Depends on the laser(s) and the weeds in question. Deep rooted weeds require different IR/UV than broadleaf.

They actually kill them because they cook the root. That's ALSO why it has to be autonomous - it can't be done at a run.

We worked on this when I was at MTD, but I think they abandoned the project after I left.

Wouldn't a microwave be easier (power, speed, penetration depth, etc)?

Depends on the wavelength/absorption. The goal was to attack both the root and the leaf. There are more mechanical methods using steam + a spike that work very well too.

Here's a very (terribly) high level technology overview from the company we were working with: https://g-neighbor.com/gni-technology/

> The reason a plant is green is because it reflects green light and for photosynthesis a plant uses blue light. Overloading the blue frequency range disrupts the enzymes in the photosynthetic process, which cuts off the food supply to the plant and it dies. Some herbicides overload the metabolic system of the plant and makes the weed burn from the inside out. I thought that overloading the photosynthetic system would maybe do the same thing.

That’s very cool. Still working on farm space projects?

Not at this time - founded a fintech company instead.

I do miss hardware though!

> Question about this tech is, does it really kill weeds, or just defoliate them?

Question from a non-farmer: if it were cost-effective to defoliate weeds once per day, would that be good enough? I.e., I would think that totally prevents the weeds from thriving.

It depends on the weed. Overall you’re going to put pressure on it. With conventional fields like the ones pictured in this article, there’s often no ground cover. If you have a ground cover (say, clover) and you’re defoliating the weeds all the time, then you have a chance.

But some weeds, like invasive blackberries here in the Pacific Northwest, are extremely resilient and will shrug off defoliation.

Thanks for the info!

> But some weeds, like invasive blackberries here in the Pacific Northwest, are extremely resilient and will shrug off defoliation.

How does that work? I thought all plants (by definition?) need photosynthesis to stay alive in non-dormant states.

Do blackberry plants have some way of getting energy other than photosynthesis in their leaves?

Invasive European blackberries can also draw energy directly from the anger of gardeners vainly attempting to remove them.

If you keep cutting it off and have control over its whole potential growing area it will eventually die. It has some scary properties like roots that travel 20 feet easily and spring up a new independent plant and a insane growth rate once it sprouts. If it’s out of control you probably need someone to first destroy the hedge with a flamethrower

They grow these enormous and very resilient root balls under ground. I was taught that the most efficient way to kill a blackberry bush was to remove the structure above ground, locate a central stalk that leads under ground, and stick the end in kerosene or gasoline I don't remember which. That gets sucked up into the root ball and kills the plant. Never done it myself, mind.

Sure that is a one-stop permanent solution for a plant which grows back its leaves very quickly but the question is, how can the plant thrive enough to harm other crops if you defoliate it every day?

What? I'm telling an anecdote about blackberries over here. It's not commentary on the broader topic.

If the crop is near a bush, then the plant can happily grow in the bush and send roots to the crop.

I’m not a botanist but my understanding is that the root balls hold a ton of energy and the plant can just keep sending out shoots, and spread underground for fairly long distances. So, eventually that energy source will run out, but they’re invasive because of how resilient they are at finding sneaky ways to hide and appear.

> I thought all plants (by definition?) need photosynthesis to stay alive in non-dormant states.

There are parasitic plants that don't photosynthesize at all, like the Monotropoideae and Rafflesiaceae.

Among photosynthesizing plants, rhubarb can be "forced" (grown in complete darkness to reduce bitterness and get an earlier harvest), and potatoes can sprout if left in the pantry for too long.

Mechanical parts have more ways to break. All of those rocks in the field are just waiting to crunch things up.

How long will weeds live if they continuously get their foiliage removed? How about when part of the root (closest to the surface) is damaged/burned as well?

I really don't know, but I imagine that if such a robot went out into the field many or most days, there wouldn't be much of an issue. The weeds would continually get weaker.

Tractors break, sure, but steel implements have been doing a pretty good job of handling rocky soil for a very long time.

Fixing a blue steel corkscrew seems easier than debugging a laser.

I very highly doubt that a farmer is generally going to debug a laser on the spot. That requires a skill set not really needed to be a farmer, and who knows how long it'll take.

Realistically, a farmer would swap out the part.

Any actual work on the laser is more likely to be done by a trained professional, if anything to cut down on accidental burns.

Correct and also you (should) benefit from the main cash crop outcompeting the weed, eventually. Just hope it doesn't go to seed before it dies

> cash crop outcompeting the weed

I thought weed was the cash crop. /s

Had the same thought, also totally agree. Looking forward to seeing more advancements in this field. Pun intended.

Thank you for sharing, unlike people with absolutely zero experience in agriculture speculating about their half baked ideas about it.

Is there a reason you need to mow your slope?

We have an upland prairie which is a vanishing ecosystem which we are conserving. It’s fairly steep. We don’t have sheep but maybe someday we’ll get some. Until then, mowing is a way to keep it healthy and free of invasive plants.

Nice! This is similar to the problem I face with my property, on a much smaller scale. Currently I'm hand weeding the invasive plants, but even for a 100' x 10' patch it's labor intensive.

For areas I manage / garden by hand, I can not say enough good things about this trail tool:

https://www.forestry-suppliers.com/product_pages/products.ph...

I use it for everything, from digging up plants, to leveraging boulders, to actually maintaining trails.

Is mowing really any less work than pulling weeds by hand? Keep in mind that insects need habitat, too, and tall grasses are key for them. Mowing obliterates insects.

Over time we’re establishing native fescues which don’t get super tall. As well as native wildflowers. All beneficial for the insects. Once established, mowing becomes less frequent. But we’re talking about 20 acre areas, so yea it’s a lot more realistic than weeding by hand.

when i was in HS i worked on one of those crews you see mowing highways and state parks (super good money for a teen but man it was hard work). Mowing on a slope with a large tractor can be very dangerous because you can tip over. Automating away the danger to a human may be worth the effort in its own right.

They make remote control (wired) mowers specifically for this use case. I've also seen some steep-slope brush mowers from Swiss companies, but those are hand-operated. Not surprisingly, the Swiss have a lot of farm equipment designed for use on very steep slopes.

The real problem is tractors aren't designed correctly for slopes, you don't need quite automation as much as a vehicle with lower center of gravity.

Defoliating weeds instead of picking them by the roots is a great way to end up with a field of weeds.

Depends on the weed and the ground cover the weeds are competing against. For many weeds, simply mowing them in the presence of decent ground cover is completely effective, as they’re optimized to grow tall quickly - defoliate them at the right time and they’ve already spent their energy reserves.