520 Journal of Agriculture, Vicioria. [ro Aug.. 1911. 



Insect Pests and Fungus Diseases. 



Citrus trees are particularly subject to scale insects; red scale, brown 

 or olive scale, white .scale, wax scale, mussel scale, and cottony cu.shion 

 scale being the most prevalent. The attacks of scale insects weaken the 

 trees very considerably, particularly attacks of the red scale. The brown 

 Lecanium scale is not so serious a trouble ; while the cottony cushion .scale 

 is kept in check by attacks of ladybird larvse and beetles. 



Various sprays have been recommended for scale troubles, such as lime, 

 sulphur, and salt, resin Avash, crude petroleum emulsion, and red oil 

 emulsion. Spraying with the best spray mixtures is only a partial remedy, 

 and has to be constantly repeated. 



Spraying citrus trees for scale is now obsolete in many parts both of 

 America and Australia. There is only one effective way of scale eradica- 

 tion, and that is by fumigation with some noxious gas, which will suffocate 

 the insect, but which will not injure the tree. 



February is the best month for fumigating evergreen trees, notably 

 trees of the citrus species, that are infested with any variety of scale. The 

 trees should be closely enveloped in a fairly air-impervious sheet or tent, 

 and hydrocyanic gas should l)e generated inside. The fumes of this gas 

 are extremely dangerous, and the process should be carried out with great 

 care. A safe charge for an average tree, that is, a tree about 12 feet high 

 and about 10 feet in diameter, would be 4 ounces of cyanide of potassium, 

 4 fluid ounces of sulphuric acid, and 12 ounces of water. An earthenware, 

 wooden, or enamel vessel should be used, and the acid should be measured 

 into this first ; then pour the water on to the acid, and when all is readv. 

 the vessel being inside the tent, the cyanide should be dropped quickly 

 into the liquid, and the tent closed down. Approximately, three-quarters 

 of an hour is all the time necessary to fumigate the tree. 



Funaigation is a dangerous operation in strong sunshine ; the result of 

 fumigating at such a time would be that the tree would probably be killed. 

 Many growers, for safety sake, prefer to fumigate at night time. If done 

 in the day time, a cloudy day should be selected, and the trees must be 

 thoroughly dry. Fumigation is the easiest and surest method of completelv 

 eradicating red scale on citrus trees ; and it has been performed with groat 

 success on both sides of the Dividing Range in Victoria. 



Fortunately, the Fruit Fly pest is not prevalent in this State, and 

 growers, as yet, are not troubled with its attacks. 



Various fungi are to be found attacking citrus trees. The Soot fungus, 

 which shows an appearance as if some sooty substance were adhering to the 

 foliage and fruit, is a common trouble. This fungus is not a parasite on 

 the tree, but is an attendant to the scale insects, and subsists on their sugarv 

 secretion. If the scale is eradicated, the fungus disappears; so that the 

 remedy is to get rid of the scales, either by spraying or by fumigation. 



" Wither tip " is another prevalent fungus di-sease. The foliage becomes 

 blotched a brown colour, the fruit is covered with scabby patches, and dul' 

 grey blotches appear on the twigs. The laterals die, commencing from the 

 tip downwards. All diseased parts should be pruned off and burned 

 immediately; the tree should be stimulated with a pound or two or sul- 

 phate of iron, and given a good spraying with Bordeaux mixture. 



By far the worst fungus trouble to be anticipated for citrus trees is 

 the Collar Rot. The bark decays in patches at the collar or at the union 

 of the scion and stock, particularly ,at or near the surface of the ground. 

 Gumming frequently accompanies the rotting. The rotting of the bark 



