Consider the following:<br/>1. Birds<br/>2. Dust blowing<br/>3. Rain<br/>4. Wind blowing<br/><br/>Which of the above spread plant diseases?

1. Birds — Birds can act as mechanical carriers of plant pathogens and also spread seeds of parasitic plants/weeds. Correct.

2. Dust blowing — Dust particles can carry fungal spores, bacteria and other inoculum from infected fields to healthy plants. Correct.

3. Rain — Rain splash is a major agent for spreading many plant diseases, especially fungal and bacterial infections. Correct.

4. Wind blowing — Wind widely disperses spores, pollen-borne pathogens and other disease-causing agents over short and long distances. Correct.

Hence, all four can spread plant diseases.