18 



CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE 



Table 6. — Physical specifications 1 of oils used in spraying experiments for tJk 

 obscure scale, Shreveport, La. 



Oil no. 



Viscosity 



(Saybolt 



at 100° 



F.) 



Volatility 

 (4 hours 

 at 105- 



110° C.)2 



TJnsuI- 



phonated 



residue 



Oil no. 



Viscosity 

 (Saybolt 

 at 100° 



F.) 



Volatility 

 (4 hours 

 at 105- 



110° C.)2 



Unsui- 



phonated 



residue 



1 



Seconds 



85 



145 



228 



^348 



100 



207 



170 



53 



70 



109 



Percent 



1.20 



12.01 



.10 



3.91 



.28 



.92 



5.26 



31.90 



31.80 



12.90 



Percent 

 64 

 

 60 

 50 

 48 

 19 

 50 



87.6 

 88 

 93.8 



11 



Seconds 



54 

 106 

 223 



55 

 100 

 105 



55 

 215 

 230 



86 



Percent 



34.60 



8.70 



9.10 



36.40 



13.80 



.72 



13.76 



5.70 



3.80 



2.20 



Percent 

 69.5 



2 



12 



67.8 



3 . . 



13 



14 



60 3 



4 3 - 



70 



5 . 



15 



16 



61 



6 



69 



7 



17 



18 



19 



78 



8 & 



57 



9 



63 



10 . . 



20 



96 







1 All analyses made by U.S. Bureau of Chemistry and Soils. 



2 Volatility of oils 1-13, inclusive, obtained for 4 hours at 105° C. and remainder for 4 hours at 110° C. 



s Oils 4, 5, and 7 were commercially prepared miscible oils, 5 and 7 being different lots of the same brand* 



* At 140° F. 



s Oils 8, 9, and 10 were commercially prepared summer oils. 



SUMMARY 



The obscure scale is an important pest of all varieties of pecans 

 throughout a large portion of the pecan belt. It attacks all parts of 

 the tree proper, developing first on the lower, inner portions of the 

 trees and spreading gradually outward and upward. Limbs up to 

 3 inches in diameter are most frequently killed by its attacks. The 

 greatest injury results from the gradual killing of branches and the 

 weakening of infested trees, which renders them more subject to 

 attack by borers, other insects, and diseases. 



Eggs are first extruded between the middle of May and early in 

 June, and crawlers can be found a few days later. Both eggs and 

 crawlers are present in large numbers throughout June and until the 

 middle of July, after which they gradually decrease in numbers until 

 by the first of August only a few remain. 



The first crawlers settle under old scale covers, and those that emerge 

 from beneath the cover of the parent scale settle within a short time 

 and usually not far away. They gradually increase in size, and their 

 covers assume the color of the surface on which they are resting. 



Most of the winter is passed by the male scale in the second larval 

 stage and by the female in the stage preparatory to the second molt. 

 Development is resumed late in the winter, and most specimens reach 

 the adult stage by the middle of April, adult males emerging as the 

 females are completing the final molt. Mating takes place at once 

 and eggs are soon formed. There is but a single generation each year. 



Parasites, predators, and diseases exert a considerable influence in 

 reducing the numbers of this scale, and in some instances appear to 

 hold infestations in check without the aid of artificial control measures, 

 though artificial control is usually necessary. 



Four-percent lubricating-oil emulsions have given good control of 

 light infestations of the obscure scale and of those scales not pro- 

 tected by old scale covers, and have proved safe when used during the 

 strictly dormant period. Five-percent emulsions have given an 

 increased degree of control but have shown a slightly greater tendency 

 to cause injury. Six-percent emulsions have given a satisfactory, 

 but not perfect, control of the heaviest infestations but have caused 

 serious inj ury in some of the tests in which they have been used . Eight- 

 percent emulsions gave excellent control but caused serious injury. 



