CITRUS CULTURE IX PORTO RICO 



27 



INSECT AND DISEASE CONTROL 



In addition to gumming and various decays of the roots- the 

 trunk, and the branches, the chief enemies of the citrus-fruit indus- 

 try include scab, several species of scales, and the rust mite. The 

 control measures used for these are not uniform. Some growers 

 spray with Bordeaux mixture for scab, others spray with lime- 

 sulphur, and still others follow the Bordeaux mixture with sulphur 

 in the powdered form. Scale insects can usually be kept in check 

 by means of beneficial fungi, provided that Bordeaux mixture is not 

 used. The use of Bordeaux mixture entails the use of scale washes, 

 and too much spraying is costly as well as harmful to the trees. 



A comparison of the efficiency of the different control measures 

 used in the different groves for the past several years fails to show 

 that one is superior to the other. It is generally agreed that Bor- 

 deaux mixture is the most efficient remedy for scab, but some growers 

 claim that practically as high a percentage of scab-free fruit can be 

 had from the consistent use of lime-sulphur as from the use of 

 Bordeaux mixture. This may be largely due to the fact that spray- 

 ing can not be done as often and as efficiently as necessary. Dusting, 

 being much the more rapid of the two methods, may overcome this 

 difficulty, but it has not yet been in use long enough to warrant its 

 recommendation. 



The use of Bordeaux mixture is objected to principally because 

 it kills the scale parasitic fungi. Scale insects can be kept in check 

 by spraying the trees with oil emulsion; yet it is not unusual to 

 find groves in which the trees as well as the fruit are very scaly. 

 This may be due to ineffective spraying, or to poorly applied sprays, 

 but usually it is due to neglecting to spray at the proper time. 

 Such neglect is often inevitable, because even with a thorough 

 equipment only a certain number of trees can be sprayed in two to 

 three weeks, and during some seasons spraying must be repeated 

 at two to three week intervals. 



Scab attacks the leaves and the fruit of the lemon, the sour orange, 

 and some varieties of the grapefruit tree. The Triumph and the 

 native grapefruit have so far been immune to scab, and the sweet 

 orange is seldom attacked by it. Grapefruit leaves are seldom so 

 severely attacked as to necessitate spraying. However, it may become 

 necessary at times to spray the nursery stock before budding is done 

 unless, of course, the Triumph type is used for stock. When scab is 

 kept out of the nursery it may likewise with great care be kept out 

 of the isolated grove in which the scab-free trees are planted. When 

 scab does attack the young trees spraying should be deferred until 

 the fruit needs it, In fact, it is better to destroy the first year's crop, 

 which consists of a small amount of coarse fruit, than to spray for 

 the purpose of keeping it free from scab. When spraying is ^ re- 

 sorted to for the second and succeeding crops the following points 

 should be kept in mind: Spray (1) before the bloom appears in 

 order to cover all the foliage, (2) at the time the petals are falling, 

 and (3) often enough to keep ever}' part of the tree covered until 

 the fruit is three-fourths to 1 inch in diameter. These directions 

 apply whether Bordeaux mixture or sulphur is used and whether 

 they are applied in the form of sprays or dust. After attaining a 



