Physiological leaf curl is most often seen as the seasons change from spring to summer but can also be caused by heavy cultivation that has damaged the roots, improper fertilization and poor watering practices. Though the plants typically self-correct with time and as conditions improve, prolonged periods of time with improper care can affect yield. To avoid leaf curl, it is important to properly harden off tomato seedlings. Use a layer of mulch around tomato plants to regulate soil moisture and temperature. Apply fertilizer as needed based on soil testing. You may also choose determinate (bush-type) varieties of tomatoes which are less susceptible to leaf curl than the indeterminate (vining) varieties. (Cynthia Domenghini)