Nightmare on Walnut Street: Thousand Cankers Disease as an Emergent Threat to Juglans

Transcription

1 Nightmare on Walnut Street: Thousand Cankers Disease as an Emergent Threat to Juglans Whitney Cranshaw Colorado State University Presentation for the International Society of Arboriculture Conference Chicago, IL July 27, 2010

2 Thousand Cankers Disease (TCD) An Insect/Fungal Disease Complex affecting some Juglans spp.

3 A fungus Geosmithia morbida A beetle walnut twig beetle

4 Jim LaBonte Walnut Twig Beetle Pityophthorous juglandis Jim LaBonte

5 Adults enter trees and excavate galleries

6 An egg gallery is produce along which eggs are laid

7 Larval feeding produces a loose network of meandering tunnels in the cambium

8 A full grown larva, preparing to pupate.

9 Teneral adults and pupa, covered with Geosmithia spores

10 Adults emerge through minute exit holes

11 The Pathogen - Geosmithia morbida

12 Walnut twig beetles emerging from infested trees are contaminated with spores of the fungus

13 Geosmithia is introduced into wounds made by walnut twig beetles

14 Growth of the fungus beyond the inoculation site creates a dead region (canker) in the cambium.

15 Multiple cankers produce girdling that seriously restricts movement of nutrients.

16 Walnut twig Death beetle exit holes by TCD Working Hypothesis Girdling from cankers (and bark beetle tunneling) restricts movement of nutrients. Trees weaken as stored energy reserves become depleted. External symptoms develop in end stages of infestations Trees ultimately die from energy depletion.

17 Flagging symptoms emerge in end stages of 1000 cankers on black walnut

18 TCD Symptoms in July 2009 (Olney Springs, CO) Tree is now dead

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21 Foliage wilting may occur rapidly on TCD-compromised limbs

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23 September 2008 June 2008 June 2009

24 Origin of Thousand Cankers Disease

25 The walnut twig beetle was originally described (1928) from Arizona walnut, Juglans major. Great picture by Jim LaBonte, OR Dept. Agriculture! Original collections of the beetle were made in 1896.

26 Published distribution of Arizona walnut

27 Arizona walnut (Juglans major) Host associated with original descriptions of the walnut twig beetle

28 Arizona walnut is a common species found in canyons and along riverways

29 In surveys, walnut twig beetle was repeatedly found in Arizona walnut at several sites in NM and AZ

30 Walnut twig beetle in AZ walnut functions as a typical Pityophthorus species of twig beetle. Attacks are normally limited to small diameter branches and function as a form of natural pruning.

31 Progression to fullblown Thousand Cankers Disease has not been observed in AZ walnut.

32 Southern California walnut Juglans californica Another native host of walnut twig beetle?

33 California records for walnut twig beetle date to the late 1950s (Los Angeles County)

34 Geosmithia morbida is also likely to be a native fungus.

35 The Geosmithia fungus is has been found consistently associated with the tunnels and frass of walnut twig beetles regardless of Juglans spp. or site of collection.

36 Evidence suggesting Geosmithia morbida is a native fungus The fungus is consistently associated with walnut twig beetle wherever walnut twig beetle occurs The genetics of Geosmithia strains collected over broad geographic areas appear to be showing diversity (data limited) No apparent genetic bottlenecks Geosmithia morbida is a warm temperature fungus Consistent with a warm climate of origin

37 Progression to fullblown Thousand Cankers Disease has not been observed in AZ walnut.

38 Resistance to Thousand Cankers Disease may often result from differences in susceptibility to Geosmithia morbida Canker formation in black walnut Canker formation in Southern California walnut

39 How did this happen? - Somehow the beetle jumped hosts.

40 Colorado Potato Beetle (Jumped from buffalobur to cultivated Solanum then moved across US and into Europe)

41 Apple Maggot Jumped from hawthorn (Cratageus) to apple (Malus)

42 Jumped from wild cotton in Mexico to cultivated cotton and spread throughout the US Cotton Belt. Boll Weevil

43 How did this happen? - Somehow the beetle (and fungus) jumped hosts.

44 Walnut Twig Beetle Range Expansion Big Bang or Buttheads

45 Spread of walnut twig beetle through the western states involved human transport of infested wood products

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47 What is Thousand Cankers Disease? Black walnut Arizona walnut

48 A canker producing fungus (with vector) + A susceptible host (black walnut) =

49 A canker producing fungus (with vector) + A nonsusceptible host (Arizona walnut) =

50 Thousand Cankers is a different disease in different Juglans hosts

51 Thousand Cankers Disease (TCD) An Insect/Fungal Disease Complex affecting Juglans spp.

52 Either the beetle or the fungus indicate presence of thousand cankers disease

53 A Brief History of the Discovery of Thousand Cankers Disease

54 Unexplained decline of black walnut in eastern Colorado has been observed since about 2001

55 The first published association of walnut twig beetle with black walnut in decline occurred in the Espanola Valley area of northern New Mexico (2002)

56 In New Mexico and Colorado the decline of black walnut and the involvement of walnut twig beetle was originally assumed to be associated with drought.

57 My personal epiphany: Idaho Hort Expo, January 2008 #1 topic of audience concern involved black walnut die-offs Idaho 2004 record of walnut twig beetle; associated with die-off of black walnut in Boise- Meridian area (Frank Merickel)

58 Other Recent New State Records for Walnut Twig Beetle Idaho 2004 record; associated with die-off of black walnut in Boise-Meridian area (Frank Merickel) Utah Widespread die-off occurred in late 1990s in Provo area. State records from that time period (1996). State record of a single beetle August 22, 1988 from Provo. (Shawn Clark, Diane Allston)

59 Other Recent New State Records for Walnut Twig Beetle Idaho 2004 record; associated with die-off of black walnut in Boise-Meridian area (Frank Merickel) Utah Widespread die-off occurred in late 1990s in Provo area. State records from that time period (1996). State record of a single beetle August 22, 1988 from Provo. (Shawn Clark, Diane Allston) Oregon Common in 2004 traps samples in the Dalles area. Review of samples identified 1997 sample from Portland (Jim LaBonte) WA Recovered from symptomatic trees in Prosser area (2008)

60 The Big Question: How can a little twig beetle be killing healthy trees???

61 Pityophthorus bark beetles are collectively known as twig beetles because they normally restrict damage to small diameter twigs.

62 Geosmithia morbida a fungus that is pathogenic in certain walnuts

63 Thousand Cankers Disease was first formally described (i.e., published in refereed journal) in August 2008

64 Areas with Walnut Twig Beetle Confirmed

65 Native Range of Juglans nigra (Black walnut)

66 Can Thousand Cankers be Contained in the West?

67 2009 Colorado Juglans Survey Goals Locate all Juglans spp. in Colorado east of the Continental Divide Do preliminary assessment of TCD incidence Do follow-up on suspect trees in edge areas

68 Preliminary Assessment Concentrate survey to find edge of infestation within state Rank trees for TCD 0 No symptoms 1 Some symptom (e.g., old dieback) worthy of note, suspicion 2 Symptoms highly suspect for TCD Follow-up on suspect trees with ground sampling

69 Some lessons learned in 2009 survey Black walnut trees in Colorado tend to be concentrated in older neighborhoods Best time for finding trees was mid June- August Best time for identifying symptoms is late June through August TCD-related flagging develops with summer stresses Other sources of flagging become prominent in late summer

70 Thousand Cankers Colorado hot spots

71 Thousand Cankers NOT spots

72 Thousand Cankers presents a new paradigm of a tree disease

73 Either the beetle or the fungus indicate presence of thousand cankers disease

74 Thousand Cankers emerged as a tree killing disease when it moved from native resistant hosts into susceptible hosts

75 Symptoms of Thousand Cankers Disease develop following sustained introductions of Geosmithia by walnut twig beetles in susceptible hosts.

76 Dutch elm disease has different epidemiology

77 DED fungus grows in and results in the plugging of the xylem.

78 Thousand Cankers Disease is associated with the cambium, and does not move systemically in the xylem or phloem.

79 Root grafting is a concern with Dutch elm disease

80 Dutch elm disease killing row of street trees

81 Thousand cankers disease killing black walnut in Olney Springs

82 Tree death from Thousand Cankers results from overwhelming numbers of individual infections not a single inoculation

83 Good News: It takes a long time (Decade? More? A bit less?) for a tree to die following initial colonization by walnut twig beetles.

84 Visual symptoms of Thousand Cankers only develop in the last 2-3 years of the life of the tree.

85 Bad News: By the time symptoms appear it can be assumed that the walnut twig beetle is generally distributed in the area.

86 Walnut twig beetles readily breed in logs

87 Two 18-in logs produced 23,040 beetles in one year after being cut

88 Bad News: Walnut wood from symptomatic trees or trees cut due to TCD infection is extremely infectious.

89 A walnut log in Denver waiting for Uncle Benny from Chicago

90 Wood salvaged from TCD-affected trees is extremely contagious

91 Beetle infested black walnut from Boulder area with bark attached as advertised on the internet

92 What about chipping?

93 Walnut twig beetles were able to complete development in larger pieces following chipping

94 Factors Affecting Course of Thousand Cankers Disease Resistance of host Species differences Vigor of host Available energy reserves Amount of local inoculum Environmental conditions

95 Native Walnuts (Juglans spp.) in North America Black walnut (J. nigra) Butternut (J. cinerea) Northern California walnut (J. hindsii) Southern California walnut (J. californica) Arizona walnut (J. major) Little walnut (J. microcarpa)

96 Relative Resistance of Juglans to Thousand Cankers Disease Preliminary Observations Highly Susceptible Black walnut (Juglans nigra) Moderately Susceptible Northern California walnut (J. hindsii) Moderately Resistant Southern California walnut (J. californica) Persian/English walnut (J. regia) Highly Resistant Arizona walnut (J. major) Little walnut (J. microcarpa)??

97 Bad News: Prospects for effective chemical control of walnut twig beetle are poor.

98 Drenching branch sprays for walnut twig beetle

99 Foliar treatments? The beetle attacks all areas of the tree. Attacks can occur over a period of several months (mid-april through mid-september). Establishment and maintenance of coverage will be very difficult.

100 Soil treatments and Walnut Twig Beetle - Anecdotes Imidacloprid may assist in slowing spread of walnut decline if it is applied prophylactically Dinotefuran, dimethoate may assist slowing spread of decline but trees are not saved Treatments are not legal on nut-bearing trees

101 Systemic insecticide soil drenches/ trunk injections? The fungus grows ahead of the beetle. Cankered areas may prevent movement of insecticide to the beetle feeding site.

102 Thousand Cankers Management & Pesticides What kind of crop is black walnut?

103 Pesticides Used on Black Walnut Must Probably legal Imidacloprid Chlothianidin be Consistent with Labels for Nutbearing Crops Not apparently legal for use on black walnut Dinotefuran Abamectin Enamectin benzoate

104 Bad News: Prospects for effective control of walnut twig beetle are poor. Insecticides may slightly slow, but will not stop the progress of TCD.

105 Key to Thousand Cankers Management Contain the Spread!!!!!

106 Forestry emphasis in the western states - #1 priority is to prevent the movement of infected wood to new areas All wood from TCD affected trees must be retained locally

107 A Juglans Quarantine Would affect logs/wood with bark intact Would not need affect Milled wood without bark Logs that have sufficiently dried so live beetles cease production (3 years?) Kiln-dried wood (questions remain about reinfestation potential) Nuts

108 States with Existing or Proposed TCD Quarantines Missouri Iowa Kansas Michigan Indiana Nebraska

109 Value of the Juglans Quarantine Announcement of quarantine vastly increases public awareness of issue severity National quarantine would empower state and local officials to develop effective containment actions

110 Where is APHIS on this issue? Current decision of this agency is that it is not their problem since insect is native to the United States

111 Emerald ash borer is to Osama bin- Laden. An analogy for regulatory people

112 as Walnut twig beetle is to Timothy McVeigh An analogy for regulatory people

113 What I said last month. Good News: Walnut twig beetle has likely not yet reached the native range of Juglans nigra (we think).

114 July 20, 2010 Very, very bad news: Thousand cankers and walnut twig beetles found in the center of the native range of Juglans nigra Note: The local foresters thought that the trees were suffering from drought stresses

115 Thousand Cankers has now breached the geographic barrier of the Great Plains!!!!

116 Good News: It takes a long time (Decade? More? A bit less?) for a tree to die following initial colonization by walnut twig beetles.

117 Bad News: By the time symptoms appear it can be assumed that the walnut twig beetle is generally distributed in the area.

118 Implications of TCD Finding in Native Range There are now no ecological or geographic barriers that will prevent TCD spread throughout the entire range of Juglans nigra Natural spread will be slow (comparably) but inexorable Containment through restrictions on movement of walnut wood products may slow spread

119 Foresters are the Front Line in the Detection of Thousand Cankers Disease! Investigate symptomatic trees Locate limbs with evidence of walnut twig beetle Trap walnut twig beetle

120 Look for symptomatic trees with flagging

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123 Black walnut showing conspicuous flagging August 2009

124 No yellow flagging yet apparent June 17, 2010

125 Limbs with previous flagging do show dieback

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127 Dieback and flagging may be due to: Hail injury Storm damage Fox squirrel girdling Herbicide injury

128 Remove flagging limb and look for evidence of walnut twig beetle and Geosmithia-produced cankers

129 Either the beetle or the fungus indicate presence of thousand cankers disease

130 Geosmithia morbida can be cultured from cankers, beetles, galleries, frass

131 Look for signs of the walnut twig beetle on dead limbs

132 Walnut twig beetle exit holes may be visible in limbs, particularly with smooth bark.

133 Walnut twig beetle trunk entry wounds with some weeping

134 Trapping

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136 Bad News: No effective traps for walnut twig beetle have been identified. Attractants with limited activity are in early development.

137 The walnut twig beetle is a minute bark beetle. Great picture by Jim LaBonte, OR Dept. Agriculture! It is one of few Pityophthorus species that develop in hardwoods.

138 There are features that are useful for identification of the walnut twig beetle

139 TCD Training Workshops Many states are now trained in TCD diagnosis

140 An Interim Web Site for TCD information Department of Bioagricultural Sciences and Pest Management Colorado State University Click on Extension and Outreach