Efficacy and physical mode of action of fungicides against leather rot of strawberry and sensitivity of phytophthora cactorum isolates to azoxystrobin
Bibliographic record
Abstract
Efficacy and physical mode of action of azoxystrobin, pyraclostrobin, mefenoxam, and phosphorous acid (potassium phosphite) for control of strawberry leather rot, caused by Phytophthora cactorum, was evaluated on a commercial farm and under greenhouse conditions.In addition, the distribution of the sensitivity of P. cactorum isolates to azoxystrobin and pyraclostrobin was determined under in vitro conditions.In field trials, foliar sprays of azoxystrobin, pyraclostrobin, and phosphorous acid were applied weekly from bloom through harvest, and mefenoxam was applied twice as a soil drench at early plant growth and at fruit set.All fungicide treatments had significantly less leather rot than the untreated control and there were no significant differences in leather rot incidence among any fungicide treatments during both years of testing.Results from these studies indicate that azoxystrobin and pyraclostrobin provide excellent control of strawberry leather rot.To determine the physical mode of action of the previously mentioned fungicides, pre-and post-infection activity was determined under greenhouse conditions.Strawberry plants ('Honeoye') and attached fruits at the green to white stage of development were sprayed with fungicides at 2, 4 and 7 days before inoculation with a zoospore suspension or 13, 24, 36, and 48 hours after inoculation.Disease incidence was recorded at 6 days after inoculation.Azoxystrobin and pyraclostrobin provided protectant activity for up to 7 days, but only slight curative activity when applied 13 hours after iii inoculation.Phosphorous acid and mefenoxam also provided protection for up to 7 days and curative activity of at least 36 hours.No significant differences in protectant activity between tested fungicides were observed.Sensitivity distributions of P. cactorum isolates, causing crown rot and leather rot, to azoxystrobin were determined based on mycelial growth and zoospore germination.Radial growth of mycelia on lima bean agar amended with 0.001, 0.01, 0.1, 1.0, 10 and 30 μg/ml of azoxystrobin plus 100 μg/ml of salicylhydroxamic acid (SHAM) was measured after 6 days.Effects on zoospore germination were evaluated in aqueous solutions of 0.005, 0.01, 0.05, 0.1, 0.5, and 1.0 μg/ml of azoxystrobin after 4 h of incubation in 96-well microtiter plates.Effective dose (ED 50 ) for mycelial growth ranged from 0.16 to 12.52 μg/ml for leather rot isolates, and 0.1 to 15 μg/ml for crown rot isolates.The Kolmogorov-Smirnov test showed significant differences (P<0.001) between the two distributions.Estimated ED 50 values for zoospores ranged from 0.01 to 0.24 μg/ml.Sensitivities of mycelia and zoospores were not strongly correlated (r=0.31).Additional experiments with pyraclostrobin showed that mycelia and zoospores were more sensitive to pyraclostrobin than to azoxystrobin.Azoxystrobin and pyraclostrobin sensitivities were moderately but significantly correlated (r=0.60).The sensitivity distribution obtained in these studies could be used as a baseline sensitivity for monitoring fungicide resistance development in P.cactorum to these fungicides.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".