Betula (Birch) – Pests and Diseases to Watch Out For

Aphids

Description: Aphids are small, pear-shaped insects, often green but sometimes black, yellow, or pink. They have long antennae and two tube-like structures called cornicles protruding from their hind end. They’re notorious for sucking plant sap, causing various issues. 

Symptoms: Infested plants exhibit yellowed, curled, or distorted leaves. Aphids leave behind a sticky substance called honeydew, which can lead to sooty mold growth. Stunted growth and reduced yields are also common. In some cases, they transmit plant viruses, causing further damage and irregular patterns on leaves.

Treatment Indoors: Treat aphids on indoor plants by wiping them off with a damp cloth or spraying with a mixture of water and a few drops of mild dish soap. For persistent infestations, apply neem oil or insecticidal soap directly to the affected areas. In most cases, the treatment will have to be repeated multiple times. Imidacloprid granules put onto the soil will also control aphids.

Treatment Outdoors: Blast aphids off outdoor plants with a strong jet of water from a hose. Encourage natural predators like ladybugs, lacewings, damsel bugs, or hoverflies. If necessary, spray affected plants with neem oil or a ready-to-use insecticidal soap, ensuring complete coverage, especially under leaves where aphids congregate. 

Birch Leafminer

Description: Birch leafminers are small sawflies whose larvae feed between the layers of birch leaves. Adult females lay eggs in the foliage, leading to larvae that create winding trails or “mines” as they consume the leaf tissue from the inside.

Symptoms: Infested leaves display irregular, translucent patches or blotches, often making the foliage appear brown and scorched. Over time, severe infestations can lead to premature leaf drop, causing reduced tree vigor and aesthetic value.

Treatment: Regular monitoring and early intervention are essential for effective control. Natural treatments involve introducing parasitic wasps, which are natural predators of leafminers. Contact insecticides can be used in early spring to kill adult leafminers before they lay their eggs. Systemic insecticides, which are taken up by the tree and transported to the leaves, can be effective in controlling the larvae within the leaf mines. It’s essential that the timing of application is correct to ensure maximum effectiveness.

Bronze Birch Borer

Description: The Bronze Birch Borer (Agrilus anxius) is a wood-boring beetle that primarily targets weakened birch trees. The primary damage is done by the larvae, which feed beneath the bark and disrupt the flow of water and nutrients within the tree.

Symptoms: Initial signs of infestation are often subtle, with the tree’s crown showing yellowing or thinning leaves. As larvae feed, they carve serpentine pathways under the bark. This disrupts nutrient flow, causing upper branches to wilt, progressing downward. Without intervention, the tree can deteriorate and eventually die.

Treatments: Cut and dispose of infested branches in fall or winter to eradicate larvae and pupae. Always prune beyond the affected zones to halt borer spread. Insecticides can combat Bronze Birch Borers if applied timely but are a last resort due to effects on other organisms. Always adhere to label directions. For intense infestations, tree removal may be essential to protect nearby trees.

Dusky Birch Sawfly

Description: The dusky birch sawfly is an insect that targets birch trees. Larvae resemble caterpillars with dark heads, yellow-green bodies, and black blotches on their side. Adult sawflies are wasp-like, black, and roughly half an inch wide.

Symptoms: Larvae chew birch leaf edges, causing a distinct, serrated pattern. Infested trees may appear “ragged.” Severe infestations can lead to considerable defoliation, especially in younger trees.

Treatments: Manually remove larvae. Use insecticidal soap or horticultural oil for mild infestations. In extreme cases, apply chemical pesticides per manufacturer instructions, ensuring minimal impact on non-target organisms.

Fall Webworm

Description: Fall webworms (Hyphantria cunea) are hairy, white caterpillars that grow up to an inch long and transform into white moths. Despite their appearance, fall webworms are generally not harmful to the overall health of the tree or shrub.

Symptoms: Trees infested with fall webworms will have conspicuous, large, silken webs at the branch tips, usually enveloping leaves. The caterpillars feed inside these protective tents, causing leaf damage.

Treatments: Physical removal, affected branches pruning, beneficial predators (birds), Bt (Bacillus thuringiensis)- A biological insecticide that targets caterpillars.

Gypsy Moth

Description: Gypsy moths are invasive pests with distinct life stages: hairy caterpillars with blue and red dots and adults with mottled brown wings. Originating from Europe, they’ve become a significant concern in North America due to their voracious appetite.

Symptoms: Trees infested with gypsy moth caterpillars show defoliated branches, with severe cases leading to almost complete leaf loss. Repeated infestations can weaken trees, making them susceptible to other pests and diseases or lead to tree death.

Treatments: In fall and winter, prune and discard egg masses from trees and surfaces; actively find and eliminate caterpillars. Employ natural predators like birds, tachinid flies, parasitic wasps, and ground beetles to manage moth numbers. Apply insecticides at optimal times to effectively curb gypsy moth populations.

Japanese Beetle

Description: Japanese beetles (Popillia japonica) are metallic green pests with bronze wings, approximately 0.5 inches long. They are active during the day and commonly found on plants and trees in summer.

Symptoms: Affected plants display skeletonized leaves, as beetles consume the tissue between veins. They also feed on flowers and fruits, causing significant aesthetic and functional damage to a wide variety of plants.

Treatments: Hand-picking, beneficial nematodes, floating row covers, knockdown sprays, natural predators, insecticides.

Lace Bugs

Description: Lace bugs are tiny, winged insects with ornate, lace-like wings. Typically under 1/8-inch long, these pests are often found on the underside of leaves, sucking the sap out of plants.

Symptoms: Lace bugs can cause a range of damage to plants, including stippling, yellowing, and wilting of leaves, as well as stunted growth and reduced vigor. The damage is typically most severe on the undersides of leaves, where the insects feed and lay their eggs.

Treatments: For minor infestations, remove and discard damaged leaves. Horticultural oil or insecticidal soaps can deter lace bugs. Encourage natural predators like ladybugs, which feed on them. In severe cases, consider systemic insecticides. Regularly check and treat the undersides of leaves.

Oystershell Scale

Description: Oystershell scale is a tiny armored insect with an elongated shell-like protective covering. Ranging from gray to brown, they attach themselves to trees and shrubs, feeding on the plant’s sap.

Symptoms: Plants infested with oystershell scale exhibit yellowing leaves, reduced growth, and branch dieback. Heavy infestations can cause bark cracking and ultimately lead to plant death.

Treatments: Prune infested branches. For mild cases, gently brush off scales during dormancy. Attract predators like lady beetles to control scales. Use insecticidal soaps, dormant oils in late winter, and summer oils when the crawlers are active. For severe cases, consider using systemic insecticides or contact insecticides.

Tent Caterpillar

Description: Tent caterpillars are hairy larvae of certain moth species. They’re recognizable by their distinct markings and the silk webbing or “tents” they construct in tree branches, which they use as shelter during the early spring months.

Symptoms: Trees infested with tent caterpillars display extensive webbing in branches. The caterpillars voraciously consume leaves, leading to defoliation, weakened trees, and a diminished aesthetic appeal. The tents are most noticeable in the spring.

Treatments: Early detection allows for the manual removal of tents. Introduce natural predators like birds or beneficial insects. Apply Bacillus thuringiensis (Bt), an organic pesticide that targets caterpillars without harming beneficial insects. Chemical Pesticides should be used judiciously, targeting the early larval stage for best results.

Anthracnose

Description: Anthracnose is a term used to describe a group of fungal diseases that affect a wide range of plants, including trees, shrubs, and crops. 

Symptoms: Symptoms include irregular-shaped brown or black leaf spots, sunken tan to red-brown lesions on stems, and premature leaf drop. In severe cases, cankers can form on branches, and fruit can exhibit dark, sunken spots.

Treatments: Remove and discard infected leaves and branches. Apply a fungicide containing copper-based compounds. Ensure good air circulation through pruning and proper spacing.

Armillaria Root Rot (Honey Fungus)

Description: Armillaria Root Rot is a destructive fungal disease affecting various trees and woody plants, causing root decay and significant damage to the plant’s health and stability. Also known as “oak root fungus,” it’s a white, fan-shaped mycelium that spreads underground, attacking and rotting the roots.

Symptoms: Early symptoms often include yellowing of the leaves, reduced growth, wilting, and early leaf drop. The crowns may thin, and branches may die back. A key identifier is honey-hued mushrooms emerging at the base of afflicted trees or shrubs during late summer to fall.

Treatments: Remove and destroy infected trees. Fumigate soil before replanting. Ensure good drainage and avoid overwatering. Use resistant plant varieties when available. Chemical treatments are limited and often not effective.

Canker

Description: Canker is a plant disease characterized by sunken, necrotic lesions on stems, branches, or trunks caused by various fungi or bacteria. These lesions disrupt nutrient flow, potentially weakening or killing the plant.

Symptoms: Symptoms include dark, sunken areas on stems or bark, sometimes oozing sap or resin. Infected branches may wilt, and leaves might yellow or drop prematurely. Over time, the cankered areas may girdle the stem, leading to dieback.

Treatments: Prune and dispose of infected branches during dry conditions. Sterilize pruning tools between cuts. Avoid wounding plants to prevent entry points for pathogens. Apply protective fungicides where appropriate and ensure proper plant spacing for air circulation, reducing fungal spread.

Heart Rot

Description: Heart rot is a fungal disease that affects the inner heartwood of trees, particularly older or damaged ones. Decay-causing fungi enter through wounds or broken branches, decomposing the core while often leaving the exterior intact.

Symptoms: Externally, trees might show mushroom or fungal growth at the base or on the trunk. There might be cavities or hollows in the trunk. Infected trees may have a weakened structure, leading to increased susceptibility to breaking in wind or storms.

Treatments: Avoid injuring trees, as wounds provide entry points for fungi. Prune dead or broken branches and ensure proper wound care. Promote tree health through proper watering and fertilization. In advanced cases, consult an arborist for potential tree removal to ensure safety.

Powdery Mildew

Description: Powdery mildew is a common fungal disease affecting a wide range of plants. It manifests as white or grayish powdery spots, primarily on the upper surfaces of leaves and stems. Though it can mar a plant’s appearance, it’s often more of a cosmetic issue than a fatal one.

Symptoms: Powdery white or grayish-white fungal growth on the leaves, stems, and sometimes fruit and flowers. Distorted or stunted growth, yellowing or curling of leaves, stunted or reduced fruit or flower production, reduced plant vigor.

Treatments: Increase air circulation, reduce overhead watering, and prune affected areas. Apply fungicides or homemade solutions like baking soda sprays. Neem oil and horticultural oils can also suppress the spread. Ensure good garden hygiene to prevent recurrence.

Rust Diseases

Description: Rust diseases are caused by fungi that produce distinctive rust-colored spores. Affecting numerous plants, rust can hinder photosynthesis and reduce plant vigor.

Symptoms: Yellow or brown spots on leaves, which can enlarge and spread to cover large areas of the leaf. Orange or yellow pustules on the undersides of leaves. Leaves that become yellow, brown, or distorted and may drop prematurely. Stunted growth, wilting, and reduced yields. Stems and flowers that become discolored, with pustules developing on their surfaces

Treatments: Remove and discard infected leaves. Avoid overcrowding. Water at the base of plants to reduce leaf wetness. Apply fungicides, following label instructions and targeting early stages. 

Sooty Mold

Description: Sooty mold manifests as a dark, dusty film on plant parts. While not directly injurious, it can impede photosynthesis by blocking light, tarnishing the plant’s appearance. Originating from fungi feeding on insect-excreted honeydew (like aphids or mealybugs), it presents as a black layer. Over-fertilization or stressful growth conditions can heighten plant vulnerability to honeydew-producing pests.

Symptoms: Appearance of dark, soot-like patches on leaves, stems, or fruit. Reduced photosynthesis can lead to yellowing and premature leaf drop. Underlying presence of sap-sucking insects.

Treatments: Prune infected parts. Treat underlying pest issues with insecticidal soap or neem oil. Improve air circulation. Enhance plant health with proper watering and fertilization.