Plant Protection and Pest Management
Pests, diseases and weeds
A pest is any organism damaging crops or stored produce. Classify pests as insects and mites, weeds, pathogens (fungi, bacteria, viruses), nematodes and vertebrates. Learn to read damage: chewing insects remove leaf tissue; piercing-sucking insects (aphids, whitefly) cause distortion and yellowing and can transmit viruses. Know complete metamorphosis (egg–larva–pupa–adult, as in moths) and incomplete metamorphosis (egg–nymph–adult, as in grasshoppers).
The disease triangle - susceptible host, virulent pathogen and favourable environment - explains why disease appears; remove one leg and the disease fails. This underpins cultural control: resistant varieties, clean seed, correct spacing, drainage, rotation and sanitation.
Integrated pest management (IPM) combines cultural, physical, biological, genetic and chemical methods, spraying only above the economic threshold. Understand pesticide terms: selective versus non-selective, contact versus systemic, pre- and post-emergence herbicides, formulations (EC, WP, granules), LD50 as a toxicity measure, pre-harvest interval, mode of action, and resistance arising from repeated use of one chemical group. Safety: correct dose, calibrated sprayer, protective clothing, safe storage and disposal, never spraying into wind.
Worked example - sprayer calibration: if the label requires 200 L per hectare and the knapsack holds 15 L, then 200 ÷ 15 = 13.3 tanks per hectare. If one tank covers 750 m², output = 15 L ÷ 750 m² × 10,000 = 200 L/ha, confirming the setting.