The War Between Trees And Their Enemies Is Natural And Unending. Man Can Decide It

Within the wonderful world of trees lies another world— that of the organisms which harbor in trees as pests and parasites. Of these there is no end in numbers or variety. New home owners are scarcely to be blamed for becoming dismayed, as they often do, upon encountering one invader after another for the first time. This writer's counsel to clients undergoing such baptism has always been: Cheer up, few kinds of attack on trees are fatal. Study of the trees' foes-learning to anticipate and counteract them—is a sporting proposition in itself. You may lose a few skirmishes, but there is a great deal that you yourself can do to win this war. Only occasionally will an owner, particularly of young trees, have to call in a tree-service task force.

The trees' invaders are from two kingdoms—the animal and the vegetable. The former are insects (and one bird) ranging from king-size larvae of the big moths down to microscopic mites, mini-wasps, and scale organisms no bigger than a pin point. The vegetable hordes are fungi, bacteria, and viruses. These are all primitive plant forms, but there is one plant parasite that is anything but primitive except in its role, assigned by mankind, as a love symbol. This is mistletoe, one of the deadliest invaders of all.

Mistletoe might well be spelled "missile toe," for its first tiny rootlets have the power to insinuate themselves into the host tree's living tissues like the fangs of a vampire. Its pallid, waxy berries, resembling seed pearls, are carried by birds and dropped into bark crevices where they germinate under protection of their own gum.* Mistletoe cannot live in soil but must steal its nourishment from a host tree's sap veins. Where it fastens on, grotesque swellings ensue and the host's deformed members writhe away from the vampire as if in horror. No amount of chopping-out short of limb amputation will eradicate the mature bushes. Fortunately for trees, and for the human kissing custom, and for Oklahoma whose State "flower" mistletoe is, the deaths it inflicts are slow and painless. Its glaucous clumps aloft even confer a macabre beauty upon the elms, hackberries, walnuts, gums, pecans, mesquites, and (rarely) oaks which it reduces to skeletons.

Mistletoes abound from lower New Jersey to Key West, all across the South, and up the west coast into Oregon. In much of this range they are accompanied by an even more picturesque growth called Spanish Moss, a member of the pineapple family. This stringy, grayish stuff hanging from trees, making them look like shaggy Arthur Rackham wizards, is not a true parasite. It is a typical air plant, of which lichens and orchids are other examples. Air plants do not suck a tree's life-juices but can, like the vines mentioned in Chapter II, smother it to death if allowed to run rampant.

Another conspicuous parasite, this a true one, is called witches'-broom. It shows up as dense, deforming twig clumps in hackberry, larch, and honey locust. It is caused by the sting of gall mites or by spores of a mildew fungus— maybe by both. Pruning is the only cure, if there is any.

Pruning or tissue surgery can sometimes head off one other class of parasite—the canker-forming fungi. Whenever such mechanical aids are attempted they should be followed up by feeding, usually with a high-nitrogen, to help the tree quickly seal off its canker lesions with healthy new cells before remnant fungoid mycelia (thread-roots) can spread, as in animals' fibroid tumors.

But chemical rather than physical warfare is necessary to combat the vast majority of tree pests and parasites. It is not within the scope of this handbook to describe all the thousand-odd kinds, symptoms, and treatments of such troubles. Some standard works on the subject are listed at the end of this chapter for readers who, grasping here the strategic outlines, may wish to arm themselves in depth to defend their trees.

"Chemical warfare" is meant literally. With ever-increasing success, men have learned to poison their trees' foes, at least in those years when the counterattacks are properly timed. How important timing is can be seen in two cases of some prevalence.

One is the poisoning, through its stomach, of an adroit one-inch herbivore called the bagworm, which spins and carries around with it a conical sack of silk and chewed-up plant material. After only a few days of foliar feeding, this creature attaches its bag to a twig and sacks in, to sleep until emerging as a moth. The only time you can hope to make it eat poison is during its brief browsing period. Otherwise it is sheathed against any attack you may make short of picking off all the bags and destroying them, which is no small task in an arborvitae hedge or a grove of maples.

*Curiously, both mistletoe and the other Christmas evergreen, holly, yield viscous exudate called "lime" (from the Latin "limere," to smear), which was used immemorially by men to snare birds.

Exact scheduling is necessary to suppress Diploctiapinea, a fungus which becomes destructively endemic in conifers, especially Austrian pine. It blights and browns-off twig tips, which must be pruned in cold weather and carried away together with all old cones, on which diplodia's dormant fruiting bodies show like black pepper. The first eruption of new spores will occur on that warm, humid spring day (but which one?) when the pine's young "candles" burst their husks. Right then you must hit diplodia with a copper or mercury spray, and hit it again at short intervals (but how short?) twice or oftener (but how much of-tener?). If the weather continues mild and damp, about ten days is the interval and thrice more, the frequency. But once it has taken hold, don't expect to get rid of diplodia permanently. You will be lucky if you keep it under control. This is why Austrian pine, and to a less degree the Scotch and red, are less popular than formerly in what has become diplodia territory.

These examples of ticklish timing are extreme. They are cited early in our account of anti-parasite strategy to emphasize that, in this warfare as in any other, timetables are critical. The seasons govern the foes' behavior and therefore our own.

Successful chemical warfare in trees consists in getting there at the right time with the right material. For not to exceed $25 the home owner can acquire hardware that will deter any invasion up to fifteen feet (add a stepladder for five feet more). To protect his natural pump-fountains he needs only a mechanical pump-fountain through which his arm can supply about twenty pounds of pressure to a column of liquid nozzled into a rain or mist.

Some one-man sprayers are designed with a tank of up to five gallons that sits on the ground while you pump up pressure. Another type rides on your back with shoulder straps and lets you pump as you walk. Since fifteen-foot trees, in leaf or dormant, require two or three gallons of material each for a thorough spraying, these small rigs take a lot of refilling. The next-largest size is a 20-30-gallon tank which you trundle in a barrow or on wheels of its own, still pumping up pressure by hand.

After that you get into motored sprayers, whose costs rise with the tankage and power. Where true neighborliness and enough trees warrant, owners sometimes club together and, for a total outlay of perhaps $600, jointly buy a 300-gallon spray-rig capable of hitting anything up to forty feet at about 200 pounds of pressure. Beyond this caliber, where strong spray materials may get out of hand and real hose-manship is called for, calling in professionals is recommended. If you have done some spraying for yourself, you will know what more you need, when you need it, and what to pay for it.

Most tree services have high-powered rigs carrying 500-600 gallons. Charges must vary with mileages and materials but they should not run above twelve to fifteen cents per gallon applied. Companies with mist-blowers can make you the best prices, if your trees are accessible.

Before defining spray targets, let us dispose of that "one bird" mentioned above. This is the sapsucker. He is the one feathered thing who is truly a tree miscreant. About half his diet, especially during migration, consists of bark, cambium, and sap. He literally taps into them with his sharp bill and licks them out with his brushlike tongue. Except when excavating nest holes, all other members of the woodpecker family perforate trees only in search of insects, which they spear with tongues like barbed nutpicks. The sapsuck-er's depredations are unique and, when sap has fermented, sometimes comical. (Sapsuckers are often followed on their rounds by migrating Hummingbirds, but these fleet and magical jewels are mainly seeking sap-attracted insects, not drink, and should not be criticized for the company they keep.) No spray known, only wrappings, will stop sap-suckers from drilling their neatly spaced holes into young apple, birch, beech, and other thin-barked bleeders. But shoo, don't shoot them. Like their beneficent kin, the sap-suckers also extract many borers and beetles.

What One Man Did in Seven Years. This owner collected, planted, and reared all his new trees himself for a total outlay of less than $100. He has spruce, pin oak, birch, willow, crimson maple, and several more species.

Top view shows the house sitting back in its grounds against native wild wood.

Bottom view, looking from back to front, shows how this owner thinned his wildwood selectively, intelligently. In row of trees on right are sassafras, then tulip poplar; on the left are older hardwoods, mostly oaks, ash, and maples.

Photograph by B. F. Shepherd

What Another Man Did in 23 Years. The three pictures on the opposite page show (top to bottom) an old grist mill in bare grounds when it was being remodeled, then four years later, then as it looks today. The owner, though strictly an amateur, planted, shaped, and cultivated all the present trees with his own hands.

The old dam and millstream were screened with maples, spruce, and dogwood

Looking from the dam toward the house.

Along the old flumeway, a hemlock aisle.

How to Overplant and get a stifling, confused effect. About fifteen years ago some nurseryman sold these kind people a fat bill of goods.

Top shows the front grounds, bottom shows the back. Detail in between shows what happens to overcrowded evergreens.

Insects occur among trees as naturally as leaves and, in Nature's code, just as rightfully. By no means all of them are harmful. Some insects are positively benign and should be recognized as such before you take spray gun in hand.

All the bees help the plant world as pollen carriers. All the larger wasps and hornets are strictly insectivorous and only one—a giant from Europe which occasionally strips twigs for nesting material—has any bad habits other than stinging savagely in self-defense.

The spiders prey on all manner of flies, bugs, and grubs without themselves ever harming plant life. (The tiny "red spider" that infests cedars, boxwood, and other plants is really a mite.) The daddy longlegs or harvestrnan is, despite his alarming physique, the meekest of spiders.

Ladybugs, shiny red or brown with dainty spots, are almost entirely non-vegetarian. They consume amazing quantities of aphids and scales. When our American orange-growers found this out they sent to Australia for more and hungrier ladybugs.

A most ferocious-looking insect in size and posture is the mantis. His first name is spelt "praying," for the way he holds up his forelegs, or "preying," for his predations of other insects. The Japanese keep mantes on long silken leashes near their beds to devour mosquitoes. There is in the United States a mantis industry, run by people who collect the gall-like egg-masses off shrubs and weeds and sell them to horticulturists for hatching where needed.

The big, black sexton beetle or undertaker, with huge frontal nippers, is another denizen of everyone's grounds that is horrendous to behold—but its diet is strictly carrion.

The insects injurious to trees fall into four main categories: Gnawers (borers, beetles, weevils), Chewers (worms, caterpillars, beetles), Suckers (aphids, scales), and Stingers (mites, minute wasps).

Gnawers. The larvae of many species which later become beetles or moths start life as vermiform borers, like the three-inch pink and brown grub of the leopard moth, largest of the lot. Unless the parents of such invaders have the habit of feeding on foliage (which few do) before laying their eggs (which are difficult to destroy), no spray can check them unless it is shot directly into their bores from a DDT or carbon disulfide pressure can, and the holes plugged. Often their entrances are invisible, being started as tiny perforations where the eggs hatch in bark crevices. Fortunately, most destructive borers advertise their presence by putting out frass (sawdust) or, in the cases of peach and pine borers, by masses of gum which ooze out behind them. When thus detected, boring grubs can be crushed in their tunnels by a wire probe, or fetched out with a crochet needle or straightened fishhook.

The gnawing beetles trace labyrinthine patterns through inner bark and cambium, but most of them emerge to breed and are then vulnerable to stomach or contact poisons. Weevils are specialized beetles which, both as larvae and adults, feed on tissues usually shallow and tender enough for penetrant poisons to reach.

Various ants gnaw wood, but only after it has begun to decay. Winged termites and long, black carpenter ants are the worst offenders because they eat on past the dead wood into live and are so voracious they can weaken trees, and even houses, structurally. Ants swarming up and down the outside of a tree are not cause for alarm. They are doubtless only tending their flocks of aphid on the leaves aloft, which you can dispatch with one spraying. Certain ants "milk" aphids just as we do cows, and even move them about to fresh pastures. The ant-aphid symbiosis (life partnership) is most damaging to the roots of corn and strawberries, not to trees.

Chewers are the most obvious of plant pests since they feed on leaves, where their inroads are quickly visible. Most such creatures bite through the whole leaf and hence can be poisoned by chemicals laid down, with some sticker like soap or a household detergent, on either surface. But some skeletonize the leaf by chewing only from the underside, where the spray sticks least well. And some go an insidious step further and chew between the leaf surfaces, eating the inner tissues. These last are called "miners" and their work eviscerates leaves to near transparency. It takes a potent dual-purpose poison—stomach and contact—to get through to them.

Suckers are insects whose feeding organs are probes which they thrust into tree tissues to extract the juices. No poisons spread in wait for them will enter their systems. Their bodies must be hit with chemicals that kill on contact. Aphids or plant life are vulnerable to such treatment, being soft-bodied, but many of the scale insects have hard shells as adults and can be shriveled by contact poisons only in their unarmored crawler stage. Knowing their life cycles is necessary to control the scales called terrapin, oyster shell, lecanium, and San Jose. In general, the scales' vulnerable moment comes in early spring, which adds importance to so-called "dormant" spraying, the year's first.

Stingers are flies, mites, mini-wasps, and some aphids which puncture leaves and twigs with their ovipositors, to insert eggs which form galls as they develop. Witches'-broom has been described. Some other galls caused by stingers are of various shapes and sizes on oaks, bladder gall on maples, flower galls on ash, cockscomb gall on elms, club gall on dogwood, Sitka gall on blue spruce, cone gall on other spruces.

Fungi, the chief vegetable parasites, have symptoms, life cycles, and remedies quite different from the insect pests. They become active about the same time in spring, for the most part, but most of them reproduce and attack far oftener than the insects. In some, new crops of spores can ripen just a few days apart and require only a spell of damp warmth to trigger a fresh outburst. When the outbursts occur, the spores literally explode from the fruiting fungus bodies and are air-borne for long distances. They thrust their mycelia into healthy parts of trees, from leaves to roots, as well as entering lesions to attack exposed tissues. Because of their virulence and the tininess of their infesting particles, fungicidal spraying is to be thought of as fumigating, to kill germs. If they could be controlled as well as liquids or dusts in the open air, gases would make the best fungicides, to penetrate and permeate as the spores do. Many fungicides are formulated so that they give off gases on the trees and are hence most effective on still days.

Symptoms of fungoid infestation can be schematized as follows:

On leaves—spots, blotches, blisters, curling, wilting, powdery deposits (mildew).

On twigs—pustules, cankers, rusts, molds, blighting, clumping.

On branches and trunks—decaying cavities, fluxing lesions, cankers (dry or bleeding), bracket mushrooms.

On roots—cankers, molds, blighting, decay lesions, threadlike appendages and interconnections, stemmed mushrooms or toadstools.

Below the fungi on plant life's ladder, bacteria and viruses cause diseases by what might be called simple infection. Crown gall in the rose family (apple, pear, cherry, almond, etc.) and in many other trees is caused by a bacterium which, entering a lesion, causes overgrowth of woody cells, resulting in rough swellings, sometimes huge, usually on the tree's base or roots but also well aloft in poplar and willow. One of the few ailments suffered by sassafras is an incurable virus called yellows, which bunches the twigs, blanches and dwarfs the leaves.

The above account of tree parasites is necessarily oversimplified. Readers are again referred to the definitive literature listed on a later page. Besides describing symptoms and their causes, the best pest books carefully specify remedies, which can be summarized here, to give the reader a base of spray knowledge to build on.

Spray materials have long been used to achieve five main effects: 1) When trees are still dormant in spring, to "burn" off by oxidation many nascent or emergent organisms; 2) to poison insect parasites internally; 3) to kill them by contact; 4) to combine effects (a) and (3); 5) to suppress fungi by poisoning their fresh spores.

In the old tree-spray pharmacopoeia, standard materials for the purposes thus listed were: 1) Miscible oil, a petroleum fraction close to kerosene, for dormant sprays; 2) Ar-senate of lead, for stomachs; 3) Lime sulfur, for contact; 4) Nicotine sulfate ("Blackleaf 40"), for contact-and-stom-achs (some old-timers made it by soaking their cigar butts in a tub); 5) Copper sulfate and lime ("Bordeaux mixture"), as a fungicide.

Pyrethrum, an extract of chrysanthemums, was long used with a light grade of miscible oil as a stand-by stomach poison less dangerous to warm-blooded animals than lead arsenate.

If your garden supply store is not up with the times, it may still carry all these remedies tried and true, and there is nothing wrong with any of them. But on modern shelves there is now a wide assortment of brave new formulations, of higher and often more specific potency. These change from year to year, as do the experts' opinions of them. DDT, an all-purpose killer, enjoyed a fifteen-year vogue which has now somewhat waned since its ill effects on unintended targets—birds, mammals, fish—became manifest and many of its insect targets developed immunities. Parathion too proved all too potent and is used now only by professionals. As of spring 1962 an adequate home arsenal of reliable, manageable spray materials might include the following:
Miscible oil for early dormant sprays. Stomach or contact poisons can be mixed with it for delayed dormant use when a lighter "summer" grade of the oil is used. Never put oil sprays on beech, walnut, hickory, or maple: you may burn their leaves. Such sprays may discolor but will not harm blue spruce.

Sevin is a carbamate stomach poison, developed for fruit trees, which is now considered right for shade trees.

Rotenone, Chlordane, and Undone are all dual-purpose sprays combining stomach and contact effects, for use against adult chewing insects, including the leaf miners. Rotenone is highly toxic to fish.

Kelthane—a good miticide non-toxic to bees.

MaUithion—a versatile contact spray for obdurate aphids, mites, beetles, weevils, caterpillars, soft-shelled scales. It has low toxicity to warm-blooded animals.

Dieldrin—a. good specific for soil-infesting insects including ants, termites, nematodes, and the grubs of the Japanese beetle.

Puratized Agricultural Spray (mercuric) and Captan (chloric) are two of the latest and best fungicides to replace copper sulfate, which is less potent. They leave less unsightly residue.

Some basic ground rules about spraying are these: Do no spraying when the temperature is below 400 or above 8o°F.

Spray materials can sometimes be mixed to obtain multiple effects with one application, but this should never be attempted without first checking that the materials are compatible. Manufacturers' charts will tell you about this. Wash out your rig after every use, to avoid an incompatibility next time.

If you use any weed- or brush-killers (2-4-D; 2-4-5-T) on your grounds, apply them with separate equipment, not your tree-spray rig. Beware tree damage through root absorption or atmospheric drift of these killers, which over-stimulate broadleaf plant life into "growing itself to death."

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.

Reliable textbooks on tree pest, parasites, symptoms, and control measures include the following:

Tree Maintenance, P. P. Pirone (Oxford University Press); Tree Care, John M. Haller (The Macmillan Co.); Insects and Diseases of Ornamental Trees and Shrubs, Ephraim Porter Felt and W. Howard Rankin (The Macmillan Co.); Diseases and Pests of Ornamental Plants (Third Edition), B. O. Dodge, H. W. Rickett, and P. P. Pirone (The Ronald Press Co.); The Wise Garden Encyclopedia, E. L. D. Seymour, ed. (William H. Wise& Co.).

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