Non-infectious diseases in plants are caused by factors that do not involve pathogens, meaning they are not transmissible between plants. Drought is a critical factor that can lead to non-infectious diseases as it directly impacts water availability, resulting in physiological stress on plants. This stress manifests in symptoms such as wilting, leaf drop, and reduced growth, without involving any infectious agent.
While pathogens, such as bacteria and fungi, are typically responsible for infectious diseases, insects can also cause direct injury and lead to secondary infections but are not categorized as a primary cause of non-infectious diseases themselves. Therefore, drought is a key abiotic stressor that can lead to non-infectious diseases in crops, making it the correct answer.