62 MANUAL OF TROPICAL AND SUBTROPICAL FRUITS 



masses on the surface of affected fruits. The markings are hard, 

 compact, and the surface is cracked or broken. The injury may 

 cover only a part or the whole surface of the fruit. It makes an un- 

 sightly fruit, but apparently does not affect the quality. The disease 

 is apparently caused by a fungus, perhaps a Gloeosporium or a closely 

 related species. 



" Another fungus, a species of Colletotrichum, is often observed in 

 diseased spots on leaves and fruits. This fungus is closely related to 

 Gloeosporium and the injuries with which it is associated resemble those 

 caused by the latter fungus. It is probably the cause of some of the 

 injuries that are classed as anthracnose. 



" In the control of these leaf and fruit spots, Bordeaux mixture 

 has given satisfactory results where applied in time. As soon as the 

 injuries begin to appear, spraying should be made and continued until 

 the disease is checked. Two or three applications may be necessary, 

 made at intervals of two or three weeks. If the fruit is near maturity, 

 it is advisable to substitute ammoniacal solution of copper carbonate 

 for the Bordeaux mixture, to prevent any disagreeable stain that may 

 result from the use of the latter. Aside from spraying, all dead wood 

 should be kept out of the trees, as this is likely to harbor these fungi 

 from one season to the next. 



"Avocado scab is of more than ordinary interest, owing to its close 

 connection with citrus scab, and the fact that it has come into existence 

 within the past three or four years. It is in all respects a new disease 

 that has had its beginning in Florida. 



" Scab is chiefly a disease of the tender growth, and at present 

 it is found more abundantly in the nurseries, where it is particularly 

 severe on seedling plants. It also attacks budded varieties in the 

 nursery. The disease has been found on young and old bearing trees 

 in the groves, affecting the leaves, and in a few cases the injury was 

 observed on fruits. At present it is more common in the nurseries, 

 but it may soon prove a serious pest in the groves. 



" Scab forms definite spots or patches on the young, tender leaves 

 and shoots, and severe attacks may cause the foliage to curl or become 

 distorted. The more mature leaf tissue is not affected, but old leaves 

 will be found bearing spots that were formed when the tissue was 

 young. The spots are usually small, raised, circular to irregular, 

 purplish brown to dark in color, and may vary from a sixteenth to an 

 eighth of an inch in diameter. They may appear scattered over the 

 surface, or several may grow together, forming irregular patches. 

 The spots penetrate the leaf tissue, and they are visible on both sides. 

 They are usually more prominent on the upper surface of the leaf, in 

 which case the under surface of the spot will be slightly bulged and 

 marked by a discolored area. The centers of the spots are composed of 

 dead cells, more or less spongy in character and brownish in color. 



