CONNECTICUT VALLEY ONION INDUSTRY 51 



ly through the hatching of eggs inserted in the leaf tissues. This second 

 spray should be applied after all the eggs have hatched, and before the 

 first appearing larvae have matured and left the plants. Because the 

 nicotine soap spray cuts down very materially larvae hatching for a period 

 of at least two days after application, the period between the sprays may 

 safely be extended to seven or eight days. 



The Critical Period in Thrips Infestation 



The data from field observations and life history studies revealed the 

 fact that reproductive activity and consequently the rate of increase vary 

 considerably' during the season. 



Infestation is comparatively light and shows no marked increase up to 

 about mid-July. From that point there is a steadj' increase through that 

 month, with a sudden rise to the climax of the season about the first of 

 August. Beyond that point there is a gradual slowing up of reproductive 

 activity for the remainder of the season. 



The critical period as regards thrips infestation, therefore, occurs dur- 

 ing late July and early August. At this time the insects have trans- 

 ferred in large numbers from sets and are rapidly developing an infestation 

 on the fields of seed onions. This source of danger, coming as it does at 

 the time of greatest reproductive activity on the part of the insect, makes 

 this point in the season a very serious one for seed onions, and emphasizes 

 the need of the follow-up spray to check the pest as thoroughly as possible 

 and give greatest protection to the plants at this particular period. 



Conchision 



Our studies to date have shown that the chief source of thrips infesta- 

 tion of seed onions is from nearby fields of set onions, and that the great- 

 est movement of thrips takes place at the time the sets mature and are 

 pulled. This coincides with the period of greatest reproductive activity on 

 the part of the thrips, and comes in late July and early August. 



Both from the standpoint of cost and of effectiveness, dusts do not give 

 satisfactory control. This is true both of the nicotine dusts and of the 

 newer calcium cyanide dusts, althougli the latter show considerable pro- 

 mise. 



The usual type of spray nozzles proved unsatisfactory for this purpose, 

 and a nozzle delivering a flat spray has been developed. This delivers the 

 spray where it is needed, and, with a pressure of 125-150 pounds causes 

 it to penetrate the axils of the leaves where the greatest number of thrips 

 congregate. 



Nicotine sulfate, 1-1500, with Good's No. 3 Potash Fish-oil Soap added 

 at the rate of 3-4 pounds per 50 gallons of spray was found to give satis- 

 factory control. A second spray application, seven to eight days after 

 the first, has been found advisable to take care of the larvae hatched from 

 eggs laid in the tissues of the plant. 



The usual types of spray machinery are not well adapted to operate 

 in large fields of onions. The development or adapation of an outfit 

 which will conform to the particular requirements for the spraying of 

 onions presents the most immediate problem. 



