Z CIRCULAR 295, U.S. DEPARTMENT OF AGRICULTURE 



strength, will fail to give control. Recommendations for the use of 

 oil sprays have varied widely, miscible oil sprays being generally 

 recommended for use at a dilution of 1 part stock solution to 15 

 parts water (7), whereas oil emulsions have been recommended for 

 use at strengths ranging from 2 to approximately 11 percent oil in 

 the diluted emulsion (3, 4, 5, 9). 



NATURE OF INJURY 



The obscure scale attacks all parts of the tree proper and in cases 

 of severe infestation has been found on leaf and leaflet stems, but 

 never on the leaves themselves or on the nuts. As there is but one 

 generation a year this scale must, for self-preservation, develop on 

 those parts of the tree which remain alive the entire year, for it 

 can not live on dead plant tissue. 



r^ra 



Figure 1.— Map of the United States showing the distribution of the obscure scale (Chrysomphalus obscu- 

 rus). The black area indicates those States in which it is an important pecan pest and the cross-lined 

 area indicates additional States in which it has been found. 



The initial infestation commonly starts in slight depressions in the 

 bark surface or about the buds. The scale tends strongly to develop 

 at first on the lower, inner portions of the tree, the infestation building- 

 up gradually until the parts first attacked are completely encrusted, 

 while it spreads slowly and gradually toward the terminal portion of 

 infested branches. A badly infested branch will usually be killed 

 before much of an infestation has been built up on its terminal 

 portion. Very few trees have been noted on which all parts have 

 been attacked alike. More often the incrustation is heavy on one 

 or more of the main leaders and their branches, or one side of the 

 tree, whereas the remainder of the tree shows only a slight infestation. 

 The examination of a number of moderately infested felled trees has 

 shown that little or no scale develops in the upper third of them. 

 On small to moderate-sized heavily infested trees the scale infesta- 

 tion reaches more nearly to the top. The general appearance of the 

 scale mass on an infested tree or branch is that of a roughened deposit 

 on the surface of the bark (fig. 2). 



