APPLE POWDERY MILDEW. 25 



plat were also sprayed in like manner. At the end of the season it 

 was plain that while there was less infection on the trees which had 

 been pruned, the difference in control was certainly not sufficient to 

 pay for the extra labor involved in the very careful examination of 

 the dormant trees. These results are contrary to those obtained by 

 Ballard and Volck (12) in the Pajaro Valley, Cal., and are un- 

 doubtedly due to the difference in spraying practices followed. On 

 account of climatic conditions it is impossible in the Pajaro Valley 

 to use lime-sulphur solutions or other sulphur sprays known to pos- 

 sess the power of easily wetting and penetrating the mildew. How- 

 ever, in the Wenatchee Valley full benefit could be had from the 

 wetting effects of the lime-sulphur solution, and consequently better 

 control could be established by spraying. 



GENERAL NOTES ON THE CONTROL OF THE DISEASE. 



It was always found that mildew first appeared before the blos- 

 soms opened — on the foliage expanding from dormant buds. By the 

 time the trees were in full bloom conidia were being shed in abun- 

 dance. This indicates that an application of fungicides must be 

 applied earlier, and the experiments have shown that the first appli- 

 cation should be made at the same time as in the case of apple scab, i. e., 

 just after the cluster buds have separated, while the blossom buds 

 are in the pink. There is little to be gained by an earlier applica- 

 tion, because so little foliage is expanded, and the delay of the in- 

 fected buds prevents an earlier spread of the disease. Most of the 

 blossom infection results from mycelium carried over in the blossom 

 buds from the previous year and not as a result of conidial dis- 

 semination of the current year. It is not, therefore, probable that a 

 spray applied at the time mentioned would have much beneficial 

 influence in preventing blossom infection, but it is extremely im- 

 portant in cleaning up incipient foliage infection and in protecting 

 the healthy leaves. If this treatment is followed by others at such 

 intervals that all of the new foliage is protected as it expands, 

 adequate protection is gained. The experiments indicate that after 

 the " pink " spray the disease can be held in check in ordinary years 

 by combining the fungicides with the first two regular applications of 

 lead arsenate used in codling-moth control. If supplemental spray- 

 ing is required, the . applications should be made at intervals not 

 greater than four weeks. 



There is a strong prejudice in the Wenatchee Valley against the 

 combination of lead arsenate and lime-sulphur or other sulphur 

 sprays. This seems entirely unwarranted, for in the course of 

 these experiments no detrimental effects were observed from the 

 use of the combined sprays except as noted in the case of the 

 sodium-sulphur materials. It has been repeatedly demonstrated 



