Brown spots on strawberries indicate underlying issues affecting fruit health. These spots stem from pathogens, environmental conditions, or pests. Understanding the reason helps address the problem and ensure a healthy strawberry patch.
Common Causes of Brown Spots
Brown spots on strawberries manifest in different ways. Identifying their appearance and accompanying symptoms on leaves or stems aids accurate diagnosis.
Fungal Diseases
Fungal infections frequently cause brown spots, thriving in moist, humid conditions. Anthracnose fruit rot appears as small, sunken, circular brown spots on green fruit, turning black as they expand on red fruit. Under high humidity, these lesions may develop pink, salmon, or orange spore masses. This fungus also causes dark brown or black, sunken lesions on petioles and runners, potentially girdling the stem, causing wilting.
Leaf Scorch, a fungal disease, presents as irregular dark purple spots on the upper leaf surface. These spots enlarge and merge, causing leaf tissue to turn purplish to bright red, eventually browning, drying, and curling at the margins, appearing scorched. The fungus overwinters on old infected leaves, with spores spreading during spring rains.
Bacterial Issues
Bacterial problems like Angular Leaf Spot cause symptoms on strawberry plants. This disease begins as small, water-soaked spots on leaf undersides and calyxes. These lesions become angular, delineated by small veins, and may exude a milky, bacterial ooze that dries to a white, scaly film. As the disease progresses, spots become reddish-brown and necrotic on the upper leaf surface, often with a translucent quality when held to light.
Environmental Stressors
Environmental factors also lead to brown spots. Sunscald occurs when strawberry fruit is exposed to excessive sunlight, especially during hot or dry conditions. Affected berries develop pale, bleached, or pinkish areas that can become leathery, sunken, or mushy on the side facing the sun. Unlike disease, sunscald does not involve mold or slimy rot.
Inconsistent watering, or water stress, can cause browning. Both insufficient and excessive watering lead to problems; too little water causes browning and shriveling, while waterlogged roots hinder nutrient circulation, leading to similar symptoms. Strawberries have shallow root systems and are sensitive to water fluctuations, with prolonged drought reducing leaf count and overall plant growth.
Pest Damage
Certain pests can cause brown spots or damaged areas on strawberry fruit. Slugs and snails, for example, feed on leaves and fruit, leaving irregular holes with ragged edges. These nocturnal pests often leave slime trails. Damaged areas can then become entry points for secondary infections.
Preventing Brown Spots
Proactive measures and good cultural practices minimize brown spots. Proper spacing allows airflow, helping foliage and fruit dry quickly after watering or rain, discouraging fungal growth. Planting strawberries in full sun also aids drying and deters pests and fungi.
Watering techniques are important; avoid overhead irrigation when possible, as splashing water can spread fungal and bacterial spores. Drip irrigation or soaker hoses are preferable to deliver water directly to the soil while keeping leaves dry. Consistent moisture is beneficial, but good drainage prevents water from pooling around plants.
Maintaining soil health and garden hygiene also contributes to prevention. Regularly weeding the strawberry patch reduces competition for resources and improves air circulation. Applying mulch, such as straw, around plants prevents water from splashing soil-borne diseases onto fruit and helps keep berries dry. Removing old or infected plant debris and fallen berries prevents pathogens from overwintering and spreading.
Treating Affected Strawberries
When brown spots appear, prompt action helps manage and limit further spread. Removing and discarding any affected fruit, leaves, or plant parts is a primary step to reduce inoculum. This also applies to entire infected plants if the disease is severe, ensuring they are not added to compost piles where pathogens could survive.
Adjusting watering practices can alleviate issues related to environmental stress or fungal diseases. If overwatering is suspected, allow soil to dry slightly between waterings and ensure proper drainage. For fungal problems, improving air circulation by pruning dense foliage can help. When fungal or bacterial diseases persist, fungicides or bactericides may be considered. Copper-based sprays can be effective against bacterial issues like Angular Leaf Spot, and natural options like baking soda or horticultural soap may help manage fungal spores.
For pest damage from slugs and snails, integrated pest management strategies are effective. Hand-picking visible pests, especially at night or during damp conditions, can reduce their population. Eliminating their hiding places by clearing weeds and debris around plants also helps.
Harvesting and Safety Considerations
When encountering brown spots, edibility is important. Berries with small, superficial brown spots, especially those caused by sunscald or minor pest damage, can be salvaged by cutting away the affected portion. However, fruit exhibiting extensive rot, mold, or signs of fungal growth, particularly if fuzzy or discolored throughout, should be discarded entirely. Mold can spread quickly and may not be safe to consume, even if only partially visible.
Proper harvesting techniques also prevent further damage and disease spread. Pick strawberries when they are uniformly red, every two to four days during peak season. When harvesting, gently pinch off the berry with about 1/4 inch of stem attached, rather than pulling on the fruit or green cap. This minimizes damage to the berry and plant, reducing entry points for pathogens and preventing the spread of existing issues. Avoid harvesting or working in the patch when plants are wet, as this can easily spread spores.