An infection caused by plant viruses, producing deformed, yellowed, or mottled foliage and stunted growth with no cure once established.
In plain terms
Viruses are the worst plant diseases. There's no cure; infected plants must usually be removed. Viruses spread via insects (aphids, whiteflies), contaminated tools, and sometimes seeds. Prevention is the only option: control aphids, use virus-resistant varieties, sterilize tools. Infected plants are typically weak and unproductive; removal prevents spread to other plants.
Why this matters
Viral diseases are incurable and spread easily. Understanding prevention and recognizing symptoms prevents epidemic spread.