386 



STATE BOARD OF AGRICULTURE. 



solution should be used as soon as the berries are about half grown to avoid 

 staining them. 



LEAF-SPOT DISEASE. (See on Currant.) 



DISEASES OF THE RASPBERRY AND BLACKBERRY. 



ORANGE BUST OF BASPBERRY AND BLACKBEBRY. 



(Caeoma luminatum Lk.) 



Fig. 36. — a, A small leaf of raspberry, showinsr blisters produced by the orange rust fungus; 

 b, spores from a blister; c, sectional view of pith cells from disea.sed cane, showing a strand of 

 mycelium m, passing between the cells and giving rise to sucker-like branches (haustoria), 

 h, h, h, which enter the cells and absorb their nourishment. Magnified. (Original.) 



The disease of the blackcap raspberries and of the blackberry, known as orange 

 rust, is probably the most serious of the fungus diseases of these plants. The 

 fungus possesses a perennial mycelium which lives in the pith of affected canes 

 and even extends into the underground portions of the host plant. In the spring 

 the leaves borne on such canes appear to be covered with small blisters of an 

 orange yellow color which often unite in irregular zigzag lines. These blisters 

 occur on the lower surface of the leaf and soon after their appearance the 

 epidermis of the leaf ruptures along the center of the swellings thus allowing 

 orange colored powdery spores to escape. These spores are capable of germi- 

 nating as soon as shed and if they fall into a drop of moisture in contact with 

 a healthy leaf of the host plant may produce an infection. After gaining an 

 entrance into the leaf the mycelium finds its way through the leaf stalk into the 

 pith of the cane where it lives until the next season to again grow out into new 

 foliage. This mycelium does not enter the cells of the host plant but passes 

 among them through the intercellular spaces sending peculiar knotted branches 

 (haustoria) into the cells. 



By some botanists the orange rust is considered to be the Aecidial stage of 

 Pnccina Peckiajia Howe, which corresponds to the winter spore stage of the rust. 

 The latter fungus also occurs later on the leaves of the raspberry, especially those 

 which bore the orange rust earlier in the season. 



The effects of this parasite are shown in the reduced vigor and size of diseased 

 plants, the new growth being sickly and slender while the entire plant eventually 

 dies. The perennial nature of the fungus enables it to appear year after year 



