Papaya
Ring Spot Virus
PRSV
Virus
In a Nutshell
- Dark green rings on fruits.
- Yellow mosaic pattern on leaves.
- Water-soaked spots and streaks on trunks and stems.
Papaya
Symptoms
Symptoms may vary slightly depending on plant age at time of infection, the plant vigor and the strength of the virus. Dark-green blister-like structures first appear on leaves. Later, these develop into a mottled pattern in different shades of green. At later stages of the disease, leaves have a shoestring appearance and show a mosaic pattern with yellow and brown necrotic spots. Leaf size is considerably reduced, resulting in stunted growth and smaller canopy. Water-soaked yellow spots and oily streaks also appear on stems and petioles. Infected fruits show many dark green, often sunken, oily ring spots of reduced size and deformed shape. If infection takes place at an early age, fruits are not marketable.
Recommendations
Organic Control
Spray white oil emulsions at concentrations of 1% to hinder the uptake and transmission of the virus by aphids. Mixtures of beneficial microorganisms including some types of bacteria, yeasts, actinomycetes and photosynthetic bacteria can reduce the incidence of the disease.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. There is no direct chemical treatment for viral infections. However, a foliar spray of di-methoate or azadirachtin can reduce the population of aphids. Apply the spray every fortnight after the first symptoms appearance.
What caused it?
The virus is transmitted by numerous species of aphids in a non-persistent manner. Since it does not multiply in aphids, the transmission from plant to plant must happen within short periods of time (no longer than one minute). The virus has a variety of alternative hosts such as watermelon and other cucurbits, but its preferred target is papaya. Infection can spread rapidly in a plantation if it coincides with large populations of winged aphids. Cool weather can also worsen the symptoms on the leaves (mosaic pattern and distortion).
Preventive Measures
- Use seeds from healthy plants or from certified sources.
- Check for resistant plants available.
- Plant in areas that are known to be free of disease.
- Plant non-host crops like maize or Hibiscus sabdarifa around orchards.
- Avoid planting cucurbit plants in the same area.
- Adjust the planting time to avoid peak populations of aphids.
- Remove plant parts affected by the virus.
- Control weeds in and around the field.
- Use nets to prevent insects from spreading the virus.
- Ensure good fertilization to avoid worsening symptoms.
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