PEIACH DISEiASEIS 



1553 



appear on the surface of fruits as little 

 velvety cushions of mold not more than 

 one-eighth or three-sixteenths of an inch 

 in diameter. See Fig. 1. The decayed 

 fruits frequently have a tendency to re- 

 main on the trees and slowly dry up, and 

 may cling to the trees during the winter 

 in a shriveled and dried up condition 

 known commonly as "mummies." The 

 fungus lives over the winter in such 

 mummies, and spores, which are pro- 

 duced from them in the spring, start 

 new infections. 



A blossom blight may result from in- 

 fection of the blossoms early in the 

 spring. A twig blight may also be pro- 

 duced, but this probably only occurs 

 when the blossoms or fruit have been in- 

 fected and the fungus has gained en- 

 trance to the twig through them. The 

 fungus is probably not able to enter the 

 twigs directly. Peaches and apricots 

 have been found to be more susceptible 

 to the twig form of the disease than the 

 other stone fruits. 



As stated above, the fungus winters 

 over in the "mummies" left hanging on 

 the trees or lying on the ground. It is 

 probable, also, that the disease may be 

 carried over the winter by spores adher- 

 ing to bud scales, twigs, etc. 



Cause 



The brown rot on plums, peaches and 

 apricots is caused by a fungus known as 

 ScleroUnia fructigena. This fungus ex- 

 ists in two spore forms. The summer 

 spore form has already been described. 

 The winter or sexual spore stage devel- 

 ops in the early spring from mummies 

 that have fallen to the ground. This 

 stage does not ordinarily develop on the 

 mummies until after they have lain on 

 the ground for 18 months. 



This stage of the fungus is developed 

 from resting masses of mycelium called 

 sclerotia, which develop in the tissues of 

 mummified fruits. A definite fruit body 

 is produced known as an apothecium and 

 commonly spoken of as a "cup fungus." 

 This consists of a slender stalk bearing 

 at the summit a cup-shaped structure, 

 one-quarter to one-half inch in diameter. 

 These are found at the surface of the 



ground, surrounding buried or half- 

 buried mummies. Several may be formed 

 from the same mummy. The inner sur- 

 face of the expanded bell-shaped portion 

 is lined by great numbers of cylindrical 

 sacks called asci, each of which contains 

 eight spores. These asci form a smooth 

 layer. The details of structure are vis- 

 ible only on miscroscopic examination. 

 The spores are ejected forcibly from the 

 asci, and, wafted by currents of air, reach 

 the trees. It is probable that much of 

 the blossom blight is caused by direct in- 

 fection from these spores. 



Control 



From what has been said, it is evident 

 that the destruction of all mummified 

 fruit in fall and winter would aid in con- 

 trolling the disease. It is a bad practice 

 to allow diseased fruits to remain in the 

 orchard, since, as shown above, the fun- 

 gus is capable of living over winter in 

 such mummies and starting the disease 

 in the spring. Plowing in the spring be- 

 fore the buds open is to be recommended 

 where possible, and when consistent with 

 good horticultural practice. This meth- 

 od would probably not entirely prevent 

 the formation of the winter spore stage 

 and therefore, where practical, the de- 

 cayed fruit should be gathered and de- 

 stroyed in the fall. 



Peaches should be thinned so that no 

 two fruits touch each other, as it is found 

 that moisture may be retained at the 

 point where the fruits touch and thus 

 favor infection. 



Where the disease is serious the trees 

 should be protected by a fungicide. Since 

 this disease is not serious in all sections 

 of the Northwest, spraying, as a general 

 orchard practice, may not be necessary 

 for all growers. Previous experience 

 must be taken into consideration in de- 

 ciding whether sufficient loss is likely to 

 occur to warrant spraying. 



It has been found in most peach-grow- 

 ing sections to be unsafe to use Bordeaux 

 mixture or commercial lime-sulphur on 

 peach foliage except in very weak 

 strength, so that a special spray known 

 as self-boiled lime-sulphur is recom- 

 mended for use on peach foliage. 



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