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Plant Growth Regulators (PGR’S)

Why:

• Reduce growth• Reduction in labor costs

• reduced mowing• reduced clippings

• Reduce growth when overseeding• Chemical edging around trees etc• Hillsides• Some PGR’s suppress poa seed head

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• Improve the health of the plant

• Density

• Drought stress-less water use

• Color

• Root development

• Increase putting green speed

• Increases in shade tolerance

• Increase wear tolerance

Why PGR’s Continued:

Original classification

Type I and Type II growth regulators:

Type I

• Compounds foliar absorbed and inhibit cell division at the meristem

• Excellent seedhead control

What are PGR’s?

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Type II

• Crown or root absorbed

• Inhibit or suppress both growth and development

• Suppression due to inhibition of gibberallic acid

• Usually less phytotoxic

• No effect on seedhead formation just elongation of seed stalk

What are PGR’s continued?

New Classification PGR’s- All reduce growth -

Class A:• Late gibberellic acid (GA) synthesis blockers (giberellic acids hormones responsible for cell elongation)

• Example Primo Max® (trinexapec-ethyl)

• Foliar absorbed

• Last 3-6 weeks depending on rate and use

Class A continued:

- poa reduction

- Color enhancement

- Overseeding reduction in competitiveness of existing species.

• germination and development of new seed is normal because of:

* late gibberellin synthesis inhibition

* class A are foliar absorbed

- Increases in shade tolerance

USE

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Class B:• Early GA synthesis blocker

• Trimmit® (paclobutrazol), Cutless®(flurprimidol)

• Root absorbed

• Use- poa reduction

Class C:• Mitotic inhibitors

• Slo Gro® (maleic hydrazide), Embark®(mefluidide), Limit® (amidochlor)

• Foliar or root absorbed

• Use- poa seedhead suppression

• May need to add fungicide, nitrogen, or iron

Class D:• Herbicidal mode

• Oust® (sulometuron-methyl), Round-up®(glyphosate), Telar® (chlorosulfuron), Prograss® (ethofumestate)

• Foliar and/or root

• Phytotoxic growth regulating response at low rates/herbicide at high rates

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Class E:• Ethylene production enhancement

• Proxy® (ethephon)

• Foliar

• Use- poa seed head suppression

Turfgrass Establishment

Applications Class A products are often used due to:

• Reduction in competitiveness of existing species when overseeding.

• Seeding germination and development is normal because of:

Late gibberellin synthesis inhibition of class A are foliar absorbed

Management of Poa annua

Class C products often used:•Direct suppression of seedhead formation

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Chicago Golf Club (Kane 2001) Mixed Bentgrass & Poa- 0.5” H.O.C. 18th Fairway

Proxy = Class E, Primo = Class A, Embark = Class CFoliar - Seed Head --- Foliar----- --- Foliar or Root ---

Pebble Beach Golf Links, #14 Fairway Pebble Beach CA (Mahady, 2001 )

Seed Heads Seed Heads Color Quality % Cover % Control

5/15/2001 5/15/2001 5/15/2001 5/15/2001Treatments 42 DAT 42 DAT 42 DAT 42 DATUntreated Check 6.8 d 8.0 b 34.8 b 0%Proxy(5) 8.0 bc 9.6 a 1.4 c 96% Proxy(5)+Primo(O.25) 8.4 ab 9.8 a 0.6 c 98% Primo(O.25) 7.6 c 8.4 b 44.8 a 0%

Typical green spray = 5oz / 1,000sq.’of Proxy

plus

.125 oz / 1000 square feet of Primo

• Turfgrass species or cultivars• Weather conditions• Soil moisture• Root absorbed PGR’s may require irrigation• Application timing• Plant health

What can affect PGR’s