Viral diseases

• Viral diseases – an overview
• Viruses, crops affected, and damage caused
• Management
• Source of information and related tools

This page provides an overview of viral diseases in vegetable crops. The related tools listed at the end of the page provided detailed information about the identification, symptoms, and management of viral diseases. It is important to have a plant diagnostics laboratory confirm the pathogen causing any diseases in a crop so that the disease can be appropriately managed.

Viruses cause major damage to many Australian vegetable crops. They are immobile and are usually transmitted from one plant to another by a living organism called a vector or carrier. The most significant vectors of plant viruses include aphids, whiteflies, thrips, and leafhoppers, which have piercing sucking mouthparts that allow the insects to access and feed on the contents of the plant cells. Viruses can also be transmitted by other insects, mites, nematodes, fungi, infected pollen or vegetative propagating material, contact between plants, and infected or contaminated seeds.

The virus is transmitted by sap-sucking insects in two ways: persistent transmission and non-persistent transmission, which relates to the time taken by an insect to acquire and transmit the virus.

Virus	Specific vector	Host plants	Primary damage
Tomato Spotted Wilt Virus (TSWV)	WFT, tomato thrips, and onion thrips.	Capsicum; tomato; eggplant; lettuce; celery; peas;potatoes; sweet basil.	Ringspots, line patterns, mottling, and chlorotic blotches on leaves.
Iris Yellow Spotted Virus (IYSV)	Only by onion thrips.	Onions; garlic; leeks; spring onions; herbs.	Eye-like or diamond-shaped spots on leaves and seed-stalk in onions; extensive chlorosis or yellowing.
Capsicum Chlorosis Virus (CaCV)	Melon thrips and tomato thrips.	Capsicum; tomato; chillies.	In capsicum: yellowing on leaf margins and between veins of young leaves; In tomato: chlorotic spots and blotches on leaves that become mottled.

Virus	Specific vector	Host plants	Primary damage
Begamoviruses - Tomato yellow leaf curl virus (TYLCV)	Silverleaf whitefly	French beans; cucurbits; capsicum; several weed species.	Affected plants stunted' interveinal chlorosis develops; leaves bent downwards and stiffened; fruit quality reduced.
Beet pseudoyellows virus (BPYV)	Greenhouse whitefly	Lettuce; beet; endive; cucumber; common weeds.	Chlorosis or yellowing between veins in older cucumber leaves, with symptoms spreading to younger leaves; severely affected plants stunted.
Tomato torrado virus (ToTV)	Both Greenhouse and Silverleaf whitefly, with the former responsible for spread in Australia.	Capsicum; eggplant; weeds including Amaranthus, Atriplex, Chenopodium, and Malva.	Early symptoms include necrotic or dead spots; affected areas may fall out, leaving shot holes in the leaflets; necrosis and mottling also extends to the remainder of the leaves.

Tobamoviruses: Not transmitted by insects, are highly infectious and very stable in the environment. Can survive on implements, contaminated clothing, crop, root debris, and also on seed.	Virus	Host plants	Primary damage
	Tobacco mosaic virus	Crop plants and weeds: eggplant; tomato; bok choy; choy sum; bitter melon; Chinese mustard; long melon; snake bean; Chinese cabbage.	Mosaic; mottling; leaf distortion; and sometimes leaf death and defoliation.
	Tomato mosaic virus	Tomato; capsicum.
	Pepper mild mottle virus	Capsicum, including chillies.	A mild mosaic or mottle.

Often the intricate relationship between the virus, host plants, and the vector or the carrier, creates problems in developing effective management systems. However, by using a combination of management options, or an Integrated Pest Management (IPM) approach, disease control can be successfully implemented.

• Exclusion or avoidance – quarantine; grow crops in regions where the virus seldom occurs or during periods when the virus or its vector are at a low activity level; and use virus-free seedling transplants.
• Reduction in virus spreading sources – control weeds and other virus hosts and insect vectors; destroy old crops promptly; separate new crops from maturing crops; and avoid overlapping crops, particularly year-round cropping.
• Protection of the host plant – plant virus-resistant varieties; use barrier crops to reduce insect vector activity in the crop; use insecticides to protect plants; and use highly reflective mulches and oil sprays to deter insects.

A key aspect of virus disease management is to accurately identify the virus causing the disease and then implement appropriate management strategies. Monitor and trap insect pests which transmit viruses.

• Plants susceptible to tomato spotted wilt virus (TSWV)
• Management of thrips and tomato spotted wilt virus
• Tobamoviruses – tobacco mosaic virus, tomato mosaic virus, and pepper mild mottle virus: Integrated virus disease management
• Aphid-transmitted viruses in vegetable crops: Integrated virus disease management
• Viruses in vegetable crops in Australia: Integrated virus disease management
• Plant viruses spread by thrips: Integrated virus disease management
• Whitefly-transmitted viruses in vegetable crops
• Western flower thrips and tomato spotted wilt virus
• Guide to common diseases and disorders of bunching vegetables in Australia
• Revegetation by design guidebook