Part 22 (2/2)

Enlarged.]

[Ill.u.s.tration: Fig. 13.--Larvae of the flatheaded apple tree borer.]

[Ill.u.s.tration: Fig. 14.--Scars on trunk of pecan tree caused by cutting out flatheaded apple tree borers from their tunnels.]

[Ill.u.s.tration: Fig. 15.--Adult of the buffalo treehopper. Enlarged.]

[Ill.u.s.tration: Fig. 16.--Twig scarred as a result of egg laying by the buffalo treehopper.]

Insects Attacking the Trunk and Branches

A number of insects cause important damage to the trunk and branches of nut trees.

~Obscure scale and others.~ The obscure scale[23] infests a variety of nut trees. On pecan the chief injury results from attacks on branches under three inches in diameter.

[23] ~Chrysomphalus obscurus~ (Comst.).

The obscure scale and other scale insects can be controlled with lubricating-oil emulsion during the dormant period. However, nut trees are often susceptible to oil damage, especially at 3 percent concentration. Since healthy trees are more resistant to oil injury, it is therefore advisable to watch for scale infestations so as to spray them before the trees are weakened.

~Twig girdler.~ Nut trees are sometimes attacked by the twig girdler[24]

(Fig. 11). This beetle lays eggs in the twigs, which are girdled so as to stop the flow of sap that would normally prevent hatching. The girdled twigs usually become detached from the trees and as a result the nut-bearing wood is reduced.

[24] ~Oncideres cingulata~ (Say).

The standard recommendation for control of this insect has been to gather and destroy the infested twigs in the orchard and from any infested trees nearby. Recent tests on pecan in northern Florida indicate that DDT and parathion may be effective against this insect.

Three applications (the first on August 26 when the first girdled twigs were observed and the others on September 9 and 23) of DDT, 4 pounds of 50 percent wettable powder per 100 gallons of water, or parathion, 3 pounds of 15 percent wettable powder per 100 gallons, gave complete control. Further experiments will be required to determine the minimum effective concentration of spray and the number of applications needed for control. It is suggested that DDT be used for the control of this insect until more information is available on how to handle and to use parathion.

~Flatheaded apple tree borer.~ The adult beetle of the flathead apple tree borer[25] (Fig. 12) deposits its eggs throughout the summer season, preferably in the small grooves of bark on the unshaded portions of the trunk of pecan and other trees. The borers (Fig. 13) hatch and tunnel through the bark to the cambium layer. Young trees may readily be girdled (Fig. 14).

[25] ~Chrysobothris femorata~ (Oliv.).

To avoid this insect as far as possible, orchard sanitation should be practiced and the trees should be kept in a healthy condition. In some plantings wrapping the trunks with paper or burlap to protect against egg laying and maintaining low branches to shade the trunk have been helpful. Cutting out the borers with a knife has also been resorted to; trunk washes have likewise been used but have not been very effective.

~Buffalo treehopper and periodical cicada.~ Buffalo treehoppers[26] (Fig.

15) and the periodical cicada[27] weaken twigs by inserting their eggs in them. The injured bark becomes roughened as it heals (Fig. 16), and the growth of the limb is r.e.t.a.r.ded.

[26] ~Ceresa bubalus~ (L.).

[27] ~Magicicada septendecim~ (L.).

Pruning of weakened twigs is recommended for wood injured by the cicada.

If treehoppers are a pest, clean cultivation will help. Cover crops of cowpeas or clovers should not be planted. In preliminary tests two or three applications of tetraethyl pyrophosphate (20 percent), 3/4 pint per 100 gallons of water, have given promising results in controlling the periodical cicada. The first application should be made after the cicadas appear and the others as needed to prevent damage.

Observations on Effects of Low Temperatures in Winter 1949-1950 on Walnuts and Filberts in Oregon and Was.h.i.+ngton

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