United States

Department of

Agriculture

Forest Service

Southern 

Research Station

Research Paper

SRS–43

Mechanical Removal of

Chinese Privet 

John Klepac, Robert B. Rummer,

James L. Hanula, and Scott Horn
John Klepac, General Engineer, and Robert B. Rummer,

Research Engineer, U.S. Department of Agriculture Forest Service, 

G.W. Andrews Forestry Science Laboratory, Auburn University,

AL 36849; and James L. Hanula, Research Entomologist, and 

Scott Horn, Entomologist, U.S. Department of Agriculture,

Forest Service, Forestry Sciences Laboratory, Athens, GA

30602-2044.

The Authors

January 2007

Southern Research Station

200 W.T. Weaver Blvd.

Asheville, NC 28804

The use of trade or firm names in this publication is for reader information and does not imply endorsement 

of any product or service by the U.S. Department of Agriculture or other organizations represented here.

PESTICIDE PRECAUTIONARY STATEMENT

This publication reports research involving pesticides. It does not contain recommendations for their use, 

nor does it imply that the uses discussed here have been registered. All uses of pesticides must be registered 

by appropriate State and/or Federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other 

wildlife if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and their containers.

Cover Photo: Small tracked machine with horizontal mulching head removing 

Chinese privet at the Botanical Gardens in Athens, GA, during October 2005.


Mechanical Removal of

Chinese Privet

John Klepac, Robert B. Rummer,

James L. Hanula, and Scott Horn
ii
iii

Contents

Page

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 1

Study Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 1

Machine Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 1

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 2

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 2

Mechanical Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 3

Chemical Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 4

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 4

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 5

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 	 5
iv
Mechanical Removal of Chinese Privet 

John Klepac, Bob Rummer, Jim Hanula, and Scott Horn

Abstract

Chinese privet (Ligustrum sinense Lour.), a highly invasive nonnative

plant, is prevalent in the Southern United States. Chinese privet

infestations can hinder regeneration of desirable species, reduce stand

productivity, and have other undesirable consequences. A combined

mechanical (mulching) and chemical (triclopyr) treatment was applied to

Chinese privet in forest stands in Georgia on an experimental basis. The

cost of removing Chinese privet was estimated to be $737 per acre when

a tracked 110-horsepower mulching machine and a two-person herbicide

application crew are employed.

Keywords: Chemical treatment, Chinese privet, Georgia, invasive

nonnative plant, mechanical treatment, mulching machine, triclopyr.

Introduction

Chinese privet (Ligustrum sinense Lour.) is one of the most

invasive nonnative plants in the Southern United States. It

infests millions of acres and is extremely difficult to control

due to its adaptability to various site conditions (http://

www.gwf.org/vol14no2.htm). Introduced into the United

States in the 1800s, it arrived without the natural controls

of insects and diseases that keep plants in their natural

balance (Miller 1999). Natural regeneration in stands

infested with Chinese privet can be adversely affected,

resulting in a loss in stand productivity. Miller suggests that

invasive exotic plants impede forest productivity, hinder

forest-use activities, and limit diversity and wildlife habitat

(Miller 1997). 

Recommended control measures (Miller 2003) include

various applications of herbicide. Control by ground

spraying can be very labor intensive, while aerial application can be extremely expensive. In many situations plants

are too tall for effective treatment using ground application methods, making it essential to incorporate alternative

treatment techniques. For example, injecting herbicide

around the trunk into the cambium layer is one alternative

but is labor intensive and time consuming. Using a combination of mechanical and chemical treatments to control

this invasive species may reduce both labor requirements

and treatment costs. Although ineffective by themselves,

both mechanical and burning treatments can give additional kill of herbicide-weakened plants and may have a

place in an integrated pest management program (Miller

1999). 

Study Overview

This study was initiated by the Insects and Diseases of

Southern Forests Research Work Unit of the USDA Forest

Service, Southern Research Station. A total of four sites

were treated, each measuring 3 to 5 acres and consisting

of both bottomland hardwood and mixed pine-hardwood

stands. Sites were all located within the floodplain of the

Oconee, North Oconee, or Middle Oconee Rivers. The

objective was to treat all Chinese privet having a diameter

> 1 inch 1 foot above the ground using a mulching machine. 

Some privet exceeded 6 inches in diameter at the sites. 

No other trees with a diameter 4 inches or larger at 4.5

feet aboveground were cut. All preexisting coarse woody

debris on the ground > 6 inches in diameter was avoided,

if possible. After mulching, a three-person crew treated cut

stumps with a 30-percent mixture of a triclopyr herbicide. 

The efficacy of the herbicide treatment will be reported in

future publications.

Production data were collected on two of the sites—the

Sandy Creek Nature Center (site 1) and the Georgia State

Botanical Gardens (site 2). Both sites are located in Athens,

GA. Site 1 was a bottomland hardwood stand comprised

mainly of sweetgum (Liquidambar styraciflua), yellowpoplar (Liriodendron tulipifera), maple (Acer spp.), and

elm (Ulmus spp.). Site 1 was flat over most of its area, with

abrupt slopes of 12 to 15 percent along approximately half

of its perimeter. Site 2 was also a bottomland hardwood

stand with boxelder (Acer negundo), sweetgum, river birch

(Betula nigra), sycamore (Platanus occidentalis), and pine

(Pinus spp.) as the predominant species. Site 2 was flat over

its entire area. However, this site did contain a beaver pond

which measured approximately 1.65 acres. The pond was

totally dry during data collection and no privet was present

in this area, but ground conditions were too soft to permit

machine operation on the dry pond bottom in any case.

Machine Overview

The mulching machine used has a 110-horsepower engine

and is mounted on 8-foot-long rubber tracks. It has a low

ground pressure (4.2 pounds per square inch) and was

appropriate for use in these low areas. The head has a horizontal shaft and 24 flail-type teeth, which rotate at 2,200
revolutions per minute. Teeth are attached to the head

with pins. Tooth life is around 150 hours, while pin life

is about 450 hours (Personal communication. 2005. Don

Pennington, Contractor, GFA Land Clearing, 1224 Devon

Street, SE, Palm Bay, FL 32907). The machine makes a

5.5-foot swath as it works through an area. The contractor

estimated fuel consumption at 6 gallons per hour.

Methods

Time study data were collected to determine machine

productivity in terms of acres per hour. A stopwatch was

used to time the machine during operation. Observations of

the machine working were taken throughout the day. After

timing was completed for an observation, a global positioning system unit was used to determine the size of the

treated area. Four observations were collected on site 1 and

three on site 2. In addition to time study data, travel speeds

were also estimated. For this, the track length was measured

to the nearest 0.1 foot using a logger’s tape and the machine

was timed as the length of the track was traversed.

While the machine progressed through a stand, a threeperson crew followed up the mechanical treatment by

applying a 30-percent mixture of the triclopyr herbicide to

the exposed cambium of severed stumps using a handheld

pressurized chemical sprayer. 

Table 1—Summary of elementary statistics for time 

study

Variable Site 1 Site 2 Site 1 Site 2

acres/pmh hours/acre

Mean 0.18 0.22 6.97 5.72

Standard deviation 0.070 0.120 4.511 3.166

Minimum 0.07 0.11 4.58 2.88

Maximum 0.22 0.35 13.73 9.13

pmh = productive machine hour.

Results

Time study data are provided in table 1. The mulching

machine averaged 0.19 acres per productive machine hour

(pmh) overall. Time spent treating 1 acre averaged 6.43

hours for the two sites. Total productive time for site 1 was

11.5 hours. Total area treated was about 2.85 acres, which

resulted in a gross productivity of 0.25 acres per pmh. 

Time study data estimated a productivity of 0.18 acres per

pmh for site 1. For site 2, total treated area was around

3.20 acres. Total machine time for site 2 was 20.5 hours,

which gave a gross production rate of 0.16 acres per pmh. 

A productivity of 0.22 acres per pmh was estimated from

the time study data. Figures 1 and 2 illustrate pre- and posttreatment conditions of a bottomland hardwood site infested

with Chinese privet.

Figure 1—Site 1: Pretreatment. 
Mechanical Costs

Owning and operating costs for the mulching machine were

estimated using a machine rate analysis (Miyata 1980) and

are summarized in table 2. Salvage value was estimated

to be 20 percent of the purchase price (Brinker and others

2002). An interest rate of 10 percent and an insurance rate

of 4.5 percent (Brinker and others 2002) of the purchase

price were assumed. Fuel cost was calculated using $2.15

per gallon for diesel fuel and a fuel consumption rate of

0.0545 gallons per horsepower hour. A rate of 36.8 percent

of fuel cost was used to estimate lube cost (Brinker and

others 2002). A repair and maintenance rate of 100 percent

of annual depreciation was assumed (Brinker and others

2002). Costs for teeth and pins were calculated using figures

obtained from talking with the owner. For a forestry heavy

equipment operator (occupation code 8160), a rate of $15

per scheduled machine hour was used, plus 30 percent for

benefits. Machine utilization was assumed to be 75 percent.

The estimated total cost of $71.40 per scheduled hour

includes owning, operating, plus labor and benefits, and 20

percent for profit and overhead. Cost per acre is the ratio of

total cost on a pmh basis to a productivity of 0.18 acres per

Figure 2—Site 1: Post-treatment.

Table 2—Cost summary for the mulching machine

Variable Cost Owning Operating Total cost $/acre

Purchase price ($) 110,000

Salvage value ($) 22,000

Depreciation ($/yr) 17,600

Average yearly investment ($/yr) 74,800

Interest ($/yr) 7,480 14.22 25.78 71.40 529

Insurance ($/yr) 3,366

Fuel and lube ($/pmh) 17.63

Repair and maintenance ($/pmh) 11.73

Teeth and pins ($/pmh 5.01

Labor and benefits ($/smh) 19.50

pmh = productive machine hour; smh = scheduled machine hour.
pmh. These machine costs reflect the average costs over the

life of the machine and do not account for taxes. 

Figure 3 illustrates the sensitivity of cost per acre to

productivity, especially in the range from 0.1 to 0.5 acres

per pmh. An increase in productivity from 0.2 acres per

pmh to 0.3 acres per pmh results in a 33-percent reduction

in cost per acre. Alternatively, going from 0.9 acres per pmh

to 1 acre per pmh results in a 10-percent reduction in cost.

Chemical Costs

About 6.75 gallons of the herbicide were applied to cut

stumps at each site. The market price for this type of herbicide is around $89 per gallon. This results in a total chem-

ical cost of approximately $200 per acre. To effectively

treat freshly cut stumps, the chemical application needs to

be concurrent with the mechanical treatment. In this study,

a three-person crew followed the machine and sprayed cut

stumps. However, a two-person crew seems adequate for

this size machine. U.S. Department of Labor wage rates

for brush thinners (occupation code 8010) in Georgia are

$11.53 per hour. With 30 percent benefits the labor cost for

a two-person crew would be around $30 per hour. If the

operation is proceeding at 0.2 acres per hour, the total cost

of chemical and labor would be $350 per acre. Assuming 20

percent for profit and overhead results in a total chemical

and labor cost of $420 per acre.

Discussion

The mulching machine used is small and maneuverable,

and maneuverability is an important factor when operating

in a residual stand. However, the small size of the machine

also resulted in low productivity in terms of acres per hour

treated and, thus, higher total treatment costs. It seems

unlikely the machine used would be capable of treating

more than 0.3 acres per pmh under the conditions observed

in this study. At this production rate, mechanical treatment

cost would be around $317 per acre. Therefore, chemical

and manual labor costs for chemical application are an

additional $420 per acre for a total treatment cost of $737

per acre. A larger machine would be more productive,

although higher owning and operating costs would also be

incurred. For example, one available machine would likely

be able to treat at least 0.75 acres per pmh. With a machine

price of $300,000 mechanical treatment cost would be

around $292 per acre. A production rate of 1.25 acres per

pmh would result in a mechanical cost of $175 per acre,

which is also possible for the larger size machine. 

It is important to recognize that mechanical treatment of

privet, by itself, is not a complete tool. Effective herbicide

application is required to control sprouting. The combined

operational costs measured in this study are about $700 per

acre with over half associated with the chemical application. However, the mulching machine ground the stumps

down to the level of the soil and distributed mulched privet

over the entire site. This made finding and treating stumps

difficult. Postponing herbicide treatment until stump sprouts

appear and then applying foliar herbicide to kill residual

privet would reduce costs because a follow-up foliar application will be required to kill seedlings and stumps that

were missed. A late fall or early winter foliar application

should effectively kill the privet with minimal impact on the

native plant community (Harrington and Miller 2005).

Figure 3—Effect of productivity on cost per acre for the mulching machine used. 

pmh = production machine hour.

Cost curve for the mulching machine used.
Acknowledgments

Funding for the Chinese privet removal study was provided

through the USDA Forest Service, State and Private

Forestry, Forest Health Protection, Special Technology

Development Grant R8–2005–01. Funding for the production study provided by the USDA Forest Service, Southern

Research Station, Forest Operations Research Work Unit.

Literature Cited

Georgia Wildlife Federation. http://www.gwf.org/vol14no2.htm/. [Date

accessed: December 2006].

Harrington, T.; Miller, J.H. 2005. Effects of application rate, timing, and

formulation of glyphosate and triclopyr for control of Chinese privet

(Ligustrum sinense). Weed Technology. 19: 47-54.

Miller, J.H. 1997. Exotic plants are invading southeastern forests. Alabama

Wildlife. Spring/Summer: 36-39.

Miller, J.H. 2003. Nonnative invasive plants of southern forests. Gen. Tech. 

Rep. GTR–SRS–62. Asheville, NC: U.S. Department of Agriculture

Forest Service, Southern Research Station. 93 p.

Miyata, E.S. 1980. Determining fixed and operating costs of logging

equipment. Gen. Tech. Rep. NC–55. St. Paul, MN: U.S. Department of

Agriculture Forest Service, North Central Research Station. 16 p. 

ii
iv
Klepac, John; Rummer, Robert B.; Hanula, James L.; Horn, Scott. 2007. Mechanical removal 

of Chinese privet. U.S. Department of Agriculture Forest Service. Res. Pap. SRS–43. Asheville, 

NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 5 p.

Chinese privet (Ligustrum sinense Lour.), a highly invasive nonnative plant, is prevalent in the 

Southern United States. Chinese privet infestations can hinder regeneration of desirable species, 

reduce stand productivity, and have other undesirable consequences. A combined mechanical 

(mulching) and chemical (triclopyr) treatment was applied to Chinese privet in forest stands in 

Georgia on an experimental basis. The cost of removing Chinese privet was estimated to be $737 

per acre when a tracked 110-horsepower mulching machine and a two-person herbicide application 

crew are employed.

Keywords: Chemical treatment, Chinese privet, Georgia, invasive nonnative plant, mechanical 

treatment, mulching machine, triclopyr.
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