Post on 26-Nov-2018
Plant Growth Regulators: Slow & Steady Wins the Race
MNLA Fall Pesticide RecertificationNovember 16, 2018
Chad P. GiblinDepartment of Forest Resources - University of Minnesota
Contacts & LinksChad Giblin
giblin@umn.edu
Urban Forestry Outreach, Research & Extension (UFore)
Nursery and Labtrees.umn.edu
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
Failure at Genus Level
0
5
10
15
20
25
Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp.
Aver
age
DBH
(in)
0%
5%
10%
15%
20%
25%
30%
35%
Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp.
30%
25%24%
6%5%
12%
27%
7%
17%
5%
0%
5%
10%
15%
20%
25%
30%
35%
Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp.
Storm %
Total %
Average DBH at Time of Failure
18.2
15.1
5.5
19.1
13.1
0
5
10
15
20
25
Tilia spp. Acer spp. Ulmus spp. Fraxinus sp. Celtis sp.
Aver
age
DBH
(in)
Number of Elm Failures by Cultivar or Variety
1
0
0
0
0
1
0
7
35
0 5 10 15 20 25 30 35 40
Accolade
American Elm (WT)
Cathedral
Commendation
New Harmony
New Horizon
Patriot
Princeton
Valley Forge
Elm Failure Percentage of Total Population
0.1%
0.0%
0.0%
0.0%
0.0%
0.5%
0.0%
0.3%
4.8%
0.0% 1.0% 2.0% 3.0% 4.0% 5.0% 6.0%
Accolade
American Elm (WT)
Cathedral
Commendation
New Harmony
New Horizon
Patriot
Princeton
Valley Forge
Failure at Genus Level
36%
27%
19%
6%5%
7%
27%
12%
17%
5%
0%
5%
10%
15%
20%
25%
30%
35%
40%
Ulmus sp. Acer sp. Tilia spp. Fraxinus spp. Celtis spp.
Storm %
Total %
Average DBH at Time of Failure
5.5
16.9
21 20.8
13.1
0
5
10
15
20
25
Ulmus sp. Acer sp. Tilia spp. Fraxinus spp. Celtis spp.
Aver
age
DBH
(in)
Number of Elm Failures by Cultivar or Variety
5
5
1
1
3
0
1
53
123
0 20 40 60 80 100 120 140
Accolade
American Elm (WT)
Cathedral
Commendation
New Harmony
New Horizon
Patriot
Princeton
Valley Forge
Elm Failure Percentage of Total Population
0.3%
0.5%
0.5%
0.9%
0.4%
0.0%
0.2%
2.7%
17.7%
0.0% 2.0% 4.0% 6.0% 8.0% 10.0% 12.0% 14.0% 16.0% 18.0% 20.0%
Accolade
American Elm (WT)
Cathedral
Commendation
New Harmony
New Horizon
Patriot
Princeton
Valley Forge
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
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!
“Electricity is consistently one of the leading causes of
worker fatalities in the tree care industry…”
Tree Care Industry AssociationFive Year Analysis of Tree Care Accidents
(2009-2013)
• 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
“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): 95–101 (2016)
• 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
“WOUND CLOSURE IN TREES AFFECTED BY PACLOBUTRAZOL”Bai et al.
Journal of Arboriculture 31(6): 273–279 (2005)
Contacts & LinksChad Giblin
giblin@umn.edu
Urban Forestry Outreach, Research & Extension (UFore)
Nursery and Labtrees.umn.edu