30 MASS. EXPERIMENT STATION- BULLETIN 293 



of spray injury to fruit and foliage. Combined sprays of lead arsenate with Mulsoid 

 sulfur, with Dritoniic sulfur, and with the combination of flotation and finely-divi- 

 ded sulfurs held scab to 1 per cent injury or less and also controlled insect pests 

 verj' satisfactorily. 



The dry form of flotation sulfur proved as eftective against scab as the paste and 

 required much less time in the preparation of the spray. Kolofog again gave very 

 satisfactory control of scab. Samples of fruit sprayed with these materials 

 showed excellent quality and finish. The use of lime-sulfur as a fungicide in the 

 early sprays followed by Kolofog or flotation sulfur in the midsummer applications 

 gave a higher control of scab than that secured by a complete season's schedule of 

 either of these materials. Spray injury was also avoided, and such a program would 

 allow a material reduction in cost to the grower. 



Control of Onion Thrips (A. I. Bourne.) Warm weather and a slight defi- 

 ciency in rainfall during the early growing season offered favorable conditions for 

 the development of thrips, and the very general practice of planting sets close to 

 seed onions practically insured an early and heavy infestation on seed onions. By 

 late June the numlier of thrips on seed onions was unusually high and some evidence 

 of injury was appearing. Weather conditions during July sufficiently arrested the 

 development of the infestation so that no serious damage resulted except in some 

 fields adjoining set onions. 



The insect was somewhat slower than usual in its seasonal development and 

 reached the peak of abundance about a week later than normal. During early 

 August there was a sharp drop in numbers of thrips per plant, from an average of 

 7,S per plant on August 1 to less than 10 per plant on the 15th, and a gradual de- 

 crease until harvest. 



It was discovered that this sharp decline in abundance of tiirips was coincirlent 

 w ith the appearance and spread of a parasitic fungus attacking the insects and the 

 presence of an unusually large number of predacious insects. E.\amination of 

 onion fields throughout the Connecticut Valley region showed that the fungus was 

 generally present and that its development coincided with a rapid decrease in 

 numbers of thrips. It could not be definitely proved that the presence of large 

 numbers of predacious lady beetles was associated with the spread of this fungus. 

 Coccinellids have, however, been reported to feed on spores of certain of the lower 

 Cryptograms and their presence in abnormal numbers very generally throughout 

 onion fields in the Valley offers a possible explanation of the general distribution 

 and rapid spread of the fungus. 



Throughout the growing season observations were made of difterent strains of 

 onions, in connection with the work of the Agronomy Department on onion 

 varieties, and a marked difference in reaction of various strains to thrips attack 

 was noted. While no strain was found to be immune, certain types were scarcely 

 affected by the feeding of thrips, which caused other types to curl badly and 

 practically terminated their growth. 



Comparative tests of nicotine sulfate, Dcrrisol, and a compound of rotenone in 

 dust form indicated that nicotine sulfate sprays gave the greatest reduction in 

 number of thrips, and their action was more rapid that that of other products. 

 The derris compound was somewhat slower in its initial action than nicotine but 

 appeared to exert considerable residual effect, which retarded reinfestation except 

 that caused by migration of thrips from adjoining fields. The rotenone compound 

 proved least effective of the materials tested, probably due to the fact it was in 

 the form of dust which, with present machinery for application, does not penetrate 

 the tight axils of t he leaves as satisfactorily as a spray. 



