Yes, you should spray your fence against the woods and pests, but take care of the surroundings. The weed chemicals and other herbicides used in the paint can be toxic to plants and animals, and can also contaminate soil and water sources. Additionally, the overspray from the sprayer can drift away from the fence and onto nearby vegetation or into waterways. Therefore, it is important to take precautions when using a paint sprayer on your fence. Make sure to use eco-friendly paint that is low in VOCs (volatile organic compounds). Wear protective clothing such as gloves, goggles, and a face mask while spraying weed vegetation to avoid any contact with the chemicals. Be mindful of wind direction when spraying for the spot treatment so that overspray does not drift away from the fence onto other areas. Do not spray weed roots, shrubs brush, and other plant types or grasses on windy days. Although the spraying process might be a time-consuming for your large pasture, you must pay attention so as not to affect different plant and pasture animal species habituating there. Finally, always clean up any spills or overspray immediately after use. Overall, spraying your fence with a paint sprayer is an effective way to protect your soil from woody plants and other weeds. However, you must take proper precautions to ensure that no harm comes to the environment in the process.