Leaf scorch on strawberries — symptoms and treatment

Severity: medium

What is Leaf scorch

Leaf scorch of strawberry is caused by the fungus Diplocarpon earlianum. It causes dark purple spots that merge on the leaves, and the name describes the end result rather than the cause: an affected plant looks as though it has been burnt, though nothing has scorched it. Severity is rated medium — the disease attacks the foliage rather than the fruit, but a strawberry plant depends on its leaves to size its berries and to build the crowns that carry next season's crop, so a scorched planting underperforms twice.

Symptoms

It begins as small dark purple spots scattered on the leaves. They then enlarge and merge, running together into irregular dark blotches that swallow the healthy tissue between them. Once enough spots have coalesced the leaf margins appear scorched — dry, browned and brittle at the edges, exactly like heat or wind burn, which is why the disease is so often misread as a watering fault. Reduced vigour follows: the plant has less working leaf, and it shows in weaker growth across the planting.

• Early: small dark purple spots scattered on the leaves
• Progressing: spots enlarging and merging into dark blotches
• Advanced: leaf margins appearing scorched; reduced vigour

The confusion worth resolving is with common leaf spot, whose lesions develop pale grey or tan centres inside a purple border. Leaf scorch spots stay dark purple throughout as they merge — no light centres.

Causes and conditions

The fungus survives on infected leaves and old foliage in the planting, and releases spores onto new leaves as the season starts. Rain, overhead irrigation and splashing water move them from the debris and from infected leaves onto clean ones. Spores need free water on the leaf to germinate, so wet weather, prolonged dew and sprinklers all drive it, while poor drainage and poor air circulation lengthen the wet periods it depends on. A perennial planting makes this easier still: the old foliage carrying the fungus sits right underneath the new growth.

Treatment

Renovation and sanitation — cultural

Post-harvest. Mow and remove old foliage after harvest. Ensure good drainage and air circulation. Renovation is the central control in a perennial planting: mowing off and taking away the infected old leaves after harvest means next season's growth starts clean. Remove the mown foliage from the bed; leaving it in place defeats the purpose.

Copper fungicide — chemical

Early spring. Apply copper-based fungicide in early spring before disease onset. The timing is the point: this is a protective application made ahead of symptoms, aimed at the new foliage as it emerges, not a cure for a bed already scorched. Pre-harvest interval: 14 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Renovate after harvest every year — mow the old foliage and remove it from the bed.
• Plant into well-drained ground and avoid low spots that stay wet.
• Space plants and thin runners so the bed does not mat into a canopy that never dries.
• Water at the base with drip rather than over the leaves.
• Start with clean planting material and do not propagate runners from an affected bed.

Frequently asked questions

Are the berries still safe to eat? Yes. Leaf scorch is a foliage disease — it does not infect the fruit. The berries may be fewer or smaller because the plant has less leaf to size them with. After a copper spray, respect the 14-day pre-harvest interval.

My leaves look burnt — is this heat damage or disease? Look at how it started. Genuine sun or wind scorch browns the exposed edges directly. Leaf scorch begins as small dark purple spots that enlarge and merge, and only then does the margin look burnt — so the spots are the tell.

Will it come back next year? It will if the old foliage stays in the bed, because that is where the fungus overwinters. Mowing and removing the foliage after harvest is what breaks the cycle.