What is Melon Necrotic Spot Virus (MNSV)?MNSV is a plant virus that affects melon, watermelon and cucumber plants. It causes brown (necrotic) spots on leaves and stems and can also impact the quality of fruit and lead to reductions in yield.

SymptomsRockmelon

On rock melons the leaves may curl, wilt and have brown and light coloured spots (Figure 1). On the outside of the fruit, indentations and brown spots can appear (Figure 2), whilst the flesh may become dark, hollow and rotten (Figures 4 & 5).

Watermelon

In watermelons, small, transparent, yellow spots appear on the youngest leaves. As the plant matures, the spots turn brown and enlarge and the leaves curl, wilt and may die.

MNSV infected watermelon fruit often displays yellow or brown spots on the skins (Figure 3). The fruit may also be misshapen; with the flesh and rind becoming discoloured hollow or watery (Figure 6). In some cases, the fruit may decay while attached to the plant.

Symptoms can vary in severity and are often worse in cooler climates. MSVN can easily be confused with bacterial blotch of watermelon.

SpreadMNSV is widespread in horticultural production areas around the world.

It can be spread via infected seed, soil, water, irrigation water, mechanical damage (grafting and plant-to-plant contact) and the microscopic, fungus-like, root inhabiting Olpidium bornovanus (O. bornovanus).

The virus can survive in soil for several years. Once the plant is infected, MNSV persists for the life of the plant.

Figure 1. Leaf spots caused by MNSV (Photo Len Tesoriero, NSW DPI)

Figure 2. MNSV symptoms on the surface of rockmelon

Melon Necrotic Spot Virus(MNSV)

Melon Necrotic Spot Virus (MNSV)

Figure 3. MNSV symptoms on the skin of watermelon (Photo Len Tesoriero, NSW DPI)

Figure 4. Mild symptoms of MNSV on rockmelon

Figure 5. Severe (left) and very mild (right) symptoms of MNSV on rockmelons

Figure 6. Necrotic spots and deformation in watermelon caused by MNSV (Photo Len Tesoriero, NSW DPI)

Management OptionsTo prevent MNSV or reduce its spread in your crop:

Ensure staff and visitors adhere to on farm biosecurity and hygiene practices

Use resistant varieties or graft onto resistant root stock

Source seed, seedlings and graft material that is free of virus and from a reliable supplier

Heat treat seeds for 144 hours at 70°C, which may kill the virus but still allow germination

Test a proportion of seed and seedlings for MNSV

Disinfect tools, propagating material and equipment with sodium hypochlorite (1% solution of a 12% concentrate of pool chlorine)

Clean farm machinery, remove dirt and plant material with a high pressure hose, if possible spray machinery with 1% chlorine. Note chlorine will rust equipment and needs to be washed off after application

Remove, feral, volunteer or wild cucurbit plants, which could otherwise act as reservoirs for the virus

Remove infected plants and fruit from the crop

Rotate crops out of cucurbits for three or more years to avoid carry-over of both the virus and O. bornovanus

Consider soil fumigation

Plan to work on younger plants before the older ones (the latter are more likely to be infected)

Control insect pests, which may spread the virus

Keep records of crop and paddock histories to enable pest and disease impacts to be monitored and traced

© The State of Victoria Department of Economic Development, Jobs, Transport and Resources 2015

This work is licensed under a Creative Commons Attribution 3.0 Australia licence. You are free to re-use the work under that licence, on the condition that you credit the State of Victoria as author. The licence does not apply to any images, photographs or branding, including the Victorian Coat of Arms, the Victorian Government logo and the Department of Economic Development, Jobs, Transport & Resources logo. To view a copy of this licence, visit http://creativecommons.org/licenses/by/3.0/au/deed.enISBN XXXXXXXXXXXXXXX

AccessibilityIf you would like to receive this publication in an alternative format, please telephone the DEDJTR Customer Service Centre on 136186, email customer.service@ecodev.vic.gov.au or via the National Relay Service on 133 677 www.relayservice.com.au. This document is also available on the internet at www.agriculture.vic.gov.au

DisclaimerThis publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

Melon Necrotic Spot Virus (MNSV)

Ensure the virus is not carried to areas free of the disease by runoff from rain or irrigation water.

Reporting and further informationPlease report any suspect detections of MNSV to the Exotic Plant Pest Hotline on 1800 084 881 (toll-free) or email plant.protection@ecodev.vic.gov.au with photographs and a contact phone number.

For further information phone 136 186 for your local Plant Biosecurity Officer or email. plant.protection@ecodev.vic.gov.au .

To arrange for virus testing, phone Crop Health Services on (03) 9032 7515.

© The State of Victoria Department of Economic Development, Jobs, Transport and Resources 2015

This work is licensed under a Creative Commons Attribution 3.0 Australia licence. You are free to re-use the work under that licence, on the condition that you credit the State of Victoria as author. The licence does not apply to any images, photographs or branding, including the Victorian Coat of Arms, the Victorian Government logo and the Department of Economic Development, Jobs, Transport & Resources logo. To view a copy of this licence, visit http://creativecommons.org/licenses/by/3.0/au/deed.enISBN XXXXXXXXXXXXXXX

AccessibilityIf you would like to receive this publication in an alternative format, please telephone the DEDJTR Customer Service Centre on 136186, email customer.service@ecodev.vic.gov.au or via the National Relay Service on 133 677 www.relayservice.com.au. This document is also available on the internet at www.agriculture.vic.gov.au

DisclaimerThis publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.