APPLE POWDERY MILDEW. 17 



An experiment begun after the development of the fruit burning 

 and designed to test Bordeaux mixture for late application showed 

 that while some measure of control could be established by the use 

 of this spray, it was objectionable because of the heavy deposit of 

 spray material which remained on the apples until picking time in 

 October and prevented proper coloring. Apples in plat 17 lacked 

 about 50 per cent of the red color which had developed on unsprayed 

 fruit of the same variety. 



Lime-sulphur solution was applied late in July to fruit which had 

 no sulphur spotting and which it was thought might have sufficiently 

 hardened the skin to be resistant to sulphur burning. The results, 

 however, demonstrated that injury might still occur from applica- 

 tions of lime-sulphur as late as July 21. 



Severe foliage injury developed in plat 13 after midsummer. This 

 injury was the result of the combination of the sodium- sulphur ma- 

 terial and lead arsenate, as is indicated by the fact that no late in- 

 jury developed in plat 12, where the lead arsenate was omitted. The 

 results prove the incompatibility of lead arsenate and the sodium- 

 sulphur sprays. 



The disease control established in 1916 on Pry or Red trees reflected 

 the cumulative effects of spraying for two years with the same ma- 

 terials, except in the case of plat 15, where a finely ground sulphur 

 material had been substituted for the iron sulphid used the year be- 

 fore. For some reason very little mildew developed on the Jonathan 

 trees, although in 1915 they had been as badly infected as the Pryor 

 Reds. The method of measuring the control established was the same 

 as that followed in 1915. Many of the trees yielded a fair crop of 

 fruit, especially on the Jonathan plats; but among the Pryor Red 

 trees the crop was uneven, and no attempt was made to obtain data 

 on fruit russeting. The results again showed the effectiveness of snU 

 phur sprays in controlling mildew and indicated that the benefits of 

 these sprays are cumulative. 



SPRAYING EXPERIMENTS IN 1917. 



The results of the spraying experiments conducted in 1917, together 

 with the resulting spray injury and the control established, are shown 

 in Table III. These experiments were confined to Pryor Red trees, 

 which, with the exception of the checks, were not included in similar 

 plats in 1916. 



As a result of the demonstration in the earlier work of the injuri- 

 ous effects of spraying with sulphur preparations during the season 

 of hot, burning sunlight, the experiments in 1917 were planned to 

 determine (1) what degree of control can be established by careful 

 and thorough spraying with sulphur sprays before the danger period 

 and (2) what sprays, if any, can be substituted for the sulphur ma- 

 terials, especially during the hot weather. 



