Application Rates for 

Ornamental Spray and Drench Uses

The majority of the applied paclobutrazol plant growth regulator (PGR) volume in the ornamental 

market segment is annual bedding plants. Typical rate use ranges for bedding plants is 30 to 50 part per 

million (ppm) applied as a foliar spray or as a container drench at 1 to 4 ppm. The primary use pattern is 

as a foliar spray given that it allows growers more flexibility in managing the growth regulation of the 

targeted crop. Both foliar spray and container drench applications allows growers of ornamental plants 

to manage growth and obtain the desired response and management for the specific growing

conditions. 

EPA’s ecological risk assessment for paclobutrazol overestimates the pounds of active ingredient per 

acre (ai/A) and overall environmental exposure by using a drench rate of 200 ppm that applies to 

amaryllis bulbs - this specific use pattern represents a very small percentage of the Floriculture 

market. The USDA 2014 Floriculture Survey lists that about 1% of the overall market is bulb uses (see 

below table – value is in Million USD). Six percent of the Potted Flowering market is for spring bulbs. 

This six percent only represents 1.18% of the overall market. Only a small portion of the spring bulb use 

is amaryllis given that most of this market are tulips, daffodils, etc. (crops other than amaryllis). 

Additionally, bulbs, such as amaryllis, are ‘forced’ to bloom indoors within a greenhouse. Bulb dips or 

drenches, such as those modeled, would occur indoors, and therefore limit outdoor environmental 

exposure from applications of paclobutrazol.

Table - Value is in Million USD

Wholesale Floriculture Market (WFM) Value Percent Segment

Annual Bedding 1356 32%

Potted Flowering 778 18%

Foliage Plants 631 15%

Perennials 602 14%

Cut Flower 419 10%

Propagative Floriculture 390 9%

Cut Cultivated Greens 77 2%

Total 4253

Potted Flowering Value Percent Segment Percent WFM

African Violets 3.86 0.5% 0.09%

Azaleas 18.97 2.4% 0.45%

Chrysantehmums 22.46 2.9% 0.53%

Easter Lily 23.56 3.0% 0.55%

Orchid 245.8 31.6% 5.78%

Poinsettia 145.9 18.8% 3.43%

Florist Rose 31.09 4.0% 0.73%

Spring Flowering Bulb 50 6.4% 1.18% Amarylis is only a small portion of this even

Other Flowering 236 30.3% 5.55%

Total 777.64 18.28%
The 200 ppm application rate (bulb drench for Amaryllis) grown in 8” pots and applied as a container 

drench application (see following table) overestimates the lbs. active ai applied by a factor of 50 relative 

to the common use pattern for annual bedding plants and the majority of use in the production of 

ornamental plants. This is 6.08lbs ai/A for the modeled rate versus 0.03 to 0.12 lbs ai/A (1 to 4 ppm) for 

the typical (and majority use) use for bedding plants. 

A similar analysis can be developed for foliar spray applications. Woody ornamentals are not a 

significantly large use pattern compared to annual bedding plants. The typical use rate for spray 

applications of annual bedding plants is 30 to 50 ppm which equates to .03 to 0.05 lbs ai/A. This is 4 

times less than the rate used in the EPA model (see following table).

For additional perspective, please refer to the listed link to an article on floriculture research by Kansas 

State University and Cornell University scientists, who report research on use patterns for PGR’s in 

Amaryllis production. 

http://www.gpnmag.com/controlling-amaryllis-height-pre-plant-bulb-soaks

Please see below detailed USDA Floriculture 2014 Survey information. 

Highlights from Operations with Sales of $100,000 or More 

Total Wholesale Value: The total wholesale value of floriculture crops sold by operations with $100,000 

or more of sales in the 15-State program is $4.25 billion for 2013, up 1 percent from the 2012 total. 

These operations account for 97 percent of the total value of $4.40 billion in floriculture crops, but 

comprise only 42 percent of all producers. California accounts for 27 percent of the total wholesale value 

in the 15-States. Florida ranks second with 21 percent; while Michigan ranks third with 9 percent, and 

Texas and North Carolina round out the top 5 each accounting for 6 percent respectively. 

Number of Producers: The number of producers with sales of $100,000 or more totaled 2,535 for 2013, 

down 5 percent from 2,655 in 2012. 
Bedding/Garden Plants: The wholesale value of all bedding and garden plants, which include 

herbaceous perennials, at $1.96 billion, is up slightly from the previous year. This plant category is the 

largest contributor to total value of sales and represents 46 percent of the wholesale value of all the 

reported crops. California, Michigan, Texas, North Carolina, and Ohio, the top 5 States in this category, 

account for 56 percent of the 15-State total bedding and garden value. 

Annual Bedding and Garden Plants: The wholesale value sales for annual bedding and garden plants 

totaled $1.36 billion in 2013, down 2 percent from 2012. This value represents 69 percent of the total 

bedding and garden category. The number of growers producing annual bedding and garden plants 

totaled 1,509, down 6 percent from 2012. 

Potted Herbaceous Perennials: Total wholesale value of potted herbaceous perennials totaled $602 

million in 2013, up 5 percent from 2012. These crops account for 31 percent of the total bedding and 

garden category. The number of growers producing herbaceous potted perennial plants totaled 1,201, 

down 6 percent from 2012. 

Potted Flowering Plants: Potted flowering plants for indoor or patio uses are valued at $778 million, up 

6 percent from 2012. California accounts for 38 percent of the 15-State value in this category, and 

Florida accounts for 22 percent. The value of Potted Poinsettias totaled $146 million, up 1 percent from 

the previous year. The value of Potted African Violets totaled $3.86 million, down 7 percent from 

previous year. There were 982 potted flowering plant producers in 2013, down 8 percent from 2012. 

Foliage Plants: The value of 2013 foliage plant sales, at $631 million, is down 1 percent from the 

previous year. Florida continues to dominate this category with 72 percent of the total value. Potted 

Foliage Plants represent 89 percent of the total foliage value. The remainder of the value is from hanging 

baskets. The number of foliage plant producers totaled 779 in 2013, down 5 percent from 2012. 

Cut Flowers: The wholesale value of domestically produced cut flowers is $419 million for 2013, down 

slightly from 2012. California’s value is $328 million, accounting for 78 percent of the total cut flower 

value in the 15-State program. In 2013, the number of producers dropped to 301. 

Cut Cultivated Greens: Cut cultivated greens wholesale value for 2013, at $77.2 million, is up 2 percent 

from 2012. Florida’s value, at $60.8 million, represents 79 percent of the category total. The number of 

producers in 2013, at 160, increased 2 percent from the previous year. 

Propagative Floriculture Materials: Total value of sales of material for propagating annual bedding and 

garden plants, potted herbaceous perennials, potted flowering plants, foliage plants, cut flowers, and cut 

cultivated greens is $390 million for 2013, up 1 percent from the previous year. The three leading States, 

California, Michigan, and Florida, account for 60 percent of the 15-State total.









Greenhouse and Nursery Crop Production with 

Retention or Recycled Irrigation Water

Based on the 2014 USDA Floriculture Survey, the table below shows 55% of all Floriculture production in 

the US is in an enclosed greenhouse structure. Another 40% of production is under shade or temporary 

cover. Only 4% of production is in an outdoor setting.
Floriculture Production area Million Sq Ft Percent

Greenhouse 405 55%

Shade or Temporary cover 294 40%

Outdoor 32 4%

Total 731

More than 50% of all application of paclobutrazol occurs in an enclosed environment, i.e. greenhouse,

which would limit non-target impact and run-off as amount of water is limited to what the crop needs 

and runoff from rain does not occur. 

The referenced article (link listed below) suggests, even in outdoor production in CA where retention 

and or recycling occurs, applied plant protection chemicals (not same class as paclobutrazol) were 

detected about half the time or less during irrigation and even lower amounts during precipitation 

events. These physical transportation rates for plant protection chemicals should be considered relative 

to known physical-chemical properties for paclobutrazol which would expect a conclusion of even lower 

movement levels under greenhouse 

cover. http://hortsci.ashspublications.org/content/43/2/393.full.pdf

Prevalence of Paclobutrazol in Tree Use Applications

Please refer to attached article from the Massachusetts EPA, which conducted a review of paclobutrazol 

applications in rights-of-way uses. Arborist Paul Sellers (who directs NStars vegetation management 

activities) states that applications of Paclobutrazol in rights-of-way activities are applied in “high visibility 

locations such as parks, historic downtowns, residential areas and other areas where trees have a 

cultural value”. NSTAR transmits and delivers electricity to 1.1 million electric customers in 81 

communities and nearly 300,000 gas customers in 51 communities. NSTAR is an operating company of 

Northeast Utilities. http://www.mass.gov/eea/docs/agr/pesticides/rightofway/docs/paclobutrazolreview-jan-2012.pdf

William R. Chaney, professor of tree physiology, Purdue University, describes the use of Paclobutrazol in 

golf course settings on “amenity” trees. The treatment information provided describes, whether as a 

soil injection or drench, both are a labor intensive activity which would inherently limit application, 

because of cost and time, to a limited number of 

trees. http://www.sepro.com/documents/profile_article.pdf

The information above, when considered in combination with the pounds of active ingredient actually 

used by the tree care market segment (provided under separate cover by registrants), indicates the 

limited use of paclobutrazol for tree management. 
1

Nguyen, Khue

From: Nguyen, Khue

Sent: Thursday, June 18, 2015 11:42 AM

To: Nguyen, Khue

Subject: FW: paclobutrazol--question re tree drench

From: Michael Russo [mailto:Michael.Russo@AgripharCropSolutions.com]  

Sent: Friday, January 23, 2015 7:24 AM

To: Nguyen, Khue

Subject: RE: paclobutrazol‐‐question re tree drench

Khue, 

This is what I found out. Our Paczol label does not include basal drench use on trees- it is limited to use on greenhouse and nursery 

grown containerized ornamentals. Drench applications for our products labeled uses would not be done with backpack equipment, as 

the volumes applied are too high, would take too long, and would require constant refilling. In fact, the same would be true for basal 

drench applications to trees- the volumes applied are so high that the applicator would be refilling his back pack after one or two 

trees! Drench applications are typically done using a high volume hand held hose connected to a large spray tank. 

Regards, 

Michael 

Michael Russo Registration Specialist, NA Agriphar Crop Solutions T + 203-575-5952 www.AgripharCropSolutions.com 
1

Nguyen, Khue

From: Nguyen, Khue

Sent: Thursday, June 18, 2015 11:50 AM

To: Nguyen, Khue

Subject: FW: paclobutrazol--question re tree drench

From: Tyler Tammy USGR [mailto:tammy.tyler@syngenta.com]  

Sent: Wednesday, January 28, 2015 10:26 AM

To: Nguyen, Khue

Cc: Ballard, Kelly; Anderson, Neil

Subject: RE: paclobutrazol‐‐question re tree drench

Khue,

I have been consulting with Steve Cosky, Product Biology Lead for Ornamentals and Craig Jakubek, Brand Manager for

Turf and Landscape, and we are convinced that drench application is not applied via backpack sprayer and the following

gives the reasoning:

Facts

 A backpack sprayer typically is designed to hold ~ 3 gal.

 As a rule of thumb, agronomists consider that 1” of rainfall (or water applied as irrigation) will wet the soil 12”

deep, depending on soil type, current amount of water in the soil, etc.

 An acre inch of water is 27, 154 gallons of water.

 Let’s apply a drench to a 12” tree and the drench is applied evenly to an area 2 feet outside the circumference of

a tree. (2 feet chosen at random)

Let’s calculate ......

 The area to be treated for a 12” diameter tree when the drench is applied 2 feet around the outside of a tree is

18.6 ft.‐2 (0.00043 A).

o The area calculation adjusts for the 0.8 ft.‐2 footprint of the tree.

 Application of a drench to wet 6” of soil (not 12”) requires 13,577 gal. of water/A.

 Applying this drench with a 3 gallon backpack requires 5.8 gallons of solution.

o The 3 gallon backpack cannot deliver the required volume without stopping to refill.

o Emptying 3 gal. of solution from backpack sprayer is time consuming.

o This is not practical.

 Even if considering smaller trees, for example with a DBH of 3”:  the same scenario for a 3” diameter tree would

actually have larger diameters at the base of the tree and consume even larger application volumes;  a 3” tree

would consume 4.4 gal. of spray solution if applied 2 feet from the base of the tree.  Still, a greater quantity than

the typical 3 gal. backpack sprayer.

Conclusion:  A hydraulic sprayer with hand held application nozzle is the most typical application tool to apply the

drench.

You then ask:

How often does mixing/loading take place?   

And how many trees are treated per applicator?   

Our estimation is that in an 8 hour shift they would do 5 stops at 1.5 hours per stop (travel, set up, treatment, clean up

and travel to next stop) – this is an amenity (high value tree application process per prior articles) – so at most 5‐10 trees

per stop – 26 to 50 trees a day “if” they do nothing but treat trees all day!   
2

With a hydraulic sprayer on a truck, a 100 gallon spray tank would not be unusual.

 A 100 gallon sprayer (using the treatment parameters above) could treat 20 trees (applying ~ 5 gal. per tree).

 Treatment time might be somewhat similar to that as soil injection, but would likely be delivering a lower

volume but higher concentration of active ingredient.

 Syngenta has witnessed the commercial soil injection of trees in Naperville, IL, this past summer.  A soil injection

may be applied in 2‐3 minutes.  It takes longer to move the application equipment from site to site.

 It is plausible that 50 trees could be treated as a drench by an applicator in a day using hydraulic application

method.

 If a drench is calculated at 5 gal. per tree and an applicator could treat 50 trees, than that is 250 gal. of

application solution.

o Therefore, a mixer/loader might mix 2‐3 times in a day if that application crew did nothing except

drench.  (How  likely is that?)

I hope this helps.  Sorry I am just getting back to you today.  Please feel free to call me or email for more questions or

clarification.  We are also prepared to meet and discuss as well!

Sincerely,

Tammy
1

Nguyen, Khue

From: Nguyen, Khue

Sent: Thursday, June 18, 2015 11:54 AM

To: Nguyen, Khue

Subject: FW: paclobutrazol--question re tree drench

From: Fred Smith [mailto:fsmith@SciReg.com]  

Sent: Friday, January 30, 2015 8:26 AM

To: Nguyen, Khue

Cc: Ballard, Kelly; Anderson, Neil

Subject: RE: paclobutrazol‐‐question re tree drench

Khue— 

See Fine’s responses below in red. Any further questions, please let me know. 

Kind regards, 

--Fred 

From: Nguyen, Khue [mailto:Nguyen.Khue@epa.gov]  

Sent: Thursday, January 22, 2015 6:27 PM

To: tammy.tyler@syngenta.com; Michael Russo; Fred Smith; Leanne Pruett; steve@pyxisrc.com; Janelle Kay; Jim Damico

Cc: Ballard, Kelly; Anderson, Neil

Subject: RE: paclobutrazol‐‐question re tree drench

Hi all,

I have been in touch with pretty much all of you today with a question regarding the tree drench use for paclobutrazol—

whether mixing/loading/applying liquids via backpack sprayer actually occurred for the tree drench use.  I have already

heard from a couple folks indicating that backpack sprayers were not used for the tree drench use, and this is good

news, but we thought it would be better to provide the context for our question.       

The revised human health assessment identified occupational handler risk for mixers/loaders/applicators

mixing/loading/applying liquids via backpack sprayer for drench tree treatments.  The assessment covered this scenario

because the labels did not preclude application via backpack sprayer for tree drench.   

Firstly, are there instances where applicators apply liquids via backpack sprayer to drench trees?  If so, how does this

occur—how often are applicators mixing/loading?  How many gallons are applied per tree?  How many trees are treated

per applicator in a day in this case (we assumed 50 in our assessment)?   

Applicators do not use a backpack to make drench applications.

Since it does not appear that applicators are using backpack sprayers for tree drenches often (if at all), what type of

application equipment is used instead?  How often does mixing/loading take place?  And how many trees are treated

per applicator?   

Drench applications are typically made using a bucket or a 2.5 gallon jug. Mixing occurs every time an application is

made as the dose is determined for each tree. We estimate 5 to maybe 10 trees would be treated per day. This is only

done when an applicator is treating a residential or perhaps a commercial property.
2

For the tree drench use we also modeled mixing/loading/applying liquids via manually pressurized handwand and that

passed.   

Any info you can provide would be helpful for risk characterization and risk management.  Please respond as soon as

possible.  

Thanks,

Khue Nguyen

Chemical Review Manager

Risk Management and Implementation Branch 1

Pesticide Re‐evaluation Division

Office of Pesticide Programs, EPA

703‐347‐0248

Nguyen.khue@epa.gov
1

Nguyen, Khue

From: Nguyen, Khue

Sent: Thursday, June 18, 2015 11:31 AM

To: Nguyen, Khue

Subject: FW: question re paclobutrazol

From: Tyler Tammy USGR [mailto:tammy.tyler@syngenta.com]  

Sent: Wednesday, June 10, 2015 11:23 AM

To: Nguyen, Khue

Cc: Moriarty, Thomas; Anderson, Neil; Parshley Tom USGR; Cosky Steve USGR; Jakubek Craig USGR

Subject: RE: question re paclobutrazol

Hello Khue,

Paclobutrazol benefits:

‐ Stronger control (single spray or single effective and tested drench rates) compared to chemistries like B‐Nine

and Cycocel (which require multiple sprays). Seasoned growers like this versus multiple labor treatments.

‐ Over 25 years of experience in our industry, growers are comfortable with using and the performance of Bonzi

whether as a spray or drench.

‐ Does not delay flowering on core crops like petunia and pansy compared to other PGR’s

‐ Does not reduce flower size at the label rates compared to other PGR’s

‐ Tested across multiple crops in propagation, production and retail post‐harvest – greater database

‐ Cyathia holding on poinsettia (the flower on a poinsettia is called a cyathia – you want these to stay on the plant

as long as possible to maintain consumer appeal – paclo helps with this)

‐ Stock plant leaf size management and water management (In the production of un rooted cuttings (plants can

either be started from seed or plant pieces called cuttings) it is important to maintain well branched, compact

plants (don’t want lush growth, with long internodes etc) – paclo offers significant benefits for this and thereby

improves cutting quality and yield.  As a result of using paclo you can also use less water which aids in a less lush

plant (leaf) which is less prone to disease in transportation and during the rooting of un rooted cuttings)

‐ Significant database on crops from academics and Syngenta trials

‐ Cost is slightly better than Sumagic or Topflor when applied at the right drench rate

‐ More activity than Ancymidol, Daminozide, Cholormequat and Fluprimodol

‐ Can be used in all application methods – Spray, Media spray, drench, bulb dip, liner dip, chemigation and

subirrigation

‐ Good value compared to other ais like Ancymidol which is only used on plugs

‐ Broad range of crops effective on unlike chlormequat chloride which is only used on geraniums, poinsettias and

hibiscus

Please let me know if you need clarification on any of these points.  I hope you find this helpful.

Sincerely,

Tammy

-------------------------------------------------------------------------------------------------------------

Tammy Tyler, Ph.D. 

Regulatory Affairs 

Fungicide & Insecticide 

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410 Swing Rd 

Greensboro, NC 

27409