Page 42 



BETTER FRUIT 



February 



that take place dur- 

 ing the growing- 

 season. Wintering 

 over, however, is 

 accomplished in 

 other ways, as these 

 summer spores are 

 short-lived. 



In wintering over 

 this fungus has two 

 well defined meth- 

 ods. The first is 

 very similar to that 

 of the tree, that is, 

 the parasite remains 

 dormant upon the 

 twigs where it was 

 growing" during the 

 summer. The mil- 

 dewed twigs are 

 seldom killed, but 

 often form terminal 

 and lateral buds 

 capable of growth. 

 These buds expand 

 in the spring along 

 with the other foli- 

 age of the tree, and 

 are usually infected 

 with the mildew 

 which covers them 

 and almost imme- 

 diately produces a 

 crop of summer spores, which then scat- 

 ter the infection. In the majority of 

 cases mildewed twigs produce an infected 

 growth the following spring, but occa- 

 sionally the new shoots are healthy, and 

 remain so during the season. 



The hibernation of the mildew on the 

 infected twigs is the principal means of 

 wintering over, but the fungus is pro- 

 vided with another method which may 

 account for some of the early spring 

 infections. In August, September and 

 October dark brown patches frequently 

 appear upon the greyish white fungus 



Winter spraying iov 

 San Jose scale m tlic 

 30U-acre orchards ul 

 C. M. Miller, Illinois 



Spraj-ing on a steep hillside 

 in Southern Ohio 



Spraying in the orchard 

 of E. R. Pooley, at Hood 

 River, Oregon 



Soulhcm |)clauai-c orcliaid, 

 showing new type sjii ayer 

 in foreground and an old- 

 timer in rear, thougii still 

 being used 



coating of infected stems. Examination 

 under a microscope shows these patches 

 to consist of large numbers of curiously 

 marked and spined, spherical bodies. 

 These bodies, known technically as per- 

 ithecia, each contain eight winter spores 

 of the fungus. Protected under the thick 

 coating of the perithecia, these winter 

 spores are capable of. enduring consider- 

 able exposure, and under favorable con- 

 ditions will germinate in the spring. 



Of the two methods of wintering over, 

 the one first described is apparently of 

 most importance to the fungus under 



the climatic conditions of California, but 

 in either case the process depends upon 

 the mildewed twigs of the last season. 

 During the winter these mildewed twigs 

 are often very conspicuous, especially 

 when the sunlight strikes them at the 

 proper angle. Under proper conditions 

 of illumination the whitened tips may be 

 visible for several hundred feet. 



Mildews, like other fungus diseases, are 

 dependent upon certain conditions of 

 heat and moisture for their development, 

 but in general are less affected by sea- 



sonal variations in 



rainfall than most 

 other classes of 

 parasitic fungi. The 

 powdery mildew of 

 the apple seems 

 especially resistant 

 to adverse weather 

 conditions, and suc- 

 ceeds in establish- 

 ing a very strong 

 infection during 

 seasons when the 

 apple scab has been 

 practically extermi- 

 nated. This is due 

 probably to the fact 

 that the mildew is 

 very hardy when 

 once established, 

 and succeeds in 

 growing in quite 

 dry air. Also, the 

 summer spores are 

 produced so con- 

 stantly and in such 

 large numbers that 

 they are always 

 present and able to 

 take advantage nf 

 any favorable con- 

 ditions for germi- 

 nation that may 

 arise. It has been 

 our experience that 



