THE RED SPIDER ON COTTON. 11 



On the other hand, should an immune crop be found and employed, 

 it is extremely probable that the pest would reinvade the fields upon 

 the return to cotton culture with as great ease and quickness as it 

 has done during any previous season, providing the sources of infesta- 

 tion were yet at hand. Eotation, then, does not promise to contribute 

 toward the solution of the problem. 



Effects of fertilisers. — A rather elaborate series of tests with fer- 

 tilizers was instituted in an attempt to determine whether the various 

 applications assisted cotton to withstand the injurious effects of 

 infestation. Since almost no infestation appeared in these test plats 

 it was impossible to deduce positive conclusions. It was very notice- 

 able, however, that plants receiving heavy applications withstood the 

 very severe drought conditions which prevailed in South Carolina in 

 1911 conspicuously better than did plants which were not so treated. 

 It seems reasonable to suppose, therefore, that plants which have 

 been fortified by a liberal quantity of fertilizer will be assisted, upon 

 occurrence of severe infestation, in resisting its effects, 



REPRESSION. 



We have just discussed cultural measures which may help to pre- 

 vent infestation. We will now consider what may be done to combat 

 the pest when it has already gained entrance to a field. 



Pulling infested plmits. — The experiment was made in one field of 

 pulling up and destroying the first few plants which showed infesta- 

 tion. In this particular case the operation was repeated three times. 

 Care was taken to find every plant showing the characteristic red 

 spots, and these were carried from the field and burned. The result 

 was most satisfactory, and the pest was completely eradicated. 



If infestation has spread until a considerable patch has become 

 involved it might be advisable, in the case of a large field, to plow 

 up the affected portion in order to save the balance of the field. Such 

 a drastic measure, however, should only be resorted to in extreme 

 cases, and the planter concerned must be the judge of its desirability. 



Insecticides. — In all, 2G spray combinations were thoroughly tested 

 under conditions entirely natural. The field used for this purpose 

 was about 1 acre in extent, and infestation had become both ver\- gen- 

 eral and very severe. A strip through the middle of the field, crossing 

 each sprayed plat, was left unsprayed to serve as a check. Since no 

 substance was discovered which could safely be used to destroy all 

 eggs in one application, it was found necessary to spray twice with 

 an interval of six or seven days, so as to destroy the hatching larvae. 

 The killing ability of all these sprays was computed, and the per- 

 centages range from 100 to 0. Each of the following six combina- 

 tions (see Table II) was found to be very satisfactory. These are 

 presented to indicate the manner of preparation, together with the 



