[Ill.u.s.tration: Fig. 7.--Injury to young pecan tree by the fall webworm.]

[Ill.u.s.tration: Fig. 8.--Larvae of the walnut caterpillar.]

[Ill.u.s.tration: Fig. 9.--Caterpillar of the hickory tussock moth.]

[Ill.u.s.tration: Fig. 10.--Rose chafer beetles on chestnut blossoms.]

Insects Attacking the Foliage

~Black pecan aphid.~ Pecan trees at times suffer sufficient damage from the black pecan aphid[15] to cause considerable defoliation (Fig. 5) during the latter part of the season. The injury to foliage in its earlier stages consists of irregularly shaped yellowish areas which turn brown when the tissues die.

[15] ~Melanocallis caryaefoliae~ (Davis).

This aphid is usually controlled with nicotine sulfate (40 percent nicotine), 3/8 pint plus summer oil emulsion, 2 quarts per 100 gallons of spray. Parathion and benzene hexachloride have given good results in experimental work but are not yet generally recommended.

~Pecan phylloxera.~ The pecan phylloxera[16] is related to aphids. It attacks princ.i.p.ally the vegetative parts of the tree such as the leaves, petioles, and shoots on which galls (Fig. 6) are produced. Pecans, hickories, and other species of nuts are subject to infestation.

[16] ~Phylloxera devastatrix~ Perg.

In the past a spray of nicotine sulfate (40 percent nicotine) 13 ounces combined with either lime-sulfur solution, 2-1/2 gallons per 100 gallons of water, or lubricating-oil emulsion, 2 quarts per 100 gallons, applied in the late dormant period has been the standard recommendation. In recent experiments in the South with some of the new organic sprays, benzene hexachloride and some of the dinitro compounds have indicated good promise.

~Fall webworm,~[17] ~walnut caterpillar,~[18] ~and hickory tussock moth.~[19] The caterpillars of these species (Figs. 7, 8, 9) are frequent pests on the foliage of nut trees. They often defoliate entire branches.

[17] ~Hyphantria cunea~ (Drury).

[18] ~Datana integerrima~ (G. and R.)

[19] ~Halisidota caryae~ (Harr.)

The best time to apply control measures is as soon as possible after the caterpillars hatch. The insects can be readily destroyed with lead a.r.s.enate, 3 pounds, or DDT (2 pounds) of 50 percent wettable powder, per 100 gallons, applied when they appear. Other new organic insecticides may also be effective but have not been widely tested.

~The rose chafer and j.a.panese beetle.~ Adults of the rose chafer[20] (Fig.

10) and the j.a.panese beetle[21] are voracious feeders on the foliage of nut trees and must be destroyed if severe injury is to be avoided.

[20] ~Marcordactylus subspinosus~ (F.).

[21] ~Popillia j.a.ponica~ Newm.

Fortunately these insects may now be controlled by spraying with DDT, 2 pounds of 50-percent wettable powder per 100 gallons of water, when the beetles appear. In the case of the j.a.panese beetle a second application may be necessary if the infestation is heavy.

~Spider mites.~ Nut trees, especially those which have been sprayed with DDT, may become seriously injured by various species of mites.[22] DDT is very toxic to the natural insect enemies of plant-feeding mites and therefore the mites build up to injurious numbers.

[22] ~Tetranychus~ sp. and others.

Of the various miticides recently tested on pecan, a spray of parathion was the most promising. In some recent tests for the control of spider mites on chestnut trees, 1-1/2 pounds of 15 percent parathion wettable powder per 100 gallons of water was effective. Do not use parathion unless you observe all the precautions contained on the package label of the material.

[Ill.u.s.tration: Fig. 11.--Larva of the twig girdler. Enlarged.]

[Ill.u.s.tration: Fig. 12.--Adult of the flatheaded apple tree borer.

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 Washington