-2- 



after application. Do not harvest for 7 days after treatment with Imidan, meth- 

 oxychlor, diazinon, or mixtures of them. There is no waiting period for mala- 

 thion. Do not apply Imidan more than once per cutting. 



Alfalfa and clover hay crops may serve as a breeding area for beneficial insects, 

 such as lady beetles, aphid lions, and wasp parasites, that attack many species of 

 aphids. When hay is cut, they move to other fields. Therefore, do not use insec- 

 ticides in alfalfa or clover fields unless it is necessary to save the crop and un- 

 less you use all the hay you can produce. If there is a choice, harvest early. 



We have recommended a form of integrated control, or insect pest management, for 

 alfalfa -weevil control for the past three years. We encouraged fall applications 

 of insecticides, or spring applications that would interfere the least with the 

 natural enemies of this pest. 



Two new insecticides, carbofuran (Furadan) and Supracide, control alfalfa weevils. 

 We have tested these materials extensively and recommend their use for November ap- 

 plication to control adult weevils. However, if these insecticides are used to con- 

 trol alfalfa weevil larvae in the spring, apply them only at half the minimum, la- 

 belled rate. 



To some, our reasoning may seem odd. But these conclusions were reached after 

 making extensive observations . 



First, tiny parasitic wasps deposit their eggs on alfalfa weevil larvae. The small 

 grubs that hatch live inside the weevil larvae. Parasitized alfalfa weevils live 

 for some time, but feed very little. We have seen as high as 80 percent of the 

 larvae parasitized in some fields of alfalfa; in past years, 50- to 70-percent lev- 

 els were common. These wasps have been helping to control the alfalfa weevil popula' 

 tions. 



Second, in order to maintain this parasitic wasp population some alfalfa weevils 

 must remain as a reservoir for the wasps. If we kill 95 percent or more of the 

 alfalfa weevils in a large area with insecticides over a period of time, the para- 

 sites will be eliminated by the chemicals and by the lack of any alfalfa weevil 

 larvae to feed on. Without the help of these parasites, it might be necessary to 

 spray several times. 



To maintain the wasp parasites so they will help control alfalfa weevils, a reason- 

 able but noneconomic number of the alfalfa weevils must remain for the wasps to feed 

 on. This is one step in integrated insect control or insect pest management . This 

 principle is effective for controlling field crop insects, since 75- to 85-percent 

 control will reduce the number of insects to noneconomic levels and will allow nat- 

 ural enemies to maintain their relative balance in the environment. 



Six years ago, we would probably have encouraged the use of these two chemicals at 

 high rates. With the knowledge we have now, however, it is clear that this would 

 have been unwise. At high rates, Carbofuran and Supracide are so effective on 

 alfalfa weevils that no parasites remain. Thus, they should be used only at low 

 rates in order to reduce weevil larvae to a noneconomic level while retaining the 

 weevils' natural enemies. This practice will also reduce insecticide costs with- 

 out yield loss. The insecticides we have recommended in the past do just this. 



