The pears of New York

by U. P. Hedrick

As with nearly all diseases of plants, some varieties suffer more than others. Sheldon, Seckel, and Flemish Beauty are more injured than Kieffer, Lawrence, and Mount Vernon. Nursery stock is more often injured the second than the first year set. Only the leaves suffer. The fungus first shows its work in minute purplish spots on the upper surface of the leaf. The mature spots measure about one-sixth of an inch in diameter, are angular in shape, with well-defined margins, and have an outer zone of brownish-purple, with a grayish center. Late in the season, dots, the spore-cases of the fungus, appear in the gray central area. The fungus passes the winter in diseased leaves which fall to the ground in late summer. From these leaves spores are discharged into the air to be carried to the leaves after growth begins in the spring. The disease is usually controlled by the sprays necessary every year to keep pear-scab in submission. In the nursery, two-year-old trees are sprayed just after the new leaves open and twice thereafter at two-week intervals. One-year-olds seldom need to be sprayed.

Leaf-blight (Fabræa maculata (Lev.) Atk.) is a common and destructive fungus in pear-nurseries in New York and is sometimes troublesome in orchards. The quince suffers even more than the pear from this fungus. In the nursery, leaves and twigs are attacked, and in the orchard the pears themselves sometimes suffer. The disease appears in the spring as minute, reddish-brown circular spots on the upper surface of the leaves, but the fungus penetrates through to the lower surface as the disease progresses. Eventually the color changes to dark brown, and later a coal-black, raised spot appears in the center. The spots sometimes run together. Young leaves shrivel under the attacks of the fungus; while old ones, if badly diseased, turn yellow and drop prematurely. Twigs and leaf-stalks are frequently girdled, and the lesions are more elongated. The spots are similar on the fruits to those on the leaves. The fungus spends the winter in fallen leaves. In the spring the spores are discharged from the fruiting organs of the fungi and are carried to the tender leaf or twig of the pear or quince. The parasite begins growth at once and in about a month a new crop of spores develop. This fungus grows on various other pome-fruits which complicates remedial measures. The treatment recommended for leaf-spot should control leaf-blight.

As are all tree-fruits in New York, the pear is attacked by crown-gall (Bacterium tumefaciens Smith & Townsend). This disease, however, is seldom a serious menace to orchard trees this far north, but the vigor of nursery stock is sapped when the galls girdle the tap-root or the stem at the collar. Moreover, trees affected by crown-gall are barred in most states by inspection laws so that nurserymen can ill afford to produce gall-infected trees. It is a wise precaution not to plant badly diseased trees. The galls are tumor-like structures on the roots of the plant, or often at the juncture of root and stem. They vary from the size of a pea to that of a large egg, forming at maturity rough, knotty, dark-colored masses. Another form of the disease appears as a dense tangle of hair-like roots arising from callous-like galls. This form passes under the name “hairy root.” Neither preventive nor cure is known. Orchard or nursery should not be planted on ground known to have been infected as the disease is highly contagious. The brambles, especially raspberries, are common carriers of crown-gall, and none of the brambles should be planted as inter-crops in pear-orchards.

Brown-blotch (Leptothyrium pomi (Mont. & Fr.) Sacc. var.) is another fungus which is sometimes troublesome. The fungus causes reddish blotches on the fruit which coalesce into rusty-brown patches often covering the whole surface of the pear. Here, again, the Kieffer suffers most although fruits of other varieties are often disfigured by the blotch. The disease is most common on heavy soils and in densely shaded trees. Pruning to let in the sun is usually sufficient to keep the fungus in check, but a late application of lime and sulphur is often necessary.

Black mold (Fumago vagans Fr.), a fungus which grows in the honey-dew exuded by the nymphs of the pear-psylla, sometimes causes a sooty covering of the pears which spoils their sale. Twigs and leaves are also covered with thin superficial growth of the fungus somewhat to the detriment of growth. The remedy is obvious—control the psylla.

Pink-rot (Cephalothecium roseum Cda.) sometimes does much damage to pears in common or cold storage. The fungus seems able to enter the skin of pears only through injuries, and when reasonable care is used in handling the fruit the rot does little damage. Not infrequently it is found on fruits unpicked, having entered the skin through ruptures made by pear-scab, black-spot, or other fungi. This, of course, seldom happens in well-sprayed orchards.

INSECTS ATTACKING THE PEAR

Several insect pests are very destructive to pear-trees, as many more are often troublesome, while perhaps in addition to the dozen that must always or occasionally be combatted some thirty or forty more have been listed as pear-pests. Young pear-trees are very susceptible to injuries of any kind and if beset by any of the common insect pests do not prosper. As the trees come to maturity, life and vigor of the tree may not be endangered by any but two or three of the worst pests, but the crop is always cut short by infestations of insects on any part of the plant which interferes with the normal life of the tree. The pests most destructive to the pear in New York, about in order of importance, are San Jose scale, psylla, codling-moth, pear-slug, and pear-leaf blister-mite.

San Jose scale (Aspidiotus perniciosus Comstock) is particularly harmful to tree and fruit of the pear. The pears, possibly, are malformed more and show the scales with their discoloration more plainly than the product of any other fruit-tree. A scale-infested pear-tree is easily recognized. Dead and dying twigs or branches and moribund trees are evidences of the dreaded pest. Examination shows the moribund parts to be covered with myriads of minute scales which give the infected bark a scurfy, ashy look. A reddish discoloration is discovered if the bark be cut or scraped. A foothold gained on trunk or branch, fruit and foliage are soon infected. Reproduction is continuous throughout the summer, and the scales increase by leaps and bounds. Smooth-barked young trees succumb within three or four years if the insects are unchecked; the rougher-barked old trees survive the pest indefinitely, although the vigor is lessened to the point of unproductiveness in many old orchards. Pear-growers find the lime-sulphur solution applied in the dormant season the most effective spray in combating San Jose scale. Several insect enemies of the scale help to keep the pest down. A quarter-century ago, it was feared that the pear industry of the State might be ruined by San Jose scale, but no energetic fruit-grower now fears the pest.

Next to San Jose scale, psylla is the most feared pest of the pear in New York. Indeed, this insect is much more difficult to combat successfully than scale, and were it as wide-spread, the pear industry in New York would be hard hit. The psylla is a minute, sucking insect, wingless in its immature stages, but winged and very active as an adult. They are nearly related to plant-lice, and like them suck the juices of the buds and new leaves. Like plant-lice also they reproduce very rapidly. The immature insects secrete a sticky honey-dew which becomes blackened with a fungus, and the presence of this blackish, sticky substance on foliage and branches is usually the first indication of the pest. The adult is about one-tenth inch long, with four membranous wings, the body dark in color and showing brownish-black markings. Seen through a hand lens, the mature insects look like tiny cicadas. The adults hibernate in crevices of the bark, and at the time buds are swelling in the spring come out to lay their eggs. The eggs hatch in two or three weeks, and there may be four or five broods in a season. The pest is best controlled by spraying with such contact insecticides as tobacco extract both to kill the hibernating insects and later the immature psylla. The winter strength of lime-sulphur solution will kill the eggs.