If it is a type of scale insect there are any number of home remedies people use for houseplants that would work on cannabis plants and be safe. Here's one.
Homemade Control of Plant Scale
Many people prefer to use homemade control of plant scale. Insecticidal soap is a safe and effective alternative to conventional insecticides. You can bleach free dishwashing liquid (1 1/2 teaspoons per one quart of water) in place of commercial insecticide soaps. Homemade control of plant scale can also be achieved with oil spray. Mix two tablespoons of cooking oil and two tablespoons of baby shampoo in one gallon of water. (Neem oil could of course also be used.) This can also be mixed with one cup of alcohol to help penetrate the insect’s shell.
If a fungus is also present, add two tablespoons of baking soda. Test the spray on a small area of the plant, beforehand and wait 2-3 days, to check for damage. Do not spray plants in the sun or on hairy or waxy-leaved plants. Shake well before and during application. Spray every 5-7 days as needed, covering both sides of the foliage. Wash the leaves individually with the soap/oil mixture and rinse well.
Other ways are:
The waxy layer that is on scales protects them from insects and other pesticides. In order to get rid of them Use a horticultural oil to kill the adult populations throughout the year. If you can combine the oil with the insecticide, such as, Orthene, Sevin, or malathion it can almost wipe out the scale population along with the sooty mold it causes!Neem soil works very well too!
You can do a few things.. more if your not nearing the end of harvest..
1) take a pack of chewing tobacco, mix it with a gallon of water, let it brew for a day.. spray the plants down as needed.. if your a cigarette smoker no worries spray em down till harvest.. watch for mold..
2) take some safers natural soap, mix it with some water so its a soapy slippery mixture, soak em down.. the idea is to suffocate the bugs in the soapy bubbles..