16 



CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE 



long period during which crawlers are present, (2) the relatively short 

 period that any of the oils tested were effective in deterring crawlers 

 from settling, (3) the comparatively high cost of oils of an effective 

 and safe type, (4) the fact that those crawlers eventually settling are 

 able to develop as normally and successfully as if on unsprayed 

 surfaces, (5) the difficulty of obtaining a thorough covering of infested 

 trees, and (6) because the cost of the treatment would be out of all 

 proportion to the benefit resulting. 



As the writer believed that the newly settled scales might be more 

 readily killed than older, larger ones, oil sprays were applied to 

 heavily infested branches by means of a hand-operated compressed- 

 air sprayer in the summer of 1931 after the height of crawler emer- 

 gence and settling had passed. These tests and the results effected 

 by them are given in table 5. 



Table 5. — Effect of oil sprays on newly settled young of the obscure scale on pecan 

 trees, Shreveport, La., 1931 



Test 

 no. 



Oil used i 



Oil 

 con- 

 tent 



Scales settled 



Scales dead 



Total 

 dead 



Con- 

 trol 





Pro- 

 tected 



Ex- 

 posed 



Pro- 

 tected 



Ex- 

 posed 



Effect on foliage 



1 



8 2 



Percent 

 1.0 

 2.0 

 1.0 

 2.0 

 1.0 

 2.0 



.5 

 1.0 

 2.0 



.5 

 1.0 

 2.0 



.5 

 1.0 

 2.0 



Num- 

 ber 

 676 

 622 

 631 

 625 

 729 

 758 

 687 

 835 

 787 

 722 

 806 

 791 

 659 

 788 

 844 

 750 



Num- 

 ber 

 325 

 386 

 369 

 381 

 272 

 242 

 313 

 175 

 219 

 281 

 227 

 209 

 341 

 214 

 162 

 250 



Percent 

 21.89 

 26.05 

 23.93 

 26.24 

 22.91 

 34.43 

 25.47 

 21.20 

 37.48 

 28.67 

 29.16 

 54.61 

 24.89 

 23.22 

 48.58 

 21.73 



Percent 

 34.15 

 49.74 

 48.78 

 51.71 

 52.57 

 71.07 

 45.69 

 37.14 

 71.69 

 55.16 

 76.65 

 99.04 

 52.20 

 56.07 

 92.59 

 44.40 



Percent 

 25.87 

 35.12 

 33.10 

 35.88 

 30.97 

 43.30 

 31.80 

 23.96 

 44.93 

 36.09 

 39.59 

 63.90 

 34.20 

 30.24 

 55.67 

 27.40 



Percent 



Minus 



10.6 



7.8 

 11.7 



4.9 

 21.9 



6.1 

 Minus 

 24.1 

 12.0 

 16.8 

 50.3 



9.4 



3.9 

 38.9 



None. 



2 



3 



4 



5 



do 



9 



do 



10 



None. 

 None. 

 None. 

 None. 



6 



do 



11 3 



None. 



8 



9 



10 



do 



do 



12 



None. 



Small amount. 



None. 



11 



12_-__ 

 13 



do 



do 



13 



None. 



Small amount. 



None. 



14„-- 

 15--.- 

 16 



do 



„—dO 



Unsprayed check. _ 



None. 



Small amount. 











1 For physical characteristics of oils used, see table 6, p. 18. 



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



3 Oils 11, 12, and 13 were emulsified according to formula no. 2, p. 17. 



None of the tests shown in table 5 gave any worth-while control, 

 test 12 giving the best, namely 50.28 percent. As with the dormant- 

 spray applications, better control was effected of the exposed scales 

 than of those developing beneath old covers. This again indicates 

 the inability of oil sprays of low dilutions to penetrate these old 

 scale covers sufficiently to effect a high kill. In addition, those oils 

 giving the best control showed a tendency to cause some injury to 

 the foliage, indicating that they could not be applied to the trees 

 with any wide margin of safety. 



RECOMMENDATIONS FOR CONTROL 



As a result of the data presented in tables 1 to 5, inclusive, together 

 with supporting data, the following recommendations for effecting 

 control of the obscure scale on pecan trees are presented: (1) If 

 the infestation is light (not heavily encrusted), use a 4-percent lubri- 

 cating-oil emulsion regardless of the prrysical condition of the trees. 

 (2) If the infestation is heavy, use a 4-percent lubricating-oil emulsion 



