I would like to know what is proper way of disposing weed treated with herbicides? Is it safe to use tree killed by herbicide as firewood?
Anything you used in your garden you can now purchase is now safe to burn. I wouldn't compost it ... that's the threat that inadequate commercial composting operations bring to your garden, the introduction of herbicide contamination that then gets applied to your plants.
It depends on the chemicals used. Glyphosate killed weeds are more than safe in your compost. Glyphosate chemistry changes so quickly you don't even have to worry about leaching. That is what I was taught and there are many refuting articles that haven't convinced me yet.
The compost pile is the best and most responsible way to dispose of weed debris and trace pesticides. Once the process of decomposition takes place that compost has a chemistry entirely different than the original ingredients. Dumping at dump sites only passes all your chemistry off in 'compost' people buy thinking it is organic and healthy. If you don't want it in your compost for your plants and vegetables then we need to call in the hazmat teams, grins.
If somehow you used chemistry that won't allow decomposition...I would dispose of it in the radioactive and industrial chemical place in our transfer station services.
Need to know what it is you used; Neem, a little glyphosate? No problem at all. Caseron? Now we are talking problems. Long half life, horribly leach-ate, very bad pre emergence herbicide. This is why buying compost made from 'clean green' and landscape debris dumped by homeowners and landscape maintenance companies and then decomposed and resold is often so full of pesticide/herbicides that a petunia can't be grown.
I doubt you've used anything toxic to worry about. Do list what you've used, please, Agent Orange, DDT?? Rotenone? List everything included soaps. Do you still have the little info book that comes with the products?
If in any doubt take all material to the local dump and let them sort if out, but if your only using shop bought chemicals then there shouldn't be a problem if left to rot down, or if burnt. As for wood again the only part contaminated would be the outer most layer not the main material in the core, and I wouldn't use it again indoors for safety or for cooking with either. if you do burn it then stay well away from the smoke for safety or dispose at the local tip- they will know what to do with it if you don't. If your thinking tonnes of material then an independent contractor should be used who is licenced to take that type of contaminated material away legally. If your using glyphosate, it should break down on contact with soil and also wash out a little with rain too- depends on how much did you use? neat or dissolved?