A. H. I.KES 361 



result was confirmed in some experimental spraying done in Hereford- 

 shire, The explanation is probably this. When lime is slaked, at 

 first there is a violent action which soon subsides. In ordinary parlance 

 the lime is now "slaked" but chemical action goes on more slowly 

 for some hours. A 40 gallon barrel of hme wash made in the evening 

 was still warm the next morning, showing that chemical action had 

 been continuing. If applied directly after the first violent action 

 has ceased, in the words of the grower put on "hot," further slow 

 slaking proceeds when on the tree, resulting in expansions of particles 

 in the coating. The expansion of small particles act like levers on 

 the rest of the coat, pushing and levering off particles that are completely 

 slaked and dry. The net result is that slaking sets in. This, however, 

 is certainly not the only cause of flaking. Wind causes much damage 

 on the smaller boughs. Owing to the bending to and fro of the twig, 

 at first the coat is too small, when the twig is convex, and then too 

 large, when concave. Another cause is frost after wet. Beating rain 

 causes washing off but not flaking. Insufficient slaking explains the 

 fact that good coatings often show completely bare patches sooner 

 than poor coatings. The poor coatings are generally made from 

 partially slaked lime or from a mixture too poor in lime. In each case 

 a more perfectly slaked mixture is obtained but a mixture which is, 

 of course, much inferior in egg covering powers. 



A thick mixture like the 2 lbs. to 1 gallon formula, allowing some 

 hours for complete slaking, not only gives a firmer coat but also a thicker 

 one, as one gets more of the very fine particles which are the most 

 important in forming a thick coat. These particles seem so small 

 that they aggregate when wet in an almost gelatinous manner so that 

 the mixture has quite a distinct viscosity. When dry this gelatinous 

 form disappears and does not reappear on wetting. 



Of all the washes so far tried the whiting, glue, farina, dichromate 

 formula gave by far the best results and it was therefore tried more 

 extensively at Long Ashton. 



It was also tried at centres in the three counties of Gloucestershire, 

 Worcestershire and Herefordshire on trees well infested with Psylla 

 eggs. One trial was spoiled by a subsequent frost cutting all the blossom 

 and another by the fact that the grower sprayed the treated trees 

 with a spring wash. The third, however, was left untouched and though 

 the application of the whiting wash was followed by heavy rain almost 

 before it was completely dry the resulting crop was good and equal 

 to trees sprayed with a summer wash only. 



