THE RED SPIDER ON COTTON. 61 



We feel that we can say that among the cotton strains the old 

 Peterkin group is probabl};- most susceptible. 



An experunent was conducted m testmg the value of thickly broad- 

 casting cotton at the boundary of a field as a trap crop for red spiders. 

 The cotton was sowed between the cotton field proper and a large, 

 heavily infested border of violets. The broadcasted cotton became 

 infested and was plowed in before there was danger of a second 

 migration to the crop proper. As a result the field remained free 

 from mites. Although we do not recommend the broadcasting 

 measures as an unportant method of prevention, still the success of 

 this experiment would indicate strongly that the cotton trap crop is 

 practicable as an auxiliary expedient to be used in controlling this 

 pest. 



It has been surmised that wide spacing of the stalks, thus prevent- 

 ing the interlacing of branches, would prevent the spread of the red 

 spider through a field. Experiments at Batesburg have shown that 

 the red spider disperses through a cotton field commonly both by 

 means of the ground and the interlacmg branches. While this shows 

 the futihty of the wide spacing as a complete preventive, it seems 

 reasonable to suppose that the movement of the red spider wiU be 

 somewhat impeded; in fact, we can corroborate this supposition to 

 some extent in that infestation was observed to spread very slowly 

 in certain checked fields. 



Since the movements of nearly aU insects, when crawlmg over the 

 ground, are retarded by pulverized soil, it appeared that by maintain- 

 ing a dust mulch in exposed cotton fields the progress of the migrating 

 mites would be checked. In the case of the ''check" cotton fields, it 

 was possible to maintain continually a thoroughly pulverized soil sur- 

 face. It was observed that the infestation in these fields progressed 

 very slowly and failed to become at all threatenmg. In fields culti- 

 vated in checks it is easy to see that leaf-to-leaf dispersion will be 

 greatly restricted and, at the same time, ground travel somewhat re- 

 tarded. Thus, by combining these two measures — spacing the plants 

 and maintaining a surface mulch — much good will doubtless result. 

 In the cultural experiments conducted, both the ordinary sweep 

 and the spring-tooth adjustable cultivator have been employed. 

 The latter implement creates a much better surface mulch than does 

 the old-type sweep. 



Early planting permits the plants to develop a maximum growth 

 of foliage and fruit by the time mites appear in large numbers, which 

 is important, inasmuch as plants of considerable size are rarely kiUed 

 by the pest, nor are well-advanced bolls conunonly sIkhI from rod- 

 spider infestation. Early planted cotton ages and soon toughens, 

 making it untcmpting to the red spider at a time when later cotton 

 offers ideal feeding conditions. Late cotton is almost always objec- 



