ONIONS IN THE CONNECTICUT VALLEY 27 



surface of the onion plants. Practically all of the run-off flowed down to the base 

 of the leaves. When the spray was applied at 175 to 200 pounds pressure it readily 

 penetrated the "chits", thus reaching the parts of the plant where thrips would 

 be principally located. (Fig. 8.) The alkali of the soap also served as an activator 

 of the nicotine. 



This nicotine-soap combination has been tested over a period of years involving 

 different weather conditions and various types of fields and degrees of infestation. 

 The results have been so uniformly successful that this spray has been used as a 

 standard by which to measure the efficiency of other insecticides. In field tests 

 in a large commercial planting at North Sunderland, one application of this 

 combination cut down the thrips population from an average of 5230 per 100 

 plants to 125, representing over 97 per cent control. In the experimental plots 

 this spray has reduced light infestations of 1200 thrips per 100 plants to 125; 

 and heavy attacks varying from 3000 to 5000 thrips per 100 plants before spray- 

 ing to 125 to 190 following the application. 



Thorough spraying to insure complete coverage of the plants usually reduced 

 the average number of thrips per plant to 1 or 2 specimens. A detailed examina- 

 tion of a field the day after the application showed the following distribution 

 of thrips. 



Percentage of No. of thrips 



plants per plant 



80 



2 15 



12 10 



6 5 



Previous to the application 94 per cent of the plants were infested, 33 per cent 

 showing an average of 30 to 50 thrips per plant. 



Of the various activators and spreading agents, Penetrol and a commercial 

 flowable pine tar soap have proved the most promising. Penetrol increased the 

 action of the nicotine but did not show as good spreading qualities as did fish oil 

 soap. The pine tar soap, however, gave excellent spreading and wetting qualities 

 and, as far as could be measured, furnished as effective a combination with 

 nicotine sulfate as fish oil soap. 



Of the other materials tested, none has proved as effective as nicotine sulfate 

 although many have shown promise. At present prices none of these, however, 

 offers any material reduction in cost over nicotine sulfate. 



The combinations of molasses with either Paris green or lead arsenate which 

 have been so effective against gladiolus thrips caused considerable burn to onion 

 plants after each application. 



Plots treated with naphthalene flakes showed comparatively slight damage 

 from thrips and this treatment appears to have promise. The material DAO, a 

 dry powder broadcasted along the rows, checked thrips somewhat but proved too 

 expensive for large areas. It also showed a tendency to burn the plants. 



Derrisol, a rotenone compound, proved somewhat slower in its initial effects 

 but showed a residual effect over an extended period so that reinfestation was 

 retarded. 



Ku-ba-tox, a rotenone compound, applied as a spray proved nearly as effective 

 as nicotine sulfate although not as rapid in its action. Like Derrisol it showed 

 considerable residual effect and consequently furnished protection over a period 

 of several days. 



