To an extent, yes. In my experience so far you can definitely tell when plants or trees are less healthy in certain areas, but by that point you’re typically able to see it by eye anyway.

I’m not really a plant person though, so anyone with more knowledge may be able to spot signs of problems sooner.

We do all the time. The NASA landst mission has been detecting in the infrared since it’s inception, and currently collexts 30 m pixels about every 15 days. Likewise the sentinel mission is collecting similar wave bands and I want to say it has more frequent procession? Maybe 10 days?

Also, most modern drones that are for doing things like crop health will have a natively 4 channel sensor gathering blue, green, red, and near infrared imagery. Sometimes they’ll even throw in multiple near infrared channels.

Back when I was flying drones for this we would run either 6 channels, or a 5 channel system with an upward looking sensor for calibration.