BOLL WEEVIL CONTROL BY USE OF POISON. 27 



afforded between the poisoned and nnpoisoned plats. Throughout 

 this work the gains have varied from nothing to over 1,000 pounds 

 of seed cotton per acre. 



The most that can be expected of poisoning is the elimination of 

 weevil injury. Soil fertility is very important and really becomes the 

 determining factor in the amount of gain which can be secured from 

 the poisoning. One interesting feature of the work which has been 

 conducted so far is the large number of tests on fields which had a 

 fairly low degree of weevil infestation and which have shown abso- 

 lutely no gain from the operation. In many cases comparable plats 

 have been selected and started with an infestation of 10 or 15 per cent, 

 one plat being poisoned and the other left unpoisoned as a check. In 

 such cases, the infestation of the check plat, instead of increasing as 

 would normally be the case, has been held in check by some climatic 

 condition so that there was only a gradual increase to a maximum of 

 from 35 to 50 per cent of the squares punctured at the end of the sea- 

 son. Usually, under such conditions, no gain in yield is shown in spite 

 of the fact that infestation of the poisoned plat was practically 

 wiped out. In other words, the degree of infestation in the check 

 plat was not sufficient to overtake the normal shed of squares and 

 thus there was no reduction in crop yield. This, of course, illustrates 

 the needlessness of poisoning unless the weevils are sufficiently 

 abundant to injure the crop. 



There are many fields where weevil infestation becomes so complete 

 by the middle or latter part of the summer that it would seem ad- 

 visable to start poisoning, but the plants in these fields may have 

 reached the limit of their production on that soil, thus being unable 

 to take advantage of any protection from weevil attack. This is 

 particularly true of many of the sandy soils upon which the plant 

 produces a very quick crop of cotton and then matures and stops 

 fruiting at an early date. This point is further complicated by vari- 

 ations in the habits of the different cottons. For example, certain 

 varieties of cotton have what is ordinarily termed a "determinate " 

 growth. They make their crop early and then stop fruiting alto- 

 gether. Consequently, any poisoning under such conditions, regard- 

 less of the degree of weevil control secured, is a useless expense unless 

 undertaken for the protection of the young bolls already set on the 

 plants. 



In still other cases there are soils of such low potential productivity 

 that even if the entire crop were saved from destruction by the 

 weevil its value would still not justify the expense of poisoning. 



To summarize the results of the experiments which can be consid- 

 ered of real value in this connection, it may be said that the actual 

 gains in seed cotton per acre have ranged from about 200 to 1,000 



