466 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 14 



insecticides in the liquid form in the control of the above mentioned 

 pests which attack the avocado. A portion of a large grove consisting 

 mainly of the Trapp and Pollock avocados of West Indian strains, 

 which were considerably infested with all the mentioned insect pests 

 was selected for a comparison of the two m.ethods. 



In conducting the dusting operations the equipment used was the 

 regular orchard power duster. At the time the applications were 

 made the weather was clear and the foliage was dry. The temperature 

 averaged between 75 and 80 degrees Fahrenheit. The dust was so 

 directed on the windward side of the trees so as to cover the trees well, 

 and the m.achine was never allowed to stop except at a large tree to be 

 certain it was well covered. 



The spraying work was perform.ed the same day a power outfit being 

 employed, using one of the spray guns at a pressure ranging from 225 

 to 250 pounds. 



In the dusting experiments several kinds of material were used among 

 which was an impalpable sulphur dust. This sulphur dust is nearly 

 piire sulphur very finely pulverized and capable of going through a 200 

 mesh screen. The other material used was a combination consisting 

 of the above dusting sulphur impregnated with a quantity of nicotine 

 sulphate, 40% solution, in the form of Black Leaf-40. Both of these 

 dusting materials are manufactured and on the market as contact dusting 

 insecticides. In the spra^dng work several sprays were tried out in 

 com.parison with the above dusts as lime sulphur solution one gallon to 

 fifty gallons of water, and lime sulphur solution at the rate of one gallon 

 to fifty gallons of water in combination with Black Leaf-40 at the rate 

 of one gallon to nine-hundred gallons in the diluted lime sulphur solution. 

 A portion of a block was left as a check experiment. 



Subsequent examinations at various intervals of the dusted and 

 sprayed portions of the grove showed that the dusting method, where 

 the dry dusting sulphur in an exceedingly pulverized form was used, to 

 be equally as effective as spraying with lime sulphur solution against 

 the avocado red spider, Tetranychus yothersi McGregor. The mites 

 were not killed immediately, however, on the dusted trees, but after 

 thirty minutes practically all the mites were killed. On examination 

 of the foliage with a hand lens the sulphur was very evenly applied, no 

 portion of the upper surface of the foliage being free from the fine 

 sulphur. In the dusted portion of the grove with the dusting sulphur, 

 the red spiders again made their appearance after a period of five weeks, 

 which was also true approximately in the block where the lime sulphur 



