April, '14] FERNALD AND BOURNE: ONION INSECTS 197 



exclusively for onion growing, the fields covering from six to ten acres 

 and separated only by narrow strips of grass used as roads. Kerosene 

 emulsion 1 to 5; whale oil soap, and tobacco whale oil soap were used 

 in the tests. To bring the cost of treatment, particularly labor, within 

 reasonable limits, a pump was placed on a hand cultivator and geared 

 to the cultivator wheels while the discharge pipe was arranged to 

 distribute to five nozzles placed opposite five rows, so that this number 

 would receive treatment at once. It was soon found that with any 

 gearing available a rapid walk was necessary to develop sufficient 

 pressure, and that the speed required to obtain this pressure meant 

 that a thorough spraying was impossible before any given plant had 

 been left far behind. Possibly this mechanical defect might have been 

 remedied, but hand tests of the material showed that it was practically 

 impossible to reach enough of the thrips to make it worth while. The 

 onion leaf is quite repellent to these materials, and as soon as the thrips 

 has worked long enough for the leaf to bend downward somewhat the 

 insect can be reached only by an underspray, and large numbers will 

 be missed in any case. 



As hand work at leisure was out of the question because of its cost, 

 and as even with an effective machine an underspray cannot long be 

 used before the growth of the plants would prevent its use by causing 

 injury during the process, these treatments were given up. Instead, 

 the careful destruction of all refuse after the crop was gathered, and 

 the burning over of all strips of grass through and around the fields 

 was advised. This practice has now been carried out for several 

 seasons with good results. The growers of one large area have coop- 

 erated in this, and now find few thrips, and those which do appear, 

 are most noticeable near the boundaries of the land which they control, 

 apparently coming in from places where burning over has not been 

 done in early spring. The adult does not appear to fly far of its own 

 volition, and unless carried by strong winds it would seem probable 

 that onion fields can, to at least a considerable extent, be kept clear 

 of the thrips by running fire over all places near, in which they hiber- 

 nate. 



Another pest which has much injured the onion crop in Massachu- 

 setts is the onion maggot, the loss in some cases running as high as a 

 hundred dollars per acre. In order to discover if possible some way 

 in which the ravages of this insect may be prevented, experiments 

 have been conducted for several years at the Experiment Station. 



A preliminary study of the literature of the subject -showed that 

 numerous recommendations as to methods of control had already 

 been made. A more critical examination, however, suggested the 

 belief that some of these at least were more theoretical than practical, 



