PGRs and TGRs
Different Modes of ActionType I and Type II
• Type I growth regulators inhibit cell
division.
• Type I growth regulators are foliar
absorbed.
Different Modes of ActionType I and Type II
• Most Type I Growth regulators are older
materials that cause some phytotoxicity on
grass.
• Mefluidide (Embark) is utilized more than
any other type I growth regulator, but it
yellows and thins turf when used during hot
weather conditions.
Different Modes of ActionType I and Type II
• Maleic hydrazide (MH-30, Royal Slo-Gro)
is one of the oldest growth regulators used
on turf, and causes extensive yellowing.
Type I- Growth Regulators
• Embark (mefluidide) is also used to
inhibit seed head formation of Poa
annua to improve the appearance and
playability of fairways.
• The rate used for seed head
suppression is 1/12-1/16 of the growth
regulation rate.
Type I- Growth Regulators
• Timing is critical- must be within two
weeks of flowering to be effective.
• Usually about two weeks after the first mowing
is a good time to apply.
• Some yellowing may still occur, but this can
be reduced by using products like
Ferremec.2
• If you are going to try it, read the label
thoroughly!
Type II Growth Regulators
• Type II growth regulators work by
inhibiting biosynthesis of gibberellin.
• Since, gibberellin causes cell elongation,
little or no elongation of cells occurs when
GA is inhibited.
Type II Growth Regulators
• Type II growth regulators include:
•
•
•
•
Cutless (Flurprimidol),
Limit (amidochlor),
Primo (trinexapac- ethyl)
TGR Turf Enhancer (paclobutrazol)
• http://www.uhsonline.com/prodframe.p
hp
Type II Growth Regulators
• Type II growth regulators generally are less
phytotoxic, and some actually have benefits
other than reduced growth.
• Amidochlor (Limit) is less damaging to turf
than type I growth regulators, but still
should not be used on high maintenance
turf.
Type II Growth Regulators
• Many superintendents have tried Type II
growth regulators as a means of reducing
Poa annua on their golf courses.
• http://www.andersonsgolfproducts.com/st_p
oaannua.asp
Type II Growth Regulators
• Growth in Poa annua is reduced more than in
Agrostis palustris, giving the creeping bentgrass a
chance to spread into the territory held by Poa
annua . (1,2,3,4,5)
• Cutless, TGR Turf Enhancer and Primo have all
been used in this way with varying degrees of
success. (1,2,3,4)
• Cutless and TGR Turf Enhancer are most effective
in suppressing Poa annua but they also cause
yellowing which may be unacceptable.
Type II Growth Regulators
• Other possible benefits of type II Growth
Regulators include:
• Reduced mowing- the duration of
suppressed growth varies considerably
(usually 4-7 weeks) depending on species,
environmental and growth factors. (1,2,3,4)
Type II Growth Regulators
• Increased shoot density- more tillering (1,2,3,4)
• Reduced water use- lower ET rates have been
observed with Primo, Cutless and TGR.
• However, Primo was the only material that
enhanced turf quality during dry down in one
study. (4)
• Longer disease suppression with contact
fungicides ??
Type II Growth Regulators
• Flurprimidol and paclobutrazol have been
shown to reduce dollar spot disease
incidence somewhat on creeping bentgrass.
• Improved green speed at mowing heights >
1/8” (research doesn’t back this theory up)
Cutless
Type II Growth Regulators
• There are also some possible negative
effects of Type I and II Growth Regulators.
They include:
• Reduced uniformity- regulation of growth
can vary between grasses resulting in nonuniform appearance.
Type II Growth Regulators
• “rebound effect”- after the growth regulator
wears off, there is often a flush of growth resulting
in reduced turf quality and a need for increased
mowing.
• Primo and Embark have caused this response.
• Increased weed problems- some weeds,like
goosegrass, have less of a reduction in growth rate
than turfgrasses.
• Moreover, some weed species like crabgrass
increase in shoot production due to increased
tillering caused by some PGRs. (5)
Type II Growth Regulators
• Slower recuperation from injury?
• Increased susceptibility to some
diseases? Type I growth regulators have
shown to cause increased disease
problems.(2)
New Classification Scheme for
TGRs
• A new way to classify growth regulators has
been developed using classes A,B,C, and D.
• Class A materials are GA inhibitors that
interfere with GA synthesis late in the
biosynthetic pathway.
• Only Trinexapac-ethyl is in the category.
New Classification Scheme for
TGRs
• Class B materials interfere with GA synthesis
early in the biosynthetic pathway.
• Fluprimidol and paclobutrozol are included in this class.
• Class C materials inhibit mitosis.
• Hyradazide, mefluidide and amidochlor are in this category.
• Class D materials are phytotoxic (can kill plants)
but have a growth regulating effect at very low
rates.
• Glyphosate (Roundup) and chlorsulfuron (Telar) are examples.
A “New” Growth Regulator for
Turf
• Proxy (ethephon) recently received a label
for turfgrass use.
• Ethephon works by releasing ethylene into
turfgrass leaves. (2)
• Ethephon has a more subtle action than
type I or type II inhibitors with no
noticeable change in growth habit for about
2 weeks.(2)
A “New” Growth Regulator for
Turf
• Ethephon does not fit into the A,B,C,D
scheme of classification either.
• Ethephon has no rebound effect like Primo
and Embark do.
A “New” Growth Regulator for
Turf
• Proxy may be very effective in battling Poa
annua with growth reduction as high as 90%
with an average of 38% over seven weeks
• Bentgrass growth reduction with Proxy was
a maximum of 50% and a 14% average over
seven weeks. (2)
A “New” Growth Regulator for
Turf
• Proxy is not labeled for greens- further
testing needs to be done.
• Proxy is also labeled for Poa annua seed
head supression.
• Nick Christians claims that Poa pratensis
treated with Proxy changed in form to an
almost stoloniferous growth habit, which
might improve wear tolerance.
Fertility and Growth Regulators
• It is generally best to keep fertility levels
somewhat higher on turf treated with growth
regulators than on non- treated turf because:
• Growth regulation effects seem to be enhanced at
higher fertility levels.
• Higher fertility levels help to mask the chlorosis
that sometimes appears when growth regulators
are used.
Seedhead Management & Plant Growth
Regulators
• Poa is not a single, uniform turf species.
• It has a large number of turf subspecies or
biotypes.
Seedhead Management & Plant Growth
Regulators
• Poa annua can range from:
• annual types that die each spring following a period of
intense seedhead formation.
• Biotypes that live for several years and flower later in
the season for longer periods of time.
• It is impossible to predict which biotypes you have
on your course.
• The many biotypes is the #1 reason its so hard to
predict precisely when the seed will form.
Seedhead Management
• At courses where Poa is tolerated, reducing seed heads
makes a difference.
• Most seed head management has relied on a combination
of cultural practices and applications of PGR’s.
• The cultural practices used to improve mowing when seed
heads are present include brushing and vertical mowing.
• Proxy is becoming the preferred chemical for seed head
management.
Seedhead Management & PGR’s
• Mefluidide is well known for its ability to slow down or
stop seedhead formation.
• Mefluidide is used to inhibit Poa Seedhead formation on
golf courses.
• Under optimal conditions, applications can result in 85 –
90% Poa annua seedhead suppression.
• There are some drawbacks of using this product.
Drawbacks of Using Mefluidide
• Varying Turf Response
-Using PGR’s to slow seedhead formation came into
use in the 90’s, but results vary greatly by location.
-Seedhead suppression will last from 3 – 6 weeks.
-To keep seedheads formation consistently low, you
will need to increase the rate gradually after each
application.
-Success depends greatly on the skill of the
superintendent to adapt the program to his or her course.
Drawbacks of Using Mefluidide
• Timing of the First Application
-Because this product does not affect seedheads that
already exist the first application needs to be made two
weeks before the first flush of seedheads.
-The first application will need to be at different times in
different location or different climates.
References
• 1. Christians, Nick, Creative Uses for Turfgrass
Growth Regulators, USGA Green Section Record,
September-October 2001, p.11-13.
• 2. Dernoeden, Peter. Creeping Bentgrass
Management. Sleeping Bear Press, Inc. Chelsea,
MI, 2000.
• 3. Diesburg, Kenneth. A New Growth Regulator
for Golf Course Turfgrass. Golf Course
Management. November 1998.
• 4. Fermanian, Tom. Managing Bentgrass Fairway
Growth with PGRs. Grounds Maintenance. May
1997.
References
• 5. Fry, J.D. Plant Growth Regulators May
Help Reduce Water Use. Golf Course
Management. November 1998.
• 6. Lowe, Todd et al. Some weeds Flourish
Under Growth Regulators. Golf Course
Management. September 1999.
LINKS
• http://www.grounds-mag.com/managing.htm
• http://virtual.clemson.edu/groups/hort/sctop/TURF
Sec/weedsci/weedsci5.htm
• http://www.cp.us.novartis.com/products/specialty/
PrimoWSB.shtml
• http://link.springerny.com/link/service/journals/10088/bibs/38n4p102
8.html
• http://www.turf.uiuc.edu/itf/tips/tt97-2.html
LINKS
• http://www.hort.iastate.edu/pages/news/turfr
pt/1999/greenpoa98.html
• http://www.msu.edu/user/rogersj/laplata.ht
ml
• http://edis.ifas.ufl.edu/scripts/htmlgen.exe?
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