Copper Toxicity in Tomato Plants

Copper (Cu)‐containing fungicides and bactericides are used extensively for disease control on staked tomatoes ( Lycopersicon esculentum Mill.) in North Florida. Since Cu moves very little in most soils, the potential for Cu buildup in tomato fields is substantial over a period of continuous tomato culture. The purpose of this research was to determine the Cu levels of soil and plant tissue, which are associated with reduced growth, and the influence of soil acidity on Cu uptake and growth response of tomatoes to soil Cu. Tomato plants were grown for approximately 6 wk in a greenhouse in pots of soil (Typic Paleudult) containing two levels of calcitic lime and six levels of copper hydroxide in a factorial treatment arrangement. Lime levels were 0 and 3.5 g kg −1 in Experiment 1 and 0 and 7.0 g kg −1 in Experiment 2. Copper levels were 0, 175, 350, 700, 1400, and 2800 mg kg −1 in Experiment 1 and 0, 44, 88, 175, 350, and 700 mg kg −1 in Experiment 2. Tissue‐Cu concentration was not a conclusive indicator of Cu toxicity in tomatoes. Soil pH and Mehlich 1‐extractable Cu provided sufficient information for determining if soil‐Cu levels were reducing plant growth. Near‐maximum Cu concentration in tomato tissue occurred at soil‐Cu levels above 104 mg kg −1 . Plant growth was reduced with soil‐Cu levels above 150 mg kg −1 and soil pH below 6.5. However, soil‐Cu levels above 330 mg kg −1 were necessary to reduce plant growth with soil pH above 6.5.