CHAPTER X.
INSECTS AND DISEASES.
The wise gardener uses the spray to prevent disease and the attacks of insects, instead of waiting to fight them after they have arrived. But if they attack your garden you must fight them intelligently and without ceasing.
The destruction by insects, is, generally speaking, easily seen, but diseases of plants are not so plain, and have only been carefully studied even by experts during the past fifty years. At present, all we know is how to fight insects and diseases by different substances, put on or about the plants. As fresh discoveries are constantly being made, we will some day get rid of all these difficulties. It is always better to get the advice of an expert when insects or diseases become troublesome.
Anything in the soil or surroundings of your garden which interferes with the plants during the growing season, weakens the crop and lays it open to attacks. Plants are like children. If they are badly fed, poorly clothed, ill housed or neglected, they are far more likely to become diseased than if they are kept in a good state. So look after your drainage, the character of the soil and the sort of cultivation you give it. All these help the crop to withstand disease. On the big western wheat fields, it has been found that drainage has a most marked effect upon blights, wilts and rust. Undrained wheat sections suffer greatly from rust.
Just how diseases are caught by one plant or section of a garden from another, is not fully known, but we know that insects often carry infection from one to another, as in fruit trees to which bees go for honey. The bee, coming from an infected tree to a perfectly healthy tree, may bring with it the germs of the disease or the eggs of the pest. Many scientific men now hold that plant diseases are transmitted by germs, which are carried not by insects only but also by the wind and the water in the soil.
The wrong use of fertilizers or barnyard manure may often induce disease, simply because the unbalanced food supply causes irregularity in growth, which weakens the plant’s resisting power. What is called a “balanced ration,” is of the utmost importance to plants. It is not enough that the soil contain an abundance of some of the elements of plant food, but that it contain all of them in nice proportion, so that the plant can draw all it needs, and not be overfed in some ways and underfed in others. That is why we add humus, why we fertilize, why we cultivate, and why we take note of our plants while growing. Only in this way can we supply their wants.
Weeds spread diseases and we should be ashamed of them. Not only are they usually favorable to the growth of insects, scales and blights, but some kinds of weeds actually breed these parasites. Moreover, they rob the soil of nourishment during the dry, hot spells, thus bringing about various kinds of rots and mildews. And now it is supposed that they give out a kind of poison, or excrement, which renders the soil unfit for crops. All this shows the necessity of clean cultivation if we would help our crops to resist both insects and diseases.