How To Grow Trees

Symptoms And Treatments

Several tree ailments have so far been generalized about, by way of examples. Now described and prescribed for specifically will be a baker's dozen of afflictions commonly encountered, and serious enough to merit real concern. The troubles listed are by no means the only ones these species suffer. They are chosen with the thought of teaching the new owner some kinds of symptoms to watch for, and some typical methods of treatment.

Spruce, Inch-long spiny growths appear on twig tips of the blue spruce, and half-inch spiny growths at twig forks of other spruces. These are not cones. They are galls caused by aphids. Control: Dormant spraying with malathion just before new growth starts; pick off all the old galls possible. Lower branches of the blue and Norway spruces brown-off and die, progressively upward. Pitch exudes and cankers appear at the edges of dying bark, where small black fruiting bodies can be seen. This is Cytospora canker. Control: Prune all affected branches when weather is dry; spray repeatedly in spring with a fungicide.

Choke Cherry and cultivated fruit trees. When leaves are scarcely half grown, white webs appear at branch and twig crotches, growing in size daily. Look closely and you will see masses of baby tent caterpillars inside. They defoliate the trees by day, return to the webs every night. Control: Blast the webs with a strong stream and drench the leaves with a mist of strong stomach-contact poison; early next spring look for this caterpillar's cylindrical egg-masses wrapped on twigs and twist them off between thumb and forefinger. Flowers, leaves, and twig tips suddenly wilt and turn black, as though scorched by a blowtorch. Open, oozing cankers appear on the branches and trunk. Bark blackens and peels. This is fire blight, a bacterial disease. Control: Prune all affected members drastically, trace around and excise smaller cankers, remove and burn all cuttings, paint the wounds with cobalt nitrate, and disinfect tools with bichloride of mercury. Spray infected and neighboring trees repeatedly during early and full blooming with an antibiotic such as agrimycin.

Oaks. Twigs and small branches start dying. Look closely for tiny pits on the deadwood and yellowish or dark-gray round scabs, about 1/16 to 1/10 inch in diameter, on the live bark. These are golden oak scale and obscure scale. They occur separately and can be fatal. Control: Dormant spray with miscible oil, followed by malathion in mid-spring. Leaves wilt and branches die, their sapwood darkly discolored. Within a year the whole tree may be dead. This is oak wilt, so far uncheckable and incurable. Trees dying of it should be removed and burned promptly. This wilt is caused by a fungus called Ceratocystis fagacearum which enters through lesions, maybe also through the roots. It is earned by flies, beetles, and borers, and maybe is also air-borne. If you hear of oak wilt in your vicinity, repair your oaks' wounds promptly. Spraying with fungicides may help. Ceratocystis can also attack apple, birch, dogwood, sassafras.

Sycamore and Planes. Singly or in clusters, leaves brown, curl, and die. Angular blotches appear on other leaves, and dark patches on their stems, which break. The whole tree may become naked, but will grow a new suit later. This is anthracnose, a disease caused by a fungus that overwinters in fallen leaves and in cankers on twigs or branches. Control: A mercuric or copper fungicidal spray when buds are swelling, and twice again ten days apart if the weather is damp. Rake up dead leaves, prune infected members.

Birch, Elm, Holly, Lilac. Lacy patterns appear in the leaves, where their green cells are chewed out by leaf miners. On the thick holly and lilac leaves these patterns will look like opaque blotches. Split the leaf membranes apart and you can see the tiny worms through a hand lens. Control: Anticipate the adults early in May with a stomach poison; hit the second generation in July with chlordane, lindane, or dieldrin.

Pines. Colonies of inch-long green or yellow worms with black or brown heads appear, chewing off needles at a great rate. When you poke at them they rear up indignantly and stiffen to simulate needles. These are sawfly larvae. Control: Any strong stomach-contact poison.

Ash. The blossoms wither and become dark clusters which stay on all winter. These are flower galls, caused by a mite. Control: Spray with malathion and a good sticker in the spring when buds are swelling.

Dogwood. New leaves are small and pale, turning red prematurely. Twigs and whole branches die. Examination of the inner bark and sapwood low on the tree will show discolorations. This is crown canker, caused by a fungus called Phytophthora cactorum which attacks through lesions in the trunk and roots. Control: Trace the lesions well back, excavate them thoroughly, and apply shellac; feed the trees to help them resist further invasion, and spray early with a fungicide.

Elm. Parts of the crown suddenly wilt and wither. Terminal twigs bend upward like shepherds’ crooks. Examination of the sapwood in dead members will show brown stria-tions. This is probably Dutch elm disease, identifiable positively only in the laboratory because other, less lethal wilts closely resemble it. The causative fungus is transmitted by a small, dark-brown bark beetle which breeds in dead or dying elm wood, all of which should be removed (including old brush or log piles) and burned, or debarked and sprayed with lindane. The bark beetle's presence in elms will be signaled by bird-work on invaded branches. Some trees die quickly, others linger. There is no cure, only prevention by pruning and well-timed spraying, which should aim also to control the greenish elm leaf beetle whose defoliation weakens the trees. Feeding, and keeping their soil's pH high, may raise the trees' resistance to Dutch elm disease.