No. 6. DEPARTMENT OF AGRICULTURE. 255 



in the cold it will thicken. If dust be admitted it will adhere to the 

 greasy surface until a layer is formed so thick that all the fatty mat- 

 ter is absorbed in it. If the surface covered by the film be absorbent 

 every particle of the vaseline will find its way into the absorbent ma- 

 terial unless a dusty or other covering absorbs it. 



Precisely this happens when a tree is sprayed with crude oil. The 

 light oil is very penetrating, and soaks at once through the scaly 

 scurf, carrying down also the vaseline and wax into contact with the 

 insect. In a very short time this light oil is gone and the greasy 

 coating alone remains: the scales absorb and hold* this. On trees 

 with a smooth, Avaxy bark like certain pears, the surface is not ab- 

 sorbent, the coating remains and no young scales can set until, by 

 growth, uncovered bark appears, or until the dust has taken up the 

 grease and the coating rubs or flakes off. 



On peach, the bark is absorbent except on the newest shoots, and 

 wliatever vaseline is left after soaking the scales gets into the plant 

 tissue. If the bark is coarse and thick and the vaseline film thin, no 

 harm is done; the inert outer layer takes it all. If the bark is thin 

 and sensitive and the coating thick, the vaseline will replace the con- 

 tents of the plant cells and kill them. It will continue to penetrate 

 until it is all absorbed and so we have kills. In 'Southern States the 

 bark on peach is more sensitive and thinner than in the North; hence 

 oil, unless carefully used, is dangerous or fatal. In the latitude of 

 Philadelphia it is safe with reasonable care. 



I have been thus explicit concerning the crude oil because I be- 

 lieve it to be the most effective material txius far employed against 

 the scale, and reasonably safe for all trees when its use is understood. 



The killing power is not only in the light oils, but in the vaseline 

 residue; in fact, coating an infested bark with vaseline would re- 

 sult in the death of every covered scale; probably also in the death 

 of the tree. 



I have treated all the ordinary orchard trees with crude oil at all 

 period.^ from recent dormancy to just starting and never killed a tree. 

 I have killed peach bud® by soaking them with oil, from a brush, 

 but secured a full crop after spraying in October. I first sprayed 

 and afterw-ard painted a young peach and had a full show^ of flowers 

 next spring. So I have drenched an apple by letting the oil run down 

 from the tips of the twigs until the whole tree had as much oil as 

 would stay on it. I killed the outer layer of bark on the trunk and 

 large branches; but this flaked off, leaving a beautifully smooth bark 

 underneath. The tree was as badly infested as it could well be and 

 a few twigs died from the combination of oil and scale; but not a bit 

 of real injury was done. Yet I know that others have been less for- 

 tunate. One careful man finds it almost impossible to nse the oil 

 safely on Ben Davis apples; another who lives not ten miles away 



