The four biocides, Bio Arc 6% WP, Bio Zeid 2.5% powder, Blight Stop and Plant Guard liquid in addition to the fungicide
Galben Copper 69.8% WP were tested against the fungus Alternaria porri (Ellis) Cifferi under laboratory, greenhouse and field conditions. The tested biocides were classified into three groups according to their efficiency against mycelial growth of A. porri. The first group contains Plant Guard liquid and Bio Zeid 2.5% powder, which gave low inhibitory activity against A. porri growth. The second group contains Blight Stop only with moderate reduction in mycelial growth. The high inhibition in mycelial growth was found in the treatment of Bio Arc 6% WP which lies in the third group.Galben Copper 69.8% WP gave inhibition in the mycelial growth reached to 84.42%. Under greenhouse conditions, Galben Copper
69.8% WP gave the highest efficiency against garlic purple blotch followed by Bio Arc and Blight Stop. Data indicated that
Trichoderma album was more effective than T. harzianum in controlling garlic purple blotch. Mostly, Bacillus megaterium was more efficient than the fungus Trichoderma species in controlling garlic purple blotch. In the open field, the experiments were conducted for two successive growing seasons, 2016/2017 and 2017/2018. Galben Copper 69.8% WP was more effective than the other tested biocides. Bio Arc 6% WP was superior among biocides against purple blotch disease on garlic, while Plant Guard liquid was the inferior one. The resulted efficiency of treatments against purple
blotch disease on garlic in the field was compatible with those obtained under greenhouse conditions. There is a positive relationship between the efficiency against purple blotch and the obtained garlic yield of all treatments.