David -

see this good fact sheet on seed corn maggot:

50% emergence of first generation of this pest is at about 350 degree 
days, using 40 F base.

this site shows degree day accumulation and other info.

If you click on degree days base 40 F and Burlington VT and April 2012 
you see that 350 DD happened in mid-April.

The second generation then peaks (50% emergence) with about 1100 DD and 
the third generation at 1800, so planting in between these windows is 
the least risky for susceptible crops. There are almost 700 DD 
acumulated now in your area so it is pretty safe to replant.


On 5/17/2012 12:31 PM, David Zuckerman wrote:
> I have been planting some green and yellow string beans on the early 
> side this year (warmer soil), and so far I keep finding that they are 
> being consumed by some sort of small (3/16 inch long) white maggots.  
> Anyone have ideas what this may be?  Is it likely that it came in from 
> some sort of fly?  or might it be in the seed in the first place?
> Dave Zuckerman
> Full Moon Farm