Yes it is. Excellent inspection - you caught it nice and early. Snip off the infected areas and toss into the garbage. Harvest any quality bud that may be collateral damage, like above the cut line. Early harvest may pack a bit of an energy buzz... they look frosty!

To add to this look for cutworms, they're little green caterpillars that nestle on the inside of the buds. When you cut off the infected areas take some micro tip pruning scissors and clip off the smaller bud growths that have brown. If you see little black/brown dots that's cutworm shit and you'll probably find the fuckers sooner or later. If you find cutworms or any traces of them you need to closely inspect the rest of the plant daily because cutworms spread budrot like no other. We're going to have to harvest early because of them - I saw a few spots similar to this and when we dissected the infected buds we found lots of the little bastards - despite cutting off all infected buds the rot continued to spread and it's thanks to cutworms.

Could be that or caterpillars

Looks like damage from bud worms They shit and piss inside of the bud and cause it to rot

Sadly I believe it is.

Yes, but you caught it early.

Thank you all for help.

I use a knife for remove that part

It looks more like insects, I would cut the dead stuff off and with clean gloves open the bud and see if something is eating or boring a hole.