Tree Information Center
Common Insect and Disease Problems
Carpenter ants – Carpenter ants are frequently found in stumps or the decaying parts of a live tree. They do not eat the live wood in trees but chew already decayed wood and then eject it as they carve out tunnels or “galleries” to create the nest they will live and reproduce in. Carpenter ants feed outside their homes on honeydew (residue from sucking insects) and also feed on other insects both alive and dead. Carpenter ants in your tree indicate the presence of decayed wood and are a good reason to have your tree inspected to determine the extent of the decay.
Hardwood borers – Hardwood borers typically attack stressed and dying trees but the borers themselves are rarely responsible for tree decline. They are a secondary pest. Once in a tree they are difficult to control but spraying the trunk with an approved insecticide can prevent further infestation. The two major wood borers found in hardwood trees are the flatheaded and roundheaded wood borers. The adult flatheaded borer is called the metallic wood boring beetle. The larvae feed by tunneling through both sapwood and heartwood. The adult emerges through an elliptical exit hole. The adult roundheaded borer is called the long-horned beetle. The larvae may feed on meristem tissue, heartwood and sapwood and after pupation the adult emerges through a round hole. The best defense against hardwood boring insects is keeping your trees vigorous. If you suspect that your trees have a borer infestation have them inspected by a professional as they may be suffering from a primary stress.
Kermes scale – Kermes scale is an armored scale insect that infests live oak trees. The signs are dieback of branch tips and sometimes whole branches of smaller trees. The scale insects are about one eight of an inch long with circular bodies and are tan in color. They can be observed clustered on the twigs of dying branches. See recommendation for control of Kermes Scale under the section on scale insects below.
Fall webworm – Fall webworm spin a tent like web up to three feet long at the end of branch tips and live, feed and reproduce within the web. The adult is a moth and the larvae are caterpillars. The larvae appear as small pale yellow worms about one inch in length. The larvae feed on the foliage within the tent until it is consumed. Their favorite host trees are pecan, hickory, sweetgum and persimmon. Control is recommended; consult with the extension service for an approved insecticide.
Psocids – Psocids are harmless insects that spin massive finely silken webs that sometimes cover the entire trunk and some of the larger branches of an oak tree. The adults are dark brown and about 1/4″ in length. If the web is peeled back you can sometimes view the psocids moving together in large groups, hence their nickname, tree cattle. The psocids do not injure the tree but feed on fungi, lichens and accumulated dead organic matter within the crevices of the bark. Chemical control is not recommended. If the web bothers you, wash it off with a garden hose.
Oak leafroller – The larvae caterpillar of the oak leafroller is yellow-green and about three quarters of an inch long. They roll or bind a leaf together and then feed inside the leaf damaging the leaf. Some years they attack trees in massive numbers. They are protected once in their roll so control is recommended at first sight of them in the early spring. Consult with a Horticultural Agent from the County Extension Service if control is needed.
Scale insects – Scale insects come in a variety of shapes and sizes although most are very small and barely visible to the naked eye. There are hundreds of species and they attack an assortment of conifers and hardwood trees as well as palms. They cause damage by piercing the plant’s vascular system and sucking sap through their piercing-sucking mouthparts. Severe infestations can kill the host plant. Because they are so small they typically go unnoticed. Very often they form as masses along stems. Early signs of scale damage are discolorations or death of foliage. Approved insecticides and horticultural oils are used as treatments.
Tree Disease Problems
Foot rot of citrus (Also called collar rots and bleeding cankers) – Several fungus species of the genus Phytophthora are soil borne pathogens that infect the root collar or roots of Citrus trees. The fungus causes cankers to appear on the root collar and lower trunk. The cankers are reddish brown to brown in color. The cankers will ooze a brownish liquid. Over time the canker will dry and crack exposing xylem wood that is stained. The damage to the root collar area disrupts the vascular flow and causes dieback in the upper crown. Ultimately this disease can kill the citrus. Phytophthora can enter through wounds in the basal area so it is important not to allow wounds to occur on the thin skinned citrus. Keep a large ring around your citrus and do not allow mulch to contact the trunk. Do not wound with a hoe or string trimmer. A recommended systemic fungicide can help control Phytophthora if treated early.
Hypoxylon canker – Hypoxylon canker (there are several species of Hypoxylon) is a fungus disease that can attack all species of oak trees that are severely stressed and ultimately causes their death. It is particularly damaging to drought stressed trees but also infests trees stressed by heat, root injury, herbicides or other diseases. Hypoxylon does not infest tree with good vitality. Hypoxlon invades the bark of the trunk and larger branches and colonizes within the inner bark, sapwood and cambial area. Its presence disrupts the tree’s vascular system causing death. The first signs of Hypoxylon are when the bark sloughs off revealing the grayish black fungus mats that developed under the bark. Hypoxylon is always present in oak trees in a latent form and can quickly invade if the tree becomes stressed. Keep your trees healthy and watered to avoid this killer.
Mushroom root rot – There are several fungi that infest roots and cause tree decline and death. Mushroom root rot is one of the most common and is caused by the fungus Armillaria tabescens. Mushroom root rot infects both conifer and hardwood species. Mushroom root rot is an opportunistic fungus that typically infects trees that are stressed and weakened. The fungus destroys the wood in the roots and can advance into the root collar area. The crown of infected trees may thin and have leaves that are small and chlorotic. In the late summer and fall the fungus will produce clumps of small tan mushrooms that are 1″-3″ in diameter and visible protruding from the grade. The mushrooms are attached to lateral roots close to the surface and the flare roots. A tree with mushroom root rot will ultimately die but before it does it is susceptible to wind throw.
Oak leaf blister – Oak leaf blister is a very common leaf surface fungus disease that alarms homeowners almost every year. The fungus (Taphrina caerulescens) causes large discolorations or a blister on the leaves of its favorite hosts the laurel and water oak. The blister appears as a reddish or blown splotch on the leaf. The blistered area is necrotic (dead) tissue. Cool wet springs cause a proliferation of this fungus. Mild infections are barely noticed as the blisters are small and confined to a relatively low percentage of leaves. But a severe infestation can cause the entire tree to defoliate and cause homeowners to believe that there tree is dying. Tree death from oak leaf blister is extremely rare and happens only after several years of severe infestations. Because this disease is rarely harmful and as it covers most of the crown, control is not recommended. If you have a tree with high ornamental value an approved fungicide will control the blister.
Sphaeropsis knot – A serious disease that is killing the East Palatka holly (Ilex x attenuata ‘East Palatka’) tree in Florida. Once infected the tree may die within five years. Early signs include galls (swollen areas on twigs) on twigs and sometimes the effect known as “witch’s broom”, the proliferation of twigs emanating from a gall. The foliage at the tips of branches will first appear chlorotic and later will die. The disease will spread to the larger branches and ultimately kill the tree. There is no verifiable prevention or treatment for Sphaeropsis knot at this time. It can be spread through pruning tools, so pruning tools should be sanitized after use on an infected tree. Sphaeropsis Knot infects oleander, citrus and bottlebrush to a lesser degree.
Sycamore anthracnose – Anthracnose of the sycamore tree is caused by a fungus and appears as scorched splotches on the surface of the leaves. Repeated infestations can weaken the branches to the point that dieback occurs and the tree can become susceptible to borers and other pathogens. Leaves should be treated with an approved fungicide prior to bud break with follow up applications.
Leaf spot – Leaf spot appears as a small discolored (usually brown or black) circle of dead tissue on a leaf surface. A single leaf may have a few or several of these spots. Leaf spot can be caused by a variety of fungi and some bacteria. The spores of leaf spot fungi that infect plants are disseminated through wind currents or are borne in raindrops that splash off infected leaves. Leaves that stay moist or grow in the shade are most susceptible. Leaf spot rarely causes serious damage to the host tree and consequently control is not recommended. In severe cases samples of the foliage should be analyzed to identify the specific pathogen and the proper fungicide apply. If you have a serious leaf spot infestation consult with a horticultural agent with the County Cooperative Extension Service.
Botryosphaeria canker – This canker is caused by the fungus Botryosphaeria dothidea and attacks many tree and shrub species but has been particularly damaging to the camphor tree. The fungus is an opportunistic pathogen that typically infests trees that have been weakened by environmental conditions such as drought or physical damage such as mechanical root loss or over pruning. Camphor trees planted on sandy soils are very susceptible as they readily suffer from drought stress during extended dry periods. Typical symptoms are branch dieback. The fungus kills sapwood tissue causing cankers (areas of dead tissue) – to appear on stems. The disease will progress inward until the entire branch is killed and finally the whole tree. The spores of the fungus often enter through open wounds. One source of prevention is to remove branches infected with cankers back to the branch collar (make a proper collar cut). If you remove a branch infected with the canker, be sure to sterilize the pruning tool blade with a disinfectant such as Lysol, 10% bleach or 70% denatured alcohol. The best prevention for Botryosphaeria canker is to water trees during drought events, avoid over pruning and do not subject the tree to mechanical root damage. Some other tree species affected by the canker include: sycamore, magnolia, wax myrtle, hickory and sweet gum.
Mistletoe – Mistletoe (Phoradendron flavescens) is a parasitic plant that attaches to the stems of hardwood tree species and takes nutrients directly from the tree’s vascular system. Once mistletoe infests a tree it can multiply throughout the tree. Mistletoe deprives the tree of needed food and can ultimately kill a tree if not removed. Mistletoe must be removed by removing the branch it is attached to at the closest fork back from the point of attachment.
Galls – Galls are swollen areas on stems or leaves that are caused by abnormal growth of plant cells induced by insects, nematodes or by pathogens such as fungi and bacteria. The primary cause of galls is caused by insects such as wasps that wound plant tissue and lay eggs in the wounded area. The plant grows tissues in response to the wounding that encases the eggs. The larvae will hatch in the gall and feed off of plant material within the gall until the insect becomes an adult. The adult will bore a hole in the gall and emerge to complete its life cycle. Some insects that cause galls to form include wasps, aphids, psyllids and midges. Galls come in a variety of shapes, sizes and colors. Some galls appear as a fruit hanging from a stem, other galls appear as a very small dot on a leaf. Galls do not cause serious damage to trees and control is not generally recommended.
Summer drop – Summer drop is a phenomenon common to sweet gum trees and to a lesser degree laurel oak. It occurs once heavy rains proceed periods of drought. The drought causes the cells of branch wood to become weaker. The sudden absorption of water overloads the weakened wood and the branch physically sheers from the tree. The only prevention is to keep trees hydrated during extended drought periods.
Squirrels – The gray squirrel damages trees by chewing the bark and stripping it from branches. Squirrels normally feed on acorns or other nut like fruit but if food is scarce they may feed on the bark of a tender young shoot. They can girdle (chew the bark all the way around the branch) the entire branch causing it to die. They also chew the bark in the crotches of young branches causing wounds and weakening the branch. There is no recommended control – squirrels and trees have co-existed for centuries.