Brown Spots on Blueberry Leaves — Causes and Fixes

Brown spots on blueberry leaves are not all the same, and treating the wrong cause makes things worse. Some spots are fungal, spread through wet weather and overhead watering, and need a different response than spots caused by sunscald, mite feeding or a reaction to chemical spray. The shape, location and pattern of the spots, combined with the time of year they appeared, narrows the cause to one of a handful of well-understood problems.

Blueberry leaf spot (Septoria)

Small, circular brown or reddish-brown spots with a darker border and sometimes a lighter centre are the hallmark of blueberry leaf spot, caused by the fungus Septoria albopunctata. Spots appear in early to midsummer and can be numerous, causing significant early leaf drop in severe cases. The disease overwinters in fallen leaves on the ground and splashes back up onto new foliage in wet weather. The most effective long-term control is sanitation: rake up and remove fallen leaves in autumn rather than leaving them to mulch around the base. Improve air circulation through the canopy by pruning out congested branches. Avoid overhead watering, especially in the evening.

Anthracnose leaf spots

Anthracnose produces larger, irregular tan or brown blotches that often appear after periods of warm wet weather. The spots may have concentric rings and can merge into larger dead patches. It affects both leaves and fruit. Remove affected tissue, improve drainage and air flow, and apply a copper-based fungicide at bud break if the disease has been persistent in previous years. Do not compost diseased material.

Phomopsis twig blight

If the brown spots appear near the growing tips and are accompanied by dying shoot tips or wilting of young growth, Phomopsis twig blight is the more likely diagnosis. This fungal disease spreads through wounded or dead wood. Prune out affected shoots to clean wood, sterilise your secateurs between cuts, and remove all dead wood from the plant promptly to remove the fungal reservoir.

Sunscald

Pale, bleached or papery brown patches that appear on the upper surface of leaves facing the sun, rather than evenly across the whole leaf, point to sunscald rather than disease. This is especially common after a plant is moved from shade into full sun, or after a period of cloud followed by sudden intense sunshine. Sunscald patches do not spread — they are fixed damage to those cells. The plant grows out of it over time.

Mite damage

Very fine speckling or bronzing of leaves, especially on the undersides, combined with a faint dusty appearance sometimes indicates spider mite feeding rather than a true fungal spot. Examine the undersides of the most affected leaves with a magnifying glass. If you see tiny moving dots or fine webbing, mites are the cause and fungicide will do nothing. A strong water jet to the undersides of leaves and, for serious infestations, a miticide or insecticidal soap resolves this.