346 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 8. 



These maggot}^ onions are allowed to remain in the fields thus giving 

 the larvae an opportunit}^ to complete their development, bore into the 

 soil to pupate and issue as flies. 



The methods of harvesting seeded onions and onion-sets are different 

 ajid have an important bearing on the destruction of the onion refuse. 

 After the leaves of seeded onions ripen down and shrivel, the bulbs 

 are removed from the ground. A few days later the leaves are cut off 

 with grass shears and the tops are allowed to remain on the ground. 

 After the onions have been removed from the fields, the tops and the 

 maggoty, decayed, injured and under-sized onions can be accumu- 

 lated in piles and burned. 



In harvesting onion-sets the leaves are cut off with a lawn mower or 

 grass shears before the bulbs are removed from the ground. The tops 

 are gathered in windrows or piles and soon begin to decay. An ex- 

 amination of this decaying onion refuse showed the presence of numer- 

 ous dipterous larvae. Some of the growers labor under the impression 

 that the onion waste will not burn. We have demonstrated to a num- 

 ber of farmers that no kerosene or fuel need be consumed if this work 

 is properly carried out. The onion refuse left in w^indrows and piles 

 will not burn, for it decays and becomes soaked with rain. If, on the 

 other hand, this material is scattered in the field, the leaves lose what 

 little moisture they retained during the ripening of the onion-sets, and 

 then all the refuse can be accumulated in piles under favorable weather 

 conditions and burned. 



Too much emphasis cannot be expressed concerning the importance 

 of clean field methods in the control of the onion thrips. When the 

 onion tops become dry in the fields, the winged thrips leave the refuse 

 and spread to the neighboring vegetation, reinfesting the onions when 

 these are planted the following season. An examination of the onion 

 tops several weeks after the crop was harvested showed the presence of 

 numerous thrip larvse beneath the sheaths of the onion leaves. These 

 immature, wingless thrips would have been destroyed if the onion 

 refuse had been burned immediately after the crop was harvested. 



Many onion growers do not practice crop rotation. Some growers 

 have planted onions on the same tract of land for a period of twelve 

 successive years. Most of the onion growers in southeastern Wis- 

 consin are not in favor of crop rotation, and grow^ onions on the same 

 land year after year until the onion smut and insect pests render onion 

 growing unprofitable. 



Fall plowing is not practiced by many of the commercial onion 

 growers in southeastern Wisconsin. In some cases the crop is barely 

 harvested when about three carloads of Chicago stock yard manure to 

 an acre is scattered over the onion refuse. Fall plowing would crush 



