

Alberta Agriculture, 1988. Control of Strawbeny Roof Weevils. Print Media Branch, Alberta Agriculture, Edmonton.

Ailen, R.T., 1979. The occurrence and importance of ground beetles in agricultural and surrounding habitats. In Carabid BeetZes: ïheir Evolution, Natural History, and Classification. T.L. Erwin (ed.), Junk Pub., The Hague, The Netherlands.

Antonelli, A.L. & R.L. Campbell, 198 1. Root weevil control on rhododendrons. Washington State University Cooperatiue Extension Bulletin 0970.

Baines, D., R. Stewart & G. Boivin, 1990. Consumption of carrot weevil (Coleoptera: Curculionidae) by five species of carabids (Coleoptera: Carabidae) abundant in carrot fields in southwestern Quebec. Environmental Entornology 19: 1146- 1149.

Balsbaugh, 1988. Distributions for two holarctic weevils which are new household pests (Coleoptera: Curculionidae). Ent~rnolo~caîNaus 99: 102- 104

Bethke, J.A. & T.D. Paine, 199 1. Screen hole size and barriers fox exclusion of iriseci pest of glasshouse crops. Journal of Entomological Science 26: 169- 177

Blatchley, W.S. & C.W.Leng, 19 16. Rhynchophora or weevils of North Eastern Amena The Nature Pub. Co., Indianapolis, Indiana

Boiteau, G., Y. Pelletier, G.C. Misener, & G. Bernard, 1994. Development and evaluation of a plastic trench barrier for protection of potato fiom mgadult Colorado potato beetles (Coleoptera. Chrysomelidae). Journal of Economic Entomology 87: 1325- 133 1.

Bradley, F.M. & B.W.Ellis, 1992. Rodale's A12-New Encyclopedia of Organic Gardening. Rodale Press, Emmaus, Pennsylvania.

Brandt, J.P., S.M. Smith &iM. Hubbes, 1996. Distribution and sampling of root weevil larvae in young ornamental conifer plantations. The Canadian Entomologist 128: 1125-1 133

Brandt, J.P., S.M. Smith & M. Hubbes, 1995. Bionomics of strawberry root weevil adults, Otiorhynchus ovatus (L.) (Coleoptera: CurcuLionidae), on young ornamental conifer trees in souîhern Ontario. The Canadian Entomologist 127: 595-604

Breakey, E.P., 1959. Control of root weevils in strawbeny planthgs. Journal of Economic Entornology 52: 11 17- 1 1 19.

British Columbia Nursery Trades Association, 1997. BC Nursery and Landsape nades Research Priorifies. BCNTA, 101-5830 176A St., Surrey, BC, V3S-4E3.

British Columbia Ministry of Agriculture, Fisheries and Food, 1993. Vegetable Production Guide for Commercial Growers, 1993-94 Edition. BCMAFF,Victoria, BC. British Columbia Ministry of Agriculture, Fisheries and Food, 1995a An overview of the BC wholesale nursery industry: New grower information package. Nursery Production Fadsheet, BCMAFF, Abbotsford, BC.

British Columbia Ministry of Agriculture, Fisheries and Food, 1995b. An Ouerviau of the British Columbia Floriculture Industry. http: / /www.agf.gov.bc.ca/agric/hortweb/fiarind.htm

British Columbia Ministry of Agriculture, Fisheries and Food, 1996a Beny Production Guide for Commercial Growers, 1996-97Edition. BCMAFF, Victoria, BC.

British Columbia Ministry of Agriculture, Fisheries and Food, 1996b. Dee Fruit Production Guide for Commercial Growers, 1997 Edition. BCMAFF, Victoria, BC.

Collman, S.J., 1990. Integrated pest management: a Seatüe street tree case study. Proceedings of the Society for Naturd Conseruution. The Society, Bethesda, Md.

Cowles, R.S., 1995. Black vine weevii biology and management. Journal of the Arnerican Rhododendron Society 49: 83-85,94-97.

Cram, W.T., 1965. Fecundity of the root weevils Brachyrhinus sulcatus and Sciopithes obscurus on strawbeny in the laboratory and outdoors. Canadian Journal of Plant Science 45: 169-176.

Cram, W.T. & H. Andison, 1959. Soil insecticides for the control of root weeviis in strawbemies in British Columbia Canadian Journal of Hant Science 39: 86-9 1.

Daar, S., H. Olkowski & W. Olkowski, 1994. 1995 Directory of least toxic pest control groducts. The PM Praditioner 16: 1-34.

Edwards, C.A., K.D. Sunderland 86 K.S. George, 1979. Studies on polyphagous predators of cereal aphids. Journal of Applied Ecology 16: 8 11-823.

Evenhuis, H.H. 1983. Role of carabids in the natural control of the black vine weevil. Mitteilungen der deulchen GesellschaftDr allgemeine und angauandte Entomologie 4: 83-85.

Feytaud, J., 19 18. Etude sur I'otiorhynque sillonné (Otiorhynchussulcatus Fabr.). Annales du Service des Bpphyties 5: 145-192.

Finch, S., 1993. Integrated pest management of the cabbage raot fly and the carrot fly. Crop Protection 12: 423-430.

Fraser Vdey Strawberry Growers Association, 1997. 1997 Research Pnorities. FVSGA, Box 2329 Clearbrook, BC, V2T 4x3.

Galford, J.R., 1986. The weevil Barypeithespellucidus (Coleoptera: Curculionidae) feeds on norîhern red oak, Quercus rubra, seedlings. Entomological News 97: 113-114

GaUord, J.R., 1987. Feeding habits of the weevil Ba?ypeithes pellucidus (Coleoptera: Curculionidae). Entomo1ogid News 98: 163- 164 Garth, S. & C.H. Shanks, 1978. Some factors decting infestation of strawberry fields by the black vine weevil in western Washington. Journal of Economic Entornology 71: 443-448.

Gaugler, R. 86 H.K. Kaya, 1990. EntomopathDgenic nematodes in biological control. CRC Press, Boco Raton, Fi.

Gerber, H.S., W.T. Cram & J. Raine, 1984. Major insect and mite pest of beny crops in British Columbia. British Columbia Ministry of Agriculture and Food, Victoria, BC.

Hardy, G.H. & E.M. Wright, 1995. An Introduction to the Theory of Numbers, 5th ed. Oxford Universtiy Press, Oxford.

Hayes, A.E., 1994. The Entomopathogenic Nematode, Steinernema carpocapsae (al1 strain), for control of black vine weevil in dry-pick cranbenies in British Columbia. MPM Thesis. Simon Fraser University, Burnaby, BC.

Holopainen, J.K. & A. Varis, 1986. Effects of a mechanical banier and formalin preservative on pitfd catches of carabid beetles (Coleoptera, Carabidae) in arable fields. Journal of Applied Entomology 102: 440-445.

Kirk, V.M., 197 1. Ground beetles in croplands in South Dakota Annals of the Entomological Society of Amenca 64: 540-544.

Kromp, B., 1989,Carabid beetie communities (Carabidae, Coleoptera) in biologicaiiy and conventiondy farxned agroecosystems. Agngnmlture,Ecosystems and Environment 27: 24 1-251.

Linâroth, C. H., 1957. The faunal connections between Europe and North Amenca John Wiley & Sons, Inc. New York. 344 pp.

Maier, C.T., 1981. Dispersal of adults of the black vine weevil, Otiorhynchus sulcahts (Coleopter= Curculionidae), in an urban area Environmental Entomology 10: 928-932.

Marchal, M., 1977. I;"ungi imperfecti isolés d'une population naturelle d'Otiorhynchus sulcatus Fabr. (Col. Curculionidae). Revue de Zoologie Agricole et de Pathologie Végétale 76: 101-108.

Masaki, M., K. Ohmura & F. Ichinohe, 1983. Host range studies of the black vine weevil, Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae). Applied Entomology and Zoology 19: 95-106.

Matthews-Gehringer, D. & J. Hough-Goldstein, 1988. Physical bamers and cdtural practices in cabbage maggot (Diptera: Anthomyiidae) management on broccoli and chinese cabbage. Journal of Economic Entomology 8 1: 354-360.

Miiiar, K.V. 6 M.B. Isman, 1988. The effects of spunbonded polyester row covers on cauliflower yield loss caused by insects. The Canadian Entomologist 120: 45-47.

Milne, L & M. Milne, 1980. The Audubon Society Red Guide to North American Insecis and Spiders. Aifked A. Knopf, New York. Moorehouse, E.R., A.T. Gillespie, & A.K. Chdey, 1990. The progress and prospects for the control of the black vine weevil, Otiorhyrzchus sulcutus by entomogenous fungi. In Roceedings and A bstracts, Vth Intemational Colloquium on Invertabrate Pathology and Microbial Control, pp. 38 1-385.

Moorehouse, E.R., A.K. Charnley, & A.T. Gillespie, 1992. A review of the biology and control of the vine weevil, Otiorhynchus sulcutus (Coleoptera: Curculionidae). Annals of Appiied Biology 12 1: 43 1-454.

Nielson, D.G., H.D. Niemczyk, C.P Balderston, & F.F. Purrington, 1975. Black vine weevil resistance to dieldrin and sensitivity to carbamate insecticides. Journul of Economic Entomology 68: 29 1-292.

Nielson, D.G. & M.J. Dwnlap, 1981. Black vine weevil reproductive potential on selected plants. Annals of the Entornologid Society of America 74:60-65.

O'Brian, C.W. & G.J. Wibmer, 1984. Annotated checklist of the weevils (Curculionidae sensu lato) of North America, Central Amenca, and the West Indies - Supplement 1. Southtuestem Entomology 9 : 286-307.

Philips, P. A.., 1989. Simple monitoring of black vine weevil in vineyards. Ca2ifomia Agriculture, May-June: 12-13.

RadUlovsXcy, S. & G.W. Krantz, 1962. The use of fluon to prevent the escape of stored- product insects fiom glas containers. Jounud of Economic Entomology 55: 8 15- 816.

SAS Institute Inc., 1988. User's Guide. SAS Institute Inc., Cary, N.C.

Schwert, D.P., T.W. Anderson, A. Morgan, A.V. Morgan & P.E. Kârrow, 1985. Changes in late Quaternq vegetation and insect commUIU.ties in southwestern Ontario. Quatemary Research 23: 205-226

Shetler, D.J., 1995. Black vine weevil (and other root weevils). Ohio State University Fczctsheet http://www.ag.ohio-state.edu/-ohioline/hyg-fact/2000/20 16.html

Statistics Canada, 1992. Agricultural Profile of British Columbia Parts I & II. Catalogue nos. 95-393 & 95-394. Statistics Canada Agricultural Division, Ottawa, Ont.

Stenseth, C., 1979. Effects of temperature on development of Otiorhynchus sulcutus (Coleoptera: Curculionidae).Annals of AppEeci Biology 9 1: 179- 185.

Treherne, R.C., 19 14. The Strawberry Root Weevil (Otiorhynchus ovatus Linn.) in British Columbia with Notes on Other Insects Attacking Strawbeny Plants in the Lower Fraser Vailey. Dominion of Canada, Department of AgricultureJ Experimental Fanns, Division of Entomology, Entomological Bulletin 8. Ottawa, Ont.

Vernon, R.S. & J.R. MacKenzie, 1998. The exclusion fence: A novel tool for Anthomyüd fly management. Canadian Entomologist, In Ress.

Wentraub, P.G., Y. Arazi, & A.R. Harowitz, 1996. Management of hsect pests in celery and potato crops by pneumatic removal. Crop Protection 15:763-769.

7.0 Persona1 Communications

Anonymous. Entomological Society of British Columbia judge, student paper cornpetition, 1997 Annual General Meeting.

Bassagnova, N. Postdoctorai feilow (entomology), Washington State University. c/o L.W. Tanigoshi, Washington State University, Research and Extension Unit, 1919 NE 78th Street, Vancouver, WA 98665-9752, USA

Coiiman, S.J. Doctoral student (urban horticulture), University of Washington. e-mail: [email protected]

Cowles, R.S. Research scientist, The Connecticut Agricultural Experiment Station, P.O. Box 1106, 123 Huntington Street, New Haven, CT 0651 1

Peters, W. Smdfruits specialist (retired), Abbotsford Agriculture Centre, 1767 Angus Campbeli Rd., Abbotsford, BC V3G 2M3

Raworth, D. Research Scientist, PacXc Agri-Food Research Centre, Agassiz, BC. e- maik [email protected]

Tanigoshi, L.W. Washington State University, Research and Extension Unit, 1919 NE 78th Sleet, Vancouver, WA 98665-9752, USA

Vernon, R.S. Research Scientist, Pacinc Agri-Food Research Centre, Agassiz, BC. e-mail: [email protected]

Webster, J.M. Professor, Simon Fraser University, Burnaby, BC. e-mail: [email protected]

Table 7. Meaning and derivation of variables used in AppendVr 1.

Variable M eaning Vahe Derivation

R radius of bowl 107 mm measured

distance between 37 mm rneasured

Plexiglas and y-O

plane

distance between measured

Plexiglas and eye

point on bowl horizontal and vertical coordinates

surface

apparent distance varies measured

Çom W to centre of

circle, measured on

Plexiglas lid

distance from W to see text see text

~0 plane

distance from W to Pythagoras' theorem

y=O plane

8 angle of bowl surface 90"-cos(x/R) basic trigonometry

at W

Appendix 2 Calculation of Parallel Trench Escape Rates

A model of arthropod movernent between three parallel trenches (Fig. 15) was used to

calculate escape rates based on the location of eopodscollected in the parallel

trench study. This model assumes that four factors do not change between trap

collection periods: the numbers of arthropods which enter the outer and hner

trenches ( Y and 2, respectively) during a standard time period (4, and the probabilities

that a surviving arthropod in any trench will die or escape (M and E, respectively)

during the same standard tirne period (0.The model also assumes that arthropods are

equdy likely to escape from either side of a trench.

Arthropod catches in her,centre, and outer trenches, respectively are represented by the variables i, c and o. The number of insects caught in the centre trench which escaped fiom the outer trench (n) represents half the total escapes from the outer trench, and was described by the following equation: n=- c.0 o+i

The trench escape rate (X) is the fkaction of arthropods which enter the outer trench that eventudly escape fkom the outer trench. It was estimated as x using the foliowing equation:

The model shows that x=O at the beginning of each collection period (@O), when aU trenches are empty (T=O=C=O) but will move towards an equilibrium as time passes

(Fig. 16A). The equilibrium reached is a function of escape rate per unit time (4 and mortality per unit tirne (M), (Fig. l6B). Figure 15. A mode1 of insect movement between three parallel trenches, using variables defined in text.

Figure 16. The calculated escape rate (4 reaches an equilibrium with pas- time (A).

This equilibrium is a hction of the actual escape rate (X) and the achial mortality rate (M) (B). In figure A, values for X and Mare set arbitrady at 0.5. This equilibrium is marked with a '+' in figure B. Time Appendix 3 Barrier cost analysis

The annuai cost of managing root weevils with an insecticide (i3)isthe cost of the insecticide (1) and labor [wage (C) x application time (A)),multiplied by the number of applications necessaty each year (N) (Table 8): P, = N(1 + AC)

The cost of a barrier depends on the fked costs of the materials (E),as well as labor costs, setup time (9and the length of the barrier. A barrier surroundhg a field with a length (L) and width ( W), is as long as the field perimeter (2L+2W). Bdercost per unit time and area (A)depends on the useful life of the banier (g,and the area protected (LW): 2(L + W)(E+ SC) Pb = LWB

A bamer might require regular maintenance, or repeated re-application of some active portion. For example, insecticide might be added to a trench every week, or

Tenon might be re-applied to an aluminum fence annually. The cost of regular maintenance is a function of the maintenance time required (II), the cost of materiais

(M), and the number of times each year that maintenance is necessary (D). The cost of a barrier requirîng regular maintenance is:

Physical barrier costs can vqsubstantidiy. Under certain circumstances (e.g. example in Table 8) physicai barriers could be much less expensive than the chernical controls currently used for roat weevil management. Under other circumstances barriers might be more expensive than insecticides. The total cost of barriers increases with increasing enclosure size (Figure l7A), but the cost per unit area fds(Figuxe

L7B). Both costs fall as the useful life of barTiers increases (Figure 17). Table 8. Calculation of root weevil control costs in a 10 x 28 m container nursery bed using regular insecticide drenches with a backpack sprayer, physical exclusion with a plastic trench, or physical exclusion with an alumG.1um fence and annual Tefion applications.

Approltimate value Insecticide Variable Description drenches Trench barrier Fence barrier Bed length 28 m Bed width 10 m Labour cost $13.h.1-1 Insecticide $0.47.m-2 cost Insecticide 0.10 hr-m-2 application time Insecticide 6 ri applications required Barrier cost N/A Bamier setup N/A time Useful iife of N/A bamer Teflon N/A applications required Teflon cost N/A Teflon N/A application time

Calcuiation of N(I + AC) control cost

Control cost $10.62m-2.yrl $0.59m-2-~rl 0.73 m-2. yr 1 Figure 17. Physical barrier cost as a function of lüéspan and area enclosed. Although total cost (A) rises as the enclosed area increases, cost per unit area (B) falls.

Physicd exclusion and chexnical control are diaerent strategies with dinerent

benefits. Physical exclusion is a proactive approach to root weevü control; it is an

attempt to keep an area which is fkee of root weevils from being invaded. Chernical

control is reactive; it is an attempt to clean up a problem which already exists.

Enclosing a root weevil infested area with a physical barrier might contain the problem, but it cannot eradicate the problem. Shce the two strategies offer different benefits, they might be best used to complement one other, not as a substitute for

each other.

The cost analysis presented here only incorporates variables which are easily measured in monetary tenns. An obvious cost whicb is not considered is the environmental cost of the control strategies. Without factoring in this cost, the first equation shows that more persistent insecticides are less expensive. The problems with this conclusion are evident now that chemicd persistence is no longer considered desirable, but missing factors in the equations for physical béder cost are not yet as obvious. One cost which is not given a monetary value in any of the equations is the loss of control by natural enemies. Some natural enernies of root weevils are susceptible to insecticides, or unable to cross physicai barriers. The fact that this control cost is difncult to measure, however, should not prevent its consideration. IMAGE EVALUATION TEST TARGET (QA-3)

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