March Pest of the Month: Tomato spotted wilt virus (TSWV)

Tomato spotted wilt virus (TSWV) causes a range of symptoms, depending on the age of plants, weather conditions and nutritional status. Symptoms include yellow mottling of leaves, ringspots, chlorotic blotches and line/mosaic patterns. Wilting and purpling of leaves can occur and necrotic lesions can develop on stems of affected plants. Plants can be stunted, have reduced vigour, or in some cases die. Symptoms are similar to, and can be confused with, nutritional disorders, bacterial or fungal diseases, or improper management techniques.

Transmission:

TSWV is transmitted by seven thrips species, four of which are present in Australia: onion thrips (Thrips tabaci), melon thrips (Thrips palmi), tomato thrips (Frankliniella schultzei), and western flower thrips (WFT) (Frankliniella occidentalis) with WFT being the most efficient vector. Thrips remain infectious for life but do not pass the virus to their offspring through the egg. Approximately five days are required from the time the thrips are infected with the virus to when the thrips are able to transmit the virus to another plant.

It is not spread by other sap-sucking insects such as aphids, whiteflies and leafhoppers, but can be spread by the vegetative propagation of infected plants, such as cuttings and bulbs. The virus is not spread in seed or on equipment, does not survive in soil or decaying crop residues, and is not spread by handling plants.

Favoured by:

An abundance of weed species that host thrips colonies, climatic conditions favouring thrip population growth. High thrips numbers and low temperatures.

Host range:

TSWV was first described on tomato plants in Australia in 1915 and is the reference virus for the Tospovirus group of plant viruses. TSWV is a major cause of crop loss throughout Australia. It has one of the largest host ranges of any plant virus, infesting over 900 species of weeds, field crops, vegetables and ornamentals. Many hosts are in the potato (Solanaceae), aster (Asteraceae) and legume (Fabaceae) families. Crops that frequently suffer major losses from TSWV include lettuce, capsicum, tomato, potato, and ornamental crops such as aster, statice, calendula and dahlia. Other crop hosts that suffer sporadic losses include peanut, tobacco, chickpea, rhubarb, eggplant, celery and a range of ornamental species.

TSWV weed hosts that occur in Australia and have a major role in the life cycle of both the virus and the thrips vectors include sowthistle (Sonchus oleraceus), capeweed (Arctotheca calendula), thornapples (Datura spp.), cobbler’s pegs (Bidens pilosa), nightshades (Solanum spp.) and Jamaican snakeweed (Stachytarpheta jamaicensis).

For further information please refer to the Pest ID Tool at: https://www.pestid.com.au/

Note that the Pest ID tool is now available with free access to industry.

An initiative of the Nursery Levy funded National Nursery Industry Biosecurity Program (NY15004) and ‘Building the resilience and on-farm biosecurity capacity of the Australian production nursery industry’ Project (NY15002).