458 



Generally speaking, then, the weevils are permitted to multiply 

 unmolested until they have become sufficiently abundant to puncture 

 more squares than would be shed normally. Poisoning is then started, 

 and every effort directed to holding the infestation below this point until 

 the plants have had time to develop beyond weevil injury as many 

 bolls as they will be able to mature. Poisoning is then stopped, and 

 the weevils are allowed to resume multiplication. Remarkably large 

 increases of yield frequently result from a comparatively slight degree 

 of control for a short time during this critical period. But a satis- 

 factory effect can only be secured by starting applications at the right 

 time, and repeating them at the correct interval. 



The time of starting depends on the percentage of squares in the field 

 that are weevil-punctured. As a general rule operations should start 

 when from 15 to 20 per cent, of the squares are punctured, and be 

 repeated often enough to prevent the infestation rising above 25 per 

 cent, until the crop is set and the bolls safe from weevil attack. In 

 certain cases in large plantations it may be possible to confine the weevils 

 to the fields in which they first appear, near their hibernation quarters, 

 as they will not migrate to the adjoining cotton if their numbers are 

 kept down. In such cases it is hardly ever necessary to poison the 

 entire acreage, but it is well to start operations at a somew^hat lower 

 percentage and continue later than usual. 



A four or five day interval is best. The eftect of the poison does not 

 last long, and this interval results in the successful control of the 

 progeny of the first weevil attack if three applications in all are 

 made under average conditions, while more applications are necessary 

 if a longer interval is allowed. At the same time, if anything happens 

 to interfere with the schedule for a day or so, it can still be continued, 

 whereas with a longer interval all control is lost. 



The poison advised is calcium arsenate used as a dust, with the 

 following specifications : — Not less than 40 per cent, arsenic pentoxide ; 

 not more than 0"75 per cent, water-soluble arsenic pentoxide ; density 

 not less than 80 nor more than 100 cubic inches per pound. Without 

 the first specification the poison will not be sufficiently insecticidal ; 

 without the second, it may scorch the plants ; without the third, it 

 will not produce a suitable dust cloud. 



The danger of the poison to man and animals is slight if proper 

 precautions are taken, but the risk of inhaling the poison or of absorp- 

 tion through the skin, as well as that of swallowing it, must be borne 

 in mind. The poison is best applied at night when the humidity is 

 high and the air calm. Rain washes it off much more readily if it has 

 been applied in very dry weather. 



Dusting machinery is of three kinds, hand guns, cart dusters, and 

 power dusters. Hand guns are only suitable for very small areas, 

 or to supplement the cart duster, while as the expense of the latter is 

 hardly justified for less than 75 acres the problem of a smaller area is 

 difficult. Power dusters are not very satisfactory. 



The expense of poisoning varies in different circumstances, but 

 speaking generally it is hardly justified unless the land is fertile enough 

 for the plants to take fall advantage of the treatment ; in fact, unless 

 the land would produce at least half a bale of cotton an acre if there 

 were no weevils. 



