CHAPTER XIV 



HARMFUL AGENTS IN SOILS AFFECTING FERTILITY 



'^Absence of harmful agents in soils'' is the one negative 

 factor named with the positive factors determining soil fertility. 

 Water, air, good tilth, helpful soil organisms, and available nitrogen, 

 phosphorus, potassium and sufficient lime are all necessary to 

 create within the soil the power for producing large crops; but 

 the presence of any harmful agents may nullify the effect of ail 

 these positive factors. In considering a case of low yield or infer- 

 tility, it is important, therefore, not only to examine into the posi- 

 tive factors determining fertility, but that investigation be extended 

 to a consideration of harmful agents within the soil as well. Some 

 of these harmful agents are discussed in the following paragraphs — 

 not fully but sufficiently to illustrate the importance of this nega- 

 tive factor. 



Worms and Insects May Destroy Crops- — ^Frequently a farmer 

 is at a loss to know why some particular crop should ''stand still" 

 or fail when all conditions seem favorable. The white grub, wire 

 worm, the corn rootworm, the maggot, and eel worms or nema- 

 todes are common "worms'' that Kve in the soil and which often 

 injure crops by feeding on their roots. 



White Grub. — In some jBelds, as in southwestern Wisconsin, 

 northeastern Iowa and northwestern Illinois, the white grub often 

 causes complete loss of the corn crop. It may also cause much 

 injury to timothy, potatoes, lawns, strawberries and beans. These 

 grubs are the larvae, or the young, of the May beetles or "June 

 bugs." They feed on the roots of various plants and on potato 

 tubers. Early October plowing will destroy many of these grubs. 



The wire worm is the young of the cHck beetle, and is generally 

 harmful to corn on old sod. These worms, like the white grub, 

 live in the soil two years before they change into the beetle form. 

 This explains why the wire worm often causes more injury the 

 second year after an old sod is broken than the first year. 



Corn Rootworm. — Corn growers in the Southern states, particu- 

 larly, suffer much damage from the corn rootworm or "bud worm." 

 In some seasons it is difficult to get a stand of corn in the lowlands 

 on account of these worms which are but the young of the twelve- 



255 



