IS A FREEZE A GOOD INSECTICIDE? 

When the temperature drops to 25^o, do the aphids and alfalfa weevils die? Can we forget about them for a few weeks? Probably not. When alfalfa stems and leaves are frosted enough to turn brown and dry in 3 or 4 days, some of the insects may run out of food. When there is a lot of green stem and leaf material left in the field, continue scouting and treating insects as though the freeze did not occur.  

Freezes in early March do little to affect overall insect populations. Some insects may be killed but other control measures must be used.