. Better fruit. Fruit-culture. Page 60 BETTER FRUIT March INJURY CAUSED BY THE APPLE POWDERY MILDEW BY W. H. VOLCK, WATSONVILLE CALIFORNIA (Continued from February Number) We have frequently observed that when arsenical spraying is done early in the season (shortly after the blossoms have fallen) the foliage may become an especially dark green color and new growth develop with more than ordinary vigor. The effect is apparently due to arsenic stimulation, and where it is pro- nounced the trees outgrow the mildew for a time. Frequently this stimulation terminates in poisoning, and the mildew may
. Better fruit. Fruit-culture. Page 60 BETTER FRUIT March INJURY CAUSED BY THE APPLE POWDERY MILDEW BY W. H. VOLCK, WATSONVILLE CALIFORNIA (Continued from February Number) We have frequently observed that when arsenical spraying is done early in the season (shortly after the blossoms have fallen) the foliage may become an especially dark green color and new growth develop with more than ordinary vigor. The effect is apparently due to arsenic stimulation, and where it is pro- nounced the trees outgrow the mildew for a time. Frequently this stimulation terminates in poisoning, and the mildew may then obtain a stronger hold than ever. Stimulation with partial subjuga- tion of the mildew has been observed, and after spraying with zinc arsenite, arsenite of lime and arsenate of lead. The above mentioned compounds and mixtures by no means exhausts the list of those that might be tried, and possibly would prove specifics against the mil- dew. The results obtained in these experiments, however, would indicate that the ultimate discovery of a substance that, when applied as a spray, will kill the mildew upon the stems is very improbable. So far purely curative treat- ments have proved very unpromising, as ail substances powerful enough to kill the well established fungus were injuri- ous to the plant. Those substances which partly sub- jected the mildew without materially injuring the foliage, or even to an extent stimulated healthy growth, offer the most encouragement. The problem of spray- ing for the mildew is somewhat similar to that of applying arsenicals. In both cases the spraying must be done without introducing objectionable substances into the tissue of the plant. With arsenicals this has been accomplished by using arsenic compounds which are insoluble in water, and up to the present time the best results with the mildew have been obtained by following a like idea with the sulphur compounds. Sulphur in the form of sulphides and the pure element has long been regard
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