December, 1911.] 



513 



Plant Sanitation. 



two causes of disfigured fruit. The 

 insects causing the worst scars on fruit 

 are the ants, small orange-leaf weevil, 

 rust mites, and red spiders. The two 

 last mentioned rust the fruit. 



All these insects, however, are held in 

 check by sprays described in this 

 bulletin. 



Mechanical injuries are caused by the 

 fruit rubbing or hitting against some 

 foreign object, as the leaves or branches. 



Emulsions. 

 Of the various oil emulsions which 

 have been introduced, the most promis- 

 ing are the miscible oils and the crude- 

 petroleum and kerosene emulsions, the 

 last two being made with crude carbolic 

 acid, 100 per cent ( dark). 



At the present time miscible oils are 

 recommended only for trees which have 

 not come into bearing. No test has 

 been made on trees with fruit. It may 

 be possible to use these emulsions on 

 trees with fruit by changing the 

 formula, but when this i3 done a second 

 and perhaps a third spraying will be 

 necessary, as the high diluted spray 

 kills only the young. 



In purchasing materials for home made 

 miscible oils great care should be 

 exercised to obtain the exact ingredients 

 called for in this bulletin. Home made 

 miscible oils will not be practical for 

 small planters, as the igredients in 

 small lots are more expensive. They 

 may be purchased, however, by an 

 association, or a number of small 

 planters may club together to purchase 

 them. 



For trees without fruit it is recom- 

 mended that the small planters use 

 kerosene or crude-oil emulsions made 

 with 100 per cent, crude carbolic acid 

 (either straw coloured or dark); use 1 

 to 5 for kerosene emulsion and 1 to 

 16 or 18 parts of water for crude oil for 

 the purple and white scales, and repeat 

 spraying in three weeks. 



For trees in fruit use kerosene or 

 crude-oil emulsions made with 100 per 

 cent, crude carbolic acid (either straw 

 coloured or dark) ; dilate them 1 to 8 or 

 1 to 25 parts of water, respectively, 

 repeating the spraying every two weeks 

 for four or five times. 



Kerosene and crude-oil emulsions are 

 greatly improved by the addition of 

 a small amount of crude carbolic acid. 

 When carbolic acid is used the oil 

 particles are more finely divided and the 

 emulsions are more uniform. This is 

 especially true of crude-oil emulsion. 

 65 



Emulsions made with sal soda are 

 especially adapted to groves having an 

 abundance of sooty mold. This fungus 

 accompanies the Lecanium scale and the 

 white fly. 



Lime sulphur wash is the best com- 

 bination for fungicide and insecticide. 

 As an insecticide it is very valuable in 

 combating the purple scale, red spider, 

 and rust mite, and as a fungicide it is 

 used for scab. 



Great care should be exercised in 

 applying fungicides, as they kill all 

 the beneficial fungi which prey upon the 

 various scales. At times fungicides 

 have to be applied, but before using 

 them the scale should be well under 

 control ; if not an insecticide should be 

 used immediately after the fungicide. 



Time op Spraying. 



Spraying conditions in Porto Rico are 

 very different from those in the United 

 States. Many insects have no definite 

 season of appearance. This is especially 

 true of the scale insects. The constant 

 appearing of the young makes the work 

 of spraying more difficult. It is only by 

 careful study and constant observation 

 that one learns to recognize the condi- 

 tion of trees, and is able to determine 

 at what time spraying is necessary. 



Sometimes it is necessary to spray a 

 crop of nearly mature fruit ; this com- 

 plicates matters, as a much weaker 

 solution will have to be used than for 

 trees without fruit. 



There is no distinct blossoming season 

 of the orange over the island, and the 

 same may be said of the trees in 

 individual groves. Some years there is 

 a very scattering bloom, some trees 

 being in full bloom, while others have 

 not begun to show the blossom growth. 

 The same trees will bloom one year in 

 February and the next year in May 

 or June. There are generally two 

 periods of blooming, one in January and 

 one in July. 



The rainy and dry seasons occur at 

 different times in different parts ot the 

 island. The Mayaguez district may be 

 having its dry season while the Rio 

 Piedras and Pueblo \iejo districts are 

 having their wet season. 



These varying conditions make it 

 impossible to give hard and fast rules 

 regarding the time of spraying. 



When the fruit is the size of a pea 

 almost any spray will injure the crop ; 

 thus spraying should be deferred until 

 the fruit has reached the size of a wal- 

 nut, as the fruits are then less liable 

 to be injured by emulsions. A weak 

 emulsion of kerosene 1 to 8 or 9, or crude 



