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 Fic. 111. — Plum-wilt. 
that plum-wilt is due to 
the fungus : Lasiodiplodia Triflore. 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 
