Appropriateness of lasers for alien plant control

Question

In my science fiction setting, it is the tail end of the twenty-first century, and most scientific fields and engineering disciplines have advanced substantially. There has been further developments in laser technology, fueled by improvements in materials science and batteries (There are commercially available batteries with comparable energy density to gasoline), and laser weapons were widely deployed among current militaries for anti-drone and missile applications. However, the known issues with laser weapons (cooling issues and energy) have prevented anti personnel deployment.

However, humanity has recently come under attack. A directed panspermia mission from an unknown nearby civilization has implanted a new and very hostile ecosystem into the Sol System, similar to The War Against the Chtorr.

While I'm not going to go in depth into the details of the ecology here, part of the invasion includes a wide variety of toxic and carnivorous plants that have a habit of cropping up in inhabited areas and ensnaring and digesting people. I wondered whether this is a rare situation where lasers could be better than the alternative.

What the military needs is a multipurpose, man-portable tool that can be used by soldiers to perform weeding duty and safely destroy toxic plant growths at a distance, as well as cut out soldiers trapped in carnivorous plants without getting close and being eaten themselves.

I think that this situation could mitigate many of the disadvantage of handheld laser anything. The fact that the targets, plants, would be stationary, means that a lower power laser could be used for cutting and weeding. This would mean less cooling and fewer batteries necessary to run the laser. My understanding is phased-array optics could give precise control over the beam. But is my understanding of the science correct? Would lasers be the best choice for this situation?

EDIT It seems that per usual in science fiction, this is not a justifiable application for laser weaponry. The multiple issues JBH mentioned plus the much lower cost of a pole saw means the laser backpack will be removed from the setting. From a narrative perspective, this might be a good thing. Having manual control over the cutting implement getting your friend out of a plant makes the story more exciting then if the targeting is done via computer.

Answer 1

This is already happening here. Have a look at the Mosquito Laser. If the targeting mechanism becomes cheap enough, then this can deny territory such as inside a house to mosquitoes. This is not the same as attacking them in open country, but it does make a lot of sense in the home, where you do not want the cumulative risks of using pesticides.

The argument against lasers is one of scale. You can use them to zap mosquitoes. You could make a bigger version to protect you against lions, but it would not be the best solution. The general principle of using some sort of vision model to recognise the target, and then organising some mechanical attack still holds. But the defence might be drones with guns or nets rather than using a laser. For your plants, you would probably want something mechanical that could take out the roots, and burn any seeds.

Answer 2

Lasers would be inefficient

There are many ways your could make lasers more viable. There's automatic machines that can drive over fields, recognise weeds and spray only those with toxins. I think I remember an UV variant as well, which is not dissimilar to a laser.

You could have small drones fly around with lasers, heat up key features of the plant to set them on fire or burn away important parts.

However, this might not he an effective method for many plants. You likely want to eradicate the whole plant. Plants live for a great part underground with their roots. This not only gathers some nutrition and water, it is also a storage of energy. Many plants will die if you mess with the above ground portion, but there's many that will live. The Japanese Knotweed comes to mind, where I read that shredding the whole plant, root and stem, can cause many of the individual shredded pieces to start growing again.

That means if you burn just the top portion, the bottom portion could happily live on, spread and regrow. Worse, as they consume live matter they might not rely on something above ground at all. It could just grow a shallow basin in the ground, fill the air with intoxicating aerosols, have people fall into the basin and down, to be consumed over time by the stuff in the basin. It could be mostly covered by the liquid it makes, making you able to attack precious little of the plant.

What would be most effective? Natural enemies. Things that can effectively eat it. Things that are parasites and leech the plants dry. You can bioengineer one or a few (micro) organisms that suppress or eradicate the plants effectively. They will naturally spread, making it easier to get all in an area. Once in a while you spread them around yourself to make sure an area is safe. This way nothing can grow in far enough to be a threat.

There is evolution or further bioengineering of the plants? You have an easier time breaking their new bio defences than they have creating them. If evolution of your own organisms doesn't do it for you.