Stake Tests of 

Northeastern Species 

Treated with Copperbased Preservatives: 

Five-Year Results 

Stan T. Lebow

Bessie M. Woodward

Steven A. Halverson

Rachel Arango

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

Research

Note

FPL–RN–0314
January 2010

Lebow, Stan T.; Woodward, Bessie M.; Halverson, Steven A.; Arango, 

Rachel. 2010. Stake tests of northeastern species treated with copper-based 

preservatives: five-year results. Research Note FPL-RN-0314. Madison, 

WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 17 p.

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Abstract

The value of some northeastern tree species could be 

increased if they could be adequately treated with preservatives and shown to be durable in outdoor exposures. This 

paper reports on research to evaluate the ground-contact 

durability of northeastern species treated with copperbased preservatives. Stakes (19 by 19 by 457 mm) cut from 

balsam fir, eastern hemlock, eastern spruce, white pine, or 

red maple were treated with one of four concentrations of 

chromated copper arsenate, copper citrate, alkaline copper 

quat, or copper azole and placed into the ground at a test 

site in southern Mississippi. Similarly treated Southern Pine 

stakes were included for comparison. For 5 years, the stakes 

were rated annually for decay and termite attack. Untreated 

stakes of all wood species failed rapidly, indicating that 

none of the species evaluated have significant natural durability. Occasional failures have occurred in treated stakes, 

typically at the lower preservative retentions. Treated 

Southern Pine and eastern hemlock stakes have experienced 

the fewest failures, with treated white pine stakes performing nearly as well. Treated eastern spruce and red maple 

stakes had the most failures, and treated balsam fir stakes 

also had substantial failures. The failures in eastern spruce 

and balsam fir stakes appear to be attributable to poor preservative penetration and retention within individual stakes. 

Failures in the red maple stakes may be attributable to the 

differences in hardwood anatomy and the distribution of 

preservative within the wood structure. Of the northeastern 

species evaluated, eastern hemlock and white pine appear to 

perform most similarly to Southern Pine when treated with 

the copper-based preservatives. However, further exposure 

time is needed to allow more definitive conclusions.

Keywords: Northeastern species, copper-based preservatives, stake tests, durability

Contents

Page

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

Materials and Methods.........................................................1

 Specimen Preparation ......................................................2

 Stake Installation and Inspection .....................................2

Results and Discussion ........................................................2

Conclusions..........................................................................9

References............................................................................9

Figures................................................................................10
Stake Tests of Northeastern Species 

Treated with Copper-based Preservatives: 

Five-Year Results

Stan T. Lebow, Research Forest Products Technologist

Bessie M. Woodward, Microbiologist

Steven A. Halverson, Physical Science Technician

Rachel Arango, Biological Science Technician

Forest Products Laboratory, Madison, Wisconsin

Introduction

Large areas of forest in the northeastern United States contain tree species that have relatively low commercial lumber 

value. The proportion of traditionally valuable species in 

these forests has declined because of selective harvesting. 

Adding value to alternative wood species would give forest 

managers more flexibility in economically managing the 

forest resource while preserving more traditional commercial species. It could also create business and employment 

opportunities in rural communities.

Before a wood species can gain acceptance for treatment 

with a particular preservative, research must demonstrate 

that adequate penetration and retention can be achieved 

with pressure treatment and that the treated wood is durable. 

Previous research has been conducted on the treatability of 

northeastern species with chromated copper arsenate (CCA) 

and ammoniacal copper arsenate (ACA). Smith (1986) reported on the treatability of eastern white pine, eastern hemlock, Norway spruce, and bigtooth aspen with CCA Type C 

(CCA-C). Preservative uptake was greatest in white pine, 

but also appeared promising in incised eastern hemlock. A 

separate treatability study of Canadian species concluded 

that eastern white spruce and balsam fir were among the 

most difficult to treat with CCA-C, although incising did 

improve treatment (Richards and Inwards 1989). A subsequent study evaluated the treatability of balsam fir, eastern 

spruce, eastern hemlock, and white pine with both CCA-C 

and ACA (Gjovik and Schumann 1992). The researchers 

found that penetration was generally greater with ACA than 

with CCA-C, and that the growth rate (fast or slow) of the 

material had no significant effect on penetration or retention. In agreement with previous researchers, Gjovik and 

Schumann found that incising significantly improved treatment. As a result of these studies and further unpublished 

efforts, eastern hemlock was added to the American Wood 

Preservers Association Book of Standards in 1997, and the 

incising requirement for eastern white pine was modified for 

CCA-C (AWPA 1997).

However, the types of preservatives used commercially 

have changed greatly since the research on treatability of 

northeastern species was conducted. ACA is no longer used 

in the United States, and the allowable uses of CCA-C have 

been greatly reduced. For most markets, these preservatives 

have been replaced with copper-based systems that do not 

contain arsenic or chromium. Arsenic-free alternatives that 

have been standardized by the AWPA include alkaline copper quat (ACQ) copper azole (CBA-A, CA-B, and CA-C) 

and copper citrate (CC). The chemistry of these newer wood 

preservatives is substantially different than that of CCA-C, 

and relatively little research has been published on their 

ability to penetrate and protect northeastern species. A study 

evaluating CCA-C and ammoniacal copper quat (ACQ-B) 

uptake in red maple reported that uptake was similar in 

sapwood, but that uptake of CCA-C was greater in heartwood (Smith and others 1996). Preservative penetration 

was not reported in that study. Since that time, ACQ-B has 

largely been replaced with the amine copper formulations 

of ACQ (ACQ Types C and D). In an earlier stage of the 

research reported in this paper, Lebow and others (2005) 

evaluated the treatability of northeastern species with either 

chromated copper arsenate Type C (CCA-C), ammoniacal 

copper citrate (CC), alkaline copper quat Type C (ACQ-C), 

or copper azole Type A (CBA-A). The results indicate that 

the arsenic and chromium-free alternatives to CCA-C can 

treat northeastern species at least as well as CCA-C and may 

offer treatability advantages over CCA-C in species such as 

eastern hemlock and balsam fir. Two species, red maple and 

eastern spruce, were not adequately treated with any of the 

preservatives, even after incising.

Because of unique interactions between wood and preservative chemistries, adequate treatment does not always ensure 

durability for a specific species/preservative combination. 

To determine preservative efficacy, the treated wood can 

be exposed in conditions that are at least as severe as those 

that would be encountered in service. This paper reports on 

research to evaluate the ground-contact durability of northeastern species treated with copper-based preservatives.

Materials and Methods

This research was conducted through the cooperative efforts 

of the Forest Products Laboratory (FPL); State and Private 
Research Note FPL–RN–0314

2

Forestry; Northeastern Forest Alliance; Vermont Department of Forests, Parks and Recreation; preservative 

manufacturers; and cooperating lumber producers in the 

Northeast. Cooperating mills supplied eastern white pine, 

eastern spruce, balsam fir, eastern hemlock, and red maple 

lumber for the study. FPL supplied Southern Pine lumber 

for comparison. Cooperating preservative manufacturers 

provided chromated copper arsenate, copper citrate, alkaline 

copper quat, and copper azole wood preservative formulations for use in the study.

Specimen Preparation

Four hundred twenty stakes (19 by 19 by 457 mm) were cut 

from lumber of each wood species and conditioned to constant weight in a room maintained at 23 °C and 65% relative 

humidity. The stakes were weighed and then sorted into 16 

groups of 25 and one group of 20 (four preservatives at four 

concentrations plus an additional 20 untreated stakes) so 

that each group had similar density profiles. An additional 

set of 400 incised specimens was also prepared for all species except Southern Pine. Because the finished stakes were 

too small to process in the incisor, 19-mm- (0.75-in.-) thick 

planks were incised and the specimens cut from the two 

edges. As a result, the specimens were only incised on three 

sides. The 25 stakes per treatment group were treated with 

one of the following solutions:

•	Chromated copper arsenate Type C (CCA-C): Actives 

composition of 47.5% CrO3, 18.5% copper (expressed as 

CuO), and 34.0% As2O5. CCA was evaluated at solution 

concentrations of 0.36%, 0.66%, 1.14%, and 1.71%.

•	Alkaline copper quat Type C (ACQ-C): Actives composition of 66.7% copper (expressed as CuO) and 33.3% 

alkylbenzyldimethyl ammonium compound. The copper is 

solubilized in a solution of ethanolamine and water. ACQ 

was evaluated at solution concentrations of 0.29%, 0.71%, 

1.14%, and 1.71%.

•	Copper azole Type A (CBA-A): Actives composition of 

49.0% Cu, 49.0% H3BO3 and 2.0% Tebuconazole. The 

copper is solubilized in a solution of ethanolamine and 

water. CBA-A was evaluated at solution concentrations 

of 0.21%, 0.52%, 0.84%, and 1.26%. Note that solution 

concentrations used for the CBA-A treatments were lower 

than intended because of an error in calculating the 

concentrations.

•	Ammoniacal copper citrate (CC): Actives composition of 

66.7% copper (expressed as CuO) and 33.3% citric acid. 

The copper is solubilized in a solution of ammonia and 

water. CC was evaluated at solution concentrations of 

0.29%, 0.71%, 1.14%, and 1.71%.

All treatments were conducted using a full-cell pressure 

process. The initial vacuum was maintained at 75 kPa for 

30 min; the pressure was maintained at 1.03 MPa for 1 h. 

Following treatment, the stakes were stacked in plastic 

bags for one week and then allowed to air-dry under room 

conditions. Twenty stakes treated with each solution were 

assigned to the exposure plot in Mississippi, while the 

remaining five were reserved for assay of preservative 

retention. 50-mm-long sections cut from the middle of the 

assay stakes were milled and digested for analysis of copper, 

chromium, and arsenic content (as appropriate) by inductively coupled plasma emission spectrometry (ICP-AES).

Stake Installation and Inspection

The Mississippi plot is located in a forested area within Harrison Experimental Forest (approximately 15 miles north of 

Gulfport–Biloxi). The location is within the American Wood 

Protection Association (AWPA) Deterioration Zone 5, which 

is considered a severe deterioration hazard (AWPA 2008). 

Although native subterranean termites are active at this site, 

the presence or activity of Formosan subterranean termites 

has not yet been reported. The stakes were placed in rows 

with 305-mm spacing between stakes within each row and 

915 mm between rows. Because of the large number of 

stakes and large area of the plot, we had some concern that 

the severity of the exposure might vary spatially within the 

plot. To address this concern, the stakes were installed in repeating sets of treatment groups, with the order randomized 

within each set. A 25-mm diameter power auger was used 

to drill holes to a depth of 229 mm, allowing the stakes to 

be buried vertically to one-half their length. The stakes were 

installed in January 2003 and inspected at 1, 2, 3, 4, and 5 

years after installation. At each inspection, the stakes were 

scraped lightly to remove soil and given a visual rating for 

decay and/or termite attack according to the 10, 9, 8, 7, 6, 

4, 0 scale as described in AWPA Standard E7 (AWPA 2008). 

Test stakes were evaluated using a visual rating system corresponding to an estimated loss of cross section (Table 1). 

The ratings shown in Table 1 apply to all subsequent tables 

of ratings. For the purposes of this paper, we report the 

lower of the two ratings (decay or termite) for each stake at 

each inspection. 

Typically, the lowest rating was associated with decay, although termites were the more destructive agent in approximately half of the failures in treated eastern hemlock and 

balsam fir stakes (Fig. 1).

Results and Discussion

As expected, untreated stakes of all wood species failed rapidly when placed in ground-contact in Mississippi (Table 2). 

The red maple and eastern hemlock stakes appeared to fail 

most rapidly, but it is evident that none of these wood species have significant natural durability when placed in the 

ground.

The combination of solution concentration, wood species, 

and incising produced a range of preservative retentions in 

the stakes (Table 3). In this paper, we have designated 

the groups of retentions produced by the four treatment 

solution concentrations as either “low,” medium-low,” 
3

“medium-high,” or “high.” However, it is important to note 

that each of these groups represents a range of preservative 

retentions and that retentions vary between species and between preservatives. Some of the retentions (for the CBA-A 

treatment, for example) are lower than anticipated, and this 

should be considered when reviewing the durability data. 

Incising did not consistently increase retention for any of the 

wood species or preservatives evaluated, perhaps because of 

the small dimensions (19 by 19 mm) of the test stakes.

Even stakes treated to the lowest preservative retentions 

were substantially more durable than the untreated stakes 

after 5 years (Tables 4–7, Figs. 2–9). Some degradation did 

occur, however, with occasional failures occurring in most 

wood species. Species from the Southern Pine group represent the vast majority of treated wood production in the 

United States and provide a useful comparison for the performance of the northeastern species. Only two of the treated Southern Pine stakes have failed (Fig. 1), and with the 

exception of one stake treated with CC (Fig. 6), the treated 

Southern Pine stakes have maintained ratings of “9” or “10” 

in the three highest retention groups. Because the CC preservative does not contain a co-biocide to complement the copper, it is possible that the failure of the CC-treated Southern 

Pine stakes is attributable to attack by copper-tolerant fungi. 

Treated eastern hemlock stakes are performing comparably 

to Southern Pine across the range of preservatives, and the 

treated white pine stakes are performing nearly as well. 

The treated balsam fir stakes have suffered one failure in 

the medium-high retention group with all the preservatives, 

and numerous failures at the lower retentions (Figs. 1, 3, 5, 

7, 9). Failures in balsam fir are likely attributable to poor 

treatment quality in individual stakes. A previous study reported that average preservative retention and penetration in 

balsam fir was less than that in eastern hemlock and eastern 

white pine (Lebow and others 2005).

Red maple and eastern spruce appeared especially vulnerable to biodeterioration (Figs. 1, 3, 5, 7, 9), although this 

trend was not always consistent. Like balsam fir, eastern 

spruce may have suffered greater attack than the other softwoods because of resistance to treatment. It tended to have 

lower preservative retentions than other species, even when 

incised. Previous researchers have also reported that CCAtreated eastern and western white spruce stakes exposed in 

Florida suffered more failures than other softwood species, 

which Richards and McNamara (1997) attributed to poor 

preservative penetration. Crawford and others (1999) also 

noted poor performance of unincised ACA-treated eastern 

spruce stakes exposed in Mississippi, but with notably better 

performance of incised stakes. In the present study, the benefit of incising was less obvious for eastern spruce, although 

incising did improve average ratings for the low retentions 

of CCA, CC, and CBA-A. The performance of both unincised and incised eastern spruce did improve with higher 

retentions (Figs. 3, 5, 7, 9), suggesting that a combination 

of poor penetration and low retention contributed to the 

failures. Incising did appear to provide some general benefit 

when viewed across all species, as only 17 of the 43 treated 

stakes that failed were incised.

The extent of attack of red maple noted in this study does 

not appear to be solely attributable to poor treatment quality, 

as average red maple retentions were similar to other 

Table 1—Typical rating scheme for evaluation of stakes

Rating Description of condition 

10 No evidence of attack

 9 Slight attack, up to 3% of cross-sectional area 

 8 Moderate attack, up to 10% of cross-sectional area 

 7 Moderate to severe attack, up to 30% of cross-sectional area 

 6 Severe attack, up to 50% of cross-sectional area 

 4 Very severe attack, up to 75% of cross-sectional area 

 0 Failure. Can be broken easily by hand or the evaluation probe can penetrate through the stake. 

Table 2—Average annual biodegradation ratings and cumulative number of failures for 20 untreated 

stakes 

Year 1 Year 2 Year 3 Year 4 Year 5 

Wood species Rating 

Failure 

(no.) Rating 

Failure

(no.) Rating 

Failure

(no.) Rating 

Failure 

(no.) Rating 

Failure

(no.) 

Southern Pine 9.40 0 6.55 6 3.50 12 0.95 18 0.40 19 

Balsam fir 9.55 0 6.75 5 2.85 13 1.10 17 0.35 19 

Eastern hemlock 8.40 2 2.30 15 0.00 20 0.00 20 0.00 20 

Eastern spruce 9.15 1 5.75 7 2.55 14 0.40 19 0.40 19 

Red maple 8.55 2 2.90 13 0.80 18 0.75 18 0.00 20 

White pine 9.65 0 6.95 4 3.00 13 0.45 19 0.00 20 

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
4

Research Note FPL–RN–0314

Table 3—Average and standard deviation of the preservative for treatment group as determined by assay 

Retention (kg/m3) (average and (standard deviation)) 

CCA group CCa group 

Low Medium-low Medium-high High Low Medium-low Medium-high High 

Southern Pine 1.60 (0.14) 3.10 (0.72) 7.26 (1.68) 8.31 (1.74) 1.21 (0.22) 3.20 (0.15) 5.18 (0.53) 10.67 (3.95) Balsam fir 1.22 (0.36) 2.59 (0.31) 3.63 (1.98) 4.76 (1.03) 0.78 (0.27) 2.26 (0.77) 5.53 (1.91) 7.81 (2.10) 

Balsam, incised 1.54 (0.30) 2.50 (0.51) 4.44 (1.12) 7.29 (1.81) 1.01 (0.29) 3.38 (0.87) 5.54 (1.25) 7.36 (1.13) 

Eastern hemlock 1.94 (0.34) 3.44 (0.97) 6.57 (1.19) 10.06 (3.60) 1.10 (0.38) 3.63 (1.08) 5.03 (1.39) 9.09 (2.06) 

Eastern hemlock, incised 

1.96 (0.33) 2.80 (0.68) 6.21 (1.33) 9.50 (1.99) 1.84 (1.24) 5.46 (2.78) 7.05 (0.43) 8.89 (4.17) 

Eastern spruce 1.02 (0.65) 1.50 (1.00) 3.18 (1.28) 4.68 (1.42) 0.70 (0.32) 2.35 (0.88) 2.98 (1.70) 6.60 (4.75) 

Eastern spruce,  incised 

1.14 (0.46) 1.84 (0.48) 2.99 (0.98) 4.12 (1.44) 0.63 (0.20) 1.51 (0.37) 2.66 (0.54) 5.06 (2.46) 

Red maple 1.86 (0.33) 2.37 (1.05) 5.27 (1.52) 7.95 (1.96) 0.99 (0.50) 3.05 (1.09) 3.87 (2.73) 13.42 (4.96) 

Red maple, incised 1.96 (0.23) 3.50 (0.37) 6.27 (0.69) 9.41 (0.60) 1.33 (0.10) 3.23 (0.34) 6.58 (0.42) 11.66 (1.81) 

White pine 1.80 (0.36) 3.65 (0.70) 6.64 (0.77) 9.28 (0.82) 1.47 (0.27) 4.37 (0.45) 6.06 (0.88) 9.27 (1.44) White pine, incised 2.13 (0.20) 4.01 (0.60) 7.39 (0.56) 10.92 (1.47) 1.21 (0.49) 4.01 (0.81) 6.93 (1.62) 10.18 (1.53) 

ACQa group CBAa,b group 

Southern Pine 2.15 (0.63) 4.78 (0.64) 7.46 (1.83) 9.38 (1.37) 1.20 (0.37) 2.69 (0.55) 4.04 (1.51) 3.18 (1.76) 

Balsam fir 1.38 (0.34) 2.82 (0.30) 5.75 (2.19) 8.45 (2.01) 0.79 (0.30) 1.10 (0.58) 3.78 (0.88) 1.53 (1.16) 

Balsam, incised 1.81 (0.26) 2.49 (0.27) 5.81 (1.56) 9.21 (2.75) 1.04 (0.26) 0.93 (0.28) 3.65 (0.73) 1.57 (0.31) 

Eastern hemlock 1.78 (0.61) 3.84 (0.82) 6.67 (0.76) 8.77 (2.34) 1.18 (0.42) 1.20 (0.31) 2.64 (1.04) 3.95 (2.71) 

Eastern hemlock, incised 

2.07 (0.30) 4.12 (0.45) 6.49 (1.18) 10.77 (1.41) 1.17 (0.41) 1.44 (0.40) 4.84 (0.90) 2.27 (0.64) 

Eastern spruce 0.92 (0.58) 2.28 (1.72) 5.33 (1.90) 5.62 (4.09) 0.38 (0.30) 0.60 (0.74) 1.45 (0.47) 1.39 (0.56) 

Eastern spruce, incised 

0.77 (0.27) 1.44 (0.50) 4.40 (1.80) 5.36 (1.91) 0.34( (0.11) 0.99 (0.65) 2.49 (0.70) 0.72 (0.44) 

Red maple 1.88 (0.15) 2.43 (0.96) 4.66 (1.50) 7.66 (3.56) 1.10 (0.13) 1.06 (0.75) 4.20 (1.72) 3.24 (2.54) 

Red maple, incised 1.86 (0.26) 3.43 (0.39) 6.79 (1.04) 9.81 (0.75) 1.11 (0.05) 2.07 (0.07) 3.34 (1.37) 4.98 (1.33) 

White pine 1.99 (0.19) 4.76 (1.01) 7.51 (3.04) 11.18 (1.89) 1.46 (0.27) 2.95 (1.17) 5.85 (1.44) 4.64 (1.97) White pine, incised 2.08 (0.45) 4.77 (0.25) 7.66 (1.22) 10.71 (1.31) 1.62 (0.27) 3.42 (0.92) 5.30 (0.80) 6.01 (2.38) 

aBased on assay of copper. Retentions of co-biocides calculated from their specified ratio to copper in the treatment solution. bNote that although these stakes were targeted to treatment at the highest retention, for many species the retention is similar to or below that of the Medium-High retention group. 
5

Table 4—Average and minimum annual biodegradation ratings for CCA-treated stakesa

Rating by year for low retention Rating by year for medium-low retention 

Wood species 

Retention

kg/m3

1 2 3 4 5

Retention

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 1.60 10 — 9.95 9 10.00 — 9.90 9 9.85 9 3.10 10 — 10.00 — 10.00 — 9.95 — 10.00 — 

Balsam fir 1.22 10 — 10.00 — 10.00 — 9.85 8 9.75 8 2.59 10 — 10.00 — 10.00 — 9.95 — 10.00 — Balsam, incised 1.54 10 — 10.00 — 9.95 9 10.00 — 9.75 9 2.50 10 — 9.95 9 10.00 — 9.90 — 9.90 9 Eastern hemlock 1.94 10 — 10.00 — 10.00 — 9.95 9 9.95 9 3.44 10 — 10.00 — 10.00 — 10.00 10 9.95 9 Eastern hemlock, incised

1.96 10 — 10.00 — 10.00 — 10.00 — 9.95 9 2.80 10 — 10.00 — 10.00 — 10.00 10 10.00 — 

Eastern spruce 1.02 10 — 9.90 9 9.45 0 9.10 0 8.15 0 1.50 10 — 10.00 — 9.95 9 9.95 — 10.00 — Eastern spruce, incised

1.14 10 — 10.00 — 9.95 9 9.95 9 9.75 9 1.84 10 — 10.00 — 10.00 — 9.90 — 9.90 9 

Red maple 1.86 10 — 9.85 9 9.40 9 9.15 8 8.85 8 2.37 10 — 9.80 8 9.10 0 8.55 0 8.30 0 Red maple, incised 1.96 10 — 10.00 — 9.80 9 9.55 9 9.30 8 3.50 10 — 9.95 9 9.90 9 9.55 — 9.40 9 White pine 1.80 10 — 10.00 — 9.80 9 9.95 9 9.40 0 3.65 10 — 9.95 9 9.95 9 9.95 — 10.00 — White pine, incised 2.13 10 — 9.95 9 9.90 9 9.85 9 9.70 8 4.01 10 — 10.00 — 10.00 — 10.00 10 9.90 9 

Retention

kg/m3

Rating by year for medium-high retention Rating by year for high retention 

1 2 3 4 5 Retention

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 7.26 10 — 10 — 10.00 — 10.00 — 10.00 — 8.31 10 — 10 — 10.00 — 9.95 9 10.00 — 

Balsam fir 3.63 10 — 10 — 9.50 0 9.50 0 9.45 0 4.76 10 — 10 — 10.00 — 10.00 — 10.00 — Balsam, incised 4.44 10 — 10 — 10.00 — 10.00 — 10.00 — 7.29 10 — 10 — 10.00 — 10.00 — 10.00 — Eastern hemlock 6.57 10 — 10 — 10.00 — 10.00 — 9.95 9 10.06 10 — 10 — 10.00 — 10.00 — 10.00 — Eastern hemlock, incised

6.21 10 — 10 — 10.00 — 10.00 — 10.00 — 9.50 10 — 10 — 10.00 — 10.00 — 10.00 — 

Eastern spruce 3.18 10 — 10 — 10.00 — 10.00 — 9.95 9 4.68 10 — 10 — 9.95 9 9.95 9 10.00 — Eastern spruce, incised

2.99 10 — 10 — 10.00 — 10.00 — 9.50 0 4.12 10 — 10 — 10.00 — 10.00 — 9.85 9 

Red maple 5.27 10 — 10 — 9.95 9 9.90 9 9.75 9 7.95 10 — 10 — 10.00 — 9.95 9 9.95 9 Red maple, incised 6.27 10 — 10 — 9.95 9 10.00 — 9.95 9 9.41 10 — 10 — 9.95 9 10.00 — 10.00 — White pine 6.64 10 — 10 — 10.00 — 9.95 9 10.00 — 9.28 10 — 10 — 10.00 — 10.00 — 9.90 9 White pine, incised 7.39 10 — 10 — 10.00 10.00 — 10.00 — 10.92 10 — 10 — 9.95 9 9.95 9 10.00 — a The minimum (lowest) rating is also shown for groups with an average less than “10.” 

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
6

Research Note FPL–RN–0314

Table 5—Average and minimum annual biodegradation ratings for ACQ-treated stakesa

Rating by year for low retention Rating by year for medium-low 

Wood species 

Retention 

kg/m3

1 2 3 4 5 Retention 

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 2.15 10.00 — 9.95 9 9.95 9 9.75 9 9.65 9 4.78 10.00 — 10.00 — 10.00 — 10.00 — 9.95 9 

Balsam fir 1.38 10.00 — 10.00 — 10.00 — 9.35 0 8.50 0 2.82 10.00 — 10.00 — 10.00 — 9.95 9 9.95 9 Balsam, incised 1.81 10.00 — 10.00 — 10.00 — 9.95 9 9.85 9 2.49 10.00 — 10.00 — 10.00 — 9.95 9 10.00 — Eastern hemlock 1.78 10.00 — 9.95 9 10.00 — 10.00 — 9.85 9 3.84 10.00 — 10.00 — 10.00 — 10.00 — 9.95 9 Eastern hemlock, incised 2.07 10.00 — 10.00 — 10.00 — 9.95 9 9.95 9 4.12 10.00 — 10.00 — 10.00 — 10.00 — 9.95 9 

Eastern spruce 0.92 9.95 9 9.45 0 9.20 0 8.95 0 8.35 0 2.28 10.00 — 9.80 7 9.45 0 9.20 0 9.00 0 

Eastern spruce, incised 0.77 10.00 — 9.85 7 9.85 7 8.60 0 8.35 0 1.44 9.95 9 9.90 9 9.90 9 9.80 9 9.75 9 Red maple 1.88 10.00 — 9.75 9 9.50 9 8.75 0 7.60 0 2.43 10.00 — 9.80 9 9.60 9 9.40 8 9.10 8 

Red maple, incised 1.86 10.00 — 9.80 9 9.55 9 9.45 9 8.90 7 3.43 10.00 — 9.90 9 9.75 9 9.15 0 9.00 0 

White pine 1.99 10.00 — 10.00 — 10.00 — 10.00 — 9.90 9 4.76 10.00 — 10.00 — 9.95 9 9.90 9 9.90 9 White pine, incised 2.08 10.00 — 10.00 — 10.00 — 9.95 9 9.80 9 4.77 10.00 — 10.00 — 10.00 — 10.00 — 10.00 — 

Rating by year for medium-high retention Rating by year for high retention 

Retention 

kg/m3

 1 2 3 4 5 Retention 

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 7.46 10 — — — 10.00 — 10.00 — 10.00 — 9.38 10 — 10.00 — 10.00 — 10.00 — 10.00 — 

Balsam fir 5.75 10 — — — 10.00 — 9.95 9 9.95 9 8.45 10 — 10.00 — 10.00 — 10.00 — 9.95 9 

Balsam, incised 5.81 10 — 9.50 0 10.00 — 9.50 0 9.50 0 9.21 10 — 10.00 — 10.00 — 10.00 — 9.95 9 Eastern hemlock 6.67 10 — 9.95 9 10.00 — 10.00 — 10.00 — 8.77 10 — 10.00 — 10.00 — 10.00 — 10.00 — Eastern hemlock, incised 6.49 10 — — — 10.00 — 9.95 9 10.00 — 10.77 10 — 10.00 — 9.95 9 10.00 — 10.00 — Eastern spruce 5.33 10 — — — 9.95 9 9.90 9 9.80 9 5.62 10 — 9.95 9 10.00 — 9.90 9 10.00 — 

Eastern spruce, incised 4.40 10 — 9.95 9 9.95 9 9.85 9 9.75 8 5.36 10 — 10.00 — 9.95 9 9.95 9 9.85 9 Red maple 4.66 10 — — — 9.90 9 9.60 8 8.95 0 7.66 10 — 9.95 9 9.95 9 9.95 9 9.30 0 

Red maple, incised 6.79 10 — 9.85 9 9.90 9 9.80 9 9.70 7 9.81 10 — 10.00 — 10.00 — 9.90 9 9.75 9 White pine 7.51 10 — — — 10.00 — 10.00 — 9.95 9 11.18 10 — 10.00 — 10.00 — 10.00 — 10.00 — 

White pine, incised 7.66 10 — — — 10.00 — 10.00 — 10.00 — 10.71 10 — 10.00 — 10.00 — 10.00 — 10.00 — 

aThe minimum (lowest) rating is also shown for groups with an average less than “10.” 
7

Table 6—Average and minimum annual biodegradation ratings for CC-treated stakesa

Rating by year for low retention Rating by year for medium-low retention 

Wood species 

Retention 

kg/m3

1 2 3 4 5 Retention 

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 1.21 10.00 — 10.00 — 9.85 9 9.25 0 9.10 0 3.20 10.00 — 9.95 9 10.00 — 9.90 9 9.90 9 

Balsam fir 0.78 10.00 — 9.70 8 8.75 0 8.85 0 7.40 0 2.26 10.00 — 10.00 — 9.95 9 9.35 0 8.55 0 Balsam, incised 1.01 10.00 — 9.50 0 9.25 0 9.00 0 8.90 0 3.38 10.00 — 10.00 — 10.00 — 9.95 9 10.00 — Eastern hemlock 1.10 10.00 — 9.80 8 9.95 9 9.15 0 8.55 0 3.63 10.00 — 9.90 9 10.00 — 10.00 — 9.90 9 Eastern hemlock, incised 

1.84 10.00 — 9.95 9 10.00 — 9.80 9 9.35 7 5.46 10.00 — 10.00 — 10.00 — 10.00 — 9.90 9 

Eastern spruce 0.70 9.95 9 9.60 7 7.65 0 6.25 0 5.60 0 2.35 10.00 — 9.95 9 10.00 — 9.70 8 9.60 8 Eastern spruce, incised 

0.63 9.95 9 9.85 8 9.15 0 8.75 0 7.55 0 1.51 10.00 — 10.00 — 10.00 — 9.65 9 9.50 7 

Red maple 0.99 9.95 9 9.65 9 9.05 7 7.40 0 5.75 0 3.05 9.95 9 9.85 9 9.55 8 9.30 8 8.10 0 Red maple, incised 

1.33 10.00 — 9.75 9 9.30 8 9.00 6 8.30 0 3.23 10.00 — 9.85 9 9.65 9 8.95 0 8.05 0 

White pine 1.47 10.00 — 9.95 9 9.75 8 8.65 0 8.45 0 4.37 10.00 — 10.00 — 10.00 — 9.90 9 9.95 9 White pine, incised 

1.21 9.95 9 9.95 9 10.00 10 9.60 7 8.40 0 4.01 10.00 — 10.00 — 10.00 — 9.50 0 9.40 0 

Rating by year for medium-high retention Rating by year for high retention 

Retention 

kg/m3

1 2 3 4 5 Retention 

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min

Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 5.18 10.00 — 10.00 — 10.00 — 10.00 — 9.50 0 10.67 10 — 10.00 — 10.00 — 10.00 — 9.95 9 

Balsam fir 5.53 10.00 — 10.00 — 10.00 — 9.85 9 9.45 0 7.81 10 — 10.00 — 10.00 — 10.00 — 10.00 — Balsam, incised 5.54 10.00 — 10.00 — 10.00 — 9.90 9 9.90 9 7.36 10 — 9.95 9 10.00 — 9.90 9 10.00 — Eastern hemlock 5.03 10.00 — 9.95 9 9.95 9 9.95 9 10.00 — 9.09 10 — 10.00 — 10.00 — 10.00 — 10.00 — Eastern hemlock, incised 

7.05 9.95 9 9.95 9 9.95 9 9.95 9 9.95 9 8.89 10 — 10.00 — 10.00 — 10.00 — 10.00 — 

Eastern spruce 2.98 10.00 — 9.95 9 9.95 9 9.65 8 9.55 8 6.60 10 — 10.00 — 10.00 — 9.95 9 9.95 9 Eastern spruce, incised 

2.66 10.00 — 9.95 9 9.95 9 9.85 9 9.80 9 5.06 10 — 10.00 — 10.00 — 9.80 9 9.70 7 

Red maple 3.87 10.00 — 10.00 — 9.85 9 9.55 8 9.10 0 13.42 10 — 10.00 — 10.00 — 9.70 8 9.20 0 

Red maple, incised 

6.58 10.00 — 9.90 9 9.70 9 9.60 8 9.50 8 11.66 10 — 10.00 — 9.95 9 9.85 9 9.35 0 

White pine 6.06 10.00 — 10.00 — 10.00 — 10.00 — 9.95 9 9.27 10 — 10.00 — 10.00 — 10.00 — 10.00 — White pine, incised 

6.93 10.00 — 10.00 — 10.00 — 10.00 — 9.50 8 10.18 10 — 10.00 — 10.00 — 10.00 — 10.00 — 

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
8

Research Note FPL–RN–0314

Table 7—Average and minimum annual biodegradation ratings for CBA-treated stakesa

Rating by year for low retention Rating by year for medium-low retention 

Wood species 

Retention 

kg/m3

1 2 3 4 5 Retention 

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 1.20 10.00 — 10.00 — 9.90 9 9.70 8 9.60 7 2.69 10.00 — 10.00 10 10.00 — 10.00 — 9.80 7 

Balsam fir 0.79 9.75 8 8.65 0 7.05 0 6.35 0 5.45 0 1.10 10.00 — 9.95 9 9.90 9 9.90 9 9.50 8 Balsam, incised 1.04 10.00 — 9.85 9 9.80 9 9.45 8 8.50 0 0.93 10.00 — 10.00 — 9.90 8 9.75 8 9.70 8 Eastern hemlock 1.18 10.00 — 10.00 — 9.70 9 9.70 9 9.40 8 1.20 10.00 — 10.00 — 9.95 9 9.90 9 9.85 9 

Eastern hemlock, incised 1.17 10.00 — 9.80 9 9.95 9 9.85 9 9.45 8 1.44 10.00 — 9.95 9 10.00 — 9.95 9 9.85 9 Eastern spruce 0.38 9.95 9 9.60 7 7.70 0 6.50 0 4.90 0 0.60 10.00 — 9.90 9 9.15 0 8.00 0 7.40 0 

Eastern spruce, incised 0.34 10.00 — 9.85 8 9.35 6 8.55 0 6.95 0 0.99 10.00 — 9.95 9 9.90 9 9.75 9 9.45 8 Red maple 1.10 10.00 — 9.60 9 8.95 7 7.85 0 6.10 0 1.06 9.95 9 9.30 0 8.95 0 8.50 0 7.85 0 

Red maple, incised 1.11 10.00 — 9.85 9 9.20 8 8.45 0 7.35 0 2.07 10.00 — 9.85 9 9.75 9 9.20 8 8.90 8 

White pine 1.46 10.00 — 9.95 9 9.90 9 9.55 8 9.05 7 2.95 10.00 — 10.00 — 10.00 — 9.45 0 9.35 0 White pine, incised 1.62 10.00 — 9.95 9 9.75 8 9.50 7 9.20 7 3.42 9.95 9 9.95 9 9.85 9 9.75 9 9.85 9 

Rating by year for medium-high retention Rating by year for high retention b

Retention 

kg/m3

1 2 3 4 5 Retention 

kg/m3

1 2 3 4 5

Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min Avg Min 

Southern Pine 4.04 9.95 9 10.00 — 9.95 9 10.00 — 9.95 9 3.18 10 — 10.00 — 10.00 — 10.00 — 9.95 9 

Balsam fir 3.78 10.00 — 9.95 9 9.35 0 9.25 0 9.30 0 1.53 10 — 10.00 — 10.00 — 9.90 9 9.90 9 Balsam, incised 3.65 10.00 — 10.00 — 10.00 — 10.00 — 10.00 — 1.57 10 — 10.00 — 9.95 9 9.90 9 9.90 9 Eastern hemlock 2.64 9.95 9 9.95 9 9.95 9 9.95 9 9.95 9 3.95 10 — 10.00 — 10.00 — 10.00 — 10.00 — 

Eastern hemlock, incised 4.84 10.00 — 9.95 9 10.00 — 9.90 9 9.85 9 2.27 10 — 10.00 — 10.00 — 10.00 — 9.95 9 Eastern spruce 1.45 10.00 — 9.95 9 9.35 0 8.50 0 7.85 0 1.39 10 — 10.00 — 10.00 — 9.75 9 9.45 8 Eastern spruce, incised 2.49 10.00 — 10.00 — 9.95 9 9.75 9 9.45 8 0.72 10 — 10.00 — 9.95 9 9.80 9 9.75 9 Red maple 4.20 10.00 — 9.90 8 9.65 8 9.30 8 9.05 8 3.24 10 — 9.95 9 9.80 9 9.60 9 9.15 7 Red maple, incised 3.34 10.00 — 10.00 — 9.95 9 9.60 9 9.40 8 4.98 10 — 9.95 9 9.90 9 9.55 8 9.55 9 White pine 5.85 10.00 — 10.00 — 10.00 — 10.00 0 9.95 9 4.64 10 — 9.95 9 10.00 — 10.00 — 9.90 9 White pine, incised 5.30 10.00 — 10.00 — 9.85 8 9.90 9 9.85 9 6.01 10 — 10.00 — 10.00 — 10.00 — 9.95 9 

aThe minimum (lowest) rating is also shown for groups with an average less than “10.” bNote that although these stakes were targeted to treatment at the highest retention, for many species the retention is similar to or below that of the Medium-high retention group. 
9

species (Table 2). Previous studies have noted that CCA can 

be less effective in protecting hardwoods than softwoods, 

possibly because of differences in the microdistribution of 

CCA within the wood structure (Butcher 1979; Daniel and 

Nilsson 1987; Smith and others 1996). The results of our 

study indicate that CCA is as effective as the newer copperbased preservatives in protecting red maple. At the lower 

retentions, it appears that the CCA provides less protection 

to red maple than to softwoods treated to equivalent retentions. However, protection of red maple may be possible if 

higher retentions are used (Fig. 3).

In many cases, the retentions evaluated in our study are 

well below those specified for protection of Southern Pine 

lumber placed in contact with the ground. AWPA standards 

specify minimum ground-contact retention of 6.4 kg/m3

for ACQ-C and CCA-C, and 6.5 kg/m3 for CBA-A (AWPA 

2008). Before its removal from AWPA standards, CC 

was standardized for ground-contact use at a retention of 

6.4 kg/m3 (AWPA 2005). Thus, it is not surprising to observe failures or low ratings, especially in the Low-retention 

group where average retentions were generally below 

2 kg/m3 and as low as 0.34 kg/m3 (CBA-A treatment of 

eastern spruce). With the exception of eastern spruce, the 

various wood species met the ground-contact specification 

at the Medium-high and/or High retentions of ACQ, CCA 

and CC, but retentions in the CBA-A treated stakes did not 

reach this threshold. Because of the Low CBA-A retentions, 

interpretation of the durability results should be limited to a 

comparison between wood species and should not be used 

as a predictor of the durability of commercially produced 

material.

The formulations of ACQ and copper azole in this study 

used copper dissolved in ethanolamine. In the last few 

years, formulations of ACQ and copper azole that use finely 

ground copper particles dispersed or suspended in the treatment solution have been developed. The findings in this 

study may not be directly applicable to these particulate 

copper formulations.

Conclusions

All but three of the 120 untreated stakes have failed after 

5 years of ground-contact exposure in southern Mississippi. A few failures have also occurred in treated stakes 

of each wood species. These treated-stake failures generally occurred in stakes treated to retentions well below that 

specified for protection of Southern Pine placed in ground 

contact. Treated Southern Pine and eastern hemlock stakes 

have experienced the fewest failures, with treated white pine 

stakes performing nearly as well. Treated eastern spruce 

and red maple stakes had the most failures, and balsam fir 

stakes also had substantial failures. The failures in eastern 

spruce and balsam fir stakes appear to be attributable to poor 

preservative penetration and retention within individual 

stakes. Failures in the red maple stakes are concentrated in 

the lower retentions and may be attributable to the differences in hardwood anatomy and the distribution of preservative within the wood structure. Of the northeastern species 

evaluated, eastern hemlock and white pine appear to be the 

strongest candidates for treatment with the newer copperbased preservatives. However, it is difficult to draw strong 

conclusions after 5 years, and the stakes will continue to 

be evaluated with a final report expected after 10 years of 

exposure.

References

AWPA. 1997. Standard C2. Lumber, timbers, bridge ties 

and mine ties—treatment by pressure processes. Book of 

standards. Woodstock, MD: American Wood Preservers’ 

Association. 31. pp.

AWPA. 2005. Book of standards. Selma, AL: American 

Wood Preservers’ Association. 441 pp. 

AWPA. 2008. Book of standards. Birmingham, AL: American Wood Protection Association. 526 pp.

Butcher, J.A.1979. Soft rot control in hardwoods treated 

with chromated copper arsenate preservatives. Part V: a 

reason for the variable performance of CCA-treated hardwoods. Material und Organismen 14(3): 215–234.

Crawford, Douglas, M.; DeGroot, Rodney, C.; Gjovik, Lee, 

R. 1999. Ten-year performance of treated northeastern softwoods in aboveground and ground-contact exposures. Res. 

Pap. FPL–RP–578. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 9 p.

Daniel, G.; Nilsson, T. 1987. Comparative studies on the 

distribution of lignin and CCA elements in birch using 

electron microscopic X-ray microanalysis. IRG/WP/1328. 

Stockholm, Sweden: International Research Group on Wood 

Preservation. IRG Secretariat. 19 pp.

Gjovik, L.R.; Schumann, D.R. 1992. Treatability of native 

softwood species of the northeastern United States. Res. 

Pap. FPL–RP–508. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 20 p.

Lebow, S.T.; Halverson, S.A.; Hatfield, C.A. 2005. Treatability of underutilized northeastern species with CCA and 

alternative wood preservatives. Res. Note FPL–RN–0300. 

Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 5 p.

Richards, M.J.; Inwards, R.D. 1989. Treatability with CCA 

and initiation of field performance testing of refractory softwoods. Vancouver, B.C.: Proceedings of the Canadian Wood 

Preservation Association. 10: 144–178.

Richards, M.J.; McNamara, W.S. 1997. The field performance of CCA-C treated sawn refractory softwoods from 

North America. IRG/WP/40085. Stockholm, Sweden: International Research Group on Wood Preservation. IRG Secretariat. 26 pp.

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
10

Research Note FPL–RN–0314

Smith, W.B. 1986. Treatability of several northeastern species with chromated copper arsenate wood preservative. 

Forest Products Journal. 36(7/8): 63–69.

Smith, W.B.; Abdullah, N.; Herdman, D.; DeGroot, R.C. 

1996. Preservative treatment of red maple. Forest Products 

Journal. 46(3): 35–41.

0

5

10

15

20

25

30

Southern

Pine

Balsam

fir

Eastern

hemlock

Eastern

spruce

Red

maple

White

pine

Wood species

Number of failed stakes

Decay

Termites

Both

Figure 1. Number of failures and primary cause of failure in 

treated stakes (combined preservatives and retentions) by 

wood species.
11

0

2

4

6

8

10

12

14

16

18

20

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Number of stakes

CCA low retention

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

CCA medium-low retention

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

CCA medium-high retention

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

CCA high retention

Wood species and incising

0 7 8 9 10 Southern Pine Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Figure 2. Distribution of Year 5 biodegradation ratings for stakes treated with four concentrations of CCA. None of the stakes treated 

with CCA had a rating of “4” or “6” after 5 years.

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
12

Research Note FPL–RN–0314

7

8

9

10

11

0 2 4 6 8 10

Average rating

Average retention (kg/m3)

Balsam

Balsam, incised

Eastern spruce

Eastern spruce, incised

Red maple

Red maple, incised

Figure 3. CCA treatment: relation between group retention and 

ratings for wood species most prone to biodeterioration.
13

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

ACQ, low retention ACQ, medium-low retention

ACQ, high retention

Wood species and incising

0 7 8 9 10

ACQ, medium-high retention

2

4

6

8

10

12

14

16

18

20

Number of stakes

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Figure 4. Distribution of Year 5 biodegradation ratings for stakes treated with four concentrations of ACQ. None of the stakes 

treated with ACQ had a rating of “4” or “6” after 5 years.

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
14

Research Note FPL–RN–0314

7

8

9

10

11

0 2 4 6 8 10 12

Average rating

Balsam

Balsam, incised

Eastern spruce

Eastern spruce, incised

Red maple

Red maple, incised

Average retention (kg/m3

)

Figure 5. ACQ treatment: relation between group retention and 

ratings for wood species most prone to biodeterioration.
15

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

Copper citrate low retention

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

Copper citrate medium retention

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

Copper citrate medium retention

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

Copper citrate high retention

Wood species and incising

0 7 8 9 10

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Figure 6. Distribution of Year 5 biodegradation ratings for stakes treated with four concentrations of copper citrate. None of the 

stakes treated with the three highest copper citrate retentions had a rating of “4” or “6” after 5 years.

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
16

Research Note FPL–RN–0314

4

5

6

7

8

9

10

11

0 2 4 6 8 10 12 14

Average retention (kg/m3

)

Balsam

Balsam, incised

Eastern spruce

Eastern spruce, incised

Red maple

Red maple, incised

Average rating

Figure 7. CC treatment: relation between group retention and 

ratings for wood species most prone to biodeterioration.
17

Wood species and incising

0 7 8 9 10

CBA-A low retention CBA-A medium-low retention

CBA-A medium-high retention CBA-A high retentiona

2

4

6

8

10

12

14

16

18

20

Number of stakes

0

2

4

6

8

10

12

14

16

18

20

Number of stakes 0

2

4

6

8

10

12

14

16

18

20

Number of stakes

0

2

4

6

8

10

12

14

16

18

20

Number of stakes

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Southern Pine 

Balsam

Balsam, incised 

Eastern hemlock

Eastern hemlock, incised

Eastern spruce

Eastern spruce, incised

Red maple 

Red maple, incised

Western pine 

Western pine, incised 

Figure 8. Distribution of Year 5 biodegradation ratings for stakes treated with four concentrations of CBA-A. None of the stakes 

treated with the three highest CBA-A had a rating of “4” or “6” after 5 years.

aNote that although these stakes were targeted to treatment at the highest retention, for many species the retention is similar to 

or below that of the Medium-high retention group (see Table 2).

Stake Tests of Northeastern Species Treated with Copper-based Preservatives: Five-Year Results
18

Research Note FPL–RN–0314

4

5

6

7

8

9

10

11

0 1 2 3 4 5 6

Average rating

Average retention (kg/m3)

Balsam

Balsam, incised

Eastern spruce

Eastern spruce, incised

Red maple

Red maple, incised

Figure 9. CBA-A treatment: relation between group retention 

and ratings for wood species most prone to biodeterioration.