Sep. 2, 1920.] Agricultural Gazette of N,S.W. 669 



Root Rot of Fruit Trees due to 



Ar mill aria mellea. 



W. A. BIRMINGHAM, Biologist's Assistant. 



One cause of root rot in many fruit trees is the "honey fungus " — Armillana 

 mellea. It is a disease existing without any marked symptoms as far as the 

 top of the tree is concerned, at least until the fungus has obtained such a 

 strong hold on the butt and root-system ^as to be almost beyond treatment. 



This fungus belongs to the botanical family Agaricacefe, of which the 

 mushroom is a common type. There is probably no fungus more destructive 

 than Armillaria mellea. It is found in abundance in Europe and America, 

 and appears to be wide-spread in certain parts of New South Wales. 



The Appearance of Diseased Trees. 



In citrus trees the grower's attention is at first drawn to the sickly yellow 

 appearance of the foliage and the dying out of certain branches. When in 

 an advanced stage the trees usually set very heavy crops. If the soil be 

 removed from around the butt and the main roots exposed, trees attacked by 

 the fungus will show a rotten condition of the bark at and below the ground 

 line. The bark can readily be peeled away, exposing the ^ white fungus 

 lying between the bark and wood. Affected roots will show slightly wavy 

 strands, dark brown to black in colour, running along the surface (Fig. 1). 

 These bootlace-like strands, or rhizomorphs, do not become free from the bark 

 as they do in the case of pome and stone fruit trees. They may travel along 

 the roots to the extremities and th»ire reach and attach themselves to the 

 roots of adjacent trees which come in contact with them. 



Toadstools may arise at the base of the tree in autumn (Fig. 2), which in 

 form resemble the common mushroom; they are the spore-bearing organs of 

 the fungus. These spoi^e bodies are usually produced in clusters. The cap 

 of the toadstool is from 2 to 6 inches broad, and is borne upon a central stalk 

 4 to 6 inches long. The stem is yellowish in colour above, but usually brown 

 •below, with a more or less persistent collar or annulus. The cap varies 

 from convex to slightly conical. It is yellow to orange-brown in colour, hence 

 the name honey fungus, the centre of the cap when younger being often 

 covered with small brown or sooty scales. On the underside of the cap are 

 white or slightly discoloured gills, distinct from one another and slightly 

 running down the stem. 



The growth and effect of the fungus on pome and stone fruit trees is 

 similar to that in citrus trees, with the exception that in the case of the two 

 former, the bootlace or rhizomorph stage is isolated from the bark, and 

 is found running over the surface of the roots (Fig. .3). 



