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April 3, 2020

Reduce growth and mowing requirements with PGRs from Quali-Pro

Reduce Maintenance with Plant Growth Regulators


Plant growth regulators (PGRs) have been around for decades, but a better understanding of how and when to use them is still evolving.  PGRs are grouped into several different classes based on their mode of action.  Two of these classes suppress growth by blocking the production of a plant hormone called gibberellic acid (GA).  GA promotes plant cell division and elongation, so lower levels result in lower growth rates.

Quali-Pro T-NEX: Trinexapac-ethyl has long been a trusted means of reducing mowing needs on virtually all grass types.  It is a Class A PGR, meaning it blocks the GA pathway at the final stage of production.  T-NEX is foliarly absorbed and suppresses vertical shoot growth, decreasing clippings by as much as 50% while improving color and density. 


Quali-Pro Paclobutrazol: Paclobutrazol is a Class B PGR, inhibiting GA production at the early stage of the pathway.  It also differs from T-NEX in that it is absorbed by roots.  Poa annua is more sensitive to Paclobutrazol than more desirable turf types, which can help give bentgrass a competitive advantage and reduce Poa populations over time.

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Timing is Everything:  Extending control duration is not as simple as increasing rates, which may lead to unwanted discoloration and overregulation.  Once inside the plant, the PGR breaks down faster at higher temperatures, making the longevity of suppression very weather dependent.  Carefully timing follow-up applications using growing degree days (GDD) allows for steady, continued regulation and avoidance of “rebound growth” based on daily temperatures.  This approach is still being developed and differs based on the PGR, turf species, and mow height.  For bentgrass greens, multiple Paclobutrazol applications are applied based on a 300 GDD model, while T-NEX applications should be scheduled on a 200 GDD model.  Fortunately, University of Nebraska-Lincoln’s free GreenKeeper app ( ) includes a PGR GDD tracker that takes these factors into account, and can be used to design a program to fit your specific needs.

Always read any product label thoroughly before use, and for additional information, visit or contact your Quali-Pro Area Manager.


Weed Watch

Spring has definitely “sprung” at this point for many, and crabgrass has begun germinating throughout the transition zone and further south.  Follow up preemergent applications this month can extend control and also help prevent goosegrass, which will begin germinating next.  If you missed your crabgrass preemergent application Dithiopyr can provide some control of very young crabgrass plants (before tillering) and give preemergent protection against many broadleaf weeds about to germinate.  Once emerged crabgrass reaches the 5 tiller stage, Quinclorac with methylated seed oil is a great selective control approach down the road.     


Insect Watch

In the northeast and Midwest, April is when annual bluegrass weevil scouting really ramps up.  Targeting the adult growth stage after they transition from wooded areas to congregate on turf typically coincides with the late blooming stages of forsythia, when they are half yellow and half green.

Further south, mole cricket flights usually peak in April, so be on the lookout for signs of tunneling.   Areas with heavier tunneling is where more egg laying will occur.  Examination of females after a soap flush can help determine when peak egg laying will happen.  Cut open the abdomen to examine eggs for firmness and color.  Darker, firm eggs will be laid within the following week or so, with hatching about 20 days later. 



Ian Rodriguez, Ph.D.

Ian Rodriguez Technical Service Manager Quali-Pro

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