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Oak Pests - A Guide to Major Insects, Diseases, Air Pollution and Chemical Injury

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Note: see bottom of page for figure descriptions.




Giant bark aphid,
Longistigma caryae;
(figure 43) with relation to other aphids, this species is very large, .25 inch (6 mm) long, long slender legs, and is covered with a bluish-white "bloom"; several generations per year.

Terminals, twigs, and branches of red and white oaks; aphids feed by sucking the plant sap; heavily infested stems are badly weakened or killed; honeydew and sooty molds mar beauty of ornamentals.



Pit scales,
Asterolecanium spp.; adult females are circular and enclosed in yellowish, waxy, translucent covering, .04 to .08 inch (1 to 2 mm) in diameter; one generation per year.

Found on twigs, branches, and trunks of red and white oaks; prefers white oaks; maturing females produce ring-like swellings or pits on the bark (figure 44) causing a rough appearance; branches and trees may be killed.



Kermes scales,
Kermes spp.; adult females are globular or gall-like, yellow-brown to black, solid or mottled, about .1 to .3 inch (3 to 7 mm) in diameter.

Scales (figure 45) occur on twigs, branches, near buds, near wounds, on leaf midribs, and petioles of red and white oaks; dieback or "flagging" of newly formed terminals, branch ends, and new leaves; early leaf drop; mar beauty of shade trees.


Obscure scale,
Melanaspis obscura;
adult female cover (figure 46) circular, grayish to black - resembling bark in color .08 to 0.1inch (2 to 3 mm) in diameter; two generations per year.

Trunks and branches of red and white oaks; infestations are often heavy and layered, killing branches, or resulting in general weakening, and sometimes death of tree.



Spider mites,
Oligonychus spp. and Eotetranychus spp.;
.02 inch (0.5 mm) long, spider- like, eight legs, sucking mouthparts; large numbers often present; many generations per year.

Foliage and buds of red and white oaks; scattered chlorotic stippling on leaves (figure 47) later yellowing or bronzing, then browning and dying of foliage; mats of webbing often present; weakens tree and mars beauty.



White grubs,
Phyllophaga spp.; larva (figure 48) is milky white, C-shaped, about 1 inch (25 mm) long, brown head; adult beetle is robust, oval, brown, about .5 to 1inch (12 to 25 mm) long.

Wide host range, including oak seedlings and young trees; larval feeding prunes and girdles roots; nurseries and young plantations often damaged; adults may defoliate trees.



Figures 43 - 48. --

(43) Nymphs and adults of giant bark aphid
(44) Pit scale on oak branch
(45) Kermes scale on oak twigs
(46) Obscure scale on oak branch
(47) Left, healthy leaves; right, chlorotic stipling caused by spider mites
(48) Left, white grubs and root injury; right, healthy roots

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