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Department of

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Southern Forest

Research Note

so-335

Experiment Statlon March 1987

Cerafocystis fagacearum in Living and Dead

Texas Live Oaks

R. Lewis, Jr.

SUMMARY MATERIALS AND METHODS

Ceratocystis fagacearum colonized Texas live oaks

(Quercus virginiana var. fusiformis) to a depth of 10

annual increments in sapwood, either before or shortly

after initial symptom expression. The fungus survived in

dead wood up to 12 months after oak wilt caused crown

mortality. Both moist wood at the root collar level and dry

wood at the d.b.h. level support C. fagacearum survival.

The fungus was isolated from dead wood in March,

June, September, and October in 2.5 percent of the

3,600 isolation samples used in the study.

INTRODUCTION

Epiphytotic levels of oak wilt (Ceratocystic

fagacearum) have been reported in central Texas

(Appel and Maggio 1984). Texas live oak (&emus virginiana var. fusiformis) is the principal species affected,

but other species are also susceptible. Research has

been focused on epidemiology and disease control in

recent years. A preliminary report on disease management is currently being used to help combat the problem

in Texas (Lewis and others 1983). Additional information

on fungal survival would enhance the value of the preliminary report and strengthen recommendations for sanitation procedures and precautions. The information in this

report provides new data on C. fagacearum colonization

and survival in living and dead Texas live oaks in central

Texas. Information on C. fagacearum survival in trees

killed by oak wilt is needed to minimize new incidences

of the disease that could be caused by transporting fuel

wood from oak wilt infested areas to noninfested areas.

Isolations were made from 13 annual layers of sapwood and heartwood from 5 living trees in Kerrville, TX,

infected with oak wilt; these trees all exhibited typical oak

wilt symptoms. Isolations were made $1 Apt ii., June, July,

and September. Successive 2-year increiments of sapwood were excised from cross-sectionai, lower trunk

disks (0.3 to 1.0 m above soil level), disinfected in

1.05 percent (a.i.) sodium hypochlorite for 30 to 90 seconds, and plated on potato dextrose agar (PDA) in petri

dishes. Ceratocystis fagacearum was identified when it

grew from the wood chips at 22 to 26 “C. From 20 to 60

isolation samples were taken from each layer of sapwood in each tree. The percent of samples with

C. fagacearum was calculated for each layer of sapwood.

Survival of C. fagacearum in dead Texas live oak

wood 6 to 12 months after crown mortality was evaluated

from 1984 to 1986 in Kerrville, TX. Twenty-four trees, all

dead to the root collar, were sampled in March, May,

June, September, and October. Oak wilt had been confirmed in each tree up to 2 years earlier. The roots were

still alive in each sampled tree, but the trunk section

60 cm above the soil line was dead and completely dried

out. Isolations were made from root collar zones (most

were dead but had high moisture content) and trunk

sections at 1.3 m above the soil line (d.b.h.). Trunk sections (about 60 cm long) were cut from each tree and

stored at 5 “C until used for isolations. Isolations were

made from three depth intervals (O-l cm, 1-2 cm, and

2-3 cm) from cross-sectional disks of each section of

wood. Twenty-five isolation samples were taken from

each depth of each disk and disinfected in sodium

Southern Forest Experiment Station/T-10210 U.S. RX&I Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mlsslsslppl, E. Oklahoma, Tennesseq E. Texas, Puerto Rico, U.S. Virgin Islands

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hypochlorite (1.05 percent a.i.) before plating them on

PDA. The number of samples with C. fagacearum isolations was tabulated.

RESULTS AND DISCUSSION

Lower bolewood of symptomatic and recently infected

trees was extensively colonized by C. fagacearum in

spring, summer, and autumn. The fungus was isolated

from sapwood formed 10 years earlier. The highest rate

of recovery was from sapwood that was formed 1 to 2,3

to 4, and 5 to 6 years prior to isolation (fig. 1). Ceratocystis fagacearum was isolated from about 20 percent of

these samples. The fungus was not isolated from heartwood or from samples of 1 1 - to 13-year-old wood.

Ceratocystis fagacearum was isolated from 9 of 24

Texas live oaks 6 to 12 months after total crown mortality. The fungus was isolated from samples taken in

March, June, September, and October, but not in samples taken in May. It was recovered from 1.7 to

6.9 percent of the isolation samples during these months

(table 1). Only 2.5 percent of the 3,600 isolation samples

yielded the fungus.

The highest rate of C. fagacearum isolation was

6 percent at the 1 to 2 cm depth of root collar sections

(table 2). The 2- to 3-cm depth of root collar sections

gave the second highest recovery rate and the 1 - to 2-cm

depth of d.b.h. sections gave the lowest. Cerafocystis

fagacearum was isolated from 3.5 percent of the .1,800

25 r

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Figure 1 .-Frequency ofCeratocystis fagacearum isolations from 7- to

13-year-old sapwood of Quercus spp. with initial oak wilt

symptoms in Kerrville, TX.

Table 1 .- Ceratocystis fagacearum isolations from Texas live oak

(Quercus virginiana var. fusiformis) bolewood 6 to 12

months after crown mortality in 1964 to 7986 due to oak wilt

at Kerrvile, TX

Month of Trees Trees with Isolation C. fagacearum

isolation sampled C. fagacearum samples isolations

_ _ _ _ _ _ _ _ _ _ _ _ Number _ _ _ _ _ _ _ _ _ _ _ _ Percent

March 6 2 900 2.7

May 6 0 900 0

June 3 2 450 4.2

September 6 3 900 1.7

October 3 2 450 6.9

Table P.-Ceratocystis fagacearum isolations from various depths of

Texas live oak (Quercus virginiana var. fusiformis) bolewood at root collar and d.b.h. levels 6 to 12 months after

crown mortality due to oak wilt at Kerrville, TX

Sample location

and depth

Root collar

O-l cm

l-2 cm

2-3 cm

D.b.h.

O-l cm

l-2 cm

2-3 cm

Isolation C. fagacearum

samples isolations

Number Percent

600 1.6

600 6.0

600 2.7

600 2.0

600 1.0

600 1.2

samples at the root collar zone, but only 1.4 percent of

the 1,800 samples from the d.b.h. levels in the same 24

trees. Ceratocystis fagacearum remained viable in

Texas live oak trunks up to 12 months after total crown

mortality but at relatively low levels.

Deep colonization by C. fagacearum makes chemical

treatments with systemic fungicides less likely to succeed because more host tissue would have to be penetrated by effective levels of the chemicals. Also, deep

colonization probably aids .fungus survival during hot

summer months. Sapwood temperatures are much

lower than ambient temperatures during the summer in

Texas (Lewis 1985).

Survival of C. fagacearum for 12 months in dead

Texas live oaks is contrary to what one might expect. In

Arkansas, Hypoxy/on spp. deplete carbohydrates in oak

wilt killed trees and inhibit C: fagacearum survival

(Tainter and Gubler 1973). Carbohydrate depletion by

Hypoxylon spp. was not found in Texas live oaks affected by oak wilt (Tainter and Lewis 1982). This might

R. Lewis, Jr. is assistant director for Research Planning and Application, Northeastern Forest Experiment Station, Broomall, PA-USDA Forest

Service.

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help explain why C, fagacearum was recovered from

trees after crown mortality.

Ceratocystis fagacearum was isolated from twice as

many root collar level samples than those from the d.b.h.

level. This difference may be explained by a more favorable xylem temperature and moisture content at the root

collar level. Root collar temperatures are lower than

d.b.h. temperatures in Texas live oaks (Lewis 1985).

Moisture content was relatively high at the root collar

zone, but low at the d.b.h. level and a reduction in moisture content of oak wood adversely affects C.

fagacearum survival (Tainter and others 1984).

The recommendation not to transport firewood from

trees killed by wilt to areas where there is no oak wilt

(Lewis and others 1983) is reemphasized as a result of

this study. Infected wood should be utilized at or near the

site of origination.

LITERATURE CITED

Appel, D.N.; Maggio, RD. 1984. Ariel survey for oak wilt

incidence at three locations in central Texas. Plant

Disease. 68: 661-664.

Lewis, R., Jr. 1985. Temperature tolerance and survival

of Ceratocystis fagacearum in Texas. Plant Disease.

69: 443-444.

Lewis, R., Jr.; Oliveria, F. L.; Walterscheidt, M. J. 1983.

How to identify and suppress oak wilt in live oak and

Texas red oak. [Phamphret] New Orleans, LA: U.S.

Department of Agricultut d, Forest Service, Southern

Forest Experiment Station; 5 p.

Tainter, F. H.; Gubler, W. D. 1973. Natural and biological

control of oak wilt in Arkansas. Phytopathology. 63:

1027-l 034.

Tainter, F. H.; Lewis, FL, Jr. 1982. Non-structural carbohydrate contents of trees affected with Texas live oak

decline. Plant Disease. 66: 120-122.

Tainter, F. H.; MacDonald, W. L.; Harner, E. J. 1984.

Survival of the oak wilt fungus in air-dried limber. European Journal of Forest Pathology. 14: 9-16.

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