🍈 Diseases of Guava

This lesson groups together important diseases affecting guava and related fruit crops, with a strong emphasis on recognizing symptoms and linking them to the correct mode of spread. That matters because fungal, viral, and vector-borne problems require very different management decisions.

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Powdery Mildew

Causal organism: Oidium caricae

The original notes describe powdery mildew as a superficial fungal disease producing white mycelial growth on leaves, flower stalks, and fruits. Severe infection causes yellowing and defoliation.

Key management logic

• spray wettable sulphur or other recommended fungicides noted in the source
• protect young, actively growing tissue
• act early, because powdery mildew spreads rapidly under suitable weather

The practical lesson is simple: once powdery growth becomes extensive, flower and fruit quality decline sharply.

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Papaya Ring Spot

Causal organism: Papaya ring spot virus

Although the folder name is guava, the source lesson also includes papaya viral diseases. Symptoms noted in the lecture include:

• vein clearing
• puckering and mosaic mottling
• severe leaf distortion
• shoe-string type narrowing
• ring spots on fruits
• stunting and poor fruit set

Spread

The lesson states that the virus is spread by aphids such as Aphis gossypii and A. craccivora, and that nearby cucurbits can act as important associated hosts.

Management logic

• raise seedlings under insect-proof conditions
• plant only healthy seedlings
• rogue infected plants quickly
• use barrier crops such as sorghum or maize
• avoid nearby reservoir hosts such as cucurbits

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Leaf Curl

Causal organism: Papaya leaf curl virus

The source notes describe:

• curling and crinkling of leaves
• inward and downward rolling
• thickened veins
• leathery and brittle leaves
• severe stunting
• failure of flowering and fruiting in badly affected plants

Spread

This disease is spread by whitefly, especially Bemisia tabaci.

Management logic

• uproot affected plants
• avoid nearby host crops that encourage vector movement
• manage the whitefly vector

This is a classic example of viral disease management through vector control plus roguing, not fungicide use.

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Anthracnose

Causal organism: Colletotrichum gloeosporioides

Anthracnose is important because it affects leaves, stems, and especially fruits. The notes mention brown superficial discoloration, sunken lesions, coalescing spots, salmon-pink spore masses under humid conditions, and mummification of fruits.

Practical significance

• reduces fruit quality
• causes pre- and post-harvest loss
• becomes severe in humid weather

Management logic

• remove infected plant parts
• reduce orchard humidity where possible
• use suitable fungicidal protection based on local recommendation

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Summary Cheat Sheet

Disease	Cause	Main symptom clue	Core management idea
Powdery mildew	Oidium caricae	White superficial fungal growth and defoliation	Early sulphur-based protection
Papaya ring spot	Virus	Mosaic, shoe-string leaves, concentric fruit rings	Healthy seedlings + aphid control + roguing
Leaf curl	Virus	Curling, crinkling, thickened veins, stunting	Whitefly control + plant removal
Anthracnose	Colletotrichum gloeosporioides	Sunken fruit lesions and pink spore masses	Sanitation + humidity reduction + fungicidal protection