The appearance of brown leaves on a blueberry bush signals an underlying issue with the plant’s environment, nutrition, or health. Browning is a symptom, not a specific illness. Diagnosing the exact cause requires a systematic approach, starting with simple cultural problems before investigating complex diseases or pest infestations. Observing the pattern of the browning—whether it starts at the edges, is spotted, or involves the entire cane—helps growers narrow down possibilities and apply effective remedies.
Environmental and Water Stress
Blueberry plants have shallow, fibrous root systems, making them highly susceptible to soil moisture fluctuations. Drought stress is a frequent cause of leaf browning, resulting in marginal leaf burn where the outer edges and tips dry out. This occurs because the plant cannot pull enough water to hydrate the entire leaf, causing the edges to scorch. Young plants are particularly vulnerable since their root systems are not extensive enough to access deeper soil moisture.
Conversely, overwatering or poorly draining soil can cause root rot, which mimics drought stress symptoms above ground. Waterlogged conditions deprive roots of oxygen, causing them to decay and become unable to absorb water effectively. The leaves turn brown and wilt because the damaged root system is non-functional, even when the soil is saturated. Inspecting the soil moisture level several inches below the surface determines if the cause is lack of water or lack of oxygen.
Sudden exposure to intense afternoon sun, especially after cloudy weather, can cause sun scald, resulting in brown patches on exposed leaves. Chemical injury from herbicide drift can also cause irregular browning and leaf distortion, often appearing suddenly on one side of the bush. These non-pathogenic issues are management-related and are corrected by adjusting watering schedules, improving drainage, or protecting the plants from environmental factors.
Soil pH and Nutrient Lockout
Blueberry bushes are acid-loving plants, thriving best in a soil pH range between 4.5 and 5.5. When the pH rises above this range, it prevents the plant from absorbing nutrients, a phenomenon known as nutrient lockout. The most common resulting issue is iron chlorosis, where the plant cannot utilize iron, a necessary component for chlorophyll production.
Iron deficiency appears as distinctive interveinal yellowing, where the tissue between the leaf veins turns light yellow or bronze-gold while the veins remain dark green. If the high pH persists, this yellowed tissue can eventually scorch and turn brown at the tips and margins. Since iron is primarily absorbed by the youngest roots, these chlorosis symptoms are most apparent on the newest growth.
Magnesium also becomes less available in high-pH soils, leading to symptoms that progress to brown necrosis. Deficiency begins on older leaves as interveinal reddening, sometimes preceded by yellowing. The outer leaf portions turn bright red or pink while the area around the main veins stays green. The final stage is the browning and death of this reddened or yellowed tissue. Growers must perform a soil test to confirm the pH level before applying elemental sulfur or ammonium sulfate to gradually lower the pH.
Common Fungal Diseases
When browning appears as distinct spots or starts from a specific point on the cane, the problem is likely a fungal pathogen rather than a cultural or nutrient issue. Fungal diseases are favored by prolonged wet weather or poor air circulation within the plant canopy. These pathogens produce defined lesions that differentiate them from the generalized browning caused by water stress or nutrient lockout.
Septoria Leaf Spot, caused by the fungus Septoria albopunctata, manifests as small, circular lesions on the leaves. These spots have a light gray or tan center surrounded by a purplish-brown margin. As the disease advances, spots may coalesce, causing the entire leaf to turn yellow and drop prematurely. Since the fungus overwinters in infected debris, sanitation and pruning are beneficial control measures.
Phomopsis twig blight, caused by the fungus Phomopsis vaccinii, results in browning and dieback of the canes. Symptoms begin in the spring with infected buds turning brown and a necrotic, reddish-brown lesion forming on the twig. This lesion spreads and can girdle the twig, causing the leaves above the affected area to wilt, turn reddish, and then brown. Pruning infected canes well below the visible lesion is necessary to prevent the fungus from spreading.
Identifying Pest Damage
After eliminating environmental factors, pH imbalances, and fungal diseases, checking for pests is warranted, as certain insects and mites can inflict damage that causes leaves to turn brown. Pest damage presents as localized or patterned browning, often accompanied by physical evidence of the organism or its byproducts. Unlike the systemic browning of root rot or nutrient lockout, pest damage is confined to specific parts of the leaf or cane.
Spider mites feed on leaf cells, causing fine, bronze or brown speckling known as stippling. This damage is most noticeable on the undersides of the leaves and is confirmed by looking for fine webbing or using a hand lens. Scale insects are immobile sap-suckers that look like small bumps and can cause entire shoots to yellow and eventually turn brown. Inspecting the stems and leaf nodes for these shell-like insects or sticky residue, known as honeydew, confirms their presence. Addressing these pests early prevents widespread browning and defoliation.