The Frank P Matthews Tree Disease and Pest Guide At Frank P Matthews, we believe that healthy trees are the foundation of a thriving garden or landscape. Trees, like all living things, can face challenges from diseases and pests. Whether you’re nurturing a cherished ornamental specimen or growing fruit trees for a bountiful harvest, understanding the threats your trees might encounter is key to their long-term health and beauty. With over 100 years of experience in cultivating high-quality trees, our team at Frank P Matthews is committed to sharing knowledge that empowers gardeners and tree enthusiasts alike. Let’s ensure your trees not only survive but thrive for generations to come. In this guide, we’ll explore common tree diseases and pests, offering practical advice on how to identify, prevent, and manage them. From fungal infections to insect infestations, our expert insights will help you protect your trees and maintain a vibrant, resilient outdoor space. How to Spot Pest and Disease Damage on Trees Monitoring and identifying pest and disease damage is essential for maintaining the health and longevity of trees. Early detection can prevent minor issues from escalating into severe infestations or infections that threaten not only the affected tree but also the surrounding vegetation. Trees under stress often display various symptoms, including leaf discolouration, deformation, dieback, growth abnormalities, or visible signs of pests such as webbing or frass (insect droppings). Changes in bark, including cracks, cankers, or peeling, may also indicate fungal infections or wood-boring insect activity, while mushrooms or fungal fruiting bodies at the base of a tree can be a sign of root rot or underground pest damage. Excessive or discoloured sap exuding from wounds, cracks, or boreholes is another telltale sign of a pest invasion or bacterial infection. A thorough inspection of a tree requires attention to specific parts. Leaves often show the first signs of trouble, with yellowing, browning, curling, or the presence of holes suggesting pest feeding or fungal infections. Twigs and branches can reveal dieback, swellings, or discolouration, with galls indicating the presence of gall wasps or fungal infections, and fine webbing pointing to spider mites or tent caterpillars. The bark should be carefully examined for entry holes, tunnels, or sawdust-like frass left by wood-boring insects, as well as for sunken or cracked areas that may signal fungal cankers. The roots and trunk base can reveal symptoms such as decay, fungal growth, or instability, which often indicate root rot or underground pest damage. Flowers and fruit, too, may display scarring, discolouration, or premature dropping, with powdery mildew leaving a distinctive white coating and pests like codling moth larvae burrowing into fruit. Pest-specific indicators can further aid diagnosis. Aphids, for example, leave sticky honeydew on leaves and stems, often accompanied by sooty mould growth. Caterpillars cause chewed leaves and fine webbing, while borers leave small round or oval exit holes in bark and tunnels beneath it. Spider mites create fine silk webbing and stippled or discoloured leaves, while scale insects appear as small, immobile bumps on stems and leaves, often accompanied by honeydew. Fungal diseases like powdery mildew create a white, powdery coating on leaves and stems, while leaf spot causes black or brown circular spots. Cankers, characterized by sunken dead areas on branches or trunks, often have fungal growth at the edges. Bacterial diseases such as fire blight blacken and curl branches, giving them a scorched appearance, and crown gall produces large, tumour-like growths at the base of the trunk or roots. Viral diseases may cause mottled discolouration on leaves or stunted growth with deformed leaves or flowers. Regular inspections, conducted seasonally or after severe weather events, are crucial for early detection. Using tools such as magnifying glasses can help spot small pests, while traps like pheromone or sticky traps are effective for monitoring pest populations. Soil testing and laboratory analysis of affected leaves, bark, or soil samples can provide precise identification of pests or pathogens. Awareness of seasonal activity is also important, as many pests and diseases follow predictable patterns, with aphids being most active in spring and fungal infections peaking in warm, wet conditions. By systematically inspecting trees and understanding the signs of pest and disease damage, early intervention becomes possible, ensuring that appropriate management strategies can be applied. Preventative care, combined with regular monitoring, is the most effective way to maintain tree health and reduce the risk of long-term damage. Biological Control: The Role Of Predators In Pest Control Biological control, which relies on natural predators, parasites, and pathogens to manage pest populations, offers an effective and eco-friendly alternative to chemical treatments. Predators play a crucial role in regulating pest populations within tree ecosystems, fostering a natural balance while reducing the reliance on pesticides. By integrating natural predators into pest management strategies, gardeners and arborists can support tree health while encouraging biodiversity. Several key predators are particularly effective in managing common tree pests. Ladybirds, are well-known allies in the fight against aphids, scale insects, and mites. Both adult ladybirds and their larvae consume significant numbers of pests, with a single ladybird capable of devouring hundreds of aphids in its lifetime. Similarly, lacewings, especially in their larval stage, are voracious feeders of aphids, thrips, whiteflies, and small caterpillars. Often referred to as “aphid lions,” they are indispensable in pest control efforts. Hoverfly larvae also target aphids, scales, and mealybugs, while adult hoverflies contribute additional benefits as pollinators. Parasitic wasps offer another layer of control by laying eggs within or on pests like scale insects and whiteflies, which eventually kills the host. Ground beetles, patrolling the soil and leaf litter, target soil-dwelling pests such as caterpillars and slugs, providing vital protection for tree roots and bark. Using predators as a control method has numerous advantages. It is environmentally friendly, significantly reducing the reliance on synthetic chemical pesticides and their associated ecological impacts. It is also sustainable, as predators establish self-regulating systems that help maintain pest populations at manageable levels over time. Unlike many chemical treatments, predators target specific pests, minimizing harm to non-target species. Furthermore, encouraging predator populations promotes overall biodiversity, creating a healthier and more resilient ecosystem. However, using predators to manage pests requires careful planning. Balancing predator and pest populations is a challenge, as predator numbers depend on the availability of prey. Additionally, predators require suitable habitats to thrive, including nectar sources for adult insects or overwintering sites like log piles and hedgerows. Timing is also critical; predators must be introduced during the pest’s active lifecycle to maximize their impact. Another consideration is the compatibility of predator-based methods with chemical treatments. Broad-spectrum pesticides often harm both pests and beneficial predators, potentially disrupting the biological control system. For best results, it’s essential to create environments that support predator populations naturally. Planting a variety of flowering plants provides food and shelter for insects like ladybirds, hoverflies, and lacewings. Avoiding pesticide use or opting for organic alternatives ensures these predators can thrive undisturbed. Creating habitats such as hedgerows, undisturbed ground cover, or leaf litter offers shelter for ground beetles and other ground-dwelling predators. In cases of severe pest infestations, commercially reared predator species can be introduced directly to problem areas, providing immediate relief while longer-term habitat improvements are established. Predator use has shown promising results in various settings. Apple growers, for example, have employed parasitic wasps to control codling moth populations, significantly reducing crop damage. Urban tree managers have successfully introduced ladybirds to combat aphids on street trees, preventing sticky honeydew deposits that can damage nearby surfaces. Forestry operations, too, have benefited from the introduction of ground beetles to manage weevils and caterpillars in young conifer plantations. With over 100 years of experience in cultivating high-quality trees, our team at Frank P Matthews is committed to sharing knowledge that empowers gardeners and tree enthusiasts alike. Let’s ensure your trees not only survive but thrive for generations to come. Nick Dunn’s Tips and Tricks There will be instances where pest and disease damage is visible but not necessarily harmful. In these instances, closely monitoring problems and using an organic and biological approach combined with predator-friendly chemicals make it possible to maintain a safe environment in your garden. We recommend cutting out severe foliage distortions caused by pests, mildew and canker. For those self sufficiently minded we would also recommend chickens as effective pest controllers. Homemade products such as garlic preparations do a great job of discouraging pests when applied to fruit trees. Healthy Growth Means Fewer Problems Healthy trees are far less susceptible to damage from pests and diseases. Pay Attention To BOTH Sides Of Your Leaves While working in your garden inspect the leaves of your trees for damage or early signs of pests or disease. Pay particular attention to the underside of your leaves as this is where the first signs of pests tend to appear! Master The Art Of Inaction Unless the leaf is becoming distorted it is best to leave it be and monitor the situation. If It Moves Fast Its Friendly You can generally tell a pest from a predator because the pest generally moves slowly. It’s an adage that is both logical and true! Leaf Disorders Once a leaf disease strikes a tree it is generally too late to solve the problem that year. Be sure to make a note to apply some preventative measures early in the following spring. This applies to scab, rust diseases and mildew in fruit and crab apples. Spray in dry weather and apply when the leaves are just emerging well before blossom time. Prevention is always better than cure. Bark Wounds Bark wounds and cankers are best treated by removing the affected branch. Do not hesitate to take firm action as most trees will respond by producing strong replacement growth quite rapidly. How To Identify And Manage Diseases, Pests And Disorders We’ve explained how to identify tree pests and diseases and even offered some solutions that apply to all conditions. Now we will tackle each pest and disease one by one to tell you everything you need to know to restore health to your garden once again! Green Apple Aphid Symptoms: Considerable leaf curling, shoot tips may be stunted or even killed. Trees Affected: Most fruit trees and Betula Period: May-July Control: Very often no action is necessary but if action is required prune out the affected area. Only spray if heavily affected. Rosy Apple Aphid Symptoms: Twisted shoots, small leaves followed by shrivelled fruit. Trees Affected: Apples Period: April – July Control: Use lacewing or ladybird larvae if unable to prune out. Damson Hop Aphid Symptoms: Considerable leaf and shoot curling. Trees Affected: Plum, Damson and Gage Period: April – July Control: Use lacewing or ladybird larvae if unable to prune out. Woolly Aphid Symptoms: Sticky white ‘wool’ produced. Galling may seriously disfigure plants. Trees Affected: Apple Period: Anytime Control: Prune out the infected area. Severe infections should be scrubbed with a wire brush and painted with methylated spirits. Blackfly Symptoms: Severe leaf curl. Shoots may become stunted and tips killed. Trees Affected: Cherry Period: April – July Controls: Remove infected leaves by hand or spray. It is important to detect infestations at early stages. Bitter Pit Symptoms: Multiple black spots throughout the flesh. Trees Affected: Apples Period: August – October Control: Take no action. Bitter Pit is often attributed to a calcium deficiency but some varieties are particularly prone. Use seaweed products as fertilisers or foliar sprays. Brown Rot Symptoms: Fruit turns brown and concentric rings of yellow mould appear. Trees Affected: Apples & Pears (Cherries & Plums) Period: August – October (July – September) Control: Remove bad fruit A.S.A.P Nectria Canker Symptoms: Sunken areas of bark are often restricted to one side of the stem. Wounds may heal disfiguring cankers at the edge. Trees Affected: Apples & Malus Period: Anytime Control: Prune out between June and August Bacterial Canker Symptoms: Amber gum oozes from affected bark that leaves darkened, sunken stem areas. Trees Affected: Plum, Cherry & Prunus Period: Anytime Control: Prune out between June and August Papery Bark Canker Symptoms: Flaking papery brown bark. Trees Affected: Apple, Pear & Malus Period: Anytime Control: Prune out the affected area. Acid/Wet conditions can be the cause. Trees can recover after pruning and correcting conditions. Green Capsid Symptoms: Corky patches on fruit (Brown spots on leaves) Trees Affected: Apple, cherry, peach & pear (Apple leaf) Period: April – September Control: No action required / use sprays if persistent. Coral Spot Symptoms: Dead twigs or patches of dead bark covered in pinkish pimples Trees Affected: Acer & Robinia Period: Anytime Control: Prune out if on side branches, trees rarely survive infections on the trunk. Hail Damage Symptoms: Brown indentations or russetted raised bumps often healed up. Trees Affected: All fruit Period: April – September Control: None required. Damaged fruit will generally heal and become edible. Leaf Curl Symptoms: Large reddish blisters on leaves leading to early leaf fall and weakening of tree. Trees Affected: Peaches Period: April – July Control: Remove infected leaves by hand. Cover wall-grown trees with polythene between April and May for prevention. Leaf Miner Symptoms: Shredding of leaves between veins. Trees Affected: Aesculus & some fruit trees Period: June – September Control: No action is required. This pest is serious but the tree will recover each spring & summer. Long term prognosis is that a predator for this pest will prevail. Pear Midge Symptoms: Shrivelled fruitless often turning black before premature drop. Trees Affected: Pear Period: May – September Control: Remove affected leaves by hand. Powdery Mildew (Fruit) Symptoms: Young leaves, shoots, and flower trusses may appear grey. Growth stunted, diseased flowers not set, leaf fall. Often affects whole trees. Trees Affected: Apple, pear & Malus Period: April – September Control: Prune out the infected area. If a severe problem spray for prevention early spring after winter pruning. Powdery Mildew (Acers) Symptoms: Often affects whole trees late summer and autumn. Trees Affected: Acer Platanoides, Acer Campestre, Quercus Period: July – October Controls: Impractical to take control measures, varies according to season. Blister Mite Symptoms: Green pustules on the upper side of leaves. Trees Affected: Acer and walnut Period: July – September Control: No action required. No harm comes to trees affected. Codlin Moth Symptoms: Grubs found in the central core. Trees Affected: Acer, apple, pear, plum, damson, walnut Period: May – August Control: Introduce pheromone traps. Males are attracted to the scent of females and are caught on sticky pads preventing mating. Fruit Tree Tortrix Moth Symptoms: Leaves spun together or a leaf attached to fruit. Trees Affected: Most fruit trees Period: June – September Control: Introduce pheromone traps. Males are attracted to the scent of females and are caught on stick pads preventing mating. Winter Moth Symptoms: All flowers and greenery may be eaten. Malformed fruits with corky scars or depressions. Trees Affected: All fruit trees Period: October – May Control: Apply tree bands. Make sure band is above tree tie otherwise tree stake will also need to be treated. Lacky Moth Symptoms: Severe defoliation. Growth and fruit production affected. Trees Affected: Apple, Cherry Period: July – September Control: Spraying necessary for a complete kill. Leopard Moth Symptoms: Accumulation of grass and wood particles. Later withering and dieback of leaves and shoots. Trees Affected: Apple, Cherry, Pear, Plum, Walnut Period: June – July (2/3 years) Control: No action is required. Very rare and worth seeing! Phytophora (Fruit) Symptoms: Bark peeling and wet black under bark at ground level. Trees Affected: Apple, Pear & Malus Period: Anytime Control: No action is required. Avoid poor drainage and excessive grass competition. Phytophora (Ornamental) Symptoms: Black oozing gum on tree bark. Trees Affected: Aesculus & Alnus Period: Anytime Control: Coppicing will reinvigorate the tree and takeaway the infection in Alnus. Aesculus is serious and is known as a bleeding canker. Fruit Tree Red Spider Mite Symptoms: Leaves become dull green, brownish, then silvery bronze. Adults shown in pictures. Trees Affected: Most fruit trees affected & some ornamentals Period: May – September Control: No action required. Rust Symptoms: Red spots on the leaf topside followed by orange pustules on the underside of the leaf. Trees Affected: Plum, Quince, Betula, Populus Period: July – September Control: Pinch off affected leaves. Gather up and compost leaves. Sawfly Symptoms: Brown, corky scares radiating out from calyx end. Grubs feed on the central core generally causing fruit to stop. Trees Affected: Apples & Pear Period: April – July Control: No action is required. Fruit damage is non-progressive and generally heals. Fruit Scab Symptoms: Fruits badly disfigured and corky areas develop. Trees Affected: Apple and malus Period: May – August Control: Use sprays. Worse in high rainfall areas where scab resistant varieties are recommended. Shot Hole Symptoms: Brown spots on leaves that die and drop out leaving multiple holes. More likely to appear during a wet season. Trees Affected: Cherry, Plum & Prunus Period: May – September Control: No action required Silver Leaf Symptoms: Silvering of leaves often seen only on part of the tree. Trees Affected: Cherry, plum & Prunus Period: Growing Season Control: Prune out between June & August. If persistent, the tree will need to be removed. Sucker Symptoms: Petals on partially opened buds turn brown. Flowers may be killed quickly. Often mistaken for frost injury. Trees Affected: Apple, Pear Period: April – October Control: No action required. Not an invasive pest. Verticillium Wilt Symptoms: Wilting of whole branches also brown streaks along water-conducting tissue under bark. Trees Affected: Acer, Tillia Period: April – August Control: Prune out the infected area. Can be serious, but few control measures are available. Water Core Symptoms: Glassy, clear flesh inside. Very seasonal. Often revered in some countries for the sweetness of the affected flesh. Trees Affected: Apple Period: Growing season Control: No action required. We hope you have found the information you were looking for in this article! There isn’t much we haven’t seen in 123 years of tree production. The majority of these pests and diseases really don’t require much action. It is however important to be aware of them, monitor any instances of them and act if you need to. Back To List Related Articles… Rootstocks for Fruit Trees Rootstocks are an essential part of growing fruit trees. This … Full Details When will my tree produce fruit? 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