APPLE POWDERY MILDEW AND ITS CONTROL. 11 



spring and summer spraying, intended to prevent foliage and twig 

 infection and to kill out any mildew that had become established. 



WINTER SPRAYING. 



The experiments in dormant spraying were conducted through two 

 winters. About 16 different materials were used, some of which were 

 tested on several plats and in various strengths. Among the mix- 

 tures used were Bordeaux mixture, lime-sulphur solution, various 

 soluble sulphids, copper sulphate, sulphuric acid (alone and in com- 

 bination with copper sulphate and iron sulphate) , and various soluble 

 copper salts. The results showed that the plats which received the 

 various dormant sprayings were just as badly attacked by mildew 

 the following spring as those which were not sprayed. 



FOLIAGE SPRAYING. 



While the investigations in winter spraying were in progress, it 

 became evident that the dormant or winter spores played a very 

 unimportant part in establishing the first infections the following 

 spring. It was seen that on each tree great numbers of mildewed 

 twigs developed from dormant-bud infections, and that on these dis- 

 eased twigs summer spores were produced in quantities and served 

 to infect the healthy foliage as it came out. 



The work of winter spraying for the direct control of the mildew 

 was, therefore, dropped, though it was taken up again later from a 

 different standpoint. Attention was given to finding a suitable fun- 

 gicide for foliage spraying and a practical method of reducing to a 

 minimum the number of dormant-bud infections. 



About 125 different materials have been tested for foliage spraying, 

 and many of them have been used in several different strengths. Ex- 

 periments with the more promising ones have been repeated through 

 several seasons, and the investigations have been in progress six years. 

 For the purposes of this bulletin it will not be necessary to give a 

 detailed account of the experimental work, but a brief statement of 

 some of the results will not be out of place. It will be remembered 

 that these remarks apply particularly to the Pajaro Valley, though 

 for the most part they will probably hold true for other sections 

 as well. 



Copper compounds in general can not be used, on account of the 

 leaf burning and fruit injury which they cause. Bordeaux mixture 

 gives very poor control of apple powdery mildew. Copper acetate 

 and copper oxychlorid give fair control of the mildew, but they can 

 not be used repeatedly on account of their fruit and foliage injuring 

 properties. Dilute lime-sulphur solution and solutions of the soluble 

 sulphids in general, such as potassium and sodium sulphid, can not 



