The USAF wants a death ray... against weeds

[Dr. Whom]

Well, they're actually calling it a Floral Disruptor

http://io9.com/5859047/air-force-wants-ray-guns-for-weed-prevention

[Jack]

Hey why spend a few bucks on weed killer when you could spend tens of millions developing a weed death ray.

[AndyC]

Something like that could make a lot of money if it could be made safe enough for the average homeowner to use, and somewhere in the price range of a lawnmower. I just can't see how it could differentiate between weeds and grass. If weeds absorbed a different wavelength of light, it would be easy to build a laser that would burn them selectively, but everything is green. You'd probably need some kind of a robot with a video camera, that would recognize leaf shapes and kill only what it's supposed to.

Selective chemical herbicides are relatively simple, because of biochemical differences in plants. Can't think of anything else that would kill weeds selectively, other than a person or a fairly sophisticated robot. I suppose if someone could walk around and just zap weeds with microwaves or infrared light, much as they would with a handheld weed sprayer, that would be an improvement. But I doubt you could ever kill the whole root that way. Another advantage of chemicals is that they'll be carried to every part of the plant. The best you could hope for is to keep burning weeds as they sprout, until they finally weaken and get choked out by the grass.

Or people could just let go of the need to have a pristine lawn with nothing but perfectly uniform grass. That's how I see it. Keep it healthy, keep it cut, and if there is something growing other than Kentucky bluegrass, so be it.

[Dr. Whom]

You could have some Roomba like device, with powerful laser rotating laser set at a certain height, that would instantly incinerate any plant growing over that level. Obviously, the Airforce would use them to keep their golf courses in trim. Now, if some terrorist could hijack one of these, just a week before the President would participate in a fund raising golf tournament. It is clear that only Nicolas Cage can save the day.
You'd have wonderful worm's eye shots of the robot sneaking up on people and cutting them off at the ankles.

That being said, I'd pay good money for any death ray that can zap gnats.