Chapter 17: Plant Protection and Post-Harvest Technology

Pests, diseases, and weeds

Crops lose yield to insects and mites, diseases (caused by fungi, bacteria, viruses, and nematodes), weeds, rodents and birds. A disease needs three things (the disease triangle): a susceptible host, a pathogen, and a favourable environment; removing any one prevents it. Correct diagnosis comes first: take a sample to an extension officer or laboratory.

Integrated pest management (IPM)

IPM combines methods to keep pests below economic damage while minimizing harm to people and the environment:

Cultural control: crop rotation, resistant varieties, clean seed, field sanitation, proper spacing, and timely planting.

Physical and mechanical control: hand weeding, traps, barriers, nets, and heat or flooding.

Biological control: natural enemies (predators, parasitoids), microbial agents (Bacillus thuringiensis, Trichoderma), and pheromone traps.

Chemical control: pesticides used only when needed, in the right dose, with the right safety.

Pesticide safety

Pesticides include insecticides, fungicides, herbicides, and rodenticides, and they are hazardous. Rules: read the label; wear PPE (gloves, mask or respirator, long clothing, boots, eye protection); mix and apply as directed; do not spray against the wind or in the heat of the day; observe the pre-harvest interval before harvesting; store in locked, labelled containers away from food; never reuse empty containers; wash thoroughly after use; and dispose of waste according to rules. Resistance develops when the same chemical is used repeatedly, so rotate modes of action. Residues on food are controlled by national and international limits.

Weed management

Weeds compete for light, water, and nutrients. Control with land preparation, mulching, hand and mechanical weeding, cover crops, water management (in paddy), and herbicides where necessary. Prevent weed seed spread through clean seed and equipment.

Post-harvest losses

A large share of fruits and vegetables is lost between harvest and consumption because of bruising, heat, moisture loss, rot, and poor handling. Reducing post-harvest loss is often cheaper than increasing production. Steps: harvest at the right maturity (colour, firmness, days from flowering); harvest in the cool of the day with clean tools; handle gently; sort and grade; pre-cool; pack in suitable containers; protect from sun; transport promptly; and keep the cool chain where needed.

Drying and storage

Grain and pulses are stored dry. The moisture content (wet basis) is . Paddy is stored safely at about 14% moisture or lower. Example: 100 kg of paddy at 20% MC contains 80 kg of dry matter. At 14% MC it weighs kg, so about 7.0 kg of water must be removed. Drying methods: sun drying (on clean floors), mechanical dryers, and solar dryers. Storage needs clean, dry, ventilated, rodent-proof stores; control of insects (for example weevils) with hygiene, hermetic bags, and, if necessary, approved fumigants; and protection against mould and aflatoxin, which grow when grain is damp.

Value addition

Processing raises the value of produce: drying, milling, juice, jam, pickles, pulp, flour, spice powders, chips, and packaged products. Success needs quality, hygiene, packaging, labelling, and a market.

Common mistakes

Spraying without PPE or ignoring the pre-harvest interval.

Storing grain that is still damp.

Harvesting too early or too late and handling roughly.

Practice questions

Find the weight of 500 kg of grain at 22% MC after drying to 14% MC. [≈453 kg]

List four elements of integrated pest management.

Explain why drying prevents aflatoxin formation in stored grain.