102 GEN:^JiAL CONSIDERATIONS 



diseases is sometimes possible through the finding of 

 immune varieties or through better cultural methods. 



The dodders and broom rapes are among the best- 

 known parasitic flowering plants. They are usually 

 pests of minor importance and like other weeds 

 should be eradicated by preventing the forming of 

 seed. 



Nematode worms are minute microscopic animals, 

 some of which are parasitic on plants. The worst 

 damage is done by one that causes gall-like swellings 

 on the roots of many of our cultivated plants. They 

 are very troublesome on many sandy soils in the South- 

 ern states and other warm countries, and they are 

 also a serious pest in greenhouses. Here they may 

 be destroyed by thoroughly sterilizing the soil with 

 live steam before placing it in pots or trenches. In 

 the fields nematodes can only be combated by care- 

 ful crop rotation. 



The mites are minute animals related to the spi- 

 ders. Only a comparatively few kinds of them are 

 troublesome, but they include such well-known pests 

 as the various red spiders and the rust mite of the 

 orange. Applications of sulphur are usually the most 

 effective remedy for mites. It may be applied as a 

 powder by means of the so-called powder gun, or it 

 may be suspended in water with a little flour paste 

 to make it stick and be applied as a spray. 



By far the greatest number of animal plant pests 

 belong to the insects. An immense variety of species 

 prey on our cultivated plants in countless numbers and 

 do damage of a great many different kinds. For prac- 

 tical purposes, however, they may all be considered 



