Common Pests and Diseases

Common Pest and Diseases found in Kentucky/Indiana Landscapes

Common Spider Mite

Common Spider Mite

There are many varieties of pest and diseases we see in the local area that can inflict damage to trees and shrubs in your urban landscape. Bob Ray Co., Inc.’s certified arborists can diagnose and recommend treatment for controlling many of the commonly seen pests and diseases.

Spider Mites

One of the more prevalent pests we come across in landscapes are various species of spider mites. Spider mites are often seen in urban landscapes and can attack both deciduous and evergreen plants. Mites are very tiny, about the size of a speck of pepper, and can be very prolific. Infestations often go unnoticed until plants are showing substantial damage. Spider mites have needle-like mouthparts and feed by piercing leaves and sucking the fluids from individual plant cells. This feeding causes the leaves to have a stippled or flecked appearance with pale dots where the fluid has been removed. Prolonged infestations can cause yellowing of the foliage and premature leaf drop that is similarly seen in drought conditions. Severely infested plants may be stunted or even killed if the infestations persist. A majority of the mites can be seen feeding on the undersides of leaves, but the damage is more obviously detected on the upper surface.

Although there are many species of spider mites, just a small number routinely inflict damage on plants in the Kentucky/Indiana area. Different species prefer different host plants, and at different times of the year, which makes it easier to determine the type of mites that are damaging your plants.

The Twospotted Spider Mite is the most common and destructive mite found on deciduous ornamentals. It feeds on many varieties of trees and shrubs in the landscape but is especially damaging to the Winged Euonymus, more commonly referred to as the burning bush. The twospotted spider mite also thrives under warm and dry conditions, usually becoming active in late Spring, and feed and populate throughout summer and even into Fall if conditions are favorable for plant growth.

Another warm season species commonly seen in the local area is the European Red Mite. The European Red Mite attacks deciduous trees and shrubs, and is often seen on flowering fruit trees–the crabapple, pear, hawthorn and serviceberry, to name a few. All life stages of the European Red Mite are a red brick color. Overwintering eggs on limbs and branches can appear as red brick dust, which makes it easy to detect. And with the presence of the overwintering eggs on the bark a spray application of dormant oil can be an effective control measure.

The Spruce Spider Mite feeds on many different species of conifers–for example, the dwarf alberta spruce, pine, arborvitae, hemlock and juniper. Spruce Spider Mites show up on the needles as tiny white specks. Prolonged infestation can cause browning and premature drop of the trees’ needles. The Spruce Spider Mite is known as a cool season mite because it is active in the early Spring and late Fall.

Another destructive mite is the Southern Red Mite. This mite is the most common mite found on broad-leaved evergreens–hollies, azaleas, and boxwoods. Feeding habits of this mite cause stippling, browning of leaves and premature leaf drop. Similar to the spruce spider mite, this mite’s population increases in the cooler periods of the Spring and Fall seasons.

Diagnosing and Controlling Mite Infestations

Inspecting plants at periods of the year favoring mite infestation is important in preventing damage to plants in your landscape. Many spider mites often attack the same plant year after year so a good place to start is to look for plants that have had mite troubles in the past. Leaves may be stippled, distorted or yellowing. Often detected on the underside of leaves, the mites will appear yellow, orange, green, black, purple or even transparent. One method for detecting the presence of mites on your landscape plants is to hold a piece of white paper under a branch as you lightly tap on the branch. If there are any mites, some will fall on the paper and will appear as dark, slow-moving specks.

Spider Mites are one of the more difficult landscape pests to keep under control. And adequate control is best if the infestation is detected early before the population reaches high levels.

The use of a Summer Horticultural Oil is beneficial in controlling mite populations during the warmer months when foliage and mites are present and actively growing. Dormant Horticultural Oils are applied in the winter months or early Spring before the buds break out. The Dormant Oil is beneficial in killing the overwintering mite eggs and will help suppress mite populations in the Spring and Summer months.

Bob Ray Co. offers spraying of both Summer and Dormant Horticultural Oils, as well as a Plant Health Care Program to control mite populations on many plants in your landscape. If you have mites inflicting damage on your trees or shrubs, Bob Ray Co.’s licensed and experienced applicators can help to protect the valuable plants in your landscape.

 

Scale

Scale is a common pest found on plants in our landscapes. Scale are sap-feeding insects that often attack most species of shade trees, fruit trees and many ornamental shrubs. Scale can weaken and even kill trees and shrubs but complete plant loss is rare. Most scale insects are small and inconspicuous due to a shell-like waxy covering that conceals their bodies. Color, shape and other features vary with the species. Scale are usually divided into two categories:

Soft Scale – Scale that produce a soft cottony, powdery or waxy protection. This type of Scale produces a large amount of honeydew (a mixture of undigested sugar and water digested and deposited onto leaves and stems).

Amored Scale – Scale with a hard shield composed of shed skins and wax that conceals the body but is unattached.

Damage to plants

Scale insects feed by sucking sap from trees and shrubs through piercing and sucking mouth parts. Feeding by scale can cause a yellowing and wilting of leaves, lack of vigor in the plant and eventual death of part or even all of the plant when infestation levels are high. In addition, the weakened plant then becomes more susceptible to drought and winter conditions and attack by other insects or infectious diseases.

While feeding, the soft scale insects deposit a sweet sticky substance, referred to as honeydew. Honeydew is a mixture of undigested sugar and water deposited on the plant and appears shiny and wet. This substance attracts flies, ants, bees, wasps and other insects. It also may encourage sooty mold, a blackened fungus that appears on the tree’s branches and trunk. Honeydew can even fall and foul sidewalks, cars and houses that are beneath heavily infested trees.

 

Managing Scale

Scale are difficult to control  due to the waxy covering that serves as a protective barrier, but effective measures can be taken with mechanical and/or chemical controls that provide satisfactory results on most trees and shrubs. When feasible in certain situations, mechanically removing heavily infested stems or branches  and then discarding them can effectively control scale populations. Chemical control is usually done with the application of a Dormant Oil prior to bud break, applying a contact insecticide in the summer months when the insects are active, or through the use of a systemic insecticide.

 

Bagworm Caterpillars

The Bagworm caterpillar is a perennial pest that prefers arborvitae, juniper, pine, spruce, cedar and other evergreens, but it also will attack some deciduous trees, such as honeylocust and sycamore. The Bagworm is easily recognized by the case or bag that the caterpillar forms from silk and bits of the host foliage.

Bagworms winter as eggs inside the bags. There may be 500-1000 inside each bag. In the Kentucky/Indiana area, Bagworm eggs hatch in mid- to late May and the larvae leave the bag to feed, each then making its own bag with silk and plant material to protect it during feeding and growth. Bagworms feed for about six weeks. When abundant, bagworms can defoliate an entire plant. And recurring infestations over consecutive years, specifically in conjunction with other stress factors, can lead to death of the plant.

In the Fall the mature larvae attach their bags to twigs and then transform into the pupal stage before becoming an adult. Males then will leave the bags in search of bags containing females. After mating the female lays her eggs, which remain in the bag until they hatch the following May.

Bagworm infestations often go undetected until the damage is done and the bags become obvious evidence of the culprit. Early detection requires careful examination of the plant for the presence of small bagworms attached to leaves or needles.

Controlling Bagworms

On small shrubs and trees you may hand pick the bags from infested plants during late fall, winter, or early spring before the eggs hatch. You should then dispose of the bags, removing them so they do not reenter your landscape.

When many small bagworms are present and feeding, usually in early June, the plant may be sprayed with an insecticide to control the bagworms. The young bagworms are hard to see but identifiable as small upright bags that look like tiny ice cream cones made of plant material. If you detect the presence of bagworms on your arborvitae or other evergreens, Bob Ray Co.’s licensed pesticide applicators can apply an insecticide to eliminate and protect your valuable landscape assets.

Anthracnose and Powdery Mildew

 

Anthracnose

 

One of the more common shade tree diseases in Kentucky and Indiana landscapes is anthracnose. Anthracnose is a fungus caused plant disease that results from an infection by one of several different fungi. These fungi winter inside diseased leaf or or stem tissue. In the spring, infectious spores are produced and carried by wind or rain to emerging leaves. Anthracnose is usually more sever when wet and cold conditions exist as new leaves are emerging. Some of the shade trees mostly affected are dogwoods, maples, elm, sycamore, oak, ash, birch and linden.

 

Identification and Damage

Anthracnose symptoms vary with the plant host, weather, and time of year infection occurs. The fungi affect developing shoots and expanding leaves. Dogwood trees with anthracnose often exhibit medium to large leaf spots with purple borders or tanned scorched blotches that can enlarge and kill a leaf. Small tan, brown, black, or tarlike spots appear on infected leaves of hosts such as elm or oak. Dead leaf areas may be more irregular on other hosts such as ash. Sycamore anthracnose lesions typically develop along the major leaf veins. If leaves are very young when infected, they may become curled and distorted with only a portion of each leaf dying.

Generally, mature leaves are resistant to infection, but when conditions are favorable, they may become spotted with lesions. Heavily infected leaves fall prematurely throughout the growing season, and sometimes trees are completely defoliated. Early leaf drop is usually followed by production of more leaves. Twigs and branches also may be attacked and killed, resulting in a tree with crooked branches. On some trees, cankers (infected areas that may or may not be surrounded by callus tissue) are another symptom of anthracnose infection. Cankers develop on twigs, branches, and the trunk, occasionally resulting in girdling and dieback. If defoliation, branch dieback, or cankering does not occur every year, anthracnose will not seriously harm plants.

 

Powdery Mildew

Powdery Mildew is an unsightly disease that affects many species of landscape ornamentals, including dogwoods, crabapple and many fruit trees. Several species of fungi can cause powdery mildew and many have a specific host range. Early in the growing season, powdery mildew can be detected easily on leaves by the presence of a white, tan or grayish dusty mildew. In the late growing season, black fungal fruit structures can appear. The disease may be spots or can cover the entire leaf and become stunted or curled.

Powdery mildews prefer cool nights followed by warm days. It also is more common in plants growing in shady or damp areas.

Fungicide Spray: Our fungicide sprays help to control anthracnose and powdery mildew, two fungal diseases that are endemic to the Kentucky/Indiana area and are found to attack our Dogwood, Apple, Sycamore trees, and several other  tree species. The treatment consists of spraying your trees and shrubs with 3 applications of fungicide, spaced 10-14 days apart, in the early to mid-Spring. The anthracnose can be controlled and prevented using this method.

Bacterial Spray: During the hot, dry summer months, many stressed trees are attacked by the bacterial disease, bacterial leaf scorch. Bacterial leaf scorch infects many trees, including many varieties of Oak and Maple, the Sycamore, Sweetgum, and Elm. Bacterial leaf scorch attacks the water-conducting tissues in a tree, which causes it to appear to be deficient in water. Several insects, including the leafhopper and treehopper, can spread Bacterial Leaf Scorch from an infected tree to a healthy tree. Fire blight is another bacterial disease that has many similar symptoms and characteristics of the Bacterial leaf scorch. For both bacterial diseases, Bob Ray Co. suggests treatment for these trees, as these diseases become worse when not treated.