Fruit & Nut Tree Management

ENTO-087 Insect and Disease Pess of Peach, Plums

Insect Pests

The list of insects that can become a problem for your fruit trees is extensive. Some of these insects attack the leaves on fruit trees. While these pests can slow tree growth and make your tree look unsightly, they don’t directly affect the fruit. Those that lay eggs in or near growing fruit or themselves feed on fruit do the most damage. The coddling moth is one of the worst pests on apple and pear trees. It lays eggs that hatch into larvae that quickly burrow into small apples and pears, feeding on the interior as the fruit grows. Aphids cause curling leaves and misshapen or small fruit, scale insects can weaken trees and deform fruit, and mites, fruit flies and borers can cause serious damage to all fruit trees.


Aphids, mealy bugs, whiteflies and many hard scales are nuisance insects that may disfigure or discolor leaves and branches, but seldom do real damage unless they descend in a plague. Many are controlled using natural enemies such as lady beetles, green lacewings, tachinid flies and parasitic wasps. Nuisance pathogens such as powdery mildew (Podosphaera spp. and Sphaerotheca spp.), which results from cool, moist weather, can be controlled with fungicides, such as copper sulfate, neem or jojoba oil, and good cultural practices, such as careful watering, pruning to improve air circulation and the use of slow-release fertilizer.


Some insects pose serious threats to fruit trees by killing young branch and leaf growth. Armored or hard scales include San Jose scale (Quadraspidiotus perniciosus) feeding on stone fruits such as apricots and plums and California red scale (Aonidiella aurantii) feeding on apples, peaches and olives. Soft scales, such as calico scale (Eulecanium cerasorum) and Kuno scale (Eulecanium kunoense) feed on stone fruits, including cherries, while brown soft scale (Coccus hesperidum) and black scale (Saissetia oleae) feed on citrus, causing more damage due to their mobility. Scale infestations require timely pruning and targeted insecticides.

 Borers and More

Borers and some other insects use fruit as a nursery for their young, laying eggs inside the fruit, giving hungry young larvae a ready source of food. Borers include American plum borer (Euzophera semifuneralis), Peachtree borer (Synanthedon exitiosa) and Shothole borer (Scolytus rugulosus) feeding on stone fruits, while Shothole borer (Scolytus rugulosus) and Pacific flatheaded borer (Chrysobothris malis) also feed on apples and pears. Other insect pests include carpenterworm (Prionoxystus robiniae), spotted wing drosophila (Drosophila suzukii) and olive fruit fly (Bactrocera oleae). Borers and other fruit eaters can ruin part or much of a crop and must be caught early in the home orchard with targeted insecticides.


Mosaic viruses target many fruits, spreading necrotic, tough patches on green wood and fruit surfaces. Although apples are particularly susceptible to mosaic virus, its effect is to reduce the harvest rather than kill the tree. Fire blight, caused by the bacterium Erwinia amylovora, is another more destructive pathogen which attacks apples and peaches. Apple and pear scabs, caused by Venturia inaequalis and V. pirina fungi are most severe in damp, coastal areas. Sphaerotheca species fungi attack stone fruits. Pathogens are managed by preventive fungicides, good cultural practices, prompt removal of fallen leaves and use of resistant varieties. Mosaic-infected trees cannot be cured.

 ***Keep records on growth, blossoming and fruiting habits of your fruit trees. This gives you an indicator on what the normal growth of your tree looks like. Reduced growth and a decline in general health may indicate crown rot or oak root fungus. Check the tree’s leaves. Look for discoloration, spots or curling on the edges. Peach, nectarine, plum and apricot trees often suffer from peach leaf curl. The primary causes of peach leaf curl include damp weather and fungus. Shriveled or damaged leaves may indicate brown rot or apple scab, particularly in pear and apple trees. Cedar-apple rust causes yellow or brown spots on the leaves.

 ***Inspect the bark on the tree. Spots of discoloration or peeling bark signal a possible bacterial canker. Other symptoms include leaf dieback in the spring, and eventually the canker site leaks a dark, gum like material.  Look for blackened leaves and stems. These symptoms could mean your tree has fire blight. The infected areas will die. Quick removal of branches with fire blight ensures the tree’s survival.  Examine the fruits on the trees regularly. Symptoms such as rotting and discolored spots on the fruits suggest one of the numerous types of rot diseases fruit trees develop. Black rot, crown rot, bitter rot and white rot all damage the fruits on an infected tree.


Fruit trees show subtle symptoms at the onset of branch dieback diseases. Initial telltale signs may show first in their leaves before their branches die. Leaves may be slower than usual to emerge in spring and they may turn pale green or yellow. Leaf margins and tips may scorch, which makes them turn brown and drop prematurely. As a disease progresses, twigs and branches die and trees may try to compensate for these losses by producing suckers on branches and trunks.

Fungal Diseases

Galls and cankers often infect fruit trees. Some of these diseases are caused by fungal pathogens, which cause branches to die and may lead to tree death. Black-knot galls, caused by the Apiosporina morbosa fungus, are warty growths on trees that commonly affect cherry and plum trees. Although young branches may die within a year of infection, larger branches may live much longer before they succumb. Cytospora, leucostoma and valsa fungal pathogens cause cankers to form on fruit trees. Bark and branches ooze a gummy residue from cracks that widen and expose diseased tissue. As the disease progresses, cankers girdle stems until branches die.

Bacterial Diseases

Some cankers are caused by bacterial pathogens (Pseudomonas spp.) that can attack all stone fruits, such as peaches and nectarines. Also called gummosis, these cankers exude a similar gummy residue as fungal cankers. Citrus Huanglongbing (HLB) is commonly called citrus greening disease because of its appearance in affected trees. It is a bacterial disease characterized by leaves that turn yellow only in one section of a tree. A small insect called a psyllid spreads this disease as it feeds on plant tissue and moves among different trees.


***Some fungal and bacterial tree diseases cause prematurely falling leaves. These diseases, except for Dutch elm disease, are usually not lethal, but may weaken trees. Shade trees, ornamental trees and fruit trees may be infected with the same disease organism but display different symptoms. Symptoms on different tree types may also vary, because the disease may be caused by a tree-specific fungus or bacterium. Some of these tree diseases can be controlled by using fungicides or by simply just removing infected debris, branches and fallen leaves.


Anthracnose is a fungal disease that causes leaf spots and cankers on twigs or branches on a large variety of trees. The anthracnose fungus spreads and infects trees during rainy or humid periods. The species of anthracnose fungus that attacks trees depends on tree type. The fungus Gnomonia leptostyla infects black walnut trees and produces circular, dark brown or black spots on leaves that enlarge until leaves turn yellow and fall prematurely throughout the summer. The Gnomoniella fraxinea fungus infects ash and causes irregular brown spots associated with leaf veins. A severe infection will cause leaf drop. During spring, the Gnomonia veneta fungus distorts leaves and creates dark spots on oak leaves and may cause premature loss of leaves. The American sycamore, Modesto ash and London plane tree are very susceptible to anthracnose.

Leaf Spot

Leaf spot is a tree disease that is caused by a large variety of fungi. The disease develops during extended periods of cool moist weather in spring and during new leaf growth. Alternaria fungi attack ash, cherry and magnolia. These fungi cause circular or angular brown spots, which may drop out creating “shot holes.” Cercospora fungi cause yellow, brown or black blotches on magnolia, fruit trees and walnut trees. The Coccomyces hiemalis fungus produces small circular purplish-reddish spots, which often fall out leaving an appearance of shot holes on cherry and maple tree leaves. With a severe infection, foliage yellows and falls prematurely.

Leaf Blister

Leaf blister, or leaf blight, can infect all varieties of oaks. It is caused by the Taphrina caerulescens fungus. The fungus creates crusty, tan spots that bubble up on oak leaves. Oak leaf blister is not a serious disease, but may cause premature leaf drop. To prevent leaf blister, keep young trees well-watered and fertilized, because a healthy tree is less likely to be infected. Clean up infected foliage, because the fungus can overwinter in fallen leaves.

Bacterial Blight

Bacterial blight, also called blossom blight or shoot blight, is a tree disease caused by the bacterium Pseudomonas syringae. It affects lilacs, walnut trees and many fruit trees. White flowering varieties of common lilac are very susceptible to the disease. The bacterium causes small, angular, black leaf spots that enlarge to irregular brown spots. The disease also causes cankers on tree branches and may brown or blacken flowers and fruits. Rainy weather promotes and helps to spread bacterial blight. Combat bacterial blight by pruning off branches with dieback or blight and by improving air circulation around trees. Bacterial blight may cause premature leaf drop, but usually does not kill trees unless cankers girdle the tree.

Dutch Elm Disease

Dutch elm disease is caused by the fungus Ophiostoma ulmi-elms (synonym Ceratocystis ulmi). Most elm trees will die; older ones taking several years before succumbing. The fungus spreads via water-conducting channels of the elm and produces gum that clogs up these channels, leading to wilting, leaf drop and death. This disease has devastated elm trees all over the United States. Dutch elm disease is transmitted by two species of bark beetles. The Siberian elm, also called Chinese elm, is partially resistant to Dutch elm disease.

Peach Leaf Curl

Peach leaf curl is one of the most serious and common peach tree diseases. The disease causes swollen and distorted leaves with red coloring. Leaves infected with peach leaf curl also end up with grayish sac-like growths containing fungal spores. This disease usually causes obvious symptoms about two weeks after peach trees grow new leaves in the spring. Untreated trees suffer from slowed growth and low fruit production. Many experts recommend controlling this disease by treating the peach trees with a copper fungicide after their leaves have fallen during autumn. Products that contain copper ammonium complex work especially well when combined with 1 percent horticultural oil.

Powdery Mildew

The fungal disease powdery mildew causes a white powdery growth on tree leaves. It can hinder the growth of new branches and leaves, and the disease can also attack the peaches themselves. Many gardeners can get rid of this disease without fungicides. Proper tree care and pruning away infected tree parts will often control it. Pruning trees to prevent branch crowding and increase air flow also helps.

 ***Peach trees (Prunus persica) are prized in the home landscape for their sweet, fragrant blossoms and juicy fruit. While they’re generally easy trees to grow, peach trees are vulnerable to a disease complex called peach tree short life disease. Because this disease is causally related to several other problems, including pathogenic nematodes, cold damage and improper cultural techniques, it is possible for home gardeners to prevent peach tree short life disease from harming their trees.


Peach tree short life disease is a complex that results from a variety of cultural and environmental factors. The term itself describes the sudden collapse and eventual death of young peach trees that typically occurs during the spring months. While peach tree short life can affect any age of tree, in most cases it affects trees that are between 3 and 7 years old.


Symptoms of peach tree short life typically include a sudden wilting of a couple of branches or collapse of the entire tree soon after bloom. When a tree dies from peach tree short life disease, it usually dies back to the soil line, with the main trunk and roots appearing perfectly healthy. However, if you examine the feeder roots, necrosis or nematode damage is often present. Beneath the bark, a sour odor is present, and browning that extends to the soil line but not below it can be seen. Because dead trunk tissue doesn’t typically extend beyond the soil line, the primary root system does not usually die and this results in root suckers appearing at the base of your tree in the summer.

Primary Causes

Peach tree short life disease is not caused by one specific factor. It is often a combination of cold damage and bacterial canker (Pseudomonas syringae). Other common factors that contribute to the development of peach tree short life include pruning your tree at the wrong time, improper rootstock selection, soil management, inadequate fertilization and rapid temperature fluctuations in late winter and early spring. The main biological factor that predisposes a peach tree to bacterial canker or cold injury, and thus to peach tree short life, is the ring nematode (Mesocriconema xenoplax).

Control and Prevention

Several practices can reduce or prevent peach tree short life disease from occurring. These practices can be grouped into three categories: site preparation, stock selection and sound cultural practices. The ring nematode increases the severity of peach tree short life, so soil should be tested before planting for the presence of this pest. If necessary, fumigate the soil before planting to suppress nematode populations. Buy peach trees only from trusted nurseries and orchards that are known for producing vigorous, disease-free trees grown in fumigated soil. Rootstock selection is also important, so ask for cultivars that are nematode resistant. In addition to choosing a healthy peach tree, carry out sound cultural practices. Prune your tree as late in the season as possible, never before January 1 and preferably after February 1. Keep the soil free of weeds and dead plant material to reduce the risk of bacterial and fungal infections. Proper fertilization and irrigation ensures a healthy tree, and this helps reduce damage from peach tree short life.

 ***The fungal disease post oak rot attacks the roots of peach trees, infecting and eventually killing the tree. Also called Armillaria root disease after the type of fungi that causes it, the fungi live on the roots of not just peach trees but many other hardwood trees. Post oak rot is also referred to as shoestring disease because of the long, thin fungal structures it produces. While the disease cannot be cured once it strikes a tree, care of the tree can prolong its life, and careful selection of planting areas can help avoid the disease.

Identify trees that may be infected with oak root rot. The fungus begins in the roots of the trees and is not visible until it has greatly damaged a tree. However, mushrooms with the same fungus often grow around the base of the tree. Above-ground symptoms of infection include discolored and thinning leaves that turn from green to yellow to black. Branches also can die back.

Maintain the health of the peach tree for as long as possible. Healthy trees will live longer and be less susceptible to the fungus. During times of little rain or drought, provide irrigation for peach trees. Also take care when mowing or weeding around the trees to not cause wounds or deep nicks in the base of the trunk that might allow other pests to infest the tree. The fungicide propiconazole can help prolong the life of the tree but will not completely control Armillaria fungus. The fungicide is infused into the root system of the tree.

Remove all traces of the peach tree once it has succumbed to post oak rot. It is not enough to take down the tree; the stump and root system must be removed to keep the soil as free as possible from the fungus. Use a stump grinder to remove the stump.

Prevent post oak rot in future peach orchards by not planting new trees in areas where the fungus has been found in the past. Areas that are prone to flooding are more likely to harbor the fungus that causes post oak rot. Propiconazole can be used on peach tree roots in the fall to prevent the fungus.

 Disease Management

Healthy fruit trees are better able to withstand diseases. Stress avoidance as a method of disease prevention is the most important management strategy. Once a disease invades a fruit tree, it is difficult, and sometimes impossible, to eradicate. Pruning infected branches back to healthy growth sometimes mitigates the spread of disease, but unhealthy trees are likely to develop more diseased tissue. Fungicides and bactericides may also retard disease symptoms, but they are most effective when applied as preventive treatments instead of after diseases take hold. Planting in well-draining soil, watering and fertilizing according to recommendations, and preventing mechanical injury from mower blades and string trimmers are strategies that help maintain optimal tree health.


Most aphids, scale insects and mites can be controlled by applying a product called a dormant oil in late winter or early spring, destroying eggs before the tree’s flower buds appear. Borers that attack peaches can be prevented by spraying in early spring with endosulfan, applied directly to trunks and branches. If you grow apples or pears, control of the coddling moth and similar insects is extremely important to protect your developing fruit. Timing is critical, with a first spray about two weeks after most petals have fallen from the tree’s blossoms, followed by a second spray one or two weeks later. Repeat this treatment in late July or early August or whenever you notice new larval holes appearing on the fruit.

***Peach trees (prunus persica) have delicious fruit and attractive blossoms. They tolerate United States Department of Agriculture Hardiness Zones 5B through 8B and are widely grown. However, many gardeners have difficulty growing peach trees because of the trees’ disease and pest susceptibility. Growths or discolorations on peach tree leaves often indicate a disease — usually a fungal infection. Two common diseases that infect peach trees are peach leaf curl and powdery mildew, both of which show up on the leaves.


It usually takes less work to prevent tree diseases than it does to get rid of them. Healthy trees are generally less susceptible to all diseases, including growths or other diseases that infect peach leaves. To grow healthy, strong peach trees, plant the trees in an area with good soil drainage. It is also important to prune them at least once per year, because they produce fruit on year-old branches. Peach trees often grow best with some fertilizer. Gardeners can have soil tests done at a lab or nursery to determine what supplemental nutrients a peach tree could use to grow well in a specific location. To prevent the spread of fungal spores, remove infected tree parts from the garden and surrounding area immediately.

Resistant Varieties

Another way to prevent peach tree growths and diseases is to plant disease-resistant tree varieties. Gardeners who have previously had difficulty because of peach leaf curl should consider planting varieties resistant to the disease, such as “Frost,” “Indian free” and “Muir.” Similarly, “Crest,” “Flame Crest,” “Flavor Crest” and “O’Henry” are peach tree varieties with a resistance to powdery mildew.

 Choosing Products

For a home gardener, certain pesticides are available that are labeled with the word “domestic” on the container. These products contain ingredients considered safe for home use, including carbaryl or Sevin, horticultural oils such as dormant oil, certain synthetic insecticides such as malathion and permethrin, and natural insecticides such as pyrethrins, which are extracted from flowers. Insecticidal soaps are also available that control aphids and certain other, soft-bodied insects. Consult product labels to identify the specific insects controlled by each product. Some convenient products contain a mixture of insecticides, formulated specifically for a home orchard and labeled to indicate the insects they control.


When deciding when and how to spray your fruit trees, be aware that many domestic insecticides also affect beneficial insects such as bees. For example, carbaryl, malathion and permethrin are toxic to bees and other harmless insects. Endosulfan is especially toxic and can harm birds; it also injures fish if the runoff from trees reaches streams or lakes. Horticultural oils are generally considered safe, with little impact on other insects, and pyrethrins are also low in toxicity. To minimize the need for spraying, remove all fruit from your trees at harvest and destroy any insect-infested fruit on the ground. This will help reduce the risk of pest problems the following year.

Fungicides for use on Prunus species
Bacterial Spot Brown Rot Peach Leaf Curl Scab Shot Hole Rhizopus Rot Rust
copper hydroxide,
benomyl, captan,
iprodione, triforine, thiophanate methyl, propiconazole,
tebuconazole, sulfur
copper hydroxide,
chlorothalonil, thiophanate
methyl, sulfur, iprodione
copper hydroxide
dicloran chlorothalonil,

***Peach tree borer- Adult is a steel-blue, clear winged moth. Adult flight is usually from late June through September and eggs are laid at on the base of the fruit tree. Larvae burrow in the crown and roots, girdle young trees and weaken others. A single larva is capable of girdling a newlyplanted fruit tree. Presence may be detected by globs of gum mixed with a granular brown frass that appear at the base of infested fruit trees. Management- Place a plastic or metal cone or barrier around base of tree to prevent entry before egg laying begins. Push the cone 1”-2” into the soil. Cone should fit snugly around the trunk at the top to prevent the tiny larvae from getting beneath it. In small home orchards a procedure called ‘worming’ may be done. Use a pocket knife, wire, or some pointed instrument to remove dirt around tree, and dig out the larvae.

—Chemical control- Spray applications onto trunk of the tree to prevent newly hatched larvae from boring beneath the bark. Carbaryl (sevin), gamma-cyhalothrin, kaolin clay (Surround at Home), malathion (peaches only), permethrin (peaches only), pyrethrins.

***Peach twig borer-Early in the season, larvae bore into buds, flowers and emerging shoots. There are three generations each growing season. Later in the season, larvae my bore into twigs and shoot terminals causing shoot tip wilting or flagging. Occasionally, they will bore into the fruit.

—Chemical control- Early sprays aimed at the newly hatched larvae before they bore into the shoot, or fruit will provide the best control. Use acetamiprid, carbaryl (sevin), efenvalerate, gamma-cyhalothrin, kaolin clay (Surround at Home) permethrin (peaches only), spinosad.

***Scale insects- Best control is achieved during the delayed dormant period (bud break) using a superior type oil. These applications target and smother the non-mobile over wintering adult and egg stages. If spring and summer scale control is required, apply during the crawler period (June and July. For growing season control us carbaryl (sevin) or imidacloprid (labeled for fruit trees).

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