PLUM DISEASES 



381 



Before wilting, diseased trees may be located by the scorched 

 appearance of their leaves. This is particularly noticeable in 

 dry weather in late summer. The edges of the leaves become 

 dry. This, however, is not a specific sign of the wilt disease 

 inasmuch as this appearance may be induced by any factor which 

 cuts off the water-supply. Trees growing in a dry, hard soil as 

 well as those with diseased 

 roots are very liable to ex- 

 hibit symptoms similar to 

 those of the early stages of 

 wilt. 



From those wilted trees 

 which die in the early sum- 

 mer, gum is exuded. Later 

 beetles bore holes in the 

 bark through which gum 

 flows freely. Death of the 

 tree follows in the fall and 

 winter, and no leaves are 

 put out the next spring. 

 Old trees are said to suffer 

 more than young ones. 



Cause. 



Recent investigations 

 have shown conclusively 

 that plum-wilt is due to 



the fungus \ Lasiodiplodia Triflorce. The pathogene gains 

 entrance into the tree by means of wounds. Observations 

 show that at least 33 per cent of the infections occur through 

 borer wounds. Borers prefer Japanese varieties, probably be- 

 cause they are budded on peach stock in which the borers make 

 their attack. Wounds made by the black-spot pathogene, 

 Bacterium Pruni, are also very common points of entrance for 

 the plum-wilt fungus. In this connection it is to be noted that 



FIG. 111. Plum- wilt. 



