474 DISEASES OF CULTIVATED PLANTS 



Collar pruning, along with removal of surface soil and 

 fresh soil added, with a layer of quicklime on the surface, 

 checked the disease. 



Massee, Kew Bulletin, 1899, p. i. 



Lemon and orange scab (Cladosporium citri, Mass.) proves 

 very injurious to orange and lemon trees in Florida and 

 Louisiana. The disease is indicated by the presence of 

 numerous small warts on the leaves and fruit. When the 

 fruit is attacked quite young the warts are often numerous, 

 and measure up to \ in. high and across, although often 

 smaller. The warts become covered with a delicate mould, 

 grey at first, then dusky, finally black. Trees growing in low, 

 moist situations are most subject to scab, in fact the develop- 

 ment and spread of the fungus requires the almost constant 

 presence of moisture in the air. The sour orange (Citrus 

 bigardia) is especially susceptible to the disease. 



Sporophores tufted, erect, branched, septate, brown, 30-75 

 X 2-4 p ; conidia fusiform, dusky, usually continuous, occa- 

 sionally 1-3 septate, 8-9X2-5-4 p. 



Spraying with ammoniacal solution of copper carbonate is 

 effectual, and should begin when the fruit is just set, and 

 continued at intervals. Bordeaux mixture injures the leaves 

 and fruit. Sour orange-trees should be cut down. 



Lamson-Scribner, Bull Torrey Bot. Club, 13, p. 181. 

 Massee, Text Book of Plant Diseases, p. 310. 

 Swingle and Webber, U.S. Dept. Agri., Bull. No. 8. 



Plum scab (Cladosporium carpophilum, Thiim.) causes a 

 disease of plums, cherries, and almonds, known as ' scab ' in 

 the United States. On half-grown fruit the fungus forms 

 greyish or olive-brown spots, which extend radially ; when 

 numerous the fruit shrivels and often cracks. 



Spots orbicular, often confluent, blackish-green, forming 

 circles ; conidia ovate, ends obtuse, continuous or rarely 

 i-septate, 10-12X4-6 p. 



Bordeaux mixture has been suggested ; it should contain a 

 little treacle or soap. Spraying should cease when the fruit 

 begins to ripen. 



Pammel, Journ. Agric. Coll. Expt. Sta., Bull. No. 23. 

 Pea leaf blotch. Lasnier points out that seedling peas are 



