86 



Iris Thrips 



Further tests for the control of iris thrips were made hv Dr. 

 L. Gordon Utter in cooperation with Dr. Floyd F. Smith of the 

 Division oi Truck Crop and Garden Insect Investigations, Bureau 

 of Entomology and Plant Quarantine, Washington, I). C. Eight 

 applications, made at weekly intervals during Mac and |nne on 

 iris plants growing in the test plots, of spray combinations of 

 derris powder (.02 per cent, rolenonc) with sulfonated castor oil 

 as a spreader, and 40 per cent, nicotine sulfate (1 — 1-50) with 

 Grasselli Spreader Sticker (1-1,000), gave 99 per cent, control of 

 the thrips. The same sprays, when applied at biweekly intervals, 

 or lour times at weekly intervals prior to the blooming oi the 

 Japanese iris, gave equally satisfactory control. Control was ob- 

 served, also, when the derris and nicotine content oi the sprays 

 was reduced, provided they were applied at weekly intervals. 



A commercial derris extract spray ( 1 per cent, rotenone) gave 

 results comparable to those found with the derris and nicotine com- 

 binations. A pvrethrum extract sprav containing 2 per cent. 

 pyrethrins was ineffective. These results confirm those obtained 

 in previous years with the same spray materials. 



During the past season tests were made, for the first time, with 

 three dusts, applied at weekly and biweekly intervals. A pv- 

 rethrum dust, containing 0.2 per cent, pyrethrins, proved entirely 

 ineffective for the control of the thrips. A large measure of con- 

 trol was obtained with a nicotine dust containing 2 per cent, nico- 

 tine, when applied at weekly intervals, although biweekly applica- 

 tions ol this dust were ineffective. The best results were obtained 

 with a derris dust (1 per cent, rotenone), somewhat more effective 

 when weekly applications were made as compared with biweekly 

 applications. Although the derris dust gives high control, it does 

 not equal the efficiency of either the derris or nicotine sprays. 



Thrips injur\- on the foliage of Japanese iris and the Yellow 

 blag was noted among the large plantings at the Botanic Garden 

 and at the State Institute of Applied Agriculture at Farmingdale, 

 N. Y. This was due to the failure to maintain an adequate 

 spraying schedule, and emphasizes the necessity of carrying out the 

 known control measures each season. 



