Differential Foliar Uptake of Copper by Two Azalea Cultivars Following Copper Hydroxide Fungicide Applications

Copper hydroxide [Cu(OH)₂] (Kocide 101^®) used as a fungicide initially increased leaf copper (Cu) in ‘Hinodegiri’ and ‘Massasoit’ azaleas (Kurume type). There was a direct relationship between Cu(OH)₂ rates and leaf Cu of ‘Massasoit’ up to 4 times the commercial rate of 3.58 grams ai/liter (3.08 lb/100 gal). Leaf Cu of ‘Hinodegiri’ was initially directly related to Cu(OH)₂. At rates greater than 0.47 grams ai/liter (0.77 lb/100 gal), leaf Cu became inversely related to the rate of Cu(OH)₂. No visual phytotoxic symptoms were observed at 4 times the commercial rate. Erroneous interpretation of leaf analysis could occur if the interpreter was not aware of recent Cu(OH)₂ fungicide applications. Growers should not eliminate Cu fertilization based on Cu(OH)₂ sprayed plants.