Esca (black measles) on grapes — symptoms and treatment

Severity: high

What is Esca (black measles)

Esca (black measles) is a complex trunk disease caused by multiple fungi. It can kill vines over several years. Unlike a leaf or fruit disease, Esca lives in the permanent wood — the trunk and arms — where it decays the vine from the inside. The foliage symptoms are a consequence of that internal decay, which is why spraying the canopy does not touch it. By the time a vine declares itself, the wood is already compromised.

Symptoms

The leaf symptom is distinctive: interveinal striping. Bands of discoloured tissue develop between the veins while the tissue along the veins stays green, giving the leaf a striped, tiger-like look. Berries develop dark spots — small, hard specks on the skin, which is what earned the disease the name black measles; badly spotted fruit is unusable and can crack.

The two things that make Esca frightening are the wood and the suddenness. Cut into an affected trunk and you find wood decay: discoloured, soft, sometimes spongy tissue where sound wood should be. And the vine may not decline gracefully — it can go from apparently healthy to sudden collapse, known as apoplexy, wilting and dying rapidly, typically in hot weather.

• Chronic form: interveinal leaf striping; dark spotted berries; gradual decline across seasons
• Apoplectic form: sudden vine collapse with no useful warning
• Internal: wood decay inside the trunk and arms

Symptoms can also skip a season — a vine may show striping one year and look normal the next. It is not cured; the fungi are still in the wood.

Causes and conditions

The fungi enter through wounds in the permanent wood, and the biggest wounds a vine ever receives are pruning cuts. Spores released in wet weather land on fresh cuts, colonise the exposed wood and work inward over years. Large cuts into old wood are the highest risk; fresh cuts are the most vulnerable, becoming less receptive as they seal.

An infection established at pruning takes years to express itself, so Esca shows up mostly in mature vineyards: what you see this season reflects wounds made seasons ago. Infected trunks and prunings left in the rows keep producing inoculum.

Treatment

There is no cure. The goal is to remove diseased wood and rebuild vines from healthy tissue.

Trunk renewal pruning — cultural

Timing: dormant season. Remove infected trunks and retrain vines from suckers. Protect pruning wounds with sealant.

This is the only genuinely useful intervention. Cut out the infected trunk, then retrain from a healthy sucker at the base — the root system is often still sound, so you rebuild the vine rather than replant it. Sealing wounds protects the fresh cuts that would otherwise let the next infection in.

Sodium arsenite (restricted) — chemical

Timing: dormant season. No effective chemical control available. Trunk injection with fungicides is experimental.

Do not plan around a chemical solution here.

Pesticide registrations vary by country — check local approval before use.

Prevention

• Prune in dry weather, not into wet spells when spores are being released.
• Seal pruning wounds, and prefer smaller cuts over large wounds into old wood.
• Remove and destroy infected trunks and prunings rather than leaving them in the rows.
• Mark symptomatic vines when you see striping, so you can find them at pruning.

Frequently asked questions

Can Esca (black measles) be cured? No. The fungi are established in the permanent wood. The best available response is trunk renewal pruning — cut out the infected trunk and retrain the vine from a healthy sucker.

My vine collapsed in a single hot week — was it Esca? Sudden collapse (apoplexy) is one of the two faces of Esca. Cut into the trunk and look for wood decay inside; that, plus any history of interveinal striping, points to Esca rather than a watering failure.