126 THE PLUMS OF NEW YORK. 



One of the commonest and most striking of the diseases of the plum is 

 black -knot' {Plowrightia morbosa (Schw.) Saccardo) characterized by wart- 

 like excrescences on shoots and branches. In early summer these knots are 

 dark green, soft and velvety, but as the fungus ripens in the fall the color 

 changes to a carbon-like black and the knots become hard and brittle. 

 The disease is usually confined to one side of the twig or branch so that 

 death of the affected part does not ensue at once. Black-knot is an 

 American malady, at one time confined to the eastern part of the continent 

 where in some localities its ravages forced the abandonment of plum- 

 growing. The fimgus is now endemic to wild or cultivated plants in prac- 

 tically all the plum-growing regions of the continent, but it is still epidemic 

 only in the East, the South and West being practically free from the dis- 

 ease. Unless especially virulent black -knot is controlled by cutting out 

 the diseased wood. Usually eradication is not possible without several 

 prunings during a season. 



Much has been made of the supposed immunity of some varieties 

 of plums to black -knot. In the vicinity of this Station, where the disease 

 is always present and often rampant, the differences in immunity are not 

 very marked in varieties of the same species. The Trifloras are less at- 



facing, pressing and labeling are important details. A well cured prune is soft and spongy, the 

 pit is loose but does not rattle, the skin is bright, the product is free from drippings or exudation, 

 the flesh is meaty, elastic, and of a bright, lively color. 



The custom has been to bleach light colored prunes with sulphur fumes. This process injures 

 the quality and possibly makes the product somewhat poisonous. Sulphuring is now regulated 

 by the Federal Pure Food Law. 



If poorly managed or if the plums are not of the best, several difficulties are encoimtered in 

 curing prunes. Thus, a syrupy liquid sometimes oozes from the prunes, besmearing and making 

 unattractive the final product. Again, the finished prunes may be covered with globules of sugar, 

 rendering them sticky and destroying the lustre. Fruit grown on poor soils, on unhealthy trees 

 or picked green may cure into small prunes of an abnormal shape called " Frogs " or they may 

 ferment and swell up in large soft prunes called " Bloaters." 



The plum chiefly used in California in making prunes is the Agen, usually called Petite, a prune 

 curing into a bright amber-colored product. This plum is easily cured, and the prune from it needs 

 little sugar in cooking. In the states north of California the Italian Prune is the favorite, produc- 

 ing a dark red, almost black product, more tart but on the whole rather better flavored than the 

 prune from the preceding variety. Other varieties more or less used are Golden Drop, the pro- 

 duct from which is known as the Silver Prune; Reine Claude, which makes a fancy product often 

 used as a confection; Yellow Egg, which sells as the Silver Prune when evaporated; the German 

 Prune, making a productmuch like the Italian Prune; "Hungarian Prune," froma very large plum 

 and making a fancy product but very difficult to cure; the Tragedy Prune, an early plum of the 

 Italian type; Golden Prune, much like the Silver and possibly better; and the Champion, Willam- 

 ette, Pacific, Tennant, Steptoe and Dosch, all of the Italian type. 



' Farlow, W. G. The Black Knot, Bulletin Bussey Institution 440-453. 1876. Halsted, B. D. 

 Destroy the Black Ivnot, etc. A^. /. Sta. Bid. 78:1-14. 1891. 



