Plant Growth Regulators: Slow & Steady Wins the Race MNLA Fall Pesticide Recertification November 16, 2018 Chad P. Giblin Department of Forest

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1 Plant Growth Regulators: Slow & Steady Wins the Race MNLA Fall Pesticide Recertification November 16, 2018 Chad P. Giblin Department of Forest Resources - University of Minnesota

2 Contacts & Links Chad Giblin Urban Forestry Outreach, Research & Extension (UFore) Nursery and Lab trees.umn.edu

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4 Tree Pruning Cycles Typical Pruning Cycles Every 5 to 10 years to NEVER! Fast growing young trees require more Every 2 to 3 years for 10 Years is IDEAL Pruning cycles that are too long Increased rate of tree failure Lower permanent canopy Smaller trees

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7 The Cost of Waiting Every Year Every Two Years Every Three Years

8 4 Years 9 Years 6 Years 4 Years

9 Photo Tom Zetterstrom

10 Photo Tom Zetterstrom

11 Photo Tom Zetterstrom

12 Photo Tom Zetterstrom

13 Photo: Tom Zetterstrom

14 Photo Tom Zetterstrom

15 Photo Tom Zetterstrom

16 Photo Tom Zetterstrom

17 Photo Tom Zetterstrom

18 Photo Tom Zetterstrom

19 Two Case Studies of Storm Failure in Saint Paul, MN

20 Storm #1 July 28, 2015

21 Failure at Genus Level 35% 25 35% 30% 30% 20 30% 27% Storm % Total % 25% 25% 25% 24% Average DBH (in) 15 20% 20% 15% 15% 10 12% 17% 10% 10% 5 5% 5% 7% 6% 5% 5% 0% 0% 0 Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp. Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp.

22 Average DBH at Time of Failure Average DBH (in) Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp.

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24 Number of Elm Failures by Cultivar or Variety Valley Forge 35 Princeton 7 Patriot 0 New Horizon 1 New Harmony 0 Commendation 0 Cathedral 0 American Elm (WT) 0 Accolade

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26 Elm Inventory Citywide

27 Elm Failure Percentage of Total Population Valley Forge 4.8% Princeton 0.3% Patriot 0.0% New Horizon 0.5% New Harmony 0.0% Commendation 0.0% Cathedral 0.0% American Elm (WT) 0.0% Accolade 0.1% 0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0%

28 Storm #2 July 5, 2016

29 Failure at Genus Level 40% 35% 36% Storm % Total % 30% 25% 27% 27% 20% 19% 17% 15% 12% 10% 5% 7% 6% 5% 5% 0% Ulmus sp. Acer sp. Tilia spp. Fraxinus spp. Celtis spp.

30 Average DBH at Time of Failure Average DBH (in) Ulmus sp. Acer sp. Tilia spp. Fraxinus spp. Celtis spp.

31 Number of Elm Failures by Cultivar or Variety Valley Forge 123 Princeton 53 Patriot 1 New Horizon 0 New Harmony 3 Commendation 1 Cathedral 1 American Elm (WT) 5 Accolade

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34 Elm Inventory Citywide

35 Elm Failure Percentage of Total Population Valley Forge 17.7% Princeton 2.7% Patriot 0.2% New Horizon 0.0% New Harmony 0.4% Commendation 0.9% Cathedral 0.5% American Elm (WT) 0.5% Accolade 0.3% 0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0% 16.0% 18.0% 20.0%

36 How Can We Reduce Tree Failures? without getting rid of all the trees!

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38 Utility Vegetation Management $20,000,000 to $50,000,000 lost annually to storm-related outages Many outages are the result of downed trees and/or branches Maintenance of vegetation can be extremely hazardous Pesticides can reduce the need for vegetation management

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44 C₁₅H₂₀ClN₃O

45 Paclobutrazol (PBZ)

46 PBZ Blocks Gibberellin Gibberellins cause cell elongation Cell elongation causes longer branches Longer branches create more pruning More pruning means more work More work means more risk!

47 Electricity is consistently one of the leading causes of worker fatalities in the tree care industry Tree Care Industry Association Five Year Analysis of Tree Care Accidents ( )

48 Photo: Tomahawk Tree Service, Ltd.

49 Image: Pacific Gas & Electric Co.

50 Image: Rainbow Treecare Scientific Advancements

51 The Efficacy of Paclobutrazol Soil Application as it Relates to the Timing of Utility Right-of-Way Pruning Haugen et al. Arboriculture & Urban Forestry 42(2): (2016) PBZ was used to slow the growth of live oak near utilities. PBZ reduced the time necessary to prune trees and process pruned material. Treatment produced shorter branches and less biomass. Ideally applied 90 days before or after pruning Overall this means easier pruning and processing

52 WOUND CLOSURE IN TREES AFFECTED BY PACLOBUTRAZOL Bai et al. Journal of Arboriculture 31(6): (2005) PBZ applications were made to nine tree species Trees were wounded to simulate pruning cuts Two-thirds of the trees showed slower wound closer after treatment with PBZ One-third of the trees showed wound closure that was unaffected after treatment with PBZ Wood discoloration/decay was not affected by PBZ

53 Next Steps Reducing Maintenance in Municipal ROWs

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59 Contacts & Links Chad Giblin Urban Forestry Outreach, Research & Extension (UFore) Nursery and Lab trees.umn.edu

60 Thanks! Environment & Natural Resource Trust Fund Minneapolis Park & Recreation Board City of Saint Paul Parks & Recreation Minnesota Turf & Grounds Foundation Minnesota State Capitol Minnesota Nursery & Landscape Association