SURVEY OF A STEM CANKER IN TEAK PLANTATIONS OF 
PUERTO RICO AND ST. CROIX, U.S. VIRGIN ISLANDS, 1983 
Steven W. Oak 
William H. Hoffard 
ABSTRACT 
Teak plantations growing on Puerto Rico and St. Croix, U.S. 
Virgin Islands are severely damaged by a canker disease. Overall, 25 
percent of the surveyed trees were cankered, and all surveyed stands 
had infected trees. Multiple cankering of the same tree was common. 
Cankers appear to result when the incitant enters the bark and kills 
the cambium in one growing season. Termite infestation of exposed 
sapwood and brown staining result in considerable internal defect. 
Decay was absent. 
A fungus, Fusarium solani, was recovered from a few 
cankers and may be the cause of cankers. Several research needs are 
identified. 
INTRODUCTION 
Plantations of teak (Tectona grandis Linn. F.) represent a valuable 
resource to the developing forestry programs of Puerto Rico and the U.S. Virgin 
Islands. 
Early thinnings yield high-quality and decay-resistant fenceposts 
that have high local demand. Seven-foot posts, 3 inches in diameter, sell for 
$2.25 each. Saw logs (12" d.b.h.) can be produced in 25 years; prices for 
finished lumber range from $8 to $11 per board foot (domestic retail). Because 
teak wood products are valuable, extensive damage of any kind would have poten­
tially great impact. 
A stem canker with wide distribution and high incidence was observed on 
three separate evaluations of tree pests of Puerto Rico and the U.S. Virgin 
Islands (Phelps and Landgraf, 1972; Cordell and Barry, 1976; Oak and Barry, 
1982). This report presents the results of a more detailed survey to evaluate 
the cause, distribution, incidence, severity, and potential impact of stem 
cankers in teak plantations. 
METHODS 
The survey was conducted in late September 1983. Eight stands on Puerto 
Rico and four on St. Croix, U.S. Virgin Islands were sampled. 
Most had been 
thinned at least once. A single, 50-tree plot was established in each stand by 
entering the stand and randomly choosing the first plot tree, leaving a suit­
ab le buffer from the boundary (several rows). Consecutive trees in a row were 
then evaluated until 50 trees were completed. Where rows were difficult to 
define, plot trees were evaluated in a transect (width varying with stocking). 
Plot trees were noted as cankered or healthy. The height to cankers was esti­
mated. Stand data included age, mean d.b.h. (10 trees), and basal area 
(obtained with a 10-factor prism). Suppressed and dead trees were not counted 
as plot trees. 
However, attempts were made to determine the cause of mortality 
when it was encountered. 
Notes were made of conditions associated with cankers 
(e.g., branches, stem wounds). 
During the survey, five diseased trees were felled and sectioned through 
the cankers with a chainsaw to assess internal defects. 
Samples from these and 
other cankers were collected and used for isolating potential causal agents. 
Samples were kept on ice for 6 to 48 hours until cultured. Growth media 
included acidified 2 percent malt extract agar (broad spectrum medium) and 
ortho-phenylphenol agar (OPP; semi-selective for decay-causing basidiomycetes). 
Individual sample chips were split, one section being plated on each medium 
after surface sterilization (flaming with 95% ethanol). 
RESULTS 
Figures 1 through 4 show variation in canker appearance. 
Externally, 
typical cankers damaged a third to a half of the stem circumference and were 1 
to 3 feet long. 
Canker margins were irregular, with healthy callus tissue. 
However, complete closing of cankers by callus formation was uncommon (Figure 
4). Cankers are probably annual (active during part of one year) because of 
the presence of healthy callus at canker margins and the lack of killed callus 
in canker faces. 
Developing cankers were inconspicuous, often just a fissure in the bark 
with dying inner bark beneath (Figures 5 and 6). 
The bark was frequently 
intact over the canker face in newly formed cankers. Older cankers had no 
adhering bark. 
Sometimes, only the surface of the inner bark was killed, leav-
ing a smooth area overlain by a loose plate of dead, furrowed bark (Figure 7). 
Cankers apparently result when the incitant penetrates the bark and kills the 
inner bark down to the cambium. 
Large areas can be killed in a relatively 
short period. 
Most fungus-caused cankers of hardwood trees in temperate 
climate zones are active during the trees' dormant season or when trees are 
stressed by drought or freezing (Shoeneweiss, 1981). 
Though tropical condi-
tions may have different influences, it is likely that teak cankers are 
probably most active during the dry (dormant) season and/or during periods of 
prolonged drought during the trees' normal growing season. 
Stem cankers were present in all surveyed stands on both islands. Table 1 
summarizes general stand data, canker incidence, and height to cankers for sur-
veyed plantations. Average incidence of cankered trees within stands was 24 
percent (range of 10 to 48 percent). 
Cankers were found on all sides of 
affected trees and occurred within 2 and 30 feet above ground (average height 
to cankers was 10 feet). 
One-third of all diseased trees had multiple cankers. 
A maximum of five discrete cankers were seen on some trees, but multiple cank-
ers in close proximity often merged, which made enumeration imprecise in those 
instances. 
Trends in canker occurrence, with regard to tree diameter or age, cannot 
be determined, because only small pole- to small sawtimber-sized stands in a 
relatively narrow age range were surveyed. 
However, local foresters have 
observed that small-diameter stump sprouts (1 to 3 inches) that develop after 
thinnings are often heavily cankered (Jose Figueroa, personal communication). 
We also noted this during our survey. 
Canker-associated tree mortality and top-kill were rare. 
When this damage 
did occur, it resulted from the girdling of the stem after multiple cankers 
coalesced . 
Dead branch stubs were at the center of a few cankers (suggesting 
the infection originated on the stem and later spread into the stem; Figure 2). 
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Figure !.--Callusing teak canker, once infested with termites. 
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Figure 2.--Teak canker with a dead branch stub as a possible indicator of the 
stem infection origin. Consistent canker-branch stub associations were 
lacking. 
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Figure 3.--Teak canker of recent or191n (1 to 3 years). A loose plate of dead 
bark attached above and below the canker was removed to reveal this damage. 
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Figure 4. --Appearance of cankers was variable . These cankers show incomplete 
compartmentalization of the affected area by callus tissue formation. 
This 
symptom was uncommon, as most cankers had open faces. 
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Figure 5.--External evidence of an active, developing canker (left). 
Bark 
removed showing dead inner bark (right). 
-7-
Figure 6.--External symptom of an active , developing canker on a basal sprout 
(left). 
Bark removed showing dead inner bark (right). 
-8-
Figure 7.--Loose plates of dead bark with smooth bark beneath suggest that 
infections occur t hat do not kill the inner bark to the cambium. 
-9-
Table 1.--lncidence and severity of cankers in 12 surveyed teak plantations, Puerto Rico and St. Croix, U.S. 
Virgin Islands, 1983. 
Cankered 
Average 
Basal 
Canker 
Trees With 
Height to 
Age 
DBH 
Area 
Incidence 
Multiple Cankers 
Cankers 
Forest 
Location 
(years) ( inches) 
(feet 
(percent) 
(percent) 
(feet) 
Rio Abajo 
Nieves 1 
43 
14 
95 
40 
40 
8 
Camba l ac he 
Los 0rtices 
42 
12 
110 
14 
43 
18 
St. Croix 
Est. Thomas 1 
28 
8 
70 
48 
50 
12 
St. Croix 
Est. Thomas 2 
28 
9 
80 
26 
23 
10 
St. Croix 
Est. Wi 11 i am 
26 
7 
105 
20 
40 
10 
I 
t--' 
0 
St. Croix 
Plessen 
26 
7 
50 
16 
25 
8 
I 
Rio Abajo 
Santa Rosa 1 
23 
7 
80 
22 
27 
- 12 
Rio Abajo 
Nieves 2 
20 
9 
100 
10 
60 
8 
Rio Abajo 
Santa Rosa 2 
16 
8 
80 
32 
44 
10 
Rio Abajo 
Las Vegas 
13 
5 
85 
26 
23 
6 
Camba 1 ache 
Burnt 
12 
6 
90 
16 
13 
6 
Camba l ache 
Camping Area 
unk 
4 
90 
22 
9 
9 
Average 
25 
8 
86 
24 
33 
10 
Bird pecks (caused by the migrating yellow-bellied sapsucker, Sphyrapicus 
varius; Figure 8) seemed to be the origin of a few others. 
However, consistent 
association of cankers with these disturbances was lacking. Tree-nesting 
termites (Kalotermes snyderi Light; identified by O. A. Nickle, USOA-ARS, 
Beltsville, MO) frequently colonize canker faces, consuming the exposed sapwood 
beneath (Figures 1 and 9), but their activities do not seem to cause cankers. 
Internal defects consisted of termite galleries (Figure 10) and brownish 
staining (Figure 11). 
The stain was present 1 to 2 feet above and below cank-
ers, and a shorter distance beyond the lateral margins. 
The darkest stain was 
associated with termite galleries, with the extent of staining beyond the 
lateral margins related to the extent of termite infestation. 
Though extensive 
wood decay was absent, it is possible that decay does develop beneath cankers, 
but is quickly consumed by termites. Close examination of stained sapwood 
revealed darkly stained, individual elements that occasionally exuded an inky 
sap (Figure 12). These may serve to compartmentalize the damaged wood. 
Fungus fruiting bodies were not observed on cankers or callus tissue, even 
after moist chambering for two weeks. 
Several fungi with the potential for 
causing disease were recovered from cankers. 
However, the most reliable 
results were obtained from developing cankers with actively advancing margins 
(Figure 6) on small stems originating from stumps or basal sprouts. 
These were 
from three wide1y separated plantations on the Carnbalache and Rio Abaja State 
Forests (Puerto Rico). 
When grown on fresh potato dextrose agar slants at room temperature with 
16 hours of fluorescent light, the fungi produced abundant tan to brownish 
mycelium. 
Microscopically, the isolates produced long, simple phialides 
(spore-producing structures; Figure 13) and abundant micro- and macroconidia 
(Figure 14). 
Though variation in colony appearance and microscopic features 
exists between isolates, they are identified as Fusarium solani (Tousson and 
Nelson, 1976; Booth, 1977). 
Older, seemingly inactive cankers yie1ded an isolate of Fusarium roseum 
(not a known tree-cankering organism) and one of Lasiodiplodia theobromae (a 
weakly pathogenic fungus of stressed trees). 
The preponderance of isolations 
were unsuccessful, yielding no fungi, nonsporulating fungi without distinctive 
features, or common contaminants. 
While the identity of the pathogen is 
uncertain, the best candidate of the identified fungi is F. solani, based on 
the condition of the host material from which it was obtaTned. 
DISCUSSION 
Cankers on teak trees growing on Puerto Rico and St. Croix, U.S. Virgin 
Islands occur wherever teak is grown and occur with high frequency. 
No sur-
veyed stand was without canker damage. 
Trees are subject to multiple infec-
tions that sometimes coalesce into large areas of damaged stem wood. 
Decay is 
absent, but termite infestation can produce extensive internal defect. 
Brown 
staining commonly occurs. Mortality and top-kill are infrequent, but can 
result when multiple cankers coalesce. 
-11-
Figure 8.--Bird peck caused by the migrating, yellow-bellied sapsucker, 
Sphyrapicus varius. Cankers were infrequently associated with bird peck. 
-12-
Figure 9.--Close-up of termite galleries at the healthy callus tissue margin of 
an old canker. 
-13-
Figure 10.--Transverse stem sections through cankered areas, showing termite 
ga ll eries, dark staining, and callus tissue formation (top). Close-up of 
termite damage beyond the margin of the canker, with dark staining (bottom). 
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Figure 11. --Transverse stem section 1 foot above the upper canker margin, 
showing brown staining. 
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Figure 12.--Close-up of a portion of Figure 11, showing darkly stained vessel 
elements. 
One element at the upper left is exuding a small amount of inky sap. 
Staining can be a compartmentalizing response to injuries in many trees. 
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Figure 13. --Photomicrographs showing phialide (spore-producing structure) 
morphology that is characteristic of Fusarium so lani isolates thought to cause 
teak cankers. (H = 10 microns) 
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NOTE: 
Photos for Figures 13 and 14 are interchanged. 
Figure 14.--Photornicrographs showing variability in spore m:irphology of the 
different Fusarium solani isolates thought to cause teak cankers. 
( H 
== 10 microns) 
-18-
Our survey showed that abundant cankers occur in trees between age 12 and 
43 years. 
Indirect evidence (observations of small diameter stump sprouts) 
indicates they also occur on much younger, small-diameter stems. 
Because all 
diameter classes seem susceptible, the lack of external symptoms of completely 
callused cankers on older trees suggests the possibility that the disease 
developed recently. 
Early accounts of the performance of the first teak plan-
tations established on the islands do not mention any such maladies. 
If 
cankers were not a problem early in the life of these stands, then the causal 
agent may have been introduced or is perhaps a native pathogen that has taken 
years to develop into the problem we observed. 
The history of the problem is important in determining the expected losses 
when harvesting and processing lumber from older teak trees. 
If cankers were 
present early in the trees' development, substantial internal defect might be 
encountered. 
Records of cull from various causes are not available for the 
sav.rnilling that has been conducted thus far. 
Losses cannot be quantified without further research. 
Most external 
defects w:::Juld be eliminated in the scrap slabs. 
Careful sawmilling and market-
ing of small boards cut from trees with internal defects would limit losses. A 
market already exists for posts resulting from thinnings of young stands, and 
sanitation cuts (elimination of cankered stems) would provide more. 
However, 
removing most cankered trees in heavily diseased stands w:::Juld result in poorly 
distributed stocking or understocking. 
This would interfere with long rotation 
management objectives. 
Silvicultural methods aimed at minimizing losses also need further 
research. While sanitation thinnings may reduce incidence in the remaining 
stand, it is also conceivable that this activity may increase susceptibility of 
the crop trees. 
The role of genetic variability in disease resistance could be potentially 
significant. 
Teak is an introduced species in the Caribbean, and the genetic 
diversity of the population is probably quite narrow. 
Since teak stands are 
established by planting 
11stumps
11 (top and root pruned seedlings) grown from 
locally collected seed, it is possible that large portions of the resource are 
closely related, genetically. Future stands resulting from stump sprouts would 
only perpetuate this situation. Screening of different geographic sources 
would be valuable, if teak is to be an important timber species for the future 
on these islands. 
Small plantings of different teak sources currently growing 
on the Caribbean National Forest; on the Rio Abajo State Forest, Puerto Rico; 
and on St. Croix are significant resources for investigations of genetic 
resistance. 
The causal agent of teak cankers in Puerto Rico and St. Croix teak planta-
tions remains unknown. 
However, F. solani is an excellent candidate as the 
pathogen. 
Reports of teak cankers in India plantations 9escribe a very similar 
condition caused by F. solani or its sexual stage, Nectr,a haematococcus 
(Bagchee, 1947). 
Freezing stress is thought to be an aggrevating circumstance 
in some locations (Bagchee, 1952). 
Further, F. solani has been consistently 
isolated from teak stem cankers in Tanzania and has killed artificially inocu-
lated teak seedlings (Hocking, 1968). 
Teak cankers also resemble those caused 
by F. solani on yellow poplar (Liriodendron tulipifera) and other hardwoods in 
the-eastern U.S. 
More extensive monitoring of teak stands followed by pathogen 
-19-
isolation and inoculation trials are required before pathogenicity can be con-
firmed. 
Because these observations were made during a short period (10 days} 
and only during the growing season, we may have missed the primary infection 
period. 'This may explain the low frequency of actively growing cankers we 
observed and the limited success we had recovering F. solani or other potential 
pathogens from cankers. 
Close examination of teak trees during or shortly 
after the dormant season and other abnormal drought periods should offer the 
best chance for detecting new cankers and recovering the pathogen. 
Inocula-
tions of seedlings and larger trees in the field must be made during the entire 
year to further illuminate important variables governing infection biology and 
disease development. 
-20-
LITERATURE CITED 
Bagchee, K. 
1947. 
An unrecorded parasite of teak (Tectona grandis, Linn.) 
reported from Oehra Dun, U.P. 
Pathological Notes: 
No. 3. 
Indian Forester 
73(7) 332-334. 
Bagchee, K. 
1952. 
A review of work on Indian tree diseases and decay of 
timber and methods of control. 
Indian Forester 78(11) 540-546. 
Booth, C. 
1977. 
major species. 
68 p. 
Fusarium. 
Laboratory guide to the identification of the 
Commonwealth Mycological Institute, Kew, Surry, England. 
Cordell, C. E. and P. J. Barry. 
1976. 
Insect and disease conditions - Puerto 
Rico and the United States Virgin Islands, 1976. 
USDA, FS, SA-S&PF, FPM. 
Rep. No. 77-1-2. 
Hocking, D. 
1968. 
Stem canker and ~nk stain of teak in Tanzania associated 
with Fusarium solani. Plant Dis. Rep. 52(8) 628-629. 
Oak, S. W. and P. J. Barry. 
1982. 
Evaluation of tree disease and insect pests 
in Puerto Rico and the U.S. Virgin Islands, 1982. 
USDA, FS, SA-S&PF, FPM. 
Rep. No. 82-1-32. 
Phelps, W. R. and A. E. Landgraf. 
1972. 
Evaluation of tree diseases and 
insect pests in Puerto Rico and St. Croix, Virgin Islands, 1972. 
USDA, FS, 
SA-S&PF, FPM. 
Rep. No. 73-1-10. 
Schoenewiess, O. F. 
1981. 
Infectious diseases of trees associated with water 
and freezing stress. 
J. Arboric. 7(1) 13-18. 
Tousson, T. A and P. E. Nelson. 
1976. 
A pictorial guide to the identification 
of the Fusarium species. 
The Pennsylvania State University Press, University 
Park, Pennsylvania. 
43 p. 
-21-
Forest Pest Management 
Asheville Field Office 
Report #84-1-4 
February 1984 
SURVEY OF A STEM CANKER IN TEAK PLANTATIONS OF 
PUERTO RICO AND ST. CROIX, U.S. VIRGIN ISLANDS, 1983 
Approved 
Entomologist 
by:~~ 
for'RarveyV.Toko 
Staff Director 
Forest Pest Management