Definitely insect damage, mites are my guess... I would suggest you use NPK Mighty Spider Mite Wash. I had bad mites in an indoor grow. Nothing I tried seemed to help. Tried different soaps and Neem combinations... They just seemed to stick around. I used this ONCE on two plants and within 48 hours every single spider mite was dead. I waited about a week and sprayed lightly again... and for the rest of the grow (another four weeks) until harvest, never saw another mite.
Best solution for spider mites I have ever found is Mighty. By far the most effective and safe solution for spider mite infestations I have ever used.
If you can get Mighty Wash it’s a great one to add to your program, as well as Permethrin (careful with pets) and Abamectin.
Hey piggybacking top reply to OPs comment
While it's true that that bud is clearly not very saveable as flower, you could extract the THC. If there are good buds left on the plant that are not already covered in webbing, here's what you can do:
You'll want to get a bug bomb that works for spider mites, and you'll want to get
https://www.amazon.com/NPK-Industries-Mighty-1-Gallon/dp/B07671JD6V/ref=sr_1_4?keywords=mighty+wash&qid=1566418942&s=gateway&sr=8-4
and a cheap pressure sprayer from home depot. The spray of mighty wash will clean most of the webbing off the buds, kill most of the mites. You want to do this quick, start up a bug bomb, turn off the lights, and get out and shut the tent.
It wont kill every single one but it will set back their numbers so low that you can get through the rest of your grow.
Now, the question of what type of bug bomb is appropriate to use for smokeable flower etc etc is seperate.
Maybe ladybugs would be good, but i wouldnt try to bother with any kind of vacuum.
It may be the best path to consider water curing or extracting the whole plant to be safe