98 



Fike-Blight. 



This disease is not of great importance in the apple orchard. 

 A large amount of twig blight, one form of the disease, often 

 occurs, but this seldom is extensive enough to reduce a crop 

 •materially or menace the trees attacked. When the disease 

 takes the form known as "collar-blight," it is likely to result 

 fatally, but seldom are many trees in an orchard affected. 

 The disease is much more destructive to the quince and pear, 

 and may spread from these hosts to the apple. 



Fire-blight is caused by a bacterium. Bacillus amylovorus. 

 It attacks blossoms, fruit, twigs and bark of limbs and trunk. 

 The disease first appears in the spring on full-blown blossoms. 

 These suddenly turn brown and wilt. In this stage the dis- 

 ease is commonly called "blossom-blight." From the blighted 

 blossoms the disease spreads downward to the spur on which 

 the leaves die. At the same time, the stage called "twig- 

 blight" may develop. On young twigs the leaves turn brown 

 from the tip downward. The dead leaves droop and cling 

 tenaciously to the dead twig, and have the appearance of 

 having been scorched. (Fig. 12.) Cankers often form on the 

 limbs, and these are usually traceable to blighted twigs which 

 may frequently be found rising from the cankered area. (Fig. 

 13.) Such cankers may spread until a limb is girdled, but 

 more often their development is checked by dry, warm weather 

 conditions. 



The most serious form of fire-blight on the apple is the so- 

 called "collar-blight" or "crown-rot." This occurs as a dead 

 area or canker in the bark near the base of the trunk. (Fig. 

 14.) Infection in such cases is usually through water sprouts. 

 These cankers have a sunken, smooth surface and may increase 

 in size until midsummer. They are likely to continue develop- 

 ment the following year, and, unless permanently checked, 

 usually completely girdle the trunk, causing death of the tree. 

 Usually, the first sign of collar- blight is a yellowing and reduc- 

 tion in size of the leaves on one or more large branches. 



Successful control measures have not been worked out. In 

 a young orchard or in the nursery, it is easy to cut out and 

 burn all blighted twigs as they appear, but in older orchards 



