Khalil I. Al-Mughrabi1
Partner: Jolly Farmer Product Inc.
Abstract: Trials were conducted to evaluate the efficacy of compost tea (CT), food nutrients (FD), and combinations of compost tea and food applied as foliar sprays against Phytophthora infestans, the causal organism of potato late blight disease, in comparison to the fungicide Manzate® (MZ). The study consisted of seven treatments: (1) uninoculated untreated control (CN); (2) inoculated untreated control (CI); (3) inoculated plants treated with MZ; (4) inoculated plants treated with FD; (5) inoculated plants treated with compost tea (CT); (6) plants treated with a combination of TF+FD 2 hours after inoculation (TF2h); and (7) plants treated with a combination of TF+FD 2 days after inoculation (TF2d). Two potato varieties, Green Mountain and Russet Burbank, were used in these studies. Treatments were applied at various dates, rates and frequencies. Percent of late blight incidence and severity were assessed three times. Green Mountain manifested higher percentage of disease severity as compared to Russet Burbank. Disease incidence for combined treatments remained the same and disease severity increased over time. MZ treatment was the best in inhibiting late blight compared to other treatments. Compared to the CN treatment, the lowest disease incidence was for MZ treatment (8.33%). None of the treatments other than CN and MZ were significantly different from the control in their effect on late blight incidence. In case of disease severity, a similar trend to that of disease incidence was observed. The lowest late blight severity was for CN treatment (0%), followed by MZ treatment (0.4%). MZ and CN treatments were significantly different from all other treatments with respect to late blight severity. Application of Manzate proved to be better than compost tea in suppressing late blight disease. A second study, comprising of 13 different treatments, was also conducted to evaluate the efficacy of combinations of compost tea and food nutrients against late blight. Treatment with a combination of compost tea and Super Flow (CT+SF) gave 36.1% reduction in late blight severity as compared to the untreated control. Treatment with a combination of compost tea and potassium bicarbonate reduced disease severity by 16.7%. Compared to the untreated control, none of the other treatments differed significantly with regards to their effect on late blight severity.
1Potato Development Centre, New Brunswick Department of Agriculture and Aquaculture, 39 Barker Lane, Wicklow, New Brunswick, Canada E7L 3S4