VEGETABLE GARDENING, OR OLERICULTURE 13 



surface of the plant materials which will discourage or prevent 

 the growth of these parasites, but when it comes to diseases which 

 act upon the interior organs of the plant, the control is a much 

 more difficult problem. As stated above, the club root of cabbage 

 is a disease which acts in this obscure way and is, therefore, very 

 difficult to control. The only means at our command, as yet, is to 

 practice a rotation so that neither cabbage nor any of its near 

 relatives shall be grown upon the soil for several years after it 

 shows an infection from this disease. 



Fungicides. The means at our command for controlling plant 

 diseases are called fungicides, because they are used for the purpose 

 of combating or controlling the growth of fungi. 



In general, applications of fungicides are made to the seed, 

 stems, or trunks of trees while in a dormant condition, and to the 

 leaves and stems of plants while in a growing condition. They are 

 usually in the form of a liquid, a dust, or a gas. For practical pur- 

 poses the liquid or dust form is most convenient and satisfactory. 

 For use in greenhouses, however, where the plants are in a con- 

 fined atmosphere, the gases are effective and satisfactory. They 

 have also been extended to field uses by means of tents or covers 

 which are temporarily placed over the plants for the purpose of 

 providing a confined atmosphere in which to expose them to the 

 action of the poisonous gas. 



The treatment for plant diseases should not be looked upon as a 

 remedy for the disease but simply as a preventive measure. There 

 are very few plant diseases for which we have absolute remedies, 

 but there are comparatively few of the more important plant 

 diseases for which we do not have a satisfactory preventive. In 

 other words, the control of plant diseases depends upon the ability 

 of the grower to detect symptoms which indicate the presence of 

 these diseases, and a knowledge of the means for holding them 

 in check before they have become sufficiently rampant to destroy 

 any considerable portion of his crop. This knowledge should now- 

 adays be looked upon as one of the most important factors in the 

 equipment of a person for success in the growing of either fruits 

 or vegetables. The special diseases to which the several crops are 

 subject and the means of controlling them will be discussed under 

 each subject considered. 



