2Different Modes of Action- Type I and Type II Type I growth regulators inhibit cell division.Type I growth regulators are foliar absorbed.
3Different Modes of Action- Type 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.
4Different Modes of Action- Type 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.
5Type 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.
6Type 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.2If you are going to try it, read the label thoroughly!
7Type 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.
8Type II Growth Regulators Type II growth regulators include:Cutless (Flurprimidol),Limit (amidochlor),Primo (trinexapac- ethyl)TGR Turf Enhancer (paclobutrazol)
9Type 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.
10Type II Growth Regulators Many superintendents have tried Type II growth regulators as a means of reducing Poa annua on their golf courses.
11Type 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.
12Type 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)
13Type 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 ??
14Type 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)
16Type 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 non- uniform appearance.
17Type 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)
18Type II Growth Regulators Slower recuperation from injury?Increased susceptibility to some diseases? Type I growth regulators have shown to cause increased disease problems.(2)
19New 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.
20New 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.
21A “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)
22A “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.
23A “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 weeksBentgrass growth reduction with Proxy was a maximum of 50% and a 14% average over seven weeks. (2)
24A “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.
25Fertility 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.
26Seedhead Management & Plant Growth Regulators Poa is not a single, uniform turf species.It has a large number of turf subspecies or biotypes.
27Seedhead 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.
28Seedhead ManagementAt 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.
29Seedhead 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.
30Drawbacks 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.
31Drawbacks 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.
32References1. Christians, Nick, Creative Uses for Turfgrass Growth Regulators, USGA Green Section Record, September-October 2001, p2. 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.
33References5. 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.