DISEASES OF CULTIVATED PLANTS 455 



too quickly removed. The canker spots frequently occur near the 

 trunk so that the life of the tree is endangered by them. Infections 

 through wounds caused by pruning can be to a great extent prevented 

 by careful attention to the details of the operation. The indiscrimin- 

 ate and careless cutting of branches frequently practiced in this state 

 is detrimental to the health of the tree aside from the opportunities 

 it offers for parasites of all kinds to enter. Long stubs should never 

 be left on the tree. Limbs should be cut close to the parent branch 

 without making the wound unnecessarily large. Wounds caused by 

 proper pruning heal without difficulty. They should be kept painted 

 or covered with Bordeaux mixture. Injuries caused by climbing 

 about in the trees can be prevented entirely by picking from ladders. 

 There is rarely any necessity for climbing the tree to pick the fruit. 

 (111. E. S. B. 70.) 



New York Apple Tree Canker. Any part of the tree above 

 ground, with the possible exception of the leaves, may be attacked by 

 the canker fungus which has been proven to be Sphseropsis malorum 

 Pk. When the larger limbs, or in rarer instances, the trunks, are at- 

 tacked, the injuries are known as cankers. Such injuries are often 

 quite conspicuous since the bark becomes thick and rough, and sa- 

 prophytic fungi soon gain a foothold causing the parts to turn black. 

 The injuries are often several feet in length; and because of these 

 striking characters, cankered limbs may be recognized at a consid- 

 erable distance. 



The fungus may live in the outer bark but here it does little harm 

 and true cankers are formed only when it gains entrance to the cam- 

 bium layer. Under favorable conditions the fungus spreads until a 

 considerable area of bark is destroyed. The limb may be girdled by 

 the fungus but borers and saprophytic fungi often complete the work 

 of destruction. An affected branch may live for a number of years 

 and bear fruit but if the wound is large the normal activity of the 

 branch is seriously interrupted. The swelling of the bark is probably 

 caused by an excess of food being deposited, as a result of the partial 

 girdling of the limb. 



When the twigs are attacked a portion of the new growth may 

 be killed in much the same manner as when attacked by pear blight. 

 Much damage may result from such attacks and the fungus may occur 

 in orchards where there is no evidence of cankers on the larger limbs. 

 The longitudinal areas of reddish bark often seen on the south and 

 southwest sides of trunk or limb are an indication of sun-scald. The 

 tissues of this discolored bark have been killed by sun and frost. At 

 the approach of warm weather, fermentation may set in and a sour 

 odor be given off from the affected parts. (N. Y. [Geneva] S. B. 

 185.) 



Leaf-Spot Diseases. There are several species of fungi that at- 

 tack apple leaves, producing brown, circular spots that range from 

 mere specks to spots one-fourth of an inch in diameter and in some 

 cases much larger. The disease may begin to appear in the spring 

 soon after the young leaves unfold, but the spots arc usually more 

 prominent between midsummer and the end of the season. This 



