Blueberry leaves curling often signals underlying problems. This guide explores common causes, including environmental stressors, pests, diseases, and nutrient imbalances, offering practical solutions.
Environmental Stress Leading to Leaf Curling
Improper watering causes blueberry leaf curling. Underwatered plants curl inward to conserve moisture. Overwatering also causes curling, often with yellowing leaves, due to root rot.
Blueberries need consistently moist, not waterlogged, soil, typically 1 to 2 inches of water per week. Check the top few centimeters of soil before watering. Mulching helps retain moisture.
Temperature extremes induce leaf curling. During excessive heat, leaves curl to protect from sunburn and reduce water loss. Cold stress, including frost damage, similarly causes leaves to curl and turn brown. Provide partial shade during hot periods, especially from western sun. Protect plants from late spring frosts with covers.
Inadequate or excessive light contributes to leaf curling. Blueberries thrive in full sun to partial shade, needing at least 6 to 8 hours of direct sunlight daily. Too much intense sun can scorch leaves and cause curling, while insufficient light leads to weak growth and curling. Optimal light conditions are important for plant health.
Soil pH imbalance is significant for blueberries, which prefer an acid pH of 4.0 to 5.5. High pH (alkaline) inhibits nutrient absorption, stressing the plant and causing leaf curling. Regular soil testing helps determine pH. Use elemental sulfur to lower pH, or lime/wood ash to raise it if needed.
Pests Causing Blueberry Leaf Curling
Pest infestations often cause leaf curling in blueberries.
Aphids are small, soft-bodied insects that feed on new growth sap, causing leaves to curl, distort, and crinkle. They leave honeydew, attracting sooty mold. Manage aphids with natural predators like ladybugs or by manually removing them with water. For severe infestations, use insecticidal soaps or neem oil in the evening to protect beneficial insects and prevent sun damage.
Spider mites also cause blueberry leaves to curl. These tiny arachnids suck sap from leaf undersides, leading to stippling, bronzing, and fine webbing. They thrive in dry, warm conditions; proper humidity management helps prevent them. Treat by washing plants with water or applying horticultural oils and insecticidal soaps.
Diseases Associated with Blueberry Leaf Curling
Certain plant diseases also cause blueberry leaves to curl.
Phomopsis twig blight: Leaves turn black, curl, and drop.
Mummy berry disease (Monilinia vaccinii-corymbosi): Infected leaves curl, turn reddish-brown, and young shoots wilt.
Blueberry stem blight (Botryosphaeria dothidea): Causes leaf curling, browning, and often severe stem dieback.
Blueberry rust: Infected leaves curl, develop reddish spots on top, and yellow pustules underneath.
Viral infections can also cause leaf distortion and curling.
Blueberry shock virus (BlShV): Causes sudden wilting and blighting of young leaves and flower clusters (grayish-black or orange). Infected plants remain carriers.
Blueberry shoestring virus (BSSV): Causes narrow, curled leaves (“shoestring” appearance) and reddish stem streaking.
Blueberry mosaic associated ophiovirus: Causes splotchy yellow, pink, and pale green discoloration with crinkled leaves.
Viral diseases have no cure; management involves removing and destroying infected plants to prevent spread.
Bacterial diseases can also impact leaf health. Bacterial leaf scorch, caused by Xylella fastidiosa, leads to leaf browning and curling, often resembling drought stress. This bacterium clogs the plant’s vascular system, hindering water and nutrient uptake. Infected plants show reduced vigor, and leaves eventually drop. Control involves removing infected plants to prevent spread, as there is no cure.
Nutrient Issues and Blueberry Leaf Curling
Nutrient imbalances, whether deficiencies or excesses, manifest as leaf curling.
Iron chlorosis is common, especially in soils with pH above 5.2, preventing blueberries from absorbing iron. This deficiency causes young leaves to yellow between veins while veins remain green, and can lead to curling. Correct iron deficiency by lowering soil pH with elemental sulfur or applying chelated iron.
Nitrogen deficiency results in pale green or yellow leaves, reduced shoot growth, and sometimes curling, often appearing first on older leaves. Address this by supplying appropriate nitrogen fertilizers or incorporating organic matter like well-rotted manure or compost.
Other micronutrient deficiencies also cause leaf curling.
Magnesium deficiency: Common in acidic soils, causes yellowing between leaf veins (interveinal chlorosis) progressing to red, often on older leaves, sometimes with curling. Remedy with dolomitic lime or Epsom salts.
Zinc deficiency: Causes small leaves, short stem internodes, yellowing between veins of young leaves, and curling.
Boron deficiency: Causes dark green, deformed young leaves with twisted margins and limited expansion.
Addressing deficiencies involves soil testing and applying specific amendments or balanced organic matter.