Review of the Plant Growth

Regulator (PGR) Program

Michigan State University

Landscape Services Department

PGR (Paclobutrazol)

Paclobutrazol inhibits the production of

gibberellin in plants

New growth is reduced

Growth is controlled for 2-3 years

Safety and ecology

Sub-soil applied

Low water solubility product

Breaks down in the soil quickly

Low toxicity LD50: >5,000 mg/Kg

Plant Health Benefits

Increased fine root-hair production

Increased woody-root production with repeated

applications

Increased carbohydrate storage

Increased resistance to drought and disease

Notably improved foliage color and appearance

Uses for PGR’s

Preservation of plant material impacted by

construction activities

Promote quicker establishment of new trees

Preservation of declining or over-mature trees

Reduction in watering volume and frequency

Reduction in pruning intensity and frequency

How do PGR’s Reduce Pruning?

Normal Growth

Controlled Growth Using a PGR

Yr 0

Yr 6 Yr 2 Yr 1 Yr 0

Yr 1

Yr 5 Yr 4 Yr 3

PGR App PGR App

2012 2013

1. Wilson Hall

Before After

Untreated PGR

1. Wilson Hall

Untreated

PGR

1. Wilson Hall

2. Birch Road

Untreated (East Side) PGR (West Side)

2. Birch Road

Untreated PGR

3. Shaw Hall

Untreated PGR

3. Shaw Hall

Untreated PGR

4. Shaw Lane

Untreated (South Side) PGR (North Side)

4. Shaw Lane

Untreated PGR

5. Owen Graduate Center

Untreated PGR

PGR

6. Hubbard Hall

Untreated (South Side) PGR (North Side)

Results

Thus far in 2012, we have realized significant

growth control on most shrubs treated

spring/early summer

Severe drought stress was reduced by 50% by

utilizing PGR on trees (<10” DBH)

Plant health and appearance improved with

PGR

$0.00

$20.00

$40.00

$60.00

$80.00

$100.00

$120.00

Taxus sp. Forsythia sp. Euonymus sp. Viburnum sp.

(Cost to Use PGR Versus One Pruning Cycle Including Labor and Equipment)

Cost Comparison per 100 Sq. Ft.

PGR Cost

Pruning Cost

Accomplishments to Date

789 trees treated

1,731 individual shrubs treated

64,613 square feet of shrub beds treated

All work was completed in 152 hours with two

applicators

78 gallons of concentrated Paclobutrazol applied

Conclusion

PGR is an innovative and cost effective tool to

preserve MSU’s environmental resources

PGR will increase the longevity and aesthetic

quality of plant materials on campus

Re-allocating labor will allow Landscape

Services to maintain a high quality of service to

the MSU campus