mee UNGUS OF ECONOMIC “IMPORTANCE 
ON THE AVOCADO 
(Persea Americana). 
By EK. M. Dorper. 
CoMPARATIVELY little is known about the fungous diseases to which the Avocado is subject. 
In Florida it is said to suffer from certain leaf and fruit spot diseases caused by a 
Colletotrichum sp., and the young growth is attacked by a scab fungus said to be identical 
with Cladosporium citri, but none of these fungi is recorded as attacking the twigs and larger 
limbs. 
During 1921 it was reported from Louis Trichardt that certain Avocado trees were in 
a very bad state, and that spraying with bordeaux mixture had proved quite ineffectual. 
The twigs which were sent for examination were covered with minute pustules, the fruiting 
bodies of an ascomycete, and as none of the diseased wood had been excised previous to 
spraying it was not surprising that the inroads of the fungus had not been checked. Asa 
consequence the trees had become so badly cankered that it was impossible to remove all 
the diseased bark without seriously affecting the vitality of the trees, and at this stage 
it was impossible to arrest the progress of the malady. 
SYMPTOMS. 
The effect of the fungus on the twigs and limbs of the Avocado is very similar to that 
produced by Physalospora cydoniae on the limbs and twigs of apple trees. 
In the earlier stages of infection the bark becomes sunken and discoloured; the 
diseased area increases in size, and gradually girdle the twig or branch, so causing the 
death of the terminal portion. Branches, 2-3 inches in diameter, are killed in this way. 
and extensive cankers are produced on the larger limbs and the trunk. The bark of the 
cankered areas is dark-coloured and sunken, the boundary between the healthy and diseased 
tissue being marked by a raised, reddish-brown line. As the bark is destroyed it dries 
out and cracks horizontally, eventually falling away from the wood, which has become dead 
and discoloured. Numerous fruiting pustules of the pathogen may be observed scattered 
over the diseased areas of the bark. 
The fruits on the diseased trees are affected, showing a corky growth at the lower 
end, which may possibly be due to the same fungus (but this fact has not been established, 
as it was not possible to obtain trees in bearing for inoculation purposes). The affected 
area 1s irregular in form and varies in size. On fruits examined it was roughly 10 x 5 cm. 
and 4x 5 cm. The surface is very much roughened, verona. brown (Ridgway) in colour, 
and deeply cracked, after the fashion of tortoise-shell. 
This affection of the fruit is apparently identical with one which occurs in Florida 
and is mentioned in a paper by H. E. Stevens, published in the ‘ Proceedings of the 
Florida State Horticultural Society ` for 1918. His description is as follows: ‘ Another 
common type of injury frequently noted on the fruits is referred to as anthracnose by 
some of the growers. This type of injury is very similar to melanose of citrus fruits in 
general appearance. It is superficial, and appears in the form of dark reddish-brown, caked 
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 unsightly fruit, but apparently does not affect the quality. The disease is 
apparently caused by a fungus, perhaps a Gloeosporium or a closely related species.” 
