MAINE AGRICULTURAL EXPERIMENT STATION. 1910. 413 



branches are allowed to remain on the trees, or old neglected 

 trees in the neighborhood produce abundant crops of fungus 

 spores from year to year. Some of the ways in which wounds 

 are made are : Barking of trunk and branches by machinery 

 in cultivating and caring for the orchard ; injuries by ladders 

 and by men in picking fruit; branches are sometimes injured by 

 props used to support a heavy load of fruit especially when they 

 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, 

 Sphaefiopsis malorum Pk. ; the bitter rot fungus occurs only 

 very rarely in this region ; Myxosporium corticolum Edgerton, is 

 very common and apparently does some damage although it does 

 not seem to be a very active parasite ; Coryneum foliicolum 

 Fckl., and Phoma mali Schulz & Sacc, have been described in 

 Bulletin 170 of this Station as causes of disease in this State; 

 Cytospora sp. may cause some damage but it is not extensive. 

 The European apple canker caused by Nectria ditissima Tul. 

 and the blister canker, Niimmiilaria discreta Tul., may be pres- 

 ent 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 following back on a smaller branch or twig. Inocula- 

 tions 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 



