Mosaic virus on fig — symptoms and treatment

Severity: medium

What is Mosaic virus

Fig mosaic virus (FMV) is transmitted by the eriophyid mite and is very common in fig orchards worldwide. Unlike a fungus, a virus lives inside the plant's own cells: it cannot be sprayed out, and an infected tree stays infected for life. On fig it is a medium-severity disease — trees usually keep growing and cropping, but leaves are patterned and distorted, fruit runs smaller and spotted, and vigour slowly slips. The reason to act is not to cure the tree but to stop the virus reaching the rest of your figs.

Symptoms

The name describes the main sign. Leaves develop a mosaic pattern of light and dark areas — irregular pale yellow or cream patches scattered through normal green tissue, with blurred edges rather than the crisp outline of a leaf spot. The pattern is uneven across the canopy and does not follow the veins tidily. Affected leaves are frequently distorted: puckered, narrowed or misshapen. Fruit on infected trees is reduced in size and may show spotting on the skin.

• Early: faint light-and-dark mottling on scattered leaves, often on just a few shoots
• Advanced: widespread mosaic patterning; leaf distortion; reduced fruit size; fruit spotting

Symptom strength varies between varieties and across the season, and mild cases are easy to write off as nutrient deficiency or sun bleaching. A deficiency tends to affect leaves evenly and follows a pattern related to leaf age; mosaic patterning is irregular and patchy, and comes with leaf distortion.

Causes and conditions

The virus is spread by the eriophyid mite — a mite far too small to see with the naked eye, which feeds on fig leaves and buds and carries the virus from infected to healthy trees. Wherever these mites move, the virus can follow: within a tree, between neighbouring trees, and on wind-blown or carried plant material.

The other main route is propagation. Because the virus is systemic, cuttings, scions and suckers taken from an infected tree are infected from the start — this is how the disease travels long distances and how a new planting can be diseased before it ever leafs out. Given how common FMV is in fig-growing regions, propagation material of unknown origin is a genuine risk. The virus does not spread through the soil or through normal handling the way some other pathogens do.

Treatment

There is no cure for a virus-infected tree. Control means managing the vector and the planting material.

Mite control and clean propagation — cultural

Timing: throughout the season. Control eriophyid mites which spread the virus. Use virus-free propagation material. Remove severely affected trees.

Keeping eriophyid mite populations down cuts the rate at which the virus moves from tree to tree. Propagating only from virus-free material stops you planting the disease. Trees that are severely affected — poor growth, unusable fruit — are best removed, both because they will not improve and because they act as a reservoir the mites keep drawing from.

Prevention

• Buy nursery trees and take cuttings only from known virus-free stock.
• Never propagate from a tree showing mosaic patterning, however good it once was.
• Monitor for and control eriophyid mites, especially on young trees.
• Inspect new arrivals before planting them near established figs.
• Remove and destroy severely affected trees rather than nursing them along.

Frequently asked questions

Can Mosaic virus be cured? No. Once a fig tree is infected it stays infected. Management is about protecting healthy trees, not rescuing sick ones.

Is the fruit safe to eat? Yes. The virus does not affect people. Fruit from infected trees is smaller and may be spotted, but it is edible.

Will it spread to my other fig trees? It can, via eriophyid mites and above all via cuttings taken from the infected tree. Control the mites and never propagate from an affected fig.