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.

[Illustration: Fig. 11.--Larva of the twig girdler. Enlarged.]

[Illustration: Fig. 12.--Adult of the flatheaded apple tree borer.
Enlarged.]

[Illustration: Fig. 13.--Larvae of the flatheaded apple tree borer.]

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

[Illustration: Fig. 15.--Adult of the buffalo treehopper. Enlarged.]

[Illustration: 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 agains