Weed killers are an effective means of removing undesirable weeds from your garden beds and lawn. Broadleaf weed killers are the most common weed killer used in these circumstances. The problem is the weed killer can't differentiate between an unwanted weed and a desirable tree or shrub. It is possible to save a sick tree from weed killer, but you must take quick action and remove as much of the weed killer as possible to prevent the loss of the tree.
Spray all the foliage of the tree to remove any residual herbicide from it. Herbicide is usually absorbed through the leaves, where it is transported down to the roots.
Soak the ground with your garden hose. This will dilute the herbicide in the soil and may even wash most of it away. This will prevent the roots from absorbing it.
Withhold fertilizing until the tree recovers. Fertilizing the tree will add additional stress to the tree and may cause more damage than good.
Prune off dead or dying branches with a pruning shears or pruning saw. This won't help the tree recover any quicker, but it will improve the appearance of the tree.