MAINE APPLE DISEASES. 37I 



are carelessly placed in position ; in some cases hail-stones split 

 the bark of small branches. Care should be taken to avoid any 

 injury which is within the control of the orchardist. Wounds 

 are sometimes kept from healing over by the woolly aphis which 

 forms little cottony patches in wounds and by delaying the heal- 

 ing over process makes a favorable place for the entrance of a 

 parasitic fungus. 



Maine has only a few of the fungi which have been reported 

 as causing canker in other parts of the country. Each section 

 of the country seems to have one fungus which is responsible for 

 a large part of the canker in that region. In this State, the fun- 

 gus which causes the greatest damage is the black rot fungus, 

 Spacropsis malorum Pk. ; the bitter rot fungus occurs only very 

 rarely in this region ; Myxosporium corticolnni Edgerton, is very 

 common and apparently does some damage although it does not 

 seem to be a very active parasite; Coryneiini foliicohim Fckl,, 

 and PJioma niali Schulz & Sacc, have been described in Bulle- 

 tin 170 of this Station as causes of disease in this State; Cyto- 

 spora sp. may cause some damage but it is not extensive. The 

 European apple canker caused by Ncctria ditissima Tul. and the 

 blister canker, Nuinmnlanadiscrcia Tul., may be present in the 

 State but they have not been observed. 



Closely associated with canker caused by fungi is the killing 

 back of small branches and twigs caused by the same organisms. 

 In searching orchards in the State for cankers we have found this 

 dying back of the branches and water-sprouts much the more 

 common of the two. The fruiting bodies of the same fungi 

 have been found on both, and cankers on larger limbs have been 

 found repeatedly which apparently started from the disease fol- 

 lowing back on a smaller branch or twig. Inoculations with 

 canker producing fungi early in the spring show that they are 

 capable of killing the young twigs very rapidly and run back 

 a considerable distance in a single season. A twig blight may 

 be caused by the pear blight bacillus, but pear blight is rather 

 uncommon in Maine. Moreover the entire absence of the char- 

 acteristic "fire blight" has been noted repeatedly on pear trees 

 growing within and alongside of apple orchards affected with 

 the fungous twig blight. 



In many ways the dying back of small branches is like the 

 development of canker. The fungus may spread back only a 



