The peaches of New York

by U. P. Hedrick

In the final stage of the disease the trees assume the yellowish leaves which give name to the trouble, though sometimes the yellow is tinged with red. Yellows is an unfortunate name since so many other troubles of the peach cause the foliage to take on the jaundiced appearance of this disease. The third stage marks the beginning of the end—sometimes three years, sometimes five or six, but always death sooner or later, there being no instance on record of a diseased tree having been cured.

This, in brief, is the usual course of yellows, but it follows no invariable rule in its development. Yellows is known to be spread as a contagion by affected buds in nursery stock, by nursery-trees, by orchard-trees, and may even be communicated by pits from affected trees. That it must be caused or transmitted in still other ways is apparent to all who have had experience with the disease. It seems not, however, to linger in the soil, for trees may be set in the very spots from whence diseased plants have been removed without danger to the newcomer. "War to the knife and the knife to the hilt"—absolute extermination, root and branch, by ax and fire, is the only known method of subduing yellows.

Little-peach is possibly a variant of peach-yellows or, at least, is very similar in nature. It seems to have been described first in Michigan in the early nineties of the last century but had attacked orchards in New York before that time so that it is now impossible to say where it first appeared. Be that as it may, the disease is not now the exclusive possession of either state but in the twenty years of its history has become as widely distributed as yellows, covering about the same territory, and seems now to be equally destructive. Outwardly the disease differs from yellows chiefly: (1) In delayed rather than premature ripening of the under-sized fruits of little-peach; (2) the leaves usually show more green than in yellows and show a decided tendency to droop or roll; (3) little-peach, as a rule, appears later in the season than yellows; (4) the characteristic, sickly, wiry shoots of yellows are seldom present in little-peach. Little-peach is kept at bay, as in yellows, by extermination of affected trees.

Rosette, though distinct in most of its symptoms from yellows and little-peach, is clearly similar in nature, is just as virulent and contagious, is communicated in the same ways and requires the same treatment. On trees affected with rosette the fruits shrivel and drop and tufts or rosettes of leaves develop freely. Rosette is not found in New York nor north of the Potomac and hence is of but passing interest to peach-growers in this State.

Brown-rot (Sclerotinia fructigena (Persoon) Schroeter), known also as fruit-mold and ripe-rot, attacks flowers and shoots of the peach, but is most conspicuous on the ripe or ripening fruits. Here its presence is quickly detected by a dark discoloration of the skin which is afterwards partly or wholly covered with pustule-like aggregations of gray spores. The decayed fruits fall to the ground or more often hang to the tree, becoming shriveled mummies, each mummy being a storehouse of fungus threads and spores from which infestation spreads to the next crop. The rot spreads with surprising rapidity on the fruits in warm, damp weather either before the fruit is picked or in baskets while being shipped or stored. Preventive remedies have so far met with but indifferent success; probably the best method of control is to destroy the mummy-like fruits and all other sources of infection either by picking them from the trees, or much better by plowing them under deeply. Even so it is impossible to exterminate all of the countless myriads of brown-rot spores. Spraying with the self-boiled lime-sulphur mixture three times at intervals of three weeks, beginning as the calyxes drop, is the appointed preventive but the results are uncertain, as this is one of the diseases in which it is difficult to touch the spot in spraying. Varieties of peaches show various degrees of susceptibility to brown-rot.

Peach leaf-curl (Exoascus deformans (Berk.) Fuckel) is the best-known and probably the most prevalent fungus disease of the peach in New York. The disease appears in early spring as the leaves unfold and continues until warm, dry, summer weather prevails. The name describes the disease so that all may know it—the leaves curl, then become puckered, distorted and much thickened, turn from normal green to yellow, tinged with red, and finally fall. In severe cases the trees may be defoliated, though a second covering of leaves almost always comes out. Leaf-curl is most prevalent and most virulent in cool, moist weather. The disease is easily controlled by spraying with lime-sulphur, bordeaux mixture or any other good fungicide applied while the trees are dormant.

In common with other species of Prunus the foliage of peaches is attacked by several fungi which produce diseased spots on the leaves, the dead areas usually dropping out leaving holes as if punctured by shot, giving the names "shot-hole fungus," "leaf-spot" and "leaf-blight." Two fungi are in the main responsible for these leaf-troubles, Cylindrosporium padi Karsten and Cercospora circumscissa Saccardo. The ravages of these fungi are prevented by the use of the self-boiled lime-sulphur mixture. With these, as with other fungi, cultivation has a salutary effect as it destroys diseased leaves which harbor the fungi during their resting period and keeps the trees vigorous enough to resist the fungi.

Peach-scab (Cladosporium carpophilum Thüm.) is a common and destructive fungus in peach-growing districts on the Atlantic seaboard and is found rather frequently in New York but seldom does much injury in the State. It appears in sooty, black spots and blotches on the surface of the peach, causing atrophy and hardening of the parts affected which, in severe cases, crack badly. Twigs and leaves may be affected. White-fleshed sorts suffer most and are ruined for the market even in mild attacks. Self-boiled lime and sulphur, if it does not wholly prevent infections, at least alleviates the trouble.

Peach-growers in New York are much plagued by a mildew yet suffer small loss from it, though the disease greatly injures peach-foliage in some regions. The delicate, white or grayish powder, giving the name "powdery mildew," consists of the spores and mycelium of a fungus (Sphærotheca pannosa (Wallroth) Léveillé) which attacks the leaves of several species of Prunus causing them to curl and crinkle and sometimes to drop. It occurs most often when there are sudden changes in temperature. When treatment is necessary, the self-boiled lime-sulphur mixture is used.

In common with all tree-fruits, the peach is attacked by crown-gall (Bacterium tumefaciens Smith and Townsend). In New York crown-gall seldom greatly injures old trees but nursery plants are sometimes girdled by the galls, seriously injuring them. Badly diseased young plants, therefore, should not be planted. The galls are tumor-like structures, usually at the juncture of top and root, which vary from the size of a pea to that of a large egg, forming at maturity rough, knotty, dark-colored masses. Neither preventive nor cure is known. Planting diseased trees is not a safe practice, nor should the peach be set in ground known to have recently had trees badly infected. The raspberry is a common carrier of crown-gall and should not be planted as an inter-crop in a peach-orchard.