Weed Management and Crop Protection (Insects, Diseases, Nematodes)
Weed Management and Crop Protection (Insects, Diseases, Nematodes)
This domain tests weed competition, critical weed-free periods, integrated pest management, disease diagnosis and nematode problems. It also checks safe and accurate pesticide calculation.
Core rules and concepts
- Weeds compete for light, water, nutrients and space. The critical weed-free period is the crop stage during which weeds must be controlled to prevent major yield loss.
- Weed management combines cultural, mechanical, biological and chemical methods. Herbicide selectivity depends on crop, weed, dose, timing and application method.
- Disease develops from a susceptible host, a virulent pathogen and a favourable environment. Insect pests have chewing or sucking mouthparts, which affect damage symptoms and pesticide choice.
- Nematodes are microscopic roundworms, not insects. Root-knot nematodes cause galls and stunting; crop rotation and resistant varieties help.
Worked example
A herbicide is recommended at 1.0 kg active ingredient per hectare. The product is a 50% wettable powder. Product required = 1.0 ÷ 0.50 = 2.0 kg/ha. For 0.4 ha, product = 2.0 × 0.4 = 0.8 kg. The reasoning is to convert active ingredient to formulated product, then scale to the field area.
Traps that cost marks
Do not apply 1.0 kg of a 50% product when 1.0 kg a.i. is required. Do not treat nematodes as insects. Do not diagnose a disease from leaf colour alone; look for lesions, spores, wilting patterns and spread. Overdosing pesticides increases cost, residue and resistance risk.