4 BULLETIN 1118, U. S. DEPARTMENT OF AGEICULTUEE. 



of wMch are scabby lesions, others coalescing to form more flattened 

 scabs. In severe infections nmnerous lesions cause a serious dis- 

 tortion of the leaf (PL VIII, Fig. 1; PL IX, Fig. 2), which sometimes 

 drops as a result of the infection. Later, the lesions become warty 

 (PL VI, Fig. 4) and assume a pinkish and still later a dirty olivaceous 

 color, largely as a result of invasion by saprophytic fungi. 



Fruit. — The incipient stages of citrus scab on the fruit are essen- 

 tially the same as on the leaf, except that the outgrowths are solid. 

 The lesions soon become cream-colored or pale yellow-orange and 

 decidedly raised, resulting in more or less distortion of the fruit (PL 

 III, Fig. 1). In a few months these spots lose their cream color and 

 usually assume a dusty gray hue. On the grapefruit these protu- 

 berances when few in number eventually flatten out, and the fruit 

 regains its normal shape (Pis. X and XI). Lesions on the sour 

 orange and the lemon seldom flatten, but ultimately produce ugly, 

 corky, slightly raised warts (PL V, Fig. 2; PL VI, Fig. 2). The out- 

 growths on tangelos are higher and more pointed than on grapefruit 

 and do not^flatten as the fruit grows (PL XII, Fig. 1). 



Twigs. — Infection of twigs takes place for the most part on very 

 succulent growth, such as rapidly growing nursery stock and involves 

 only the most susceptible varieties (PL VIII, Fig.l; PL IX, Fig. 1), 

 The lesions appear as small cream-colored slightly raised warts, 

 later becoming somewhat pinkish and still later taking on a dusty 

 color, due to secondary invaders. 



Several types of injury may be confused with citrus scab. Prob- 

 ably the most frequent confusion is between the so-called thrips 

 injury and old flattened scab lesions. The scars produced by the 

 former are never raised and are much smoother than those caused 

 by scab ; they frequently have a characteristic silvery sheen, and the 

 position and pattern are usually distinctive. Another type of injiu-y 

 which causes confusion in the field, even to pathologists, is wind 

 injury to young leaves caused by blowing sand or rubbing efl^ects. 

 This condition is found only on trees exposed to sweeping winds in 

 such positions as are found near a wide expanse of open land or a 

 lake front. Frost injury at a distance may also be mistaken for 

 citrus scab. The minute features are quite distinct. 



Citrus canker has been confused with citrus scab because of its 

 warty and corky appearance. An individual citrus-canker lesion 

 grows to be much larger than one of citrus scab. It extends much 

 deeper into the spongy tissue of the fruit rind and entirely through 

 the leaves. The canker spots are surrounded by a yellowish oily 

 zone, which is very distinctive. Citrus canker readily attacks 

 succulent twigs of the common varieties of citrus. 



