Field Sprays of Bacillus subtilis and Fungicides for Control of Preharvest Fruit Diseases of Avocado in South Africa

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Abstract
In 3 consecutive years, preharvest applications of Bacillus subtilis field sprays integrated with copper oxychloride or benomyl consistently reduced severity of avocado black spot (BS), caused by Pseudocercospora purpurea at Omega, Republic of South Africa. Control was equal to that obtained with copper oxychloride or benomyl-copper oxychloride in the first and third years of spraying at Omega. In the second year, only the integrated treatment controlled BS, while copper oxychloride proved ineffective. The antagonist was applied on its own or integrated with copper oxychloride sprays at two other geographically distinct locations, Westfalia Estate and Waterval. The integrated and biological treatments at these localities were less effective than copper oxychloride sprays in controlling BS disease. Integrated control was more effective than B. subtilis sprays at Westfalia. On continuation of the biological spray program at Waterval for an additional three seasons, control was as effective as copper oxychloride in the last 2 years of spraying. Sooty blotch (SB), caused by an Akaropeltopsis sp., was reduced by the integrated treatment at Omega during the second season and at Westfalia during the first season. Although the two fungicide treatments reduced SB at Omega in the first season, copper oxychloride increased it above that of the control in the third season. Only the copper oxychloride treatment reduced SB at Waterval in the third season, while the B. subtilis treatment increased disease above that of the control in the fourth season.