igii 



BETTER FRUIT 



Page 33 



FUNGOUS DISEASES OF FRUITS -THEIR REMEDIES 



BY W. S. BALLARD, DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C. 



THE successful horticulturist uncon- 

 sciousLy acquires, by his daily asso- 

 ciation, a mental picture of what 

 he considers a typical form of the par- 

 ticular kind of trees, bushes or vines he 

 is growing. He becomes so expert in his 

 judgment that he quickly recognizes any 

 abnormal appearance, and immediately 

 begins to search for the possible cause. 



He is particularly interested in pro- 

 ducing fruit that is as good, or a little 

 better, than the best in his section, or 

 any section that he can learn of, and he 

 is not satisfied until he has acquired that 

 goal, or has come as near it as possible. 

 The disease problem is one of the chief 

 factors that claims his attention in this 

 endeavor to produce the best grade of 

 fruit. With our present facilities for 

 transcontinental shipment and the fre- 

 quent introduction of fruit or plants from 

 various parts of the world, there is an 

 ever present possibility of introducing 

 new pests to add to those already pres- 

 ent, and the successful enforcement of 

 quarantine laws is our chief protection 

 against these foreign introductions. We 

 may feel thankful that it occasionally 

 happens that a new pest does not thrive . 

 in its new environment, but it frequently 

 happens that the new environment is 

 more congenial than the old. 



When the pest problem asserts itself as 

 a controlling factor in the agriculture of 

 any locality the ability to grow crops 

 then becomes largely a matter of the suc- 

 cess of the methods of overcoming such 

 pests, and the willingness of the growers 

 to adopt the proper practice and carry it 

 out thoroughly and strictly in accordance 

 with the proper recommendations. 



One of the chief methods of fruit pest 

 control is spraying; and the investigator 

 of these troubles in continually endeav- 

 oring to impress upon the grower the 

 three very important factors in success- 

 ful spraying: First, the proper material 



must be used in the proper strength; 

 second, the work must be done at the 

 proper time, and, third, it must be done 

 thoroughly and in the proper manner. 



It is correctly said that the pest prob- 

 lem in the United States is largely instru- 



fungus. The so-called California peach 

 blight is caused by another fungus, and 

 still another one produces peach leaf 

 curl. Root rot is commonly caused by 

 one of the toadstool fungi, and pear 

 blight by one of that large group of 



mental in making apple growing a 

 profitable business, for the grower who 

 is not willing to fight soon ceases to be 

 a commercial grower, and if there were 

 no difficulties connected with the busi- 

 ness the profits would be proportionately 

 small. 



Of the various types of fruit diseases, 

 we are concerned in this discussion with 

 those caused by fungi. The fungi con- 

 stitute a large group in the plant king- 

 dom. They are plants just as surely as 

 are the grape vine or the peach tree upon 

 which some of them grow parasitically 

 and produce disease. 



Apple scab is caused by a fungus 

 growing in the outer layers of the skin 

 of the fruit, and also in the leaves. Pear 

 scab is of a similar nature, but is caused 

 by a different, though very similar. 



organisms called bacteria. The fungus 

 group is, therefore, a very large one, 

 including, indeed, probably as many dif- 

 ferent species as all the rest of the plant 

 world together; and when we speak of 

 the fungus diseases of plants we refer to 

 the diseases caused by the members of 

 this group. 



It is often supposed that rain in itself 

 is the cause of these plant diseases, or 

 that rain causes fungi. The progressive 

 fruit grower is rapidly coming to realize 

 that these are mistaken ideas. The dis- 

 eases are usually produced by fungi; but 

 the damp weather merely makes it pos- 

 sible for the fungus to grow, just as 

 moisture is required to start garden 

 seed, for the fungus plant grows from 

 little bodies called spores, which corre- 

 spond in function to the seeds of higher 

 plants, and the rain enables these spores 

 to germinate and give rise to the fungus 

 plant, just as it enables corn to sprout 

 and eventually give rise to the corn 

 plant. The spores are microscopic in 

 size and are easily blown about by the 

 wind, so in an orchard or a locality 

 where, for instance, peach blight has 

 been prevalent we may be sure that the 

 spores of the peach blight fungus are 

 well distributed through the trees; and 

 \vhen the proper' conditions of moisture 

 and temperature arise an outbreak of the 

 disease will occur unless spray material 

 is already present to kill the young 

 fungus plant as soon as the spore ger- 

 minates and before it gains entrance to 

 the peach twigs. For, once is has 

 worked its way into the inner tissues of 

 the bark it is protected, and no spray 

 applied to the outside can have any effect 

 in killing it. Thus it comes that we 

 must spray for peach blight in the fall, 

 before the rains set in. 



The first attempts at spraying were 

 made by the growers themselves. Such 

 men no doubt had very little informa- 

 tion or conception of the real nature or 

 cause of the particular diseases they were 



