Research Note so-263

1961

Twig Girdler, Oncideres Cingulata (Say), Attacks Terminals

of Plantation-managed Pecans

H. E. Kennedy, Jr., J. D. Solomon, and R. M. Krinard

Sweet pecan, a prized species for use in fine

furniture and paneling, is subject to branch and

terminal damage by the pecan twig girdler that could

cause deformities in the trees. In the young plantationstudied, 55 percent of the trees in disked plots

and 40 percent in mowed plots were damaged by the

twig girdler, but only 19 percent in control plots were

damaged. Twig girdlers had easier access to trees in

mowed and disked plots because trees were larger,

and other woody and herbaceous plants had been

reduced or eliminated. Trees were smaller in control

plots and had been overtopped by the competing

vegetation.

Additional keywords: Carya illinoensis, cultural treatment, Sharkey clay, hardwoods, Oncideres cingulata.

Sweet pecan (Carya illinoensis (Wangenh.) K.

Koch) is a prized species for use in fine furniture and

paneling. During recent years, it has been commonly

called the “black walnut of the South.” Many forest

managers are expressing greater interest in pecan

(Adams 1977, McKnight 1980) for plantation management as a timber species because of its high stumpage value.

In 1979, large numbers of terminals in research

plantings of pecan intended for timber production

were severed by the twig girdler, Oncicferes cingulata

(Say); notorious for its pruning damage to pecan and

other hardwood species (Baker 1972, Bilsing 1916).

Previous reports on pecan, however, have dealt largely with twig or branch pruning on orchard or ornamental trees grown for nut production (Gill 1924,

Herrick 1904, Payne et al. 1979). This paper reports

on terminal and branch damage in young, plantationgrown trees and discusses differences in incidence

of attack under three cultural treatments.

METHODS

This study was superimposed on a study originally

intended to test the effects of three levels of cultural

intensities on survival and growth of six hardwoods

on the Delta Experimental Forest near Greenville,

Miss. Cultural treatments included disking (clean

cultivation), mowing, and control (no treatment). The

soil is Sharkey clay, a member of the montmorillonitic,

thermic family of Vertic Haplaquepts. Six replications

of each cultural treatment included 24 one-year-old

seedlings per subplot planted at 3X3 m (1O’XlO’)

spacing. Sweet pecan, one of the species tested,

was planted in February 1971. Plots were disked or

mowed 3 to 5 times per year through the first 5

years. During years 6 through 9, disking was continued in half the disked plots and half was mowed

for weed control. Likewise, mowing was continued

in half the mowed plots, while the other half was

disked.

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

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.

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Twig girdler damage was assessed after observations indicated heavy insect attack on terminals and

branches of the pecans. Only the pecan plots were

used for this study, and results are based on the

originally assigned treatments. The following determinations were made for each plot: (1) total height,

(2) diameter at breast height (dbh), (3) survival, (4)

diameter of terminal or branch at point of girdle,

(5) length of terminal or branch from point of girdle.

to tip, (6) number of trees with terminals attacked,

(7) number of trees with branches attacked, (6) total

number of girdled branches per tree, (9) number of

trees with old gi.rdles and feeding damage. Total tree

heights were measured to the nearest 0.03 m (0.1

foot) with a measuring pole and dbh to nearest 0.25

cm (0.1 inch) with calipers. Diameters at the point of

girdle were measured to the nearest mm with vernier

calipers and lengths of girdled terminals and branches

to the nearest cm with a meter stick.

Averages for each variable were calculated and

statistical analyses were conducted for a randomized

complete block design. Means were compared using

Duncan’s Multiple Range Test. Arcsin transformations of percentages were made before analyses.

Statistical tests were conducted at the 0.05 level of

significance.

RESULTS AND DISCUSSION

Average heights, diameters, and survival are shown

in table 1. Disking resulted in significantly larger

trees and better survival than mowed or control plots.

No significant differences occurred between the

mQwed and control plots.

Fifty-five percent of the trees in disked plots and

40 percent in mowed plots had branches or terminals

(fig. 1) girdled in the fall of 1979 (table 1). Only 19

percent of the trees were damaged in control plots,

significantly fewer than in the mowed and disked

plots. No significant differences appeared in the

amount of girdler damage in mowed and disked plots

except for mean number of girdled branches. Differences in girdler damage between the control and

other treatments probably reflect woody and herbaceous vegetation overtopping the pecan in control

plots. No differences in tree size appeared between

the control and mowed plots, although competing

vegetation in the mowed plots was kept at a low level

and vegetation grew unchecked in control plots. In

the control plots, most of the pecan had been overtopped by faster growing sprouts of pecan, green

ash, and sycamore-apparently making larger pecan

sprouts more accessible than the smaller planted

pecan. Twig girdlers had easy access to trees in

mowed and disked plots with larger trees and reduced

or eliminated woody and herbaceous vegetation.

Percentage of trees with girdled terminals ranged

from 12.5 percent in control to 21.5 percent in mowed

plots (table 1). There were no significant differences

by cultural treatment.

Disked plots had significantly higher percentages

of old girdles than mowed and control plots. Feeding

damage (fig. 2) was significantly higher in the disked

and mowed plots than in control plots, probably because of differences in tree size and competing vegetation in the different cultural treatments.

Cultural treatments caused no significant differences in the size of branches and terminals girdled.

Diameters ranged from 10.5 mm in disked plots to

Table 1 .-Average heights, dbh, survival, and twig girdler damage on pecan by cultural treatments

Variable’ Control Mow Disk

Height-m (ft)

Diameter-cm (in.)

Survival-%

Terminals attacked-%

Trees attacked-%

Mean no. branches girdled per plot

Diameter at girdle-mm (in.)

Length girdled branches-cm (in.)

Old girdles-%

Feeding damage--o/o

1.6 (5.4)a

1.3 (05)a

57a

12.5a

19.0a

4 a

10.6 (0.4)a

64.5 (25.4)a

17.0a

33.5a

1.7 (5.6)a

1.5 (0.6)a

59a

21.5a

39.713

llb

11.4 (0.4)a

56.2 (22.1 )a

13.8a

57.313

2.8 (9.0)b

3.1 (1.2)b

84b

14.5a

55.0b

24c

10.5 (0.6)a

54.1 (21.3)a

38.71,

68.5b

‘Within an individual variable, means followed by the same letter are not significantly different at the 0.05 level

by Duncan’s Multiple Range Test.

H. E. Kennedy, Jr., is Principal Silviculturist, J. D. Solomon is Principal Research Entomologist, and R. M. Krinard is Mensurationist at the

Southern Hardwoods Laboratory, maintained at Stoneville, Miss., by the Southern Forest Experiment Station, Forest Service-USDA,

in cooperation with the Mississippi Agricultural and Forestry Experiment Station and the Southern Hardwood Forest Research Group.

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Figure 1 .-l-feavy branch damage from the twig girdler.

11.4 mm in mowed plots (table 1). Lengths ranged

from 54.1 cm in disked plots to 67.5 cm in mowed

plots.

Twig girdler damage was also noted on some Nuttall oak (Quercus nuttallii Palmer) in the plantation.

No measurements were made on tree size, but this

first report of damage to Nuttall oak by the girdler

indicates that Nuttall oak could suffer in years with

high twig girdler populations.

The results of this study show that young pecan

trees grown in plantations for timber purposes may

be heavily damaged by twig girdlers, especially when

plantations are kept free of competing vegetation.

Injury by this insect is characterized by girdling and

usually complete or nearly complete severing of the

terminal or branch. Terminal damage is potentially

more serious than injury to branches because of

forks and crooks resulting from girdling. Affected

trees show reduced timber quality and loss of height

growth, This study reports most of the growth for the

Figure 2.-Terminal being girdled by a twig girdler.

previous 2 years lost when a terminal was girdled.

Loss of girdled branches is less serious but may

reduce growth when serious pruning occurs.

Stem girdling occurs in late summer and fallbeginning in August, peaking in September, and

ending about the time of the first frost. Forest managers growing pecans should check their young plantations annually in early fall for damage. In plantations

isolated from infested natural stands, some control

can be obtained by destroying the girdled stems

containing eggs and larvae. If increased twig girdler

populations cause serious damage, registered insecticides may be used to control infestation.

LITERATURE CITED

Adams, John C., and Bart A. Thielges.

1976-77. Research underway on pecan timber

improvement. La. Agric. 20(2): 14-15.

Baker, W. L.

1972. Eastern forest insects. U.S. Dep. Agric.

Misc. Publ. 1175, p. 190-192.

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Bilsing, S. W.

1916. Life history of the pecan twig girdler. J.

&on. Entomol. 9:ll O-l 15.

Gill, J. B.

1924. Important pecan insects and their control.

U.S. Dep. Agric. Farmers Bull. 1364, p. 43-47.

Herrick, G. W.

1904. Insects injurious to pecans. Miss. Agric.

Exp. Stn. Bull. 86, p. l-l 1.

McKnight, J. S., and R. L. Johnson.

1960. Hardwood management in southern bottomlands. For. Farmer (23rd Manual Ed.) 39(5):30-

39.

Payne, J. A., H. L. Malstrom, and G. E. Kenknight.

1979, Insect pests and diseases of the pecan. U.S.

Dep. Agric., SEA, Agric. Reviews and Manuals,

ARM-S-5, p. 18-19.

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