140 



There it follows chiefly the black scale {Lecanium oUce) and the cottonj' 

 cushioa scale {leery a purchasi). In Louisiana it is very common on 

 the orange, following chiefly, as in Florida, the mealy wing and wax 

 scale. It is also qui e common in Spain, Italy, and many other orange 

 growing countries.( ^) 



Symptoms — Sooty mould may be readily recognised by the dense 

 sooty-black membrane which it forms over the fruit and upper surfaces 

 of the leaves. This membrane is made up of the densely interwoven, 

 branched mycelial filaments (threads) of the fungus, the individual 

 filaments of which can in some cases be distinguished with a hand lens. 

 When isolated the filaments are seen to vary in colour from olive green 

 to dark brown. They are at first loosely interwoven, but gradually 

 become very numerous «nd crowded. Finally they become cemented 

 together, forming a dense compact membrane. The fungus as nearly 

 as can be determined, is entirely superficial. Small projections occur 

 on the filaments, but no proof Jias been found that these penetrate the 

 tissue of the leaf. Apparently they are merely organs of attachment. 

 Large disks (hyphopodia) are also frequently developed, which evi- 

 dently serve as organs for attaching the mould to the leaf Reproduc- 

 tive bodies of several forms are developed in great abundance, and 

 these are easily carried from tree to tree or from grove to grove 

 through the agency of tlie wind, insects*, birds, or animals. 



This disease injures the plant by interrupting the process of assimi- 

 lation. This is brought about by the cutting off of light and by hin- 

 dering the passage of necessary gases in and out of the plant. The 

 accompanying insects further injure the plant by sucking the nutritious 

 juices from the cells of the leaves. The growth of the tree is usually 

 greatly retarded, and in serious cases is frequently entirely checked 

 until some relief is found. The blooming and fruiting are commonly 

 light, and in very bad cases are wholly suppressed. In slight droughts 

 the leaves wither quickly and curl up, resembling those on blighted 

 trees. The young fruit becomes covered with the sooty mould and is 

 retarded in its development, frequently never reaching completematurity. 

 It is usually smaller and less juicy than that normally developed, and 

 remains very insipid. It does not change to the normal bright 

 orange colour of mature fruit till very late, and if the membrane of 

 the sooty mould covering it is quite thick the rind remains somewhat 

 green, apparently for an indefinite period, rendering the fruit unsal- 

 able. The black coating formed by the sooty mould renders the fruit 

 unsightly and unsalable until it is thoroughly washed, which necessi- 

 tates a considerable expenditure of time and labour. Even when care- 

 iully washed, a process which injures the keeping quality of the fruit, 

 much of it being still small and green is unfit for market. 



Treatment. — Where sooty mould followed the attacks of the orange 

 mealy wing, spraying with resin wash or fumigation with hydrocyanic 

 acid gas was found to be very effective. When resin wash (^2) is used, 

 the best time for treatment is in winter, between December and the 

 first of March. During this period the mealy wing cannot fly away 



(1) In Jamaica, it is common on the Rose Apple, Eugenia Jambos, Linn. 



(2) The following is the formula for resin wash : Resin, 20 pounds ; caustic 

 soda (98 per cent), 4| pounds ; fish oil (crude), 3 pints ; water to make 15 gallons i 



