Evaluation of Trunk-injected Bactericides and Prohexadione-calcium for Environmentally Friendly Control of Fire Blight (Erwinia amylovora) in Apples

Trunk injection is a novel delivery method for plant protective compounds in agriculture. It could increase sustainability of fruit production through target-precise disease control. We evaluated trunk-injected antibiotics, copper chelate (CC), and prohexadione-calcium (PC) in control of fire blight on apples. After 1-2 spring injections of oxytetracycline (OX), kasugamycin (KS) and CC, we evaluated inoculated apple trees for blossom and shoot blight incidence. In a separate study, after spraying or injection of PC, we evaluated shoot blight severity after inoculation. At a high disease pressure, OX, KS and CC provided blossom blight control of 60.6, 31.7 and 15.5-17.8%, respectively. The same compounds provided control of shoot blight incidence of 60.7, 42 and 24.5-33.9%, respectively. The results indicate that shoots initially accumulate more of the injected compound than flowers, due to their higher transpiration driven by larger green tissue area. Sprayed PC reduced shoot blight severity for 25.6% and caused expected reduction of shoot length, while trunk-injected PC failed to cause any of these effects. This indicates that PC did not translocate into the canopy due to its strong binding in the xylem. With the development and use of injectable formulations, proper dosing, and optimal injection timing, delivered compounds could have more time for accumulation in the canopy and thus provide better fire blight control. Hence, trunk injection could become an effective option for fire blight control on apple trees.