The critical period of weed control in canola (Brassica napus L.) in Manitoba
Bibliographic record
Abstract
The critical period of weed control is the time during the lifecycle of a crop during which it must be kept weed-free to prevent yield loss from weed interference. The advent of soil-applied herbicides and herbicide-tolerant canola varieties in western Canada has increased interest in research to find the proper timing for weed control in canola. A critical period experiment was performed at three sites in southern Manitoba in 1998 and 1999 and consisted of two sets of treatments. In the first set of treatments the crop was kept weed-free for increasing lengths of time to find the minimum weed-free period required to maintain maximum yield. In the second set of treatments, weeds were permitted to grow in the crop for increasing lengths of time to find the maximum tolerable weed-infested period. It was found that canola must be kept weed-free until the 6th leaf stage (20-39 DAE) to consistently prevent greater than 10% yield loss. In addition, the crop required the removal of weeds by the 4th leaf stage (14-32 DAE) to prevent greater than 5% yield reduction from interference. It was also found that after the 4th leaf stage not many weeds emerged, and those which did emerge did not accumulate significant biomass to compete with the crop. Comparative growth analysis of weed-free and weed-infested plots revealed that total dry weight, crop growth rate, leaf area index of the canola crop was reduced by weed interference. The stem weight ratio was increased, while the leaf weight ratio was reduced by weed interference. The presence of weeds also decreased the amount of branching observed in the crop and increased the proportion of biomass allocated to reproductive parts. This information will be useful for making weed control recommendations to canola producers, in developing w ed-crop interference models, and for breeding more competitive canola varieties.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| 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".