Sodium hypochlorite and calcium hypochlorite are both forms of bleach that are used in sanitising and disinfecting applications. They can be used to kill weeds and should be handled with caution.
Sodium hypochlorite (NaOCl) is commonly called bleach or 13 per cent active chlorine. It comes in liquid form. To eliminate invasive noxious weeds such as thistle, cut the budding flower head off and spray sodium hypochlorite directly onto the cut stalk. Apply this treatment on sunny days so rain does not wash off the chemical before it can take effect.
Calcium hypochlorite (CaCl2O2) has many common names, including lime chloride, BK powder, hypochlorous acid and calcium salt. It is available as a white powder and is used to disinfect water, including drinking water and swimming pools. Since it kills algae and fungus, it could be used with extreme caution to kill weeds. Mix the powder with water and spray on weed foliage.
Both chemicals are toxic if ingested and can cause skin and eye irritation or injury. Hypochlorites are caustic and can be explosive. Do not mix sodium hypochlorite with ammonia or acids, and do not inhale calcium hypochlorite dust or handle with bare hands. Keep children, pets and other animals away from treated areas.