16 CIRCULAR 6 5 6, U. S. DEPARTMENT OF AGRICULTURE 



crude petroleum, nitrobenzene, oil of citronella, oil of sage, oil of 

 eucalyptus, camphor gum, dipentene, isovaleric acid, amyl butyrate, 

 pine tar, borneol, butyric acid, calcium cyanide, Paradow, anthracene, 

 eugenol, Black Leaf 40, methyl sulfide, Evergreen (alcohol solution of 

 the active principle of pyrethrum), naphthalene, castor oil, fish oil, 

 transmission oil, medium paraffin oil, crankcase drainage, Crisco, 

 rapeseed oil, tallow, butyric ether, oil of peppermint, oil of lemon, and 

 amyl valerianate. 



These substances, if compatible, were incorporated in a wax paint 

 and applied, or, if incompatible with wax, were applied in a water 

 paste of kaolin. Aphicidal and aphid-deterring properties were 

 determined by covering part of a wound callus, usually where the 

 aphids were already feeding, and recording later whether or not 

 aphids were feeding on the untreated bark in close contact with the 

 paint. None of the substances used, even those having the foulest 

 odor, was either attractive or repellent to the woolly apple aphid. 

 A film of oil seemed to be very objectionable to the aphids, but a light 

 oil was soon volatilized and a heavier oil caused disturbance to the 

 tissue, thus making its use questionable. 



In the course of the experiments, attempts to increase the efficacy of 

 waxlike dressings against the woolly apple aphid included repeated 

 trials with nicotine through several years. The nicotine improved 

 aphid control, as was also reported by Childs (5), but it was necessary 

 to add lethal concentrations (10 to 25 percent) of Black Leaf 40, 

 which greatly increased the cost. Dressing No. 541, by its protective 

 covering alone, usually controlled the aphid satisfactorily without 

 nicotine, if wounds were not painted until midsummer when callus 

 formation was about over and before the usual heavy aphid attack in 

 early fall had begun. 



CONCLUSIONS AND PRACTICAL CONSIDERATIONS 



The work reported in this circular emphasizes the importance of 

 the time of the year in which pruning wounds are made. The later 

 in the growing season pruning is done, the less time there is for callus 

 formation that growing season, and completely uncallused wounds 

 are subjected to enlarging by drying and dying till callus formation 

 begins the next spring. As only side wounds were made in the 

 summer wounding reported in this circular, the shock effect resulting 

 from removing limbs when in leaf was probably not operative. 



If wounds are made in the fall and early winter, the unhealed 

 wounds are subjected to cold injury and other conditions that cause 

 dying and extension. In regions where severe cold sometimes occurs, 

 winter pruning may cause extensive enlargement of the wounds or 

 even general winter injury to the whole tree. Even in the com- 

 paratively mild winters occurring when this work was done, there 

 was more longitudinal enlargement of the wounds made in the winter 

 than of those made in the spring. The same principle is illustrated 

 by the fact that the dressings that were slightly injurious produced 

 more injury in the winter treatments than in the spring treatments. 

 Also, the increased longitudinal enlargement of wounds on a weak 

 limb was much greater than on a more vigorous one. 



