02 



JOURNAL OF AGRICULTURE OF P. R. 



T®r-«t?y^ 



trees. Of late years, however, the disease has been distinctly on the 

 wane, possibly due to natural influences, but attributed in large 

 part to improved cultivation, use of resistent stocks, and increased 

 knowledge on the part of the growers. 



Foot-rot, or mal-di-gomraa as it is known to many, is readily 

 recognized. In the majority of cases the first symptom noted will 



be tbe exudation of gum Mt one or 

 more points at the crown or base of 

 the tree. On examination the l)ark at 

 these points and for varying distances 

 around will be found dead and gum 

 infiltrated, resulting in a deep brown 

 color. The wood beneath infected bark 

 also dies. The disease is accompanied 

 by a very characteristic odor, so dis- 

 tinct at times as to be readily noted 

 some distance from the infected tree. 

 The diseased areas are generally irreg- 

 ular in shape, extending ultimately, if 

 not checked, a distance of one or two 

 feet up the trunk, and a similar dis- 

 tance out along the main roots. 



The disease progresses with great 

 rapidity at certain seasons, commonly 

 during the spring months, and remains more oi- less dormant at 

 others. During this latter period the tree makes an attempt by the 

 formation of callus to throw off the disease, but is seldom successful, 

 unless aided by the grower. These alternate periods of growth and 

 ((uiescence result in rough scaly cankers at the crown. A tree will 

 survive one or several seasons following attack, all depending upon 

 the I'apidity with wliicli the disease girdles the trunk. The 

 presence of t'oot-rot is evidenced in the top by a yellowing of the 

 leaves, a general unthriftiness, dying back of terminal twigs, and 

 very often by an exceedingly heavy bloom, which sets very little 

 fruit. Such fruit as is present is dropped in the final stage of the 

 disease, together with the leaves. As would be expected where gird- 

 ling is involved, the death of an affected tree occurs very suddenly. 



Cause. 



Fig. 2. — Foot rot. Base of grape- 

 fruit tree, showing cankers 

 and wood rot of an advanced 

 case. 



The exact cause of mal-di-goma has been in some doubt, several 

 theories having been advanced by the numerous workers who have 



