Page 10 



BETTER FRUIT 



July 



MAIN OFFICE AND FACTORY 



SAN FRANCISCO, CAL. 



BRANCH ES AT 



LOS ANGELES, FRESNO, PORTLAND 

 SEATTLE, SALT LAKE CITY, HONOLULU 



Cork, Drouth Spot and Related Apple Diseases 



By A. J. Mix, Geneva, New York, Agricultural Experiment Station 



TWO little-known apple diseases are 

 found in the Champlain Valley. 

 These are perhaps only different types 

 of the same disease, are non-parasitic 

 in nature, and are apparently closely 

 related to the well-known fruit-pit or 

 stippen disease. The names cork and 

 drouth spot are proposed for them. 

 Associated with the drouth spot are ab- 

 normal conditions of the twigs and 

 foliage; it is proposed to call these 

 drouth die-back and drouth rosette. 



Cork is also found in Ontario and in 

 New South Wales. It affects chiefly the 

 Fameuse variety. Apparently the drouth 

 spot has occurred in Maine and Vir- 

 ginia; and a closely related trouble 

 occurs in the Pacific Northwest. Rosette 

 has been reported from Colorado, Cali- 

 fornia and Idaho; and both the rosette 

 and die-back from the irrigated sec- 

 tions of Washington and Oregon. In 

 the Champlain Valley certain orchards 

 and even individual trees are more 

 affected than others. It is only in 

 these particular cases that the diseases 

 assume economic importance. 



Cork is evident in late June as dead 

 brown spots beneath the skin of the 

 fruit or around the core. The fruit is 

 normal externally. Later the fruit 

 becomes distorted and knobby, and 

 brown corky areas are found scattered 

 throughout the flesh. Drouth spot 

 occurs in early June and fresh stages 

 may develop throughout the summer if 

 the weather continues dry. Superficial 

 or sunken, irregular, dead, brown spots 



show in the skin of the fruit, and dead 

 brown areas may occur in the flesh be- 

 neath. In late stages the apple becomes 

 cracked and deformed. The internal 

 spots of both diseases are in close 

 proximity to branches of the vascular 

 system, and superficial drouth spots 

 often show a wavy pattern of wrinkles 

 apparently marking the subepidermal 

 vascular network. 



Under the microscope these spots 

 show cells with brown amorphous con- 



tents shrunken away from the walls. 

 Sometimes cells are collapsed. 



Die-back consists in the death of a 

 portion of the twig from the tip back- 

 ward. Beyond this a brown discolora- 

 tion in the cambial region extends back 

 into healthy wood. The dead twig may 

 be replaced by a healthy lateral from 

 the base; but often there is found near 

 the base of the twig a rosette-like 

 cluster of dwarfed, lanceolate leaves. 

 This appearance and one in which a 

 compact cluster of similarly dwarfed 

 leaves crowns a long, bare twig have 

 been included under the name rosette. 



Field observations show that these 

 diseases may occur on the best types 

 of soil in the locality, under conditions 

 of careful culture, and in young and 

 vigorous trees. In certain cases a shal- 

 low soil seems connected wtih their 

 development. They may appear, how- 

 ever, on deep soils of good physical 

 condition. A condition of soil con- 

 ducive to poor moisture supply 

 seems connected with severe outbreaks. 

 Drouth accompanied by high, dry 

 winds seems to bring on a large amount 

 of drouth spot and cork; a subsequent 

 rainy period, as in 1915, causes them to 

 disappear. In a rainy spring, as in 

 1916, some disease occurs in trees that 

 have been previously affected, but the 

 amount is inconsiderable and the 

 period of development much shortened. 



The initial stage of die-back is found 

 on the season's growth in midsummer. 

 The following spring this die-back and 

 the accompanying rosette are very 

 noticeable. Dry weather in late sum- 

 mer seems directly responsible for die- 

 back of the season's growth. If a wet 

 summer follows a dry spring, this die- 

 back is practically absent, and there is 

 evident recovery from its preliminary 

 stages. No abnormal condition of the 

 roots is necessary to the occurrence of 

 die-back and rosette. 



Since these diseases may appear, to 

 a limited extent, in a rainy season, lack 

 of soil moisture cannot be considered 

 their sole cause. It is, however, the one 

 predisposing factor. Other factors, yet 

 unknown, may be operative. 



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