Virus diseases of capsicums

Virus diseases of capsicums in Western Australia

BY DR CRAIG WEBSTER DEVELOPMENT OFFICER, DPIRD

Several viruses can affect capsicum production in all regions of Western Australia. It can be difficult to tell the difference between the three viruses by the symptoms alone. Most importantly, the best way to control of each viruses differs so accurate identification is important.

The three main viruses detected in capsicum include Tomato spotted wilt virus (TSWV) (see Figure 1), Cucumber mosaic virus (CMV) (see Figure 2) and Pepper mild mottle virus (PMMoV) (see Figure 3). A fourth disease that is occasionally seen is a phytoplasma (see Figure 4), which is a type of bacteria. When infected by each virus, the symptoms in capsicum are very similar, and can often not be distinguished by eye alone. The symptoms of a plant being infected differ with the variety of capsicum but they usually cause the leaves to become pale in colour (chlorotic) and can be reduced in size or distorted in shape. These will first appear on the newest leaves and often cause the plant to stop growing or grow only very slowly. The size of the fruit can be affected and ripen unevenly. Necrosis in spots or rings may also be observed on the fruit. Once a plant is infected, all the remaining fruit will continue to show the same symptoms, and nothing can be done once the plant has become infected. Each virus is spread in a different way so knowing which virus is causing the disease will help focus on the best approach to control the disease. 1. TSWV is spread by thrips and they need to be born and feed for a long time on an infected plant to spread the virus. This means the disease moves relatively slowly. It is not spread by seed but it is spread by thrips moving from volunteers, weeds and adjacent infected crops with thrips can cause virus to be continually spread into the crop.

3 TSWV is spread by thrips and they need to be born and feed for a long time on an infected plant to spread the virus.

Each virus can also be found in weeds, volunteers or adjacent crops.

a

b

c

FIGURE 1. TOMATO SPOTTED WILT VIRUS a. Young leaves of a capsicum showing yellowing and necrosis caused by TSWV; b. Capsicum fruit with necrosis caused by TSWV; c. Capsicum fruit with uneven ripening caused by TSWV.

a

FIGURE 2. CUCUMBER MOSAIC VIRUS c. Distorted fruit with necrotic spots caused by CMV. 2. CMV is spread by several types of aphids including green peach aphid and melon aphid. Aphids only need to feed for several seconds to spread the virus and it can be spread by aphids, which don’t live on capsicum but just fly through the crop-like melon aphids. This virus can also spread by seed, so it is important to use seeds from a reputable source. in that it doesn’t need an insect to spread; instead it is very stable and can survive for long periods of time in plant material and spread by contact of infected plants with healthy plants. It can also be seed borne and move longer distances through contaminated tools or machinery. FIGURE 3. PEPPER MILD MOTTLE VIRUS

b

c

a. Pale yellow and distorted leaves of a capsicum infected with CMV; b. Distorted shape and uneven ripening caused by CMV;

3. The last virus, PMMoV, is different Blistering of capsicum fruit infected with PMMoV. FIGURE 4. PHYTOPLASMA Pale yellow leaves and very bushy appearance of a capsicum infected with a phytoplasma.

Each virus can also be found in weeds, volunteers or adjacent crops. These plants often do not show obvious signs of being infected but insects feeding on them can spread the virus.

Control options

Methods of control are different for each virus but resistant varieties can be used to control each disease. 1. Rogue out infected/sick plants immediately. When plants are seen with symptoms it is important to remove them and discard them away from production areas to stop them allowing disease to spread to more plants. Wearing gloves or washing your hands after handling diseased plants will help stop spread.

2. Remove weeds near to crops, which This growth is pale yellow in colour but can be infected and host insects. doesn’t have the blistering or necrosis

These may not be obviously sick so sometimes seen when capsicums are controlling all is the best option. infected by a virus. They are spread by 3. Controlling insect populations can help but is not enough on its leaf hoppers, which have to feed for a long time to spread the disease. own. CMV can be spread by aphids Usually only a small number of plants before insecticides can kill them, become infected and it does not and thrips have several life stages, spread enough to cause large losses. which don’t feed on Removing them and discarding plants and hide on the them away from production ground so aren’t killed. areas will prevent the spread

Monitoring crops, including with yellow sticky traps, so sprays Controlling insect populations can help. to other plants. Weeds such as nightshade can also be a source of phytoplasmas. are only used when insects are present. 4. Best Practice Option: Use MORE INFORMATION all three listed above to help This project has been funded control virus diseases in your crops. by Hort Innovation using vegetable industry Phytoplasmas levies and contributions from the Australian Government, with co-investment from the The phytoplasmas are very different in Queensland Department of Agriculture appearance and cause plants to grow and Fisheries; Victorian Department of very bushy, which leads to the name Witches’ Broom Disease. The fruit and flowers will not develop properly. Economic Development, Jobs, Transport and Resources; the Northern Territory Department of Primary Industry and Resources; Western Australia’s Department of Primary Industries and Regional Development; and the University of Tasmania. It is supported by a second smaller project led by the New South Wales Department of Primary Industries and similarly-funded by Hort Innovation using vegetable industry levies and contributions from the Australian Government and the NSW Department of Primary Industries. • Contact Craig Webster on 0499 997 563 or email craig.webster@dpird.wa.gov.au

• https://ausveg.com.au/infoveg/infovegsearch/management-of-thrips-andtomato-spotted-wilt-virus/ • www.agric.wa.gov.au/capsicumsand-chillies/cucumber-mosaic-viruscapsicum • www.agric.wa.gov.au/viruses-virus/ pepper-mild-mottle-virus-pmmov

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