How to treat oak tree diseases

Oak Tree Diseases: How to Treat Them

You pull on your gloves, carefully place safety glasses atop your nose, and grab your tools. It’s time to do surgery — well, at least some minor cosmetic work — on your landscaping.

But sometimes, when you head out to trim and prune, you don’t know where to start. You may see something that looks off. Some discoloration. Unusual shapes. Maybe even an odd scent. Some are harmless; others can signal a disease.

It’s important to recognize what you’re dealing with, so you can remedy the ailment properly. With countless pests and fungi waiting to wreak havoc on any of the U.S.’s 90 varieties of oak trees, there’s a lot to consider when it comes to caring for these arbors.

Prevention Is the Best Medicine

As is true with most things, proper care is the best defense against any illness or setback. Oak trees, like all plants, benefit from adequate water, sunlight, and good soil conditions. To keep trees healthy and stress-free, ensure the following:

  • Apply about 3 inches of organic mulch from the trunk out to the dripline; do not pile mulch against the trunk.
  • Do not apply weed killers near the tree.
  • Use slow-release fertilizers in early April if necessary.
  • Water trees during droughts, providing about 1 inch of water weekly.
  • Protect trees and root systems from damage during construction in the area.
  • Promptly remove and dispose of infected trees, and grind stumps to prevent disease spread.

Disease Identification for Oak Trees

Many diseases present in oak trees can be identified with only a little knowledge. By inspecting leaves and trunks, and looking for dead branches, you can figure out what ails your oaks. Fortunately, many diseases require no treatment. Others, though, indicate immediate removal. Read on for a primer in disease identification and treatment.

Actinopelte leaf spot

Symptoms: Circular, dark to reddish-brown spots on the leaves; can run together creating blotches. Severe infections cause premature leaf drop.

Causes: Wet weather increases the vigor of this complex fungus.

Season: The disease can survive winter in infected twigs and leaves that do not drop, with signs emerging following bud break.

Treatment: Remove all infected plant material to slow spread. Spraying may be indicated for small trees that have lost their foliage several years in a row.


Symptoms: Dead areas appear between leaf veins, mostly on lower branches. Brown spots form on the lower leaf surface and on dead twigs.

Causes: Cool, wet weather helps to incubate this fungus that is easily spread.

Season and risk level: Springtime and cool summers are ideal for this illness to take hold. All oaks, as well as many plants and vegetables, are prone to this infection.

Treatment: In general, pruning dead twigs and branches during dormancy is the best treatment. For further protection, apply an appropriate fungicide to protect new growth.

Armillaria root rot

Symptoms: Honey-colored mushrooms form annually at the base of the tree. These growths appear in large groups and are followed by a white fan of fungal growth under the bark at the base.

Causes: Borne in soil, wet weather, and improper drainage increase the likelihood of infection.

Season and risk level: All varieties of oak are susceptible, and damage will appear in late summer and fall.

Treatment: This root rot leads to a slow decline. Remove infected trees and protect healthy ones from stress.

Bacterial leaf scorch

Symptoms: Edges of oldest leaves turn brown, beginning on the inner and lower portions of the tree. A reddish-colored band sometimes develops between the brown and green on the leaf and branches begin to die.

Causes: Leafhoppers and spittlebugs carry the xylella fastidiosa bacteria, which causes a disruption of water movement throughout the tree.

Season and risk level: Symptoms appear late summer to fall, typically following a summer drought. Most common in pin, red, white, bur, and single oak varieties.

Treatment: Oxytetracycline injections by a professional can calm symptoms but will not cure the disease. Eventually, trees will need to be removed. If replanting, consider proper spacing to prevent movement of fungi-carrying bugs.

Bacterial wetwood, aka slime flux

Symptoms: Dark streaks of sap oozing from the bark, which typically carries an unpleasant odor.

Causes: Many different bacterias cause this as they enter the tree through wounded bark.

Risk level: All oaks can develop this, but pin oaks are especially prone.

Treatment: Avoid wounding the bark to prevent further stress. Care for sick trees as normal and minimize stress as possible.

Ganoderma root rot

Symptoms: Shelf-like structure forms on the wood near the soil line; usually brown to reddish. With time tree growth slows and dying branches produce small, yellowed leaves.

Causes: The fungi-carrying spores spread through the wind, leading to wood decay. Drought and physical injury increase the risk of infection.

Risk level:  All species of oak are susceptible, but proper care reduces risk.

Treatment: This may take years to kill the tree, but in the meantime, it will be susceptible to significant wind damage. Trees located near structures should be removed for safety purposes.

Hypoxylon canker

Symptoms: This white-rot fungal disease leads to the death of branches and leaves at the tree’s crown. There will be eventual dieback, and outer bark will slough off.

Causes: Reduced water uptake by trees, usually caused by some form of damage to the root zone, including drought and construction damage.

Risk level: Most species are susceptible. Post, water, southern red, white, and blackjack varieties are most likely to develop this disease.

Treatment: There is no treatment, but removing damaged branches can help slow the progression of the illness.

Inonotus root rot

Symptoms: Branch dieback and fewer leaves, which are usually yellowed. Illness begins far out in the root structure, and the tree may topple before visible signs are noticed. Visible signs also include conks at the base of the tree.

Causes: Fungi enter through wounds in the bark, including pruning injuries.

Season: Infection occurs at any time, and severe damage becomes noticeable in summer and early autumn.

Treatment: Sadly, this disease is terminal. The only option is to immediately remove the tree.

Laetiporus root rot

Symptoms: Large groups of yellow to pink, shelf-like fruiting structures turn white with age; the bark where these form becomes depressed and cracked.

Causes: Fungal infections and poor drainage from the roots.

Season: Growths form in summer and autumn, and fall off in winter.

Treatment: By the time fruiting structures grow, significant damage is already done and the tree has become susceptible to wind damage and toppling. The tree should be removed at the first sign of infection.

Leaf spot

Symptoms: Irregular, brown spots from between leaf veins. Spots will turn reddish-brown, and a yellow halo may appear with time.

Causes: Iron chlorosis takes hold during wet, humid, and mild conditions, typically as buds break.

Season and risk level: Spring and mid- to late summer; spores causing this illness can spread in the wind.

Treatment: Because little damage results from this, there’s no need to treat it. If you’re very bothered, you can apply a fungicide at bud break.

Oak leaf blister

Symptoms: Small spots that turn light green as the leaf grows; the center of the spot raises like a blister due to rapid cell growth.

Causes: Fungi secretions lead to overgrowth of leaf tissue, and tend to occur during especially damp spring seasons.

Risk level: Red and black oaks are most susceptible.

Treatment: Landscaped trees don’t require any treatment as spotting is usually minor and leaves do not drop prematurely.

Powdery mildew

Symptoms: A white growth on the surface of the leaves, both top and bottom. Severe infections may cause foliage to be malformed and can lead to early leaf drop.

Causes: This fungus prefers young foliage in shade, as there is a likelihood of moisture in which the disease thrives.

Season: Spring and autumn, when weather is cooler, provide conditions for this disease to thrive.

Treatment: The late onset of this disease means there is no significant damage, and therefore no treatment is required. If the issue is especially bad, a fungicide can be applied when the tree is dormant.

Oak wilt

Symptoms: Leaves at the top of the tree turn brown around the edges and wilt; damage progresses down the tree. Eventually, branches and twigs die altogether. Extensive leaf drop occurs by mid-summer.

Causes: The pathogen blocks water and nutrients from moving properly throughout the tree; usually affects closely planted trees.

Season and risk level: Damage appears in spring and early summer. Red oaks are most susceptible, while white oaks are somewhat resistant.

Treatment: Trees typically die within one year of infection. Remove infected trees quickly and inject neighboring oaks with a fungicide to inhibit spread.

Call the Doctor

There’s a time and place for professionals, and severely sick oak trees often require the help of licensed arborists. If you haven’t been able to remedy the issue in one or two growing seasons, and the disease is one that will ultimately kill the tree, it’s time to bring in support.

For severely damaged arbors, particularly those that are prone to windthrow and breakage, it is always best to seek out a licensed, insured, and experienced tree care expert. With some varieties reaching heights of 100-feet, oaks need to be handled carefully and skillfully.

Main Photo Credit: Pexels

Alison Hoover

Alison is a Midwesterner through and through, and loves to spend her time baking and reading. Always at home in the dirt, as a kid, Alison raised a vegetable garden with her dad, and flower gardens with her mom.

Posts by Alison Hoover

Oak Diseases & Insect Pests

Although many types of oak trees (Quercus species) are well adapted to South Carolina, they still may be affected by a variety of insect pests and diseases. Always maintain healthy oak trees by following recommended cultural practices, which are the first line of defense in preventing most of these problems. For more information, see HGIC 1017, Oak.


Oak leaf blister on water oak.
Andrew J. Boone, South Carolina Forestry Commission,

Oak Leaf Blister: Oak leaf blister is a disease caused by the fungus Taphrina caerulescens. Most oak species are susceptible, but the red and black oak groups are especially so. Minor infections cause little harm, but midsummer defoliation can occur when infections are severe. Blister-like patches appear on the leaves. They are often lighter green than the surrounding tissue and later turn brown. The blister-like patches result from an overgrowth of infected leaf tissue caused by substances secreted by the fungus.

The fungus survives the winter as spores in leaf buds. The spores germinate in the spring to infect the leaves. Infected leaf tissue grows much faster than uninfected tissue, resulting in distorted blisters. The fungus grows and produces spores within the leaf until the cuticle (surface wax layer) is ruptured by the mass of fungal tissue. Spore dispersal occurs in the fall.

Prevention & Treatment: Leaf blister is rarely severe enough to require control measures. Once an infection has occurred, fungicide treatments usually are ineffective. If the infection is very heavy and if the tree is small enough to obtain good coverage, a fungicide could be applied in the spring just before bud break. Rake up and dispose of fallen leaves in the fall.

Browning of edges of leaves caused by bacterial leaf scorch.
Edward L. Barnard, Florida Department of Agriculture and Consumer Services,

Bacterial Leaf Scorch: This disease is caused by the xylem-limited bacterium Xylella fastidiosa and is characterized by a disruption of water movement, decline of vigor, marginal reddening or yellowing, followed by margins of leaves browning, leaf drop, dieback, and eventual death. The symptoms usually first appear in early fall, following summer drought. Because trees infected with bacterial leaf scorch will decline gradually, it may take five to ten years before a tree may need to be removed. This disease more commonly affects pin oak, red oak, white oak, bur oak, shingle oak, and sycamore. It damages red, silver, and sugar maples, hackberry, elm, and sweetgum.

Prevention & Treatment: Remove infected trees and replant the area with resistant tree species. Avoid planting all the same species close together. Leafhoppers and spittlebugs spread the bacterium, so start by controlling the weeds and wild plants that support these insects. Extra care to fertilize and irrigate may prolong the infected tree’s life, but trees with extensive leaf scorch and dieback should be removed. Currently, spray treatments are not available. However, certified arborists can perform annual root flare injections of antibiotic treatments using oxytetracycline (such as Bacastat), which can reduce symptoms by suppressing the pathogen.

Actinopelte Leaf Spot: This fungal disease may be a serious problem in wet weather. It is caused by the fungus Tubakia dryina (formerly called Actinopelte dryina). The symptoms are circular, dark to reddish-brown leaf spots with a diameter of ¼ to ½ inch. Spots may run together to form irregular blotches. Tiny black specks in rings are visible in the spots and blotches. Severe infections cause the trees to lose their leaves prematurely. Trees of low vigor that are repeatedly defoliated may die.

Prevention & Treatment: Destruction of all infected plant material will reduce the spread of the fungus. Rake up and dispose of fallen leaves. Small trees defoliated several years in a row may need spraying. Apply mancozeb, chlorothalonil, thiophanate-methyl, or a copper fungicide according to the instructions on the labels. Complete coverage is necessary for control. See Table 1 for examples of specific products.

White coating on leaf caused by powdery mildew.
Petr Kapitola, State Phytosanitary Administration,

Powdery Mildew: This disease is caused by several fungi (Erysiphe trina, Microsphaera alni, Phyllactinia corylea, and or Sphaerotheca lanestris). The symptoms consist of white, powdery growth on both leaf surfaces. The foliage may be malformed, dropping prematurely, or drying out and shriveling. Sometimes the grayish-white fungal growth changes to tan and then to brown with age. Tiny black dots (fungal fruiting bodies) may be seen in the brown felt abundant in some years but rarely in others.

Prevention & Treatment: Control is usually not practical nor warranted. Myclobutanil or thiophanate-methyl sprays may be used to control powdery mildew in severe cases and on small trees. Follow the directions on the label. See Table 1 for examples of specific products.

Armillaria root rot mushrooms near infected oak tree.
Joey Williamson, ©2013 HGIC, Clemson Extension.

Armillaria Root Rot: This root rot disease is caused by the fungus Armillaria mellea and is widespread on oak. The symptoms are a slow decline of the tree. Mushroom fruiting structures on or near the root collar are prevalent in late summer and fall, especially during wet weather. Clusters of these honey-colored mushrooms may appear outward from the tree as they follow the major roots.

Prevention & Treatment: Remove diseased trees and as much of the root system as possible. Do not replant the site with a susceptible host. Trees that are resistant or tolerant to Armillaria root rot include bald-cypress (Taxodium distichum), Chinese elm (Ulmus parvifolia), dawn redwood (Metasequoia glyptostroboides), eucalyptus, ginkgo (Ginkgo biloba), Japanese cedar (Cryptomeria japonica), Leyland cypress (Cupressocyparis leylandii), maple (Acer species), sourwood (Oxydendrum arboreum), and sweetgum (Liquidambar styraciflua).

Asexual brown fungal stroma and black sexual stage of Hypoxylon on oak.
Meg Williamson, Plant Problem Clinic, Clemson University

Hypoxylon canker: This is a white-rot fungal disease primarily of oaks, hickories, and pecans in South Carolina and is caused by Biscogniauxia atropunctata var. atropunctata (formerly called Hypoxylon atropunctatum). Many species of oaks are susceptible to this disease, but post oak, water oak, southern red oak, white oak, and blackjack oak are most often affected. This opportunistic pathogen is a common inhabitant of the bark of hardwood trees, but it is only of consequence when the trees are under severe stress. Environmental stress caused by drought, as well as by root injury during construction, utility trenching in the root zone, soil grade changes, soil compaction, and root diseases, all can play a role in weakening the trees and the subsequent infection by B. atropunctata var. atropunctata. Any root injury will reduce water uptake by trees, and drought stress appears to be the most significant factor in infection.

As the fungus spreads and forms cankers, the first symptom that may be observed is the dying back of the crown (top) of the infected tree. However, other tree problems may also result in dieback. Subsequently, the outer bark begins to slough off in areas of infection, and pieces of bark can be seen at the base of the tree. This bark loss exposes the first sign of the fungus, which is a brownish fungal stroma where conidia (or asexual spores) of the pathogen are produced. This area may be several inches to several feet long on limbs and trunks. These conidia are wind-disseminated and can cause new infections on other trees.

As the infection continues to develop, the exposed area of fungal stroma changes to a gray or silver color and finally to black as a second type of spore is produced. This is the sexual stage of the fungus, and these spores, which are also infectious, are spread by splashing rain or insects to nearby trees.

Prevention & Treatment: There are no controls for Hypoxylon canker on these hardwood trees once the infection has begun on the trunk. If the infection is observed on branches, these may be removed and burned, but there may be other infection sites that are not yet apparent on the tree.

Stress reduction is the key to prevent infection. Keep the trees as healthy as possible.

  • Protect trees from damage during home construction and utility repairs. For more information, see HGIC 1002, Protecting Trees During Construction.
  • Water trees during periods of summer drought with 1 inch of irrigation water per week. For more information on proper irrigation, see HGIC 1056, Watering Shrubs & Trees.
  • Trees should be mulched with a 3-inch layer of organic mulch from the trunk to the dripline, but don’t pile mulch against the trunk. For more information on mulching trees, see HGIC 1604, Mulch.
  • Do not apply weed killers near the tree, especially beneath the limb canopy.
  • Fertilize trees with slow-release tree and shrub fertilizer during early April. For more information on proper fertilization, see HGIC 1000, Fertilizing Trees & Shrubs.
  • Remove and burn or dispose of any infected trees, and cut the remaining stumps flush with the soil.

Pine-oak gall rust spore-containing pustules on an oak leaf.
Robert L. Anderson, USDA Forest Service,

Pine-Oak Gall Rust (Eastern Gall Rust): The fungus Cronartium quercuum causes gall rust on approximately 25 to 30 species of pine and oak. Infection of oak causes small brown or yellowing areas on the leaves. On the underside of the leaves, pustules with yellow to orange powder (spores) are visible.

Prevention & Treatment: All fungal spores, which infect both pine and oak, are primarily windborne. High humidity increases the incidence of infection. Chemical control is usually not warranted. The fungicide myclobutanil may be applied to oaks according to the directions on the label. Follow the directions on the label. See Table 1 for examples of specific products.


Mistletoe infestation becomes obvious during winter.
Randy Cyr, GREENTREE Technologies,

If oak trees still have clumps of green in the limb canopy after leaf drop in fall, the trees may be parasitized by mistletoe (Phoradendron species), which are parasitic plants. Although mistletoe does obtain water and minerals from the tree, it does not depend totally on the tree for food (i.e., carbohydrates). The green leaves of this plant contain chlorophyll and are capable of making their own food. Mistletoe produces small white berries, which are extremely toxic to humans. The stems and leaves are also toxic and are reported to cause skin irritation on contact in some people.

Prevention & Treatment: Mistletoe can be controlled by cutting out infected limbs 1 to 2 feet below the point of attachment. In a few instances, breaking out the tops of the mistletoe has proven an effective means of control. Ethephon (Florel Brand Fruit Eliminator) is labeled for mistletoe control. Large infestations may be difficult to control with a single spray application, and retreatment may be required. Make applications after fall leaf drop through mid-winter.


A lichen is an unusual organism composed of a fungus and an alga and/or a cyanobacterium living together symbiotically. The alga converts sunlight and carbon dioxide in the air to food (i.e., carbohydrates). The fungus surrounds the alga, protecting it from drying, and lives off of the food it provides. Lichens appear as green to gray-green leafy or crusty growths on the trunk and branches of trees that typically are in poor health. However, lichens are totally harmless and are in no way responsible for the poor health of the tree. The reason they are associated with declining plants is that as woody plants lose vigor and decline, the number and size of leaves begin to decrease. This allows more sunlight onto the tree limbs and the trunk, which lichens require for growth.

Prevention & Treatment: If plant health is restored by correcting the real cause of decline, leaves will increase in size and number; less sunlight will get to the trunk and limbs, and the lichens will gradually disappear. However, for dormant season lichen control on tree trunks and limbs, there are a few products containing potassium salts of fatty acids that can be used to manage lichens. These products are: Bonide Moss Max RTS1, Bayer BioAdvanced 2 in 1 Moss & Algae Killer & Cleaner RTS1, and Scott’s MOSS-EX 3-in-1 RTS1. These algae and moss killers also have lichens listed on the labels. They are for use only on the hardened bark of trees.

Spanish Moss

Heavy growth of Spanish moss weighting live oak limbs in rain.
Karen Russ, ©2008 HGIC, Clemson Extension

Spanish moss (Tillandsia usneoides) is an epiphytic plant. An epiphyte is an organism that lives upon another plant and only uses that plant for support and protection. Spanish moss does not feed directly on the tree but obtains its water and nutrients from the air and rain. Spanish moss is limited to warm, humid areas of the southern and coastal regions of the state. Each bundle of moss is made up of a mass of long, gray-green filaments, which are its stems and leaves. Since the leaves of Spanish moss require sunlight to produce their own food, it is usually found in trees that are in a state of decline. Heavy infestations of Spanish moss may lead to further tree decline by shading out lower leaves, and the weight of large masses of wet Spanish moss can lead to limb breakage.

Prevention & Treatment: Increasing tree vigor through proper watering and fertilization is one way to restrict the growth of Spanish moss. Removal by hand may also be necessary to rid the tree completely.

Insects & Related Pests

Large oak apple gall, one of many types of oak galls. |
James Solomon, USDA Forest Service,

Galls: There are at least 750 different galls that have been identified on oak. In fact, more galls occur on oak than on any other kind of plant. Galls are defined as irregular growths or swellings, and they vary greatly in size, shape, and location on the plant. Gall development is a reaction by the plant tissue to feeding or egg-laying by various mites and insects. While most galls do not seriously harm oak trees, most are unsightly and detract from the beauty of the tree. However, twig galls may kill individual limbs and sometimes the whole tree.

Control: Many gall-producing insects and mites are parasitized by other insects and are fed upon by various birds and animals. Simple removal and destruction of fallen leaves with galls will help to reduce the number of emerging adults that will produce the next generation. Where possible, all twig galls should be pruned out while green or before emergence holes appear. In most cases, chemical control is not practical or effective. This is especially true in the case of large trees.

Orangestriped oakworm in mid to late summer.
USDA Forest Service – Northeastern Area Archive, USDA Forest Service,

Oakworms: Three closely related moths (Anisota senatoria, A. stigma, and A. virginiensis) occur in South Carolina, and their larvae (or caterpillars) are pests of oaks and feed heavily on the leaves. The orangestriped oakworm (Anisota senatoria) is the most commonly occurring. At maturity, it is about 2-3/16 inches (5.5 cm) in length and has two long slender black ‘horns’ that project from the second segment behind the head. In the fall, it crawls to the ground and burrows into the soil. It overwinters (survives the winter) in the soil and matures to an adult (moth). The moths then appear in June and July, and the female moths lay clusters of eggs on the undersurfaces of oak leaves. When the larvae hatch, they are small and greenish-yellow. While small, the caterpillars typically feed in groups and eat all of the leaf blades except for a lacy network of veins. These orangestriped caterpillars mature and reach their full size by early fall and are black with yellow or orange stripes running the length of their bodies. Older caterpillars tend to be solitary feeders and eat all of the leaf tissue except the main veins.

As a result of the caterpillar feeding, small trees may lose all their leaves by midsummer. While healthy trees can tolerate feeding by oakworms, young trees may be weakened if they lose all their leaves several years in a row. Mature trees may lose enough leaves to suffer twig dieback as a result of sunscald damage.

Control: With a light infestation on young trees, caterpillars can be handpicked and destroyed. On large trees, control is more difficult. Where possible, rely on birds, parasites, and diseases to control their numbers naturally. Bacillus thuringiensis (B.t.) is a microbial insecticide that contains spores of this bacterium. It is effective against young larvae and is a safer alternative when spraying up into a tall tree. Follow the directions on the label. If chemical control becomes necessary on smaller trees, the following insecticides are recommended: spinosad, permethrin, cyfluthrin, cyhalothrin, bifenthrin, or acephate. See Table 1 for examples of specific products.

Oak lecanium scale on small twigs.
James Solomon, USDA Forest Service,

Scale: Various kinds of scale insects are pests of oak. Scales are unusual insects in appearance because, as adults, they are small and immobile, and with no visible legs. They vary in appearance depending on age, sex, and species. Scales feed on sap by piercing the leaf or stem with their mouthparts and sucking. As they feed on plant sap, some scale insects (soft scales) excrete a sugary waste substance called honeydew. The sooty mold fungus grows on the honeydew, resulting in an unsightly dark fungal coating on leaves and stems.

Oak lecanium scale (Parthenolecanium quercifex) is a common pest on oaks. The adult females are 1/16 to ¼ inch (2 to 6 mm) in diameter. They are round and reddish-brown. Males have wings and are brown. The female lays eggs in April and May. Crawlers (immature scale insects) hatch from the eggs, crawl to new foliage, and suck sap from leaves. Serious scale infestations may result in stunted plant growth, small flowers, yellowing of leaves, and early leaf drop. In addition, the presence of the honeydew and sooty mold results in dark splotches on the surface of the leaves.

Control: A combination of various natural enemies, including ladybird beetles (ladybugs) and parasitic wasps, usually keep scales under control. On small trees with a light infestation, the scales can be scraped off, or the infested branches can be removed and destroyed. On a larger tree, controlling scale insects with pesticides is not always practical because of the size of the tree, the need for specialized equipment, and the cost may prohibit this solution.

Scales are not easily controlled with chemical insecticides once the adults are protected by their waxy covering. For heavy infestations of scale insects, spray with a 2% horticultural oil in the spring and fall to manage adults, crawlers, and eggs by smothering them. Be sure to coat the trunk and all of the branches thoroughly.

However, crawlers (the mobile immatures) are susceptible to conventional insecticides. Monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Insecticides labeled for use by homeowners against scale crawlers on oaks include cyfluthrin, permethrin, bifenthrin, cyhalothrin, and malathion. Apply one of these materials when crawlers appear and repeat the spray application in 10 days. As with all pesticides, read and follow all label instructions and precautions. See Table 1 for examples of specific products.

Note: Chemical control of diseases and insects on large trees is usually not feasible since adequate coverage of the foliage with a pesticide cannot be achieved. The use of horticultural oil is a safer alternative to insecticides for spraying upward into a large tree.

Table 1. Insecticides & Fungicides to Control Oak Insect Pests & Diseases.

Insecticides & Fungicides Examples of Brand Names & Products
Acephate Bonide Systemic Insect Control Concentrate
Bacillus thuringiensis (B.t.) Bonide Thuricide Bt Concentrate
Garden Safe Bt Worm & Caterpillar Killer Conc.
Monterey Bt
Natural Guard Caterpillar Killer Spray with Bt Conc.
Safer Caterpillar Killer with Bt Concentrate
Southern Ag Thuricide Bt Caterpillar Control Conc.
Bifenthrin Bifen I/T Concentrate
Ferti-lome Broad Spectrum Insecticide Concentrate
Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate
Monterey Mite & Insect Control Concentrate
Ortho Outdoor Insect Killer Concentrate
Ortho BugClear Insect Killer for Lawns & Landscapes Concentrate; & RTS1
TalStar P Concentrate
Up-Star Gold Insecticide Concentrate
Chlorothalonil Bonide Fung-onil Multi-Purpose Fungicide Conc.
Ferti-lome Broad Spectrum Landscape & Garden
Fungicide Concentrate
GardenTech Daconil Fungicide Concentrate
Hi-Yield Vegetable, Flower, Fruit & Ornamental
Ortho Max Garden Disease Control Concentrate|
Southern Ag Liquid Ornamental & Vegetable Fungicide
Tiger Brand Daconil
Copper-based Fungicides Bonide Liquid Copper Concentrate
Bonide Copper Fungicide
Camelot O Fungicide/ Bactericide Concentrate
Monterey Liqui-Cop Fungicide Concentrate; & RTS1
Southern Ag Liquid Copper Fungicide Concentrate|Natural Guard Copper Soap Liquid Fungicide Conc.
Cyfluthrin Bayer BioAdvanced 24 Hour Lawn Insect Killer RTS1|
Bayer BioAdvanced Complete Insect Killer for Soil &
Turf I RTS1
Bayer BioAdvanced Insect Killer for Lawns RTS1
Horticultural Oil Bonide All Seasons Spray Oil Concentrate
Ferti-lome Horticultural Oil Spray Concentrate
Monterey Horticultural Oil Concentrate
Safer Brand Horticultural & Dormant Spray Oil Conc.
Southern Ag Parafine Horticultural Oil
Summit Year Round Spray Oil Concentrate
Cyhalothrin Spectracide Triazicide Insect Killer for Lawns &
Landscapes Concentrate; & RTS1
Martin’s Cyonara Lawn & Garden Concentrate; & RTS1
Malathion Bonide Malathion Concentrate
Hi-Yield 55% Malathion Insect Spray
Gordon’s Malathion 50% Spray Concentrate
Martin’s Malathion 57% Concentrate
Ortho Malathion Plus Insect Spray Concentrate
Southern Ag Malathion 50% EC
Spectracide Malathion Insect Spray Concentrate
Tiger Brand 50% Malathion Concentrate
Mancozeb Bonide Mancozeb Flowable with Zinc Concentrate
Southern Ag Dithane M-45
Myclobutanil Spectracide Immunox Multi-Purpose Fungicide Conc.
Ferti-lome F-Stop Lawn & Garden Fungicide Conc.;
& RTS1
Monterey Fungi-Max
Permethrin Bonide Eight Insect Control Vegetable Fruit & Flower
Bonide TOTAL Pest Control – Outdoor Concentrate
Bonide Eight Yard & Garden Ready to Spray RTS1
Hi-Yield Indoor/ Outdoor Broad Use Insecticide Conc.
Southern Ag Permetrol Lawn & Garden Insecticide
Tiger Brand Super 10 Concentrate
Propiconazole Banner Maxx Fungicide
Bonide Infuse Systemic Disease Control Concentrate
Ferti-lome Liquid Systemic Fungicide II Concentrate
Martin’s Honor Guard PPZ
Quali-Pro Propiconazole
Spinosad Bonide Captain Jack’s Deadbug Brew Conc.; & RTS1
Bonide Colorado Potato Beetle Beater Concentrate|Ferti-lome Borer, Bagworm & Leafminer Spray Conc.
Monterey Garden Insect Spray Concentrate
Natural Guard Spinosad Bagworm, Tent Caterpillar &
Chewing Insect Control Concentrate & RTS1
Southern AG Conserve Naturalyte Insect Control
Conserve SC Turf & Ornamental Concentrate
Ortho Insect Killer Tree & Shrub Concentrate
Thiophanate-methyl Cleary’s 3336-WP Turf & Ornamental Fungicide
Southern Ag Thiomyl Systemic Fungicide
1RTS = Ready to spray (hose-end applicator)

Pesticides are updated annually. Last updates were done on 2/21 by Joey Williamson.

Originally published 09/00

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Diseases and pests of oak and their treatment


  • Diseases and pests of oak
  • Gall midge
  • Fungal diseases and rot
  • Bacterial dropsy

Oak is a powerful and beautiful tree. Like many other plants, it can get sick. To prevent this from happening, you need to take care of the tree, especially if it grows in a garden plot. If, however, the oak is affected by the disease, it should be correctly identified, then the treatment will be productive.

Oak diseases and pests

The most dangerous problem is wood disease. In nature, there are only a few infectious diseases of this direction:

  • Non-rotten.
  • Rotten.

The first group includes vascular diseases, various tumors and ulcers, sapwood and necrosis. In case of infection, all important tissues are affected, which, if not treated, will lead the tree to dry out and die.

As a result of the appearance of ulcers and tumors, the tree disappears slowly but surely. The most common causative agents are fungi and bacteria.

Vascular diseases spread very quickly. A tree can completely dry out in a couple of years, and there have been cases that in a couple of months.

Necrosis is almost always caused by a fungus. It also spreads rapidly, affecting tissues. Promptly strikes neighbors.

Rot diseases affect branches, trunk, bark, root system.

Another significant problem can be various pests. They take an active part in the drying of the plant. Nowadays, there are a huge number of pests. Their development is facilitated by changing climatic conditions, drying out, violation of the water and light regime.

Referring to a large number of literary sources, we can conclude that there are a huge number of oak pests:

  • Pests that damage foliage:
  • Silkworms - about 5 varieties.
  • Moths - about 6 varieties.
  • Moth - about 8 varieties.
  • Sawflies - about 8 varieties
  • Scoops - about 5 varieties.
  • Leaf rollers - 2 varieties.
  • Nutworms - about 12 varieties.
  • Weevils - about 5 varieties.
  • Aphid - 2 varieties.
  • Ticks - about 3 varieties.
  • Ploshki - 2 varieties.
  • Acorn pests:
  • Codling moths - 2 varieties.
  • Weevils - about 3 varieties.
  • Nutcracker.
  • Pests damaging the trunk and branches:
  • Bark beetles - about 8 varieties.
  • Barbels - about 7 varieties.
  • Horntails - about 3 varieties.
  • Woodbiter - 2 varieties.
  • Flat rover.
  • Sharpeners and wood borers.

In fact, not all of these species of insects are often found on oaks, but they can still infect the oak.

Gall midge

One of the most common diseases is gall midge. It is expressed in the appearance of pink-yellowish balls (galls) on the leaves. Outwardly, the balls look like medium-sized cherries.

The gall midge is the cause of galls. In appearance, it resembles a tiny fly. The insect has a sharp ovipositor, with which it lays eggs right inside the leaf. After a certain period, a ball appears at this place. If at the end of autumn you break this ball, then a small worm will turn out to be white inside - this is a larva. Perhaps you will see an already formed insect. Sometimes there are oaks that are literally dotted with such galls, on each leaf there are several cones.

Interesting to know! Sometimes galls (bumps) are called ink nuts. The name is not invented, but quite justified. Since the time of Pushkin, ink has been prepared from them. It is quite simple to do this, a decoction is boiled from the nuts, and a solution of iron sulfate is added to it. Surprisingly, the result is jet black.

Fungal diseases and rots

Based on statistical data, it turns out that 25% of oaks have such a disease as mushrooms (fruiting bodies). They arise on already weakened trees, and take an active part in dying off.

Putrefactive processes are formed mainly after the winter period, when the cracks from frost have not healed. Also, many fungal infections penetrate through such cracks.

Insects play an important role in infecting wood with rot diseases. Pests such as goldfish or oak sapwood, barbels make moves in the trunks. Through them, the infection not only penetrates inside, but also actively spreads throughout the tree.

Pests that are in the middle of the tree actively spread vascular mycosis and other fungal infections. It has been noticed that fruiting bodies appear in the habitat of the yellow-gray mulberry. It is here that the flow of juice from the trunk is formed.

Pests can be divided into several categories:

  • Primary.
  • Secondary.

The first appear mainly on a healthy tree. Huge damage is done by their massive colonies. If the problem is not eliminated in time, then in a few years the tree may die. Pests diligently eat the foliage of the plant. Leaf rollers appear mainly in areas where the climatic conditions for the growth of oaks are violated. Active eating of foliage can reduce growth, and subsequent eating will cause the trees to dry out.

Weak and diseased oak trees suffer secondary attack by stem insects. Symptoms are expressed in the drying of the tree.

Oak bark may initially be damaged by various factors:

  • Splits due to frost or sun exposure.
  • Human injury.

In such cases, the tree can heal itself by healing the wounds. Also, damage can serve as an "entrance" for various infections.

Another type of infection penetration is old branches and twigs. A tree can die for various reasons, both from weather conditions and as a result of the attack of pests and viruses on it. In this case, water shoots can actively develop, which will significantly reduce the flow of moisture to the oak crown. The result is the death of not only individual branches, but the entire crown.

It is not uncommon for oak to be damaged in various ways. To prevent this from happening, maximum attention should be paid to the trees, and of course, no harm should be done.

Bacterial dropsy

Such a disease occurs not only in oak, therefore, there is a high probability of infection from a neighbor tree. The problem manifests itself in drying branches, while the crown is significantly reduced and thins. The barrel ceases to be spectacular, defects appear on it in the form of redness and swelling, sometimes, a kind of “wounds”. If the disease is not identified in a timely manner, it will quickly spread to all nearby trees.

Most often, bacterial dropsy affects already mature trees, their age is over 40 years.

On the trunk of an oak, almost under the crown, water shoots grow. Their life cycle is very short due to rapid drying. During the vegetative period, round swellings appear under the young bark. They may have different sizes. Inside the swellings there is a liquid, it is transparent and mucous. It is in this fluid that bacteria (exudate) are located. After some time, the bark in such a swelling will crack. The same exudate flows out of the cracks, which, when solidified, forms a brown-red, or with a brown tint of a spot. Over time, these cracks form wounds. In that part of the trunk, which has a strong and durable bark, swelling will not be visible, only brown spots will appear.

Exudate has a pronounced acid odor. Actively begins to flow in the warm season. Looking under the bark of such a tree, you can see fresh and moistened wood, a brown bast, and the same sour smell.

The disease looks different in young trees. In problem areas, depressions will stand out instead of growths. The bark that dies off turns brown, gets wet, like the wood inside.

The most dangerous period for a tree, and favorable for the development of bacterial dropsy, is the beginning of the growing season. Promotes the spread of rainwater. The infection penetrates under the bark through various damages (notches, splits from weather conditions, cracks, wounds, etc. ). The older the tree, the faster the disease will spread. Also, active watering of oak contributes to it. Also, favorable conditions for development are a dry period, pests, and sudden changes in temperature.

If the tree is actively attacked by pests, for example, leaf-eating, the crown will thin out significantly by the middle of the growing season. It is during this period that the oak is most susceptible to bacterial dropsy. It penetrates the cortex through a large number of lesions.

The consequences of bacterial dropsy are very serious. A drying tree is attractive to most pests. It is they who accelerate the process of death.

The drying process can take place without the participation of insects. A dried tree is not a source of infection, so if pests do start growing in it, they are not able to spread bacteria to other trees.

Bacterial dropsy quickly spreads to nearby trees. Birch trees are under great threat. For several years now, the problem has been gaining mass character. Therefore, it is very important to identify the problem in a timely manner, and begin to actively deal with it.

In order to minimize the damage from the disease, a number of measures should be taken:

  • It is necessary to constantly monitor the affected tree, especially from late spring to early autumn. This period is the most dangerous.
  • In winter, the infection does not spread, it stops in its development. Dead branches need to be pruned.
  • If fresh wood has been cut, it must not be stored near trees. It may have foci of infection, so it is better to take it out.

Much depends on the care of the tree, therefore, it must be timely and correct:

  • Oaks in the first years of life need fertilization of the soil. To do this, use mineral top dressing. Over the years, the roots go deep enough into the ground that subcorking is not required. Watering only.
  • Young seedlings must be protected from animals so that they do not damage the trunk.
  • Pesticides will come to the rescue from pests.

Oak treatment

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Let's talk about the common problems of oak plantations growing in forests and private areas. In central Russia, in the natural environment, the well-known English oak is found. In private areas, other types of oaks are also used in landscape design: rocky, red, white, chestnut-leaved, cork. All these species, except cork oak, tolerate our frosts well and are widely used in landscaping. But the common oak is the most common.

Major oak problems

Major oak problems can be classified as follows.


  • necrosis and vascular diseases,
  • cancers,
  • wood decaying stem rot,
  • root rot.


  • gall formers,
  • miners,
  • sucking pests,
  • trunk pests (xylophages),
  • pests of buds, young shoots and leaves (phyllophagous),
  • pests of acorns (carpophagi).

All oaks are long-lived, can endure extremely difficult conditions, can lose parts of the crown, trunk and roots and still survive, no matter what. In recent years, two main problems have been noted in our oaks, which lead to the death of even the most stable, powerful specimens. These are outbreaks of pests uncontrolled by forestry and cancerous diseases of oaks, for example, bacterial cancer (bacteriosis). Treatment of oaks in both cases should be comprehensive.


At the beginning of the third millennium, mass outbreaks of pests that had not previously been recorded with increasing speed occur. For example, in 2014-2016, boxwood plantations in a yew-boxwood grove in Sochi in the Caucasus were completely destroyed. But most of the specimens of the grove were classified as relic, they were more than 1000 years old. The same thing happens with oaks in central Russia. Trees that survived terrible frosts, hurricanes, droughts, are now dying from a mass attack of leafworms, moths and silkworms. There are primary and secondary oak pests. For example, leaflets are primary. Primary pests are those insects that attack completely healthy trees and, if a mass outbreak occurs, can lead to the death of plantings. Secondary, as a rule, attack already weakened plants, also lead to death. But now cases of death of oaks from both groups of pests are recorded.

Pest control

Oak pest control works best on strong trees not weakened by chronic disease. Preventive measures should be aimed at eliminating the factors that cause weakening of trees. This is an improvement in growing conditions, sufficient watering of trees, especially during droughts, soil improvement, measures for the regeneration of roots in case of damage. If the pest attack has already taken place, then they are treated with insecticidal or acaricidal agents. Treatments can be both external and intra-stem, when the active substances are fed into the tree's water supply system using special injection equipment.

Bacterial canker of oak

Bacterial dropsy of oak (bacteriosis, bacterial canker) is a dangerous infectious disease that gradually affects the vessels of the tree, first leads to the death of the crown, and then to the death of the whole plant. In the last century, there have been many cases of mass drying of oaks both in Russia and abroad. For example, in 1952, about 30% of all oaks on the territory of present-day Ukraine near Berdyansk died from this disease. There is still no exact understanding of the main cause of bacteriosis. Scholars are divided on this point. The complex of problems leading to the death of trees from this disease is considered to be drought, damage to root systems, dry winds and a decrease in the level of groundwater. In areas with an active recreational load, oaks suffer from soil compaction, the absence of mycorrhiza in the root layers, moisture stagnation, root death due to vandal construction, etc.

Studies have shown that in some dead plantations, the cause of drying out is a cancerous vascular disease that occurs due to the joint damage of trees by marsupial fungi of the genus Ophiostoma, Diaporthe and bacteria that are in water-conducting vessels. There is also the development of a pure bacterial infection, without mycosis. With droughts or pest damage, a bacterial vascular infection develops rapidly and leads to the death of the tree. Trees not infected with bacteriosis endure this without consequences, while those infected die. In old oaks, this process can take decades. The tree gradually loses its crown, the bark dies off, extensive dry sides and hollows form, the wood decays due to the activity of secondary wood-destroying fungi, skeletal branches and entire trunks break. Cambium (bark) dies from top to bottom - from the crown to the trunk. Long-dead branches and trunks remain in the crowns for a long time, and large branches gradually break out along the annular nodules. In the place of breaking, a large non-healing wound remains for a long time, in which wood-destroying fungi develop. Hollows are formed into which moisture from precipitation enters. The bacteria is getting worse.

What does a bacterial cancer of oak look like?

If an oak loses about a quarter of the crown, then the death of the cambium is observed only in the crown. It looks like this: the crown becomes openwork, transparent, the leaves are crushed and turn pale, some of them turn into a characteristic brown color, small shrunken branches appear in the crown, which break off in strong winds.

Trees with half or 3/4 shrunken crowns have extensive stripes of shrunken combium, descending down the trunk, often to the very root collar. On the bark, in places of lesions, black stripes may be noted, remaining from the outflow of juice. In wet weather, liquid can ooze in a variety of places in the bark, but most often in places of mechanical damage. The liquid is foamy, watery or gelatinous (depending on weather conditions - the drier, the more viscous consistency), it has an unpleasant sour smell. To the oak, oozing this liquid, insects fly up, which are attracted by the smell: wasps, hornets, flies. In the crown there may be completely shrunken large branches and even trunks. In places of old lesions of the cambium, deep hollows are formed.

Fallen acorns rot without sprouting. Already in the crown you can see the uneven and unhealthy brown color of the acorns, which should be green. Young seedlings die from a secondary infection - powdery mildew, unable to resist it. When cutting the stems on an even cut, brown spots and dots are also found.

When sawing trunks and branches, red-brown uneven spots with a border and stripes are visible on the saw cuts.

An acute process is difficult to confuse with another disease. The liquid oozing from the bark of a tree always has an unpleasant odor and attracts insects. If wasps or hornets flock to the oak and an elusive sour smell comes from the tree, it is possible that the wound is in the crown of the tree. Then you need to carefully examine the crown through binoculars. The main symptom of the old chronic dropsy is the abundance of dry branches in the crown of the tree, the sparseness of the crown, old hollows and non-overgrowing dry sides. Hollows and dry boughs can also form due to other diseases of oaks - kolpom and villemine necrosis; stepwise and hepatic cancer. But if a liquid with an unpleasant odor appears in the wound, this is a bacterial dropsy of oak.

How to treat?

In forestry, the treatment of affected plantations is cardinal - felling followed by planting and cultivation of resistant species. This approach is unacceptable on private plots in urban plantations, in forest parks and parks, and when it comes to valuable tree specimens (for example, oaks with a rich history, 200 years old or more).

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