See Herbs for a detailed discussion of these diseases. Rust symptoms appear in early summer as light yellow or brown spots on stems, petioles, and mid-veins of leaves. Upon close examination, the spots are powdery with rust spores. This disease can result in some defoliation, especially when plants are crowded. This disease can be minimized by cleaning up plant refuse in the fall and by adequate spacing of the plants to promote good air circulation.
Infected plants are slow to grow in the spring and often have a bronze cast.
Lower leaves yellow and wilt during warm or dry weather and plants can die. The fungus is soilborne and enters through the roots and becomes systemic in the water transport system of the plant. One of the key strategies for control of Verticillium wilt is prevention. Therefore, it is important to avoid planting mint in infested soil. It is also helpful to maximize plant vigor by good cultural care and watering.