Viruses in vegetable crops in Australia

How do viruses survive?With very few exceptions, viruses cannot surviveoutside living host plants or insects.Viruses survive adverse conditions and intervalsbetween crop cycles in alternative annual andperennial weed hosts, volunteer crop plants,abandoned crops, infected seeds and vegetativeplant parts. Persistently-transmitted viruses may alsosurvive in the insect vector.How can you manage virus diseases?Plants cannot be cured once infected by a virus.Instead, disease control aims to prevent or delay theinfection of plants. destroy old crops promptly separate new crops from maturing crops and avoidoverlapping crops, especially continuous yearroundcropping.Protection of the host plant virus-resistant or virus-tolerant varieties use highly reflective mulches and oil sprays todeter insects use barrier crops and bare land to reducevector activity use insecticides strategically to protect plantsfrom insects.No single method is likely to provide perfect control.Nevertheless, by using a combination of the followingmanagement options disease control can besuccessfully implemented.Virus management can be achieved by plantingresistant varieties. The zucchini variety on the left isvirus susceptible; the variety on the right is resistant.Tomato mosaic is easily spread by contact and oncontaminated seed.Exclusion/avoidance plant virus-free seed and seedling transplants grow crops in regions where the disease seldomoccurs or during periods when the virus or its vectorare at a low level quarantine (international, state and regional).Reduction in virus inoculum levels control weeds and other virus hosts andinsect vectorsInsecticides are more effective against persistentlytransmitted viruses because insects are killed beforethey have time to acquire and transmit the virus.Vectors of non-persistent viruses will eventually bekilled after feeding on plants sprayed with systemicinsecticide. However, because these viruses can betransmitted within seconds, many plants becomeinfected before the insect dies or moves out of the crop.In fact, some insecticides agitate the insects andencourage movement and feeding of greater numbersof plants, resulting in increased transmission rates.A key aspect of virus disease management is toaccurately identify the virus causing the disease andthen implement appropriate management strategies.