Main Fig Pests and Diseases: Longhorn Beetles, Rust, and Crown Rot

Fig is a relatively easy fruit tree to cultivate, but left unmanaged it can fall prey to pests that kill the plant itself or diseases that substantially reduce yields. In Japan, longhorn beetles (carpenterworm) and fig canker disease are particularly troublesome, with the difficulty that damage is often already advanced by the time it is noticed. This section systematically addresses the principal pests and diseases likely to occur in home cultivation, organizing symptoms, management, and prevention from a practical standpoint.

Longhorn Beetles (Roundheaded Wood Borers)

Larvae called "Teppou insects" are the most serious pest of figs, tunneling through the interior of trunks and main branches. Wood dust resembling sawdust (frass) around the base of the plant indicates infestation. If left untreated, the pest blocks the passage of water and nutrients, causing the entire plant to die.

Symptoms

• Sawdust-like frass appears at the base of the trunk or on knobby sections.
• The tree suddenly loses vigor, with leaves wilting or yellowing.
• Entry holes (openings) are present at the base of the trunk.

Management and Prevention

• From June to September, when adult insects emerge, inspect the base of the plant frequently.
• When a fig wasp (flus) is found, insert wire into it or inject a registered insecticide into the hole.
• Wrap the base of the trunk with insect netting or specialized tape to prevent egg-laying.
• Remove weeds at the base of the plant and ensure adequate sunlight and air circulation.

Rust disease

A disease characterized by orange to rust-colored spots spreading on the undersides of leaves. As the condition progresses, early defoliation occurs and tree vigor declines. The disease proliferates in high temperature and humidity conditions from summer onward. Continued defoliation may affect fruit set the following year.

• Remove diseased leaves and fallen leaves promptly and dispose of them to prevent infection sources from persisting.
• Avoid planting too densely; improve air circulation through pruning.
• Avoid excess nitrogen and maintain plant health.
• In areas with frequent occurrence, apply registered fungicides preventively.

Crown decline disease

Soil-borne pathogens enter through wounds on roots and stems, disrupting vascular function and killing the plant. This is one of the most feared diseases in Japanese fig-growing regions. Once established in soil, recurrence is likely, and treatment is difficult; prevention is therefore essential.

• Remove affected plants early and dispose of them entirely, including the roots (avoid replanting in the same location).
• Take care not to inflict unnecessary wounds to roots and trunks when pruning or cultivating.
• Ensure good drainage and avoid excessive moisture.
• 接ぎ木では ブラックイスキア など比較的強いとされる系統を台木に使う方法もある

Rust

A disease that tends to appear on the base of the plant and fruit following the rainy season or extended wet periods. Affected fruit becomes waterlogged, softens, and rots; when the base is invaded, the plant weakens. Management focuses on reducing soil splash and excessive moisture.

• Apply mulch or straw to prevent mud splash from rain.
• Remove crowded branches to ensure the entire plant dries easily.
• Remove damaged fruit promptly.

FMV (Fig Mosaic Virus)

A viral disease that causes mosaic-patterned discoloration and leaf deformation, transmitted primarily through fig rust mites or contaminated scion wood and nursery stock. No cure exists, and many varieties are said to potentially harbor the virus.

• If symptoms are mild, maintaining tree vigor often poses little practical concern.
• Cuttings and grafting scions should be taken from plants that are growing as vigorously and healthily as possible.
• Be mindful of controlling mites such as spider mites that may act as vectors.

When uncertain whether leaf mottling is mosaic disease or a characteristic pattern and growing variation inherent to the variety, it can be helpful to check similar cultivars in the variety guide or consult the forum with photographs rather than relying on self-diagnosis.

Regular prevention is the most effective approach.

The foundation of pest and disease management is "early detection" and "prevention." Longhorn beetles and die-back disease in particular tend to be difficult to control once established, so make regular inspection of the base of the plant, air circulation, and drainage part of routine care. Selecting healthy nursery stock and maintaining consistent, appropriate management practices are the most direct path to sustained harvests.