Weed Science and Weed Management
Weed Science and Weed Management
This domain tests weed identification, crop-weed competition, herbicide selectivity and integrated weed management. You must choose a method by weed group, crop stage and mode of action.
Core rules
- Grasses have narrow leaves with parallel veins; sedges have triangular stems and are often mistaken for grasses; broadleaf weeds have net veins and two cotyledons.
- The critical period of crop-weed competition is the early crop stage when weeds must be removed to protect yield; it varies by crop.
- Integrated weed management combines preventive, cultural, mechanical, biological and chemical methods.
- Herbicide selectivity depends on crop, dose, timing, placement and mode of action. Crop injury can follow wrong stage or drift.
- Rotate herbicide modes of action and include non-chemical methods to delay resistance.
Worked example
A transplanted rice field has barnyard grass and sedges. Reasoning: a pre-emergence herbicide such as pretilachlor is labelled for early grasses and some sedges; a post-emergence choice such as bispyribac-sodium covers grasses, sedges and some broadleaf weeds at the labelled stage. Check the label, water level and crop stage before choosing.
Traps
Spraying a post-emergence herbicide on dry foliage, ignoring sedges because they look like grasses, mixing incompatible products, and repeating one mode of action are mark-losing errors.
Key distinction
A triangular stem and no ligule point to a sedge, not a grass.