Fire blight, caused by <i>Erwinia amylovora</i>, is one of the major bacterial disease of apple and pear, causing enormous economic losses worldwide. Several control measures against <i>E. amylovora</i> have been reported till date, however, none of them have proved to be effective significantly against the pathogen. In this study, mechanisms of the copper-based control agents (CBCAs): copper oxychloride (COCHL), copper oxide (COX), copper hydroxide (CHY), copper sulfate basic (CSB), and tribasic copper sulfate (TCS) and their disease severity reduction efficacy against <i>E. amylovora</i> were analyzed. Bis-1,3-dibutylbarbituric acid trimethine oxonol, carboxyl fluorescein diacetate succinimidyl ester, and 5-cyano-2,3-ditolyl tetrazolium chloride staining were used to check the damage of membrane potential, cytoplasmic pH<sub>in</sub>, and respiration of CBCAs-treated <i>E. amylovora</i>, respectively. High disturbance in the membrane potential of <i>E. amylovora</i> was found under COX and COCHL treatments. Similarly, higher significant changes in the inner cytoplasmic pH<sub>in</sub> were observed under COX, COCHL, and TCS treatment. CHY and COCHL-treated <i>E. amylovora</i> showed a significant reduction in respiration. <i>In vitro</i> bioassay results revealed that CHY, CSB, and TCS at 2,000 ppm reduced the severity of fire blight both in pre- and post-treatment of CBCAs in immature apple fruits and seedlings. Overall, the most effective CBCAs against <i>E. amylovora</i> could be CHY at 2,000 ppm as its showed inhibition mechanisms and disease severity reduction.