You most likely have a pest known as corn borers.
The only thing I know to do for them is mostly only preventative, and won't help once they are already in the weed.
Next time you grow in that spot, sprinkle some boric acid on the ground around your plant. Be careful not to get any ON your plant, as it can cause stress, and hermaphrodites.
The good news is, they won't much effect the quality of the buds they don't eat.
psteve Reviewed by psteve on . worms in stalks outdoor grow- have had a problem with some sort of worm or larvae eating my stalks- the pest enter the stalk at ground level and bore their way upward- have had several plants attacked in the last two weeks- they are hollow at leat 3 inches up from ground level- I have put 7dust on and around stalk base and supported stalk by wrapping paper tape around the wound- i have seen this before many years ago- I feel that since there has been NO RAIN here for 5 weeks all bugs have been attracted to my Rating: 5