April, '15] 



SCOTT: BARIUM SULPHIDES 



209 



young were found in abundance on the unsprayed trees, but none could 

 be found on the badly infested trees which had been marked for exam- 

 ination in each of the sprayed plots. Subsequent examinations made 

 on August 19 and November 27 showed no change in the results except 

 that the infestation on the unsprayed trees grew steadily worse. 



In 32 pounds of the dry barium product there is about the same 

 amount of sulphur as is contained in 59 pounds (5J gallons) of the lime- 

 sulphur solution used and yet 16 pounds of the former material to 50 

 gallons of water were sufficient to control the San Jose scale. A dilu- 

 tion as weak as 10 pounds to 50 gallons of water apparently killed the 

 scale, as shown in plot 11, but this strength was used in only the one 

 experiment and the results should, therefore, not be considered con- 

 clusive. However, the strength of 16 pounds to 50 gallons of water 

 was used in several different orchards with uniformly good results, 

 which would indicate that, when combined with barium, less sulphur 

 is required to kill the scale than when combined with lime. 



An experiment for the control of the oyster-shell scale was conducted 

 in the laboratory at Baltimore and here again the dry barium-sulphur 

 product proved to be as effective as lime-sulphur solution. On March 

 3, 1914, poplar branches badly infested with this scale insect were 

 placed in jars of water in a warm room and sprayed with these 

 materials. A similar branch was left unsprayed as a check. The 

 branches threw out roots from the cut surface in the water and kept 

 alive long enough for the conclusion of the experiment. The old 

 female scales were gorged with eggs which began to hatch on April 2, 

 when 83 young were counted crawling over the unsprayed branch. 

 No young were out crawling on any of the sprayed branches but by 

 removing a few mother scales it was found that the eggs were beginning 

 to hatch. 



At the conclusion of the experiment, April 17, all of the eggs on the 

 unsprayed branch had apparently hatched and the writer counted 

 300 young which had settled down and formed a scaly covering. On 

 the branch sprayed with barium-sulphur (BaS4H20+), 5 ounces to 1 

 gallon of water, about 90 per cent (estimated) of the eggs hatched and 

 most of the young died without emerging from beneath the mother 

 scales. Thirty-four young had succeeded in emerging but only two 

 of these remained alive. On the branch treated with 7.7 ounces of 

 barium-sulphur to 1 gallon of water, all the young died without emerg- 

 ing from beneath the mother scales. On a third branch treated with 

 10 ounces of barium-sulphur to 1 gallon of water the same results were 

 obtained, except that 30 young emerged, all of which died without 

 settling down. On a branch sprayed with 1 pint of lime-sulphur 

 solution to 50 gallons of water, 300 young issued but all died with- 

 out settling down. 



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