Browning in strawberry plants is a common symptom of stress. Healthy plants should have deep green foliage, so discoloration suggests a problem. Determining the cause requires careful observation, as the brown patterns, location, and accompanying symptoms serve as a diagnostic guide.
Browning Caused by Cultural and Environmental Stress
The most frequent causes of leaf browning relate to cultivation practices and environmental conditions, which are often the easiest problems to correct. Inconsistent watering is a primary culprit. Underwatering causes leaves to wilt and droop, leading to dry, brittle, and crispy brown edges or tips as the plant conserves moisture.
Conversely, overwatering or poor soil drainage restricts oxygen absorption by the roots, causing wilting and yellowing that progresses to brown edges. Chronically overwatered plants may also develop a soggy crown or dark, mushy root tips due to rot. Adjusting the watering schedule and ensuring excellent drainage are the first steps toward recovery.
Temperature extremes inflict direct damage on foliage. Intense heat (above 30°C/86°F) causes heat stress, resulting in scorched or sun-bleached brown patches. Providing afternoon shade mitigates this damage. Freezing temperatures or late spring frosts cause cold stress, leading to necrosis (brown or black discoloration) on the leaves and flowers within 24 hours.
Diagnosing Fungal and Bacterial Diseases
Infectious pathogens often create specific browning patterns that differentiate them from environmental stress. Fungal diseases like Leaf Scorch (Diplocarpon earliana) begin as small, irregular purplish spots on the upper leaf surface. These spots enlarge and merge, with the centers turning brown, eventually causing the leaf margin to curl and dry up, giving it a burned appearance.
Another common fungal issue, Leaf Spot, starts as circular, deep purple spots. The centers turn pale tan or white with a reddish-purple border as the lesion matures. Management involves removing infected material to reduce the pathogen load. Improving air circulation reduces leaf wetness conducive to fungal spore germination.
Root and Crown diseases (Phytophthora species) are destructive, causing rapid browning from the base up. The plant may appear healthy before suddenly wilting and collapsing as the pathogen destroys the vascular system. Diagnosis is made by cutting the crown tissue lengthwise, revealing a reddish or cinnamon-brown discoloration within the core, indicating crown rot.
Nutrient Deficiencies and Soil pH Issues
Browning is the final stage of nutrient deficiency, where chronic chlorosis (yellowing) progresses to necrosis (tissue death). A deficiency in potassium (K) is often seen first on older leaves as marginal necrosis, where the edges turn brown and dry. This browning progresses inward between the veins, leaving a green triangle near the leaf base.
Magnesium (Mg) deficiency also targets older leaves, causing interveinal chlorosis where the tissue between the veins yellows while the veins remain green. This yellowing eventually turns to a patchy brown as the cells die. These deficiencies can occur even if the nutrients are present in the soil, pointing to a problem with soil pH.
Strawberries prefer a slightly acidic environment (optimal pH 5.5 to 6.5). If the pH is too high or too low, the plant cannot properly absorb essential nutrients, known as nutrient lockout. A high pH reduces the availability of micronutrients like iron, while a low pH limits calcium uptake. This leads to deficiency symptoms that progress to brown tissue.
Insect Pests That Cause Browning
Certain insect pests cause browning as a direct result of their feeding activity, damaging the plant’s cellular structure. Spider mites, particularly the two-spotted spider mite, feed by piercing plant cells and sucking out the contents. This feeding initially creates fine, pale stippling, which progresses to a bronze or dusty brown appearance, often starting on the underside.
Severe spider mite infestations are identified by the fine webbing left behind on the leaves and stems. Root weevil larvae, such as the black vine weevil, cause browning indirectly by feeding on the roots and tunneling into the crown. This root damage inhibits water and nutrient uptake, leading to wilting, stunting, and eventual death.
Horticultural oil or insecticidal soap can manage mite populations. Adult weevils are sometimes confirmed by small, semi-circular notches they chew into the leaf edges.