Field crops are infested by a large number of weeds, insect pests and diseases. If weeds and pests are not controlled at the appropriate time then they can damage the crops so much that most of the crop is lost. When the crop is in the field, it needs protection against:

• Weeds e.g.– Xanthium, Parthenium (weeds are considered to be harmful as they compete for food, space and light with the desired crop. They reduce crop production taking up the nutrients meant for the crops.
• Insect Pests - 

Insect pests attack the plants in three ways: 

(i) they cut the root, stem and leaf, 

(ii) they suck the cell sap from various parts of the plant, and 

(iii) they bore into stem and fruits. They thus affect the health of the crop and reduce yields.

• Pathogens- Microbes like bacteria, fungi and viruses cause diseases. Spores of these pathogens may be transmitted through soil, water and air.

To control these :

Herbicides, Pesticides, fungicides should be used.

Weed control methods also include mechanical removal. Preventive methods such as proper seed bed preparation, timely sowing of crops, intercropping and crop rotation also help in weed control. Some other preventive measures against pests are the use of resistant varieties, and summer ploughing, in which fields are ploughed deep in summers to destroy weeds and pests.

Prevention for preventing the growth of weeds,

• Proper seed bed preparation,
• timely growing of crops,
• intercropping, crop rotation,
• use of resistant varieties and
• summer ploughing is done.