30 PEACH LEAF CURL: ITS NATURE AND TREATMENT. 



Fetich leaf curl appears to be more prevalent in late than in early 

 springs. This is probably due to the lower temperature and greater 

 rainfall usuall}^ accompanying the former. Of 80 growers who gave 

 their experience in relation to this matter, 43 stated that curl affects 

 trees most in late springs, 23 believed it affects them most in early 

 springs, and 14 had noticed no difference. 



The question as to whether peach leaf curl affects trees most after a 

 cold or warm winter was submitted to the growers, and of the 67 who 

 replied, 27 stated that trees were most affected after a cold winter, 21 

 that they were most affected after a warm winter, and 19 growers had 

 observed no difference. 



The question of the influence of heavy dews on curl was also sub- 

 mitted to the orchardists, and the views expressed in their replies 

 exhibit a remarkable agreement, 47 out of the 58 exi^ressions of 

 opinion received stating that the disease is no worse after a series of 

 heavy dews. To the writer it appears probable that these answers are 

 in perfect accord with the facts. Heavy dews can exert ]>ut slight 

 influence upon the tissues of the peach, as they occur at night, when 

 transpiration from the leaf is largely checked by the reduced light and 

 lowered temperature of the atmosphere, resulting in the stomata being 

 nearly closed. With the return of light and warmth the dew evajDO- 

 rates with the resumption of transpiration, and can have but little 

 influence upon the tissues of the leaf. It might seem that dew would 

 have a direct action on the germination of the spores of the fungus 

 and in that way lead to a serious development of the disease after one 

 or more heavy dews. This view, however, is not supported ])y observa- 

 tions either in the field or in the laboratory. In regions having little 

 cloudy weather, with exceptionally clear sky, as in many portions of 

 the Southwest, the heat of the soil radiates rapidly after sunset. In 

 such sections of the country the days are hot and the nights cool or 

 cold in comparison, the range of temperature between night and day 

 being often considerable. In such regions dew is conuuon and often 

 heavy, but it is here that least curl occurs. 



Relative to the action of dew on the germination of the spores of 

 Exoascm deformans^ it may be said that something more than dew is 

 reciuired for such germination. The writer has tested this matter 

 most thoroughly, not only with dew, but with many forms of culture 

 media at various temperatures and with varying supplies of oxygen. 

 Brefeld has also shown that moisture alone is not suflicient for germi- 

 nation, behaving utterly failed to induce germination in a single instance 

 after months of work with culture media in liquid form. Budding of 

 the spores is easy to obtain in all liquids, and is more abundant and 

 continuous in suitable nourishing cultures than in dew or rain water. 

 Fifty-eight growers replied to an inquiry on this suliject, 47 stating 

 that the disease is no worse after a series of heavy dews, 7 that it 

 is worse, and 4 that no difference was observed. 



