OBSCURE SCALE ON THE PECAN AND ITS CONTROL 15 



From observations made by the writer it would appear that one 

 factor more than all others likely to determine whether injury will 

 result from the application of dormant oil sprays to pecan trees is 

 the physical condition of the trees themselves. Strong, healthy, 

 vigorous trees enjoying the benefits of good soil, cultivation, fertiliza- 

 tion, moisture, and healthy foliage apparently withstand heavier 

 dosages of oil sprays than trees growing in poor, unfertile, uncultivated, 

 unfertilized, or eroded soil and suffering from drought or premature 

 defoliation. 



SUMMER SPRAY APPLICATIONS 



In addition to the attempts that have been made to secure control 

 of the obscure scale by means of dormant spray applications, addi- 

 tional efforts have been made to limit its spread and development by 

 the use of summer applications of oil sprays. 



During the emergence period of the crawlers in 1931 and again 

 during the same period of 1932, tests were made to determine whether 

 the application of oil sprays to the trees would prevent or deter the 

 crawlers from settling, or, permitting them to settle, perhaps prevent 

 or interfere with their normal development. 



In 1931, oils 1, 6, 11, 12, and 13 (table 6) were emulsified according 

 to formula no. 2, page 17, and applied to good-sized limbs on orchard 

 trees at dilutions of 0.5, 1, and 2 percent of oil by means of a com- 

 pressed-air sprayer. Oils 8, 9, and 10, commercially prepared sum- 

 mer oils, were applied in the same manner at dilutions of 1 and 2 

 percent of oil. At regular intervals twigs were cut from the sprayed 

 limbs and taken to the laboratory, and crawlers were transferred to 

 them as long as the oil seemed to affect the settling of the crawlers. 

 The high- viscosity low-volatility oils exerted the more pronounced 

 and most lasting influence on the settling of the crawlers, the degree 

 of and duration of the influence being directly proportional to the 

 strength of oil used. The dormant-type oils caused foliage injury 

 when used at dilutions exerting any pronounced deterring influence 

 on the settling of the crawlers. The summer oils caused no injury. 

 Oil 9 at 2-percent and oil 10 at 1 -percent dilution exerted a pronounced 

 deterring influence on the settling of crawlers for a 3-day period, 

 while oil 10 at 2 percent exerted a strong influence over a period of 2 

 weeks. 



In 1932, oils 8, 9, 10, and 20 were used in similar tests, except that 

 potted trees were sprayed instead of orchard trees. Oil 20 was 

 emulsified according to formula no. 2 (p. 17). Two trees were sprayed 

 with each oil at dilutions of 1 and 2 percent of oil, respectively, in the 

 diluted emulsion. Crawlers were transferred to them at regular 

 intervals as long as any of the oils appeared to be exerting any influ- 

 ence on the settling of the insects. Oils 8, 9, and 10 showed no 

 deterring influence after the third day whereas oil 20, much lower in 

 volatility than any of the others, exerted a considerable influence at 

 both the 1- and 2-percent dilutions for 2 weeks and some influence 

 at 2 percent for a slightly longer period. About 1 month after the 

 final transfer of crawlers those specimens successfully settled on the 

 oil-sprayed potted trees appeared to be developing just as normally 

 and successfully as those settled on unsprayed check trees. 



The spraying of pecan trees infested with the obscure scale during 

 the crawler-emergence period to kill the crawlers or prevent their 

 settling is not deemed practical, for the following reasons; (1) The 



