The experiment was conducted in 2021 with ‘Gold Challenger’, a powdery mildew susceptible pumpkin variety. The main program tested consisted of 1 preventive application of a biopesticide (Sil-Matrix, Howler, or Theia), then 3 applications of targeted fungicides (Proline, Vivando, Proline) started when threshold reached and alternated with 3 applications of the biopesticide (two alternation orders tested). The last application was the biopesticide. The IPM action threshold recommended to growers for initiating fungicide applications is 1 out of 50 old leaves with symptoms. In addition to an untreated control, 3 other treatments were included for comparison to assess efficacy of the biopesticide + conventional fungicide programs: just the 3 applications of targeted fungicides (same timing as for the 2 treatment orders tested), and grower standard fungicide program consisting of weekly applications of targeted, conventional fungicides.
Treatment and amount/A (application week):
Sil-Matrix (1, 3, 5, 7); Proline 5.7 fl oz (2, 6); Vivando 15.4 fl oz (4)
Howler 5 lb (1, 3, 5, 7); Proline 5.7 fl oz (2, 6); Vivando 15.4 fl oz (4)
Theia 3 lb (1, 3, 5, 7); Proline 5.7 fl oz (2, 6); Vivando 15.4 fl oz (4)
Proline 5.7 fl oz (2, 6); Vivando 15.4 fl oz (4)
Theia 3 lb (1, 4, 6, 7); Proline 5.7 fl oz (2, 5); Vivando 15.4 fl oz (3)
Proline 5.7 fl oz (2, 5); Vivando 15.4 fl oz (3)
Proline 5.7 fl oz (2, 4, 6); Vivando 15.4 fl oz (3, 5, 7)
Powdery mildew was first observed in this experiment on 26 July in one of the 36 plots on only one of the 720 leaves examined (0.14%). A biopesticide was applied one day later for the four treatments with biopesticides. This application was considered to be preventive because it was before symptoms would be found through routine scouting. On 2 August symptoms were found in 31 of the 36 plots on 76 of 540 leaves examined (14%). The fifth application scheduled for 24 August was delayed by two days because of extensive rainfall (2.6 in.) with Hurricane Henri on 22-23 August. The last application was applied early due to rain forecast with remnants of Hurricane Ida starting late on 1 September (3.3 in. total). It is possible efficacy of treatments was affected by the impact of these storms on application timing, product residues, and/or disease development. Severity was low throughout August especially on upper leaf surfaces, which may be partly due to some contact activity for powdery mildew of the pesticides applied for Phytophthora blight and insect pests. On 30 August, one day before the sixth application, severity in the untreated control plots averaged 3% on upper leaf surfaces and 52% on lower surfaces. Severity increased substantially over the next week reaching 51 and 66%, respectively, on 7 September.
All four programs with biopesticides and conventional fungicides effectively suppressed powdery mildew on upper and lower leaf surfaces providing 98 to 100% and 84 to 90% control, respectively, based on AUDPC values. However, these treatments were not significantly better than the two parallel treatments with just the three applications of the conventional fungicides made on the same dates, documenting the excellent efficacy of Proline and Vivando. The grower standard conventional program with these fungicides applied weekly provided slightly but significantly better control than all other treatments based on AUDPC values for severity on lower leaf surfaces (99%). On 20 Sep, 2 weeks after the last application, the grower standard was the only treatment still providing control on upper leaf surfaces (92%) and one of two providing control on lower surfaces (80%), documenting residual activity of Vivando. All treatments had less defoliation than the control through 20 Sep; only the grower standard had significantly less through 12 Oct, five weeks after the last application. All treatments had significantly better fruit quality on 27 Sep than the control; only the grower standard did on 12 Oct.
The following experiment overviews taken on 5 August, 2 days after 2nd fungicide application and IPM action threshold reached.
The following photos taken on 10 September, 3 days after the 7th (last) treatment.
