IN THE CITRUS INDUSTRY 31 



Scale insects of assorted varieties probably give the most 

 trouble, and the principal mode of procedure against them 

 is fumigation with hydrocyanic acid gas. This fumigation 

 is required once a year or once in two years, and is done 

 in the fall and early winter. Fumigation is carried on at 

 night to keep from scorching the foliage, and the method 

 is as follows: A heavy canvas is thrown completely over 

 and around the tree, and is allowed to extend to the ground 

 on all sides. A receptacle containing a mixture of sulphuric 

 acid, sodium or potassium cyanide and water, varying in 

 amount according to the size of the tree, is then inserted 

 underneath the canvas, thus exposing the insects to the 

 poisonous fumes for half an hour or longer. At the end 

 of this time the "tents" are removed to other trees. An- 

 other method of proceeding against scale insects is by a 

 distillate spray, but this is not practiced as commonly as it 

 was in former years. Red spiders are controlled by sulphur- 

 ing the trees. 



Pnming is an important aspect of orange and lemon 

 culture, but one about which it is difficult to lay down gen- 

 eral statements. Common practice varies from no pruning 

 at all to almost constant pruning. In general, orange trees 

 are pruned much less than lemons. With oranges the main 

 ideas are to keep down the sucker growth and open the 

 tree here and there to the air so that new fruiting brush 

 will be stimulated. On the other hand the lemon is such 

 a vigorous grower that drastic cutting is necessary to re- 

 move sucker growth and also to keep the tree from be- 

 coming so large that it cannot be economically picked or 

 fumigated. Fruit of the highest quality is produced on 

 the interior branches so pruners keep this point in mind 

 in the case of both oranges and lemons. Citrus trees some- 

 times have a tendency to bear heavier loads than their 

 branches will support, so pruners aim at making the frame- 

 work of the tree stocky and sturdy. 



