Thrips are tiny insects that eat like plant vampires, sucking out fluids from leaves to get their nutrition. Cannabis growers either currently have thrips, have dealt with them before, or will be have them soon. They're one of the most common pests we deal with in indoor gardens. They're hard to photograph, but their leaf damage is distinctive, so I've taken some photos and closeups to help raise awareness.
Note... My friends @Futuremind and @Jonyoudyer both tried to photograph their thrip damage recently, but the images can be hard to see. My attempt might not be any better, so if you have some great pictures of this topic, please share!
Silvery patches of irregular shape in random locations on the leaf. Some leaves are untouched, others increasingly affected.
Same shot, zoomed out. The spots never go away. Usually, they spread.
You may notice there are no visible insects. This baffled me, too. What's doing the damage? Is it inside the leaf tissues? Or just too small to notice on the surface?
Same shot, zoomed in. Now we can see little black dots on the leaf surface, near the silvery damage. The dots don't move. They almost look like ink.
Some leaves have dead spots that turn brown, as seen here. They're different than the silvery patches, but seem to have started about the same time. Before this, all my leaves were pristine (no spots, discolourations, deformities, etc).
In this shot, I think there's finally a thrip visible - that little light-green cylinder thing. It's not perfectly focused on that part of the leaf, so it's hard to be sure.
Same shot, zoomed in. We can see the black dots and the green cylinder better.
Same leaf, flipped over. There are those black dots again, and the silvery damage looks spread out more on this slide.
I've been removing some of the affected leaves. Here's the back of the worst one I've found so far:
And a zoom:
Another of those cylinders (thrips?), plenty of black dots, and lots of diffuse silvery damage.
Not good
Thrips aren't like traditional vampires, which often kill their hosts after draining some liquid nutrients. They like to keep the fun coming, by letting the plant live. Thrips 'merely' take sugars and nutrients from the plant's fluids, robbing efficiency, but not killing the plant. They also tend to avoid buds, focusing on fan leaves.
But they're not good. You don't want thrips.
One partial remedy is diatomaceous earth, which is powdered fossils of diatoms (tiny corals). As long as you don't breathe in large amounts, it's safe to handle and use. It just destroys insects on contact. I mix some into my soil, and then sprinkle some on top as needed. I rarely apply directly to leaves, but that can be done.
There are products available that can help control thrips, but I'm keeping these plants totally untouched by anything but air, light, water, and soil. Some people use ladybugs and other carnivorous insects. Outdoor plants generally have spiders and other predators on them, so thrips get taken care of naturally out there. Indoors, adjustments to humidity and temperature may help control these pests.
If you have more information, photos, or remedies, please comment.
Hopefully these photographs are helpful to the blockchain canna-community!
Grow in peace.
DRutter