I went to Delaware's annual Pesticide conference today. Some brought up the topic of a product called the Weed Seeker. It's driven by a computer($1500) and a spray head(s)($1000 each) that has an infared lens that can tell the difference between weed and non-weed plants. It then will automaticly spray the weeds. You mount it to your mower or atv and just drive over the area. You can even spray at night, because infared doesn't need sunlight.