Home Is Where Your Trees Are

Pests And Parasites. Part 2

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 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.

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.