38 BULLETIN 616, U. S. DEPARTMENT OF AGRICULTURE. 



beneath. Where the liquid collected in large drops it formed a 

 thick amber to black scab which did not slough off readily. The in- 

 jury was most severe in places previously injured by thrips. 



INJURY FROM LIME-SULPHER. 



A small percentage of the fruit sprayed with lime-sulphur mixture 

 diluted 1-28 (Series I, plat 2) developed in the rind slight hardened 

 depressions resembling burns or scalds. Such injury occurred largely 

 in spots previously injured by thrips, and in one case in a katydid 

 scar. Less than 2 per cent of the fruit was spray-injured even by 

 this strength of solution. In plat 3 (lime-sulphur 1-56) not more 

 than one-half of 1 per cent of the exposed fruit was slightly injured 

 in similar fashion. 



In a special test on four orange trees, using lime-sulphur at the 

 rate of 1 gallon to 15 gallons water and making the applications on 

 the hottest days of the summer, very severe injury developed. By 

 the first of June some of the fruit developed severe blisters, or hard, 

 puffy, excrescences of the rind, and a small amount of the, fruit 

 fell to the ground. Unlike the injury from resin wash, that from 

 the strong lime-sulphur soon attained its severest degree and was 

 always most severe on oranges exposed to the direct rays of the sun, 

 particularly the afternoon sun. It was also particularly severe in 

 places where the fruit had been bruised or where it had been injured 

 by insects. By fall, from 18 to 25 per cent of the fruit had developed 

 spray injury, the average for all four trees being 21 per cent. 



Lime-sulphur is harmless to fruit or leaves when used weaker than 

 1 part to 28 parts water. It has a remarkably stimulating effect 

 upon the leaf growth of orange trees. In all plats where lime-sulphur 

 was used, no matter what the dilution, the trees sprayed with it pro- 

 duced a growth of foliage much in excess of that produced by their 

 unsprayed neighbors. 



SUMMARY OF RECOMMENDATIONS FOR CONTROLLING THE CITRUS THRIPS. 



SPRAY MIXTURE AND TIME OF APPLICATION. 



Plain lime-sulphur solution, 1 to 56 of the 36° Baume density or 

 1 to 50 of the 33° Baume, is recommended as the most reliable of the 

 four best mixtures resulting from the tests. 



The thrips first occur in injurious numbers at the same time that 

 the navel orange blossoms drop most of their petals; they transfer 

 from the leaves to the fruit gradually as the petals fall. The first 

 spray application therefore should be made when four-fifths or more 

 of the petals have fallen. This will check the thrips at a time when 

 the orange is most susceptible of deep injury. The exact date for 

 the application can not be given, as the period when the petals fall 

 and the thrips transfer to the fruit will be as much as 30 days later 

 in some seasons than in others, depending on the spring weather. 



