There are two broad methods to control plant diseases as stated below:

1. Weed control: Weeds are unwanted plants growing in the cultivated fields that compete with the crops for food, space, and light. Hence, they deprive the crops of nutrients leading to the growth of unhealthy plants.

There are four methods to control weeds:

(i) Mechanical method: These include uprooting, weeding, hand hoeing, interculture, ploughing, burning, and flooding.

(ii) Cultural method: These include proper bed preparation, timely sowing of crops, intercropping, and crop rotation.

(iii) Chemical method: These include spraying of chemicals called weedicides or herbicides that kill the weeds.

(iv) Biological method: These include the use of insects and other microorganisms that feed and destroy the specific weeds.

2. Insect pest control: Many of the insects are pests of crop plants. They attack the parts and products of plants and lowers the yield of crops. Insect can attack the plant in three ways-that is, by chewing the crop plants, by sucking the cell sap from various parts of plants, and by damaging the crop internally.

There are three methods to control insect pests:

(i) Mixing insecticides with the soil helps in controlling root-cutting type insects.

Example: Chloropyrifos.

(ii) Dusting or spraying the insecticides helps in getting rid of stem- and leaf-cutting and boring type of insects.

Example: Malathion.

(iii) Spraying systemic insecticides (that enters the plant tissues via roots or shoots) helps in controlling sap-sucking insects such as aphids.

Example: Dimethoate and metasystox.