looks like fusarium, i would say stem rot but that is almost always at the base of the stem. If it is only a month it will probably survive. but fusarium will spread to all your plants. I would put some hydrogen peroxide on it, use a q-tip just dab it on dont let the stem get to wet. Or maybe a fungicide but i wouldnt this close to flowering.
Hope that helps, also if it is fusarium it will have spores
clean whole room with bleach solution