DISEASES OF CULTIVATED PLANTS 643 



Rust. In Europe the blister rust fungus (Cronartium ribi- 

 colum Peridermium strobi) has been long known as a serious draw- 

 back to the culture of the white pine. Curiously enough this rust 

 has until recently not been known in the United States. Not long 

 since warning was sent out by the Department of Agriculture that 

 this rust had appeared in America and should be sought for upon its 

 alternate hosts, the white pine (Aecidia) and the currant and goose- 

 berry. (Uredo- and Teleutospores.) Upon the pine the aecidial 

 stage develops numerous orange cluster cups infecting the stem to- 

 ward the base. This causes high mortality among the young pines. 

 Upon the currant and gooseberry the uredospores show yellow color 

 which darkens as the teleutospores form. These are to be sought in 

 August or early September, and by reason of the importance of this 

 rust merit early attention by students of these diseases. 



POPLAR. 



Anthracnose. Species of poplar or cottonwood are at times 

 attacked by anthracnose (Marsonia populi). It produces similar ef- 

 fects to those of anthracnose upon sycamore. 



Rust. The leaves of poplars are frequently attacked by the rust 

 (Melampsora populina) which disfigures the leaves by the spots 

 caused through its development. The thrifty growth of poplars 

 usually overcomes these foliage diseases under favorable conditions. 



SPRUCE. 



Leaf-Spot. Norway spruce in Ohio has suffered seriously in 

 1908-9 from attacks by a leaf-spot fungus (Phoma). This fungus 

 causes the discoloration of the leaves (needles) also their dropping. 

 The fruit bodies of the fungus occur upon the scales of the branches 

 as well as upon the leaves and are evidently capable of surviving 

 from year to year. This leaf-spot or leaf blight has been reported 

 from several counties upon hedge plantings, upon large shade trees 

 and upon sizes grown for Christmas trees. Drouth conditions in 1907 

 were a large factor in this matter causing the death of many spruce 

 trees in 1907 and 1908. It is believed that winter and early sum- 

 mer sprayings will have some effect in checking the leaf trouble. 

 This experience shows the need for mulches about Norway spruce, 

 especially in the southern portion of Ohio. Seedling diseases are 

 liable to prove troublesome thus checking efforts to grow seedlings 

 of spruce. (Ohio E. S. B. 214.) 



CHESTNUT BARK DISEASE. 



The disease is caused by the fungus Diaporthe parasitica. The 

 spores of this fungus, brought by some means from a previously dis- 

 eased tree, enter the bark through wounds; possibly also in other 

 ways. The leaves and green twigs are not directly affected. From 

 the point of infection the fungus grows in all directions through the 

 inner bark until the growth meets on the opposite side of the trunk 

 or limb, which in this way is girdled. The wood is but little affected. 

 Limbs with smooth bark attached by the fungus soon show dead, dis- 

 colored, sunken patches of bark covered more or less thickly with 

 the yellow, orange, or reddish-brown pustules of the fruiting fungus. 

 In damp weather or in damp situations the spores are extruded in the 



