Applying herbicides to gardens and lawns comes with a variety of potential hazards gardeners must be aware of. One of the most common threats of applying herbicides is to the surrounding trees, which can be damaged or killed. Although not all herbicides are dangerous for trees, gardeners must take precautions to ensure that their nearby vegetation is safe from harm.
Herbicides come in two varieties: selective and nonselective. Selective herbicides are able to remove weed infestations without harming the plants gardeners are cultivating. Nonselective herbicides do not make this distinction and will kill all plant matter that it comes in contact with or is absorbed by the roots. Signs of herbicide damage on trees include yellow, spotted leaves and spiraling patterns on the bark tissue of the trunk.
It is important to rule out other possible threats to the tree before deciding whether or not it has been damaged through herbicide injury. Many of the symptoms developed from this threat are similar to poor soil conditions, drought stress and disease. Gardeners should look for similar damage in nearby vegetation or specifically designed soil tests that can determine the presence of herbicides.
Herbicide damage will present itself typically within the first few days of application, although extreme damage may take a few weeks to appear. The only known exception is when the soil has been treated with a sterilant. In this unique case, it can take years for the symptoms to fully present themselves.
Trees that have not been injured by fungal disease or insect threats can better resist damage from herbicidal damage. To ensure this, provide the tree with additional fertilization, plenty of water and sunlight. Recovery from this damage depends entirely on the extent of chemicals applied, the type used and the time of year the tree was sprayed.
Prevention is the easiest way to avoid herbicidal damage. Use herbicides that are specifically designed to harm weeds and not nearby vegetation and avoid spraying anywhere near the tree's canopy. Never spray herbicides during precipitation or windy weather, as it will more easily spread chemical vapors.