SPRAYING TO CONTROL ENEMIES OP CITRUS TREES. 3 



devitalization is well known and admitted by the citrus growers, 

 but few really appreciate the magnitude of this type of damage. 

 Thousands of trees have been seen so injured by the purple scale that 

 all the inside foliage and small limbs had been killed, and only a 

 mere " shell " of foliage remained. In one small community in 1915 

 it was estimated that the damage amounted to $30,000. It cost four 

 times as much to remove the dead wood resulting from insect attack 

 as it would have cost to prevent the damage, and two crops of fruit 

 were lost in addition. At least 75 per cent of the total damage could 

 have been prevented for less than $2,000. Many citrus growers, 

 realizing that this injury to the trees follows severe scale infestation, 

 apply extra fertilizer so that the trees may have enough nourishment 

 not only for the production of a good crop of fruit, but also to meet 

 the demands made upon their vitality by the feeding scales. The be- 

 lief is general that more fertilizer is required to get results in a 

 grove heavily infested with scale insects and white flies than in one 

 that is comparatively free from these pests. 



To express the extent of this devitalizing effect in a statistical way 

 or on a percentage basis is very difficult. In the two instances given 

 below the damage caused by insect pests and mites is most strikingly 

 shown. Although it is only proper to admit that these two cases rep- 

 resent extreme injury by pests, they indicate that the devitalizing 

 effect which results in diminished yield is much greater, on an aver- 

 age, than most growers have thought possible. 



In one instance a row of 16 trees was left unsprayed for three sea- 

 sons, 1913, 1914, and 1915. The remainder of the grove was sprayed. 

 The citrus white fly was making its first appearance in the grove. 

 During the year 1913 there was little or no difference in the yields of 

 the sprayed trees and the unsprayed check trees. In 1914 the un- 

 sprayed row had about 5 boxes of fruit, a\nd the adjoining row of 

 16 sprayed trees about 60 boxes. All common species of fungi para- 

 sitic on the white fly and scale insects were present in great abun- 

 dance. In 1915 the difference was not so great; the unsprayed row 

 had about 20 boxes of fruit, and the adjoining sprayed row about 50 

 boxes. 



As another instance, in a grapefruit grove at Safety Harbor 34 

 trees left without treatment during the summer of 1914 averaged 

 two-thirds of a box per tree less than the trees adjoining which were 

 sprayed. The reduction in the yield due to failure to spray was 

 caused by the smaller size of the fruit resulting from rust-mite 

 attack. There seems to be no evidence that the actual number of 

 grapefruit on the unsp-rayed trees was less than on the sprayed trees. 



During the year 1915 the same trees received the same treatment 

 as during 1914. The sprayed trees had at least a good half crop, 

 or about four boxes per tree. The trees adjoining which were left 



