Using vinegar as a household cleaner or plant preservative can be a great way to kill unwanted pests. But it's also important to remember not to spray directly on your plants. Spray on your leaves, but not your bark or wood. Vinegar should only be applied to the plant's surface where the pest will feed or crawl. For example, it doesn't kill aphids, but it will have the desired effect if you're using it to combat plant bugs.