394 Diseases of Economic Plants 



The twigs and even entire trees are stunted and yellowed. 

 Cankers may almost or quite girdle the stem, the diseased 

 area becoming dark. Prune as for blight of pear. 



OAK 



Leaf-curl ^^^ (Taphrina coerulescens (D. & M.) Tul.). — 

 Though close kin to peach curl, only a small proportion of 

 each leaf, spots 1-2 cm. in diameter, is involved. Defoliation 

 may result in extreme cases, and continued disease each 

 year may cause death. Affected leaves should be burned 

 and if the tree value warrants it sprayed as for peach curl. 

 Powdery-mildews (Microsphcera) . — These appear late and 

 do little harm except upon nursery stock. Flowers of sul- 

 fur or Bordeaux mixture are useful. Twig-blight {Diplodia 

 longispora C. & E.) does some injury. Blight. See sycamore. 



OSAGE ORANGE 



Rust (Physopella fid (Cast.) Arth.). — The sori which 

 are scattered thickly over large areas of the lower side of 

 the leaf are small, 0.1-0.3 mm. in diameter and are pale 

 cinnamon-brown. This rust is known from South Carolina 

 to Texas. 



PECAN 415- 416 



Scab {Fusicladium effusum Wint.). — In the Southern 

 States, particularly Florida, Louisiana, Georgia, Oklahoma, 

 and Texas, twigs, leaves, and nuts are affected with a dark 

 green, smoky, superficial growth. Upon leaves and petioles 

 dead spots, distortion, and defoliation are caused. The new 

 growth of twig is often killed, but the greatest injury is to the 

 nuts which drop before maturity. 



Spraying with lime-sulfur or Bordeaux mixture, or dusting 

 with sulfur has proved effective. 



Powdery-mildew {Microsphcera alni (Wallr.) Salm.). — 

 During certain years in the South the pecan crop has been 



