Efficacy of bioagents and chemicals against pear shoot blight

Outdoor experiments were carried out during spring and summer of 2003 and 2004 to test the efficacy of biological control agents and chemicals against fire blight. Pseudomonas spp. strains IPV-BO 4027C, IPV-BO G19, A506 and the biopreparations BS-F4 and Serenade (both based on Bacillus subtilis strains) were applied on growing shoots of pear scions cv. Abbe FRel 24 h before and after wound inoculation with a local Erwinia amylovora strain. During three weeks before inoculation, the growth retardant Regalis (prohexadione-Ca, 10% WG) was applied three times at 7 to 9 day intervals; during two weeks before inoculation, Bion (acibenzolar-S-methyl 50 WG), Aliette (fosetil-Al 80% WG) and the mineral powder Myco-Sin were applied twice at 7 day intervals; copper compounds were applied at different concentrations 24 h before inoculation, as were water and streptomycin sulphate (controls). In 2004, strain IPV-BO 4027C, BS-F4 and Serenade were applied a few hours after application of the copper oxychloride (Cu 0.5 g/l). In 2003, the growth retardant Regalis, the copper peptidate Peptiram 5 and BS-F4 were very active in reducing shoot blight incidence and, referred to the positive control, gave the highest relative protection (approx. 96%, 85% and 82%, respectively). In 2004, the levels of relative protection given by Regalis and by both the bioagents A506 and IPV-BO 4027C were approx. 52% and 44%, respectively. In a laboratory experiment on detached pear flowers, IPV-BO G19 and A506 provided essentially the same high level of relative protection (86%).