Contact allergies to a plant called Wandering Jew cause red, irritated feet. This common ground cover is often used as a quick-growing filler in garden beds and is incredibly hardy.
There are different types of Wandering Jew, including Purple Heart, Moses-in-a-Cradle, Scurvy Weed, Zebrina, Trad, Turtle Vine and Inch Plant. They are all related plants that tend to be invasive weeds. They are generally fleshy, spreading plants that love shady areas under trees and also love to grow in amongst other plants.
Some examples of what this plant looks like include:
If your dog regularly licks or chews his feet, keeping him away from Wandering Jew can be an easy way to solve the problem. For some dogs simply wiping down the feet with a wet towel after walking on the plant can help reduce irritation. Avoid the plant and those itchy feet usually improve, so long as there is no secondary infection.