APPLE DISEASES 



449 



sometimes the trunk. In some cases it 

 seems to cause merely a greater rougli- 

 ening of the bark, but where a broken 

 twig or other Injury furnishes an en- 

 trance to the actively growing tissue of 

 the host the effects are often much more 

 pronounced. In serious cases the bark 

 may be killed over considerable area 

 and become conspicuously cracked and 

 roughened (Fig. 1). It is set off from 

 the living bark by a very definite bound- 

 ary. Limbs are often so nearly girdled 

 that the parts beyond die. Pycnida 

 similar to those on the fruit are found 

 on the canker. 



Like the other diseases attributed to 

 Sphaeropsis Malorum, the leaf spot is of 

 general occurrence. The disease makes 

 its appearance on the leaves shortly 

 after they unfold from the bud. Infec- 

 tion continues throughout the spring, 

 but notes taken the past two years In- 

 dicate that it Is uncommon after the 

 middle of June. At first the spots are 

 small, purple areas, but as growth pro- 

 gresses they become yellowish-brown In 

 color and attain a diameter of from one- 

 eighth to one-half inch (Fig. 1). They 

 are quite uniformly circular in outline. 

 The margins are somewhat elevated, giv- 

 ing to the spot a sunken appearance. As 

 the spots become older a secondary 

 growth may spread from the central 

 affected area, producing a somewhat ir- 

 regular blotch in which the outline of 

 the original spot can always be recog- 

 nized. (See Fig. 1.) It often happens 

 that several of these areas become con- 

 fluent, and thus the greater part of the 

 leaf may become affected. Spotted leaves 

 fall from the trees early in the fall and 

 their working efficiency is always greatly 

 reduced by the middle of the summer. 

 Trees thus robbed of their foliage from 

 year to year must eventually become 

 greatly impaired in their vigor. 



The cause of the leaf spot has occa- 

 sioned no little difficulty. A number of 

 fungi have been found to be present in 

 the spots, but inoculation experiments 

 have indicated that Sphaeropsis Malorum 

 is probably the only one that is of Im- 



portance in the production of the dis- 

 ease. 



Treatment 



The fact that one fungus is responsible 

 for three different forms of disease 

 makes its destruction a matter of special 

 importance and rather unusual difficulty. 

 Spraying has been quite effective in con- 

 trolling the leaf spot. In the summer 

 of 1908 the per cent of leaves spotted 

 in the orchards referred to under apple 

 scab was reduced from 97 to 26 by the 

 use of Bordeaux and to 21 by the use 

 of lime-sulphur solution. Five sprayings 

 were made, but it is probable that only 

 the first three were effective for leaf 

 spot. Sprayings made at various times 

 in the summer have had little or no 

 effect upon the number of spots of rot 

 on the fruit at picking time. The de- 

 struction of the affected fruit seems to 

 be the most efficient treatment for this 

 form of disease. All cankered limbs 

 should be cut out and burned. Large 

 wounds should be protected by a cover- 

 ing of paint. Thorough spraying is of 

 value in protecting the limbs. Heavy 

 applications made when the trees are in 

 a dormant condition are probably espe- 

 cially efficacious. 



Charles Brooks, 



Durham, N. H. 



Blackspot Canker or Apple Tree 

 Anthracnose 



yeofabraea Malicorticis (Cordley) 

 Jackson 

 Bt W. H. Lawkence 

 Plant Pathologist and Horticulturist for 

 Hood River Apple Growers, Hood 

 River, Oregon 

 More than a decade has passed since 

 Blackspot Canker or Anthracnose made 

 its appearance in apple orchards through- 

 out the Pacific Northwest and became so 

 destructive that Information concerning 

 its control was sought. Although the 

 cause and control of the disease has been 

 determined and fully demonstrated the 

 disease has been allowed to continue year 

 after year in some of the orchards of 

 each of the apple-growing sections. Con- 

 tinuous and scattering observations as 



