Table 4.
Cercospora leaf spot lesion sporulation (Sp) and C. beticola isolation frequencies (Is) from soil-incorporated sugarbeet leaf samples collected from Michigan studies at post-harvest timepoints following fall-applied treatments in 2019-2020, 2020-2021, and 2021-2022.
| Trial Year | Treatment z | 0-DPH y | 45-DPH | 90-DPH | 135-DPH | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sp x,w
(%) |
Is v
(%) |
Sp (%) |
Is (%) |
Sp (%) |
Is (%) |
Sp u
(%) |
Is (%) |
||||||
| 2019-20 | Control | 78.1 | a | 38.3 | a | 17.6 | 0.0 | 1.2 | 0.0 | 0.3 | 0.0 | ||
| Plow | 60.3 | b | 43.3 | a | 0.6 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||
| Heat (1.6 kmph) | 1.1 | c | 3.3 | b | 0.7 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | |||
| Desiccant | 59.8 | b | 38.3 | a | 13.2 | 0.0 | 0.6 | 0.0 | 0.1 | 0.0 | |||
| SE | 4.5 | 10.3 | 7.4 | 0.0 | 0.5 | 0.0 | 0.1 | 0.0 | |||||
| P-value t | < 0.0001 *** | 0.0235 * | 0.2601 | NS | 0.1879 | NS | 0.158 | NS | |||||
| LSD | 13.4 | 25.9 | - | - | - | - | - | - | |||||
| 2020-21 | Control | 77.9 | a | 5.0 | 22.2 | a | 0.0 | 7.2 | a | 2.5 | 8.8 | 0.0 | |
| Plow | 66.4 | ab | 2.5 | 0.0 | b | 0.0 | 0.0 | b | 0.0 | 1.6 | 0.0 | ||
| Heat (1.6 kmph) | 0.0 | c | 0.0 | 0.0 | b | 0.0 | 0.0 | b | 0.0 | 0.0 | 0.0 | ||
| Desiccant | 50.1 | b | 7.5 | 32.2 | a | 0.0 | 7.5 | a | 0.0 | 0.9 | 0.0 | ||
| Heat (4.8 kmph) | 7.7 | c | 0.0 | 0.0 | b | 0.0 | 0.3 | b | 0.0 | 0.3 | 0.0 | ||
| SE | 5.8 | 3.3 | 6.2 | 0.0 | 1.9 | 1.1 | 2.7 | 0.0 | |||||
| P-value | < 0.0001 *** | 0.4802 | 0.0083 ** | NS | 0.0267 * | 0.4449 | 0.2113 | NS | |||||
| LSD | 19.7 | - | 19.8 | - | 6.1 | - | - | - | |||||
| 0-DPH | 35-DPH | 70-DPH | 168-DPH | ||||||||||
| 2021-22 | Control | 90.8 | a | 7.5 | 10.1 | a | 0.0 | 2.9 | a | 0.0 | 0.0 | 0.0 | |
| Heat (4.8 kmph) | 62.8 | b | 10.0 | 0.6 | b | 7.5 | 0.0 | b | 0.0 | 0.0 | 0.0 | ||
| SE | 4.3 | 4.4 | 1.3 | 3.4 | 0.2 | 0.0 | 0.0 | 0.0 | |||||
| P-value | 0.0183 * | 0.3910 | 0.0202 * | 0.2152 | 0.0022 ** | NS | NS | NS | |||||
| LSD | 19.0 | - | 6.6 | - | 0.9 | - | - | - | |||||
z Non-treated control, plow with a 3-m tandem disc set to invert soil 15 cm. immediately post-harvest, heat treatment using a propane-fueled burner (Multi-Trail Enterprises LLC) calibrated to heat foliage to 649-871°C at 1.6 kmph and 4.8 kmph prior to defoliation, and a desiccant (Sharpen 0.07 L/ha, methylated seed oil 1% v/v, ammonium sulfate 2037 g/L) applied seven days pre-harvest.
y Days post-harvest (DPH).
x Percent lesion sporulation (Sp) determined following a 3-d incubation in a moist chamber at 21-23.9°C. Lesion sporulation assessed for 1,636 to 3,895 lesions per timepoint (across all treatments) in 2019. Lesion sporulation assessed for 1,020 to 1,600 lesions per timepoint in 2020. Lesion sporulation assessed for 312 to 548 lesions per timepoint in 2021.
w Column values followed by the same letter were not significantly different based on Fisher’s Protected LSD (α = 0.05).
v Frequency of C. beticola isolation (Is) determined from morphological confirmation of C. beticola growth from 15 (2019) and 10 (2020 and 2021) representative lesions, plated on half-strength clarified V8 juice agar (Miller, 1955) amended with 0.5 g/L streptomycin and 0.25 g/L ampicillin.
u Late-winter sporulation observations may be limited by unknown lesion maturity (e.g., number of prior in-season sporulation events).
t Asterisk designations correspond to p-value thresholds<0.05 *,<0.01 **,<0.001 ***; NS indicates no significant differences were detected as data were all zeroes.