THE PLUMS OF NEW YORK. 1 29 



eases of the foliage are prevented to some degree by the proper use of 

 bordeaux mixture, which, on the Triflora plums at least, must be used with 

 great care to avoid injury. Cultivation has a salutary effect as it destroys 

 the diseased leaves which harbor the fungi. 



Another disease of plum foHage, occurring rarely on the fruit, is the 

 plum -leaf rust ' {Puccinia pruni-spinosae Persoon) which produces so 

 considerable a number of spore cases on the underside of the leaves as 

 to give the foliage a brownish cast and to cause defoliation in severe infec- 

 tions. The fimgus is most apparent in the fall and most troublesome in 

 warm, moist climates. Bordeaux is used as a preventive. 



Stewart and Rolfs have shown that trunks and branches of plums 

 affected by sunscald in New York are almost invariably infested by a 

 fvingus ' {Valsa leucostoma Persoon) which in the Old World is known 

 as the " die back " of the peach. The disease manifests itself on plums 

 chiefly by affected areas much depressed at the boimdary between the 

 living and the dead bark, these areas usually, not always, having connec- 

 tion with sunscald injiu-ies on the trunk. The disease is accompanied by 

 more or less gumming. 



In common with nearly all rosaceous plants, in nearly all countries, 

 the plum is sometimes seriously injured by the powdery mildew ' (Podo- 

 sphaera oxyacanthae DeBary). The affected leaves have a grayish appear- 

 ance caused by the parts of the fungus which project beyond the leaf 

 tissue ; when badly diseased the leaves are more or less arched and curled. 

 Mildew is seldom prevalent enough on plimis to require treatment. 



The crown gall,* (Bacterium tmnefaciens Smith and Townsend) 

 is a parasite on all of the fruits of the order Rosaceae and is especially 

 common on nursery stock, attacking plums in many soils but rarely, how- 

 ever, to the great injury of the plant. These galls are perennial structures 

 of very varying duration. They are to be foimd on the loots, usually 

 at the collar of the plant, and vary from the size of a pea to that of a man's 

 fist, forming at maturity, rough, knotty, dark -colored masses. Means of 



' Scribner, F. L. Leaf Rust of the Cherry, etc. U. S. Dept. Agr. Rpt. 353-355, PI. 3. 1887. 

 Hedrick, U. P. Prune Rust Oreg. Sta. Bui. 45:67. 1897. 



'Stewart, F. C. .V. Y. Sta. Bui. 191:323-324. 1900. Rolfs, F. M. Die Back of Peach Trees 

 Science 26:87. 1907. 



' Duggar, B. M. FungoJiS Diseases of Plants 226. 1909. 



* Smith, E. F. and Townsend, C. O. A Plant Tumor of Bacterial Origin Science 25:671-673. 

 1907. Tourney, J. W. Cause and Nature of Crown Gall Ariz. Sta. Bui. 33:1-64, figs. 1-3 1. 

 1900. Hedgcock, G.C. Crown Gall.etc. U.S. Dept. Agr. Bur. PI. hid. Bui. 90:15-17, Pis. 3-5. 1906. 



