Another important disease of prunaceous trees in cooler climes is the 'scab' of 

 apple and pear {Fusicladium dentriticum and F. pyrinum). Only the local varieties of 

 these fruit trees, the early bloomers, fall prey to this malady, as they flower at a time 

 when rain and high humidity are frequent. European varieties, which form blossoms 

 and leaves three to six weeks later, when rain has already ceased and temperature 

 gone up, escape the disease (Pelberger, 1944), 



Very interesting is the occurrence of 'rust' (Puccinia pruno - spinas ae) on pruna- 

 ceous trees, especially almond. Whereas it is very serious in humid climates and even 

 in the California coastal regions (Goldsworthy & Smith, 1931) due to the frequent fogs, 

 it makes its appearance in Israel in June, after the cessation of the 'khamsin' wind 

 season. In the interior valleys it is non-existant (Perlberger, 1943). 



Another important disease of stone-fruits is 'brown rot' (Monilinia fruticola) 

 This species is a menace to fruit cultivation in cool, humid countries (Heald, 1933; 

 Walker, 1950), but does not appear in Israel, even under irrigation, for low soil mois- 

 ture and air humidity, combined with the high temperature, of the summer, impede the 

 attack upon the fruit blossoms. 



Mediterranean trees. An interesting illustration of the controlling effect of xero- 

 thermic climate upon plant disease is provided by the diseases of some Mediterranean 

 trees. First among these is the downy mildew of grapevine (Plasmopara viticola) which 

 occurs in Israel only in the coastal region, and is checked in the interior valleys and 

 in the higher altitudes of the Jerusalem area and the upper Galilee (Reichert, 1927). 

 In valleys the appearance of the disease is hampered by the high prevailing tempera- 

 ture, amounting to 29- 29.9°C during the growing season, which is the maximal ger- 

 minating temperature of the conidia of the pathogen. In elevated localities, on the 

 other hand, the lower relative humidity and the scarcity of dew through wind action 

 precludes the occurrence of the disease (Reichert, 1927). 



It might be worth mentioning that another important disease of the vine, anthrac- 

 nose (Cloeosporium amp el op ha gum) does not occur at all in Israel and neighbouring 

 countries. The reason for its absence here lies in its tropical origin ; it is prevalent 

 in the warm, humid climates, of the low- latitude Atlantic countries of Eurafrica, the 

 Western Caucasus, south-eastern North America and parts of the southern hemisphere. 

 It may be of interest to mention the fact that wine growers in our country had treated 

 vines against this disease for more than thirty years, having been influenced by French 

 instructors to whom the disease was a common thing. We were able to convince them 

 that the treatment was unnecessary, since the disease is non-existent here. 



Another serious vine disease of cooler countries that does not occur in Israel and 

 the rest of the eastern Mediterranean area, nor in the arid parts of the U.S. and other 

 countries, is Botrytis cinerea. The high humidities required by this pathogen are not 

 present in these countries during the summer. 



A characteristic disease of olives, Cycloconium oleaginum, which causes leaf- 

 drop, is to be found here chiefly in the coastal region since the interior valleys and 

 Galilee have not the high humidity that the parasite demands. When olive trees are 

 irrigated however, the disease becomes evident to a small extent even there. 



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