Lets look at this in a different manner, what if you weren't going to use say bacterialogical, but insted maybe gas or kerosene. crash into michigan statium on a sunday afternoon and ?? There are many ways to use an ag plane as a weapon and it doesn't have to be used only when the wind isn't blowing or too humid or too hot.
One of the articles about the four journalists being killed brought up the Japanese terrorists putting sarin gas into a Tokyo subway system.
The author wrote that to test the gas, the terrorists drove down a small street 'spraying' the gas behind them.
Can Sarin Gas be sprayed from a crop duster?