Green Industry - A Knowledge Portal for Commercial Horticulture in Wisconsin (sponsored by University of Wisconsin-Extension)
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Diagnostics
Woody Ornamentals-Conifer
Boxwood (Buxus)
- Armillaria root rot (Armillaria species)
Also known as shoestring root rot, this is an often lethal disease of woody plant roots and lower stems. It can affect almost any conifer or hardwood species, from seedling to maturity. Trees and shrubs stressed due to drought or defoliation are more susceptible. The fungi produce tough, cord-like strands called “rhizomorphs” that grow from decaying stumps and roots through the soil. Infection of other trees or shrubs can result from penetration of intact roots by rhizomorphs. In late summer or early fall, honey-colored mushrooms of Armillaria fungi develop near the bases of colonized plants and produce spores that are distributed by wind. Infection also can occur after these spores germinate in wounds on stems or roots. Above-ground symptoms include slow growth, yellowing and dwarfing of foliage, and thin crowns. Dieback of twigs and branches also may occur. Symptoms may develop slowly and intensify over many years or kill their host rapidly. Bark on lower stems or roots may be killed and crack, with flow of resin common on conifers. Thin white mats of fungus tissue called “mycelial fans” may be present within and beneath killed bark. Stem and root wood decayed by Armillaria fungi is often water-soaked, creamy to yellow in color, and spongy or stringy in texture. Rhizomorphs are commonly seen on or beneath the bark and growing from decayed stumps and roots. - Armored scale (Diaspididae family)
Armored scales are oval, somewhat elongate (think oyster shell), small (1/20-1/8") insects that secrete a hard, waxy cover. During the adult stage, no body parts are visible except the cover. Eggs are laid under the cover and hatch into crawlers, which can move around and are susceptible to sprays and oils. - Cold/Frost Damage ()
Any part of a plant may be affected by cold damage. In spring, it's usually tender growth, which will appear watersoaked and may turn black. Flower buds can sustain damage during winter dormancy or during the blooming period. Plants will either have reduced numbers of blooms, and hence fruit set, or won't bloom at all. In fall, if plants aren't hardened off, they can sustain cold injury in temperatures well above those tolerated by acclimated plants. Root injury is rare unless plants are in raised beds or containers. Generally younger plants are more susceptible than mature plants. Cold injury on woody plants usually presents in the form of frost cracks in wood or bark. Mature leaves may turn red, purple, brown or black and may or may not fall off the tree or shrub. - Gas Injury ()
Symptoms of gas injury can range from slow growth to total plant death, and initially resemble symptoms of water stress. Gas injury may also be mistaken for compacted soil, root disease, herbicide injury or air pollution. Symptoms include: slow growth, small leaves, wilt and leaf drop. Roots may be bluish and water-soaked, and surrounding soils may turn bluish gray or black. The injury may progress over time. Gas injury may occur from gas released into the soil or into the air. Root zone injury from gas leaks in soil usually stems from gas or sewer-line breaks (rapid damage) or gases leaking from landfills (gradual damage). The extent of damage depends on the size of the leak, when it occurs (summer is worse), soil type (heavier is worse) and the amount of paving surrounding the plants. Gas injury due to atmospheric gas leaks usually stems from vents, chimneys, smokestacks or industrial equipment, and may or may not be phytotoxic. These releases are usually accidental and short-lived. - Girdling ()
Decline and dieback caused by girdling, either by roots or man-made objects, usually affect mature trees moreso than young ones. Symptoms may include: thinning crown, leaf scorch, sparse foliage, leaves in tufts, branch dieback, early fall color, and leaf drop. - Herbicide Damage ()
Herbicides can damage any type of plant and injury usually happens as a result of drift, careless application or evaporation during hot weather. Symptoms of herbicide injury may include: twisted plant stems; stem fasciation; narrow, curling or leathery leaves; or excessive callus formation on roots and stems along with secondary root growth. At extremely low application rates, broadleaf herbicides such as 2,4-D, MCPP or dicamba usually will not kill plants, although they will act as growth regulators. - Mealybug (Pseudococcidae family)
Characteristically mealybugs are covered in white granular or cotton-like wax. Mealy bug bodies are always soft and the females are oval and flat with distinct segmentation often visible in the wax. Eggs are usually laid in a white cottony material underneath the female. Widespread in greenhouses and indoor plants; not an outdoor problem. Depending on temperature, one generation can develop every 1-3 months. - Nectria canker (Nectria (Neonectria))
Nectria canker is characterized by the production of sore-like wounds (cankers) that form on twigs, branches, and trunks. Cankers can form at leaf scars and wherever injuries occur. Injuries can be caused by pruning (particularly improper pruning), frost, hail, cracking from heavy snow or ice, sunscald, insects, or mammals. Cankers appear first as slightly sunken areas on the bark, but can grow for years, becoming target-shaped or elongated. Small branches girdled by cankers can wilt suddenly, fail to leaf out, and die. - Overwatering ()
Overwatering, whether acute or chronic, is usually a death sentence for plants, especially when accompanied with poor drainage. Waterlogged soils limit oxygen uptake by plant roots, which in turn affects the plant's metabolism, nutrient uptake, water absorption and photosynthesis. Symptoms vary from slow growth to plant death and can include: leaf necrosis, dieback, root discoloration, soil blackening, foul odors, slow growth, thinning canopy and chlorosis. Overwatered conifer symptoms are similar, except they can also exhibit needle drop. Overwatering is common in irrigated landscapes, plantings at the bottoms of slopes and in poorly drained containers. - Planting Too Deeply ()
Trees planted too deeply in the soil exhibit a gradual decline in their growth and development. Deep planting acts as a primary stress factor and can lead to stem girdling roots which will eventually choke the trunk. It can also make trees more susceptible to disease and insect pests, and frost cracks; can cause roots to grow up toward the surface where they will have to compete for nutrients and water; and can activate suckering shoots or adventitious roots that grow from the underground part of the trunk. If you cannot see the root flare of your woody plant, then it is planted too deeply. - Root rot (woody plants) (Cylindrocladium species)
Root infections are characterized by many dark brown to black lesions often with longitudinal cracks. Severe root disease leads to stunting, wilting, yellowing and death. Stem infections of both conifers and broadleaves arise at the leaf bases and may girdle small stems. Diseased conifer needles turn yellow or red-brown. Dark lesions form in the leaves of broadleaf plants. Leaf blight leads to defoliation. - Soft scale (Coccidae family)
Soft scales are usually broadly oval becoming larger and more humped as eggs mature underneath the protective cover. Look for adults on twigs or small branches and immature stages on leaves or needles. - Sunscald ()
Often the first symptom of sunscald is the reddish-brown discoloration of bark. Then, the bark shrinks, appearing sunken, splits and peels back in chunky patches exposing sapwood underneath. Often cankers develop. Severe sunscald may cause the entire trunk to be girdled, or only individual branches. Look for sunscald on the south, southwest or west side of trunks or branches. It most commonly affects trees suffering from water stress or young trees with thin bark. Newly planted or transplanted are most susceptible and container-grown plants are more likely to get sunscald than field-grown ones. Species particularly prone to sunscald include: Liriodendron, Acer, Tilia, Prunus, Pyrus, Malus, Juglans, and Ulmus. - Two-spotted spider mite (Tetranychus urticae)
This most common spider mite is miniscule (0.5mm) and prefers to colonize and lay eggs on leaf undersides of most host plants. When populations are high, these mites can be found on all leaf surfaces and stems. - Verticillium wilt (woody plants) (Verticillium species (W))
The first signs of Verticillium wilt that you may notice are individual branches that suddenly wilt and die. Affected branches may occur on one side of the tree or may be scattered throughout the tree. If you carefully peel away the bark of these branches, you may see brown or green streaking in the sapwood. Streaking is common in trees such as maple or redbud, but often is not visible in ash.
Fir (Abies)
- Armillaria root rot (Armillaria species)
Also known as shoestring root rot, this is an often lethal disease of woody plant roots and lower stems. It can affect almost any conifer or hardwood species, from seedling to maturity. Trees and shrubs stressed due to drought or defoliation are more susceptible. The fungi produce tough, cord-like strands called “rhizomorphs” that grow from decaying stumps and roots through the soil. Infection of other trees or shrubs can result from penetration of intact roots by rhizomorphs. In late summer or early fall, honey-colored mushrooms of Armillaria fungi develop near the bases of colonized plants and produce spores that are distributed by wind. Infection also can occur after these spores germinate in wounds on stems or roots. Above-ground symptoms include slow growth, yellowing and dwarfing of foliage, and thin crowns. Dieback of twigs and branches also may occur. Symptoms may develop slowly and intensify over many years or kill their host rapidly. Bark on lower stems or roots may be killed and crack, with flow of resin common on conifers. Thin white mats of fungus tissue called “mycelial fans” may be present within and beneath killed bark. Stem and root wood decayed by Armillaria fungi is often water-soaked, creamy to yellow in color, and spongy or stringy in texture. Rhizomorphs are commonly seen on or beneath the bark and growing from decayed stumps and roots. - Armored scale (Diaspididae family)
Armored scales are oval, somewhat elongate (think oyster shell), small (1/20-1/8") insects that secrete a hard, waxy cover. During the adult stage, no body parts are visible except the cover. Eggs are laid under the cover and hatch into crawlers, which can move around and are susceptible to sprays and oils. - Cold/Frost Damage ()
Any part of a plant may be affected by cold damage. In spring, it's usually tender growth, which will appear watersoaked and may turn black. Flower buds can sustain damage during winter dormancy or during the blooming period. Plants will either have reduced numbers of blooms, and hence fruit set, or won't bloom at all. In fall, if plants aren't hardened off, they can sustain cold injury in temperatures well above those tolerated by acclimated plants. Root injury is rare unless plants are in raised beds or containers. Generally younger plants are more susceptible than mature plants. Cold injury on woody plants usually presents in the form of frost cracks in wood or bark. Mature leaves may turn red, purple, brown or black and may or may not fall off the tree or shrub. - Cytospora canker (Cytospora species)
A stem and branch disorder affecting many different types of conifers. In Wisconsin, Colorado Blue Spruce is the main species that is affected. - Gas Injury ()
Symptoms of gas injury can range from slow growth to total plant death, and initially resemble symptoms of water stress. Gas injury may also be mistaken for compacted soil, root disease, herbicide injury or air pollution. Symptoms include: slow growth, small leaves, wilt and leaf drop. Roots may be bluish and water-soaked, and surrounding soils may turn bluish gray or black. The injury may progress over time. Gas injury may occur from gas released into the soil or into the air. Root zone injury from gas leaks in soil usually stems from gas or sewer-line breaks (rapid damage) or gases leaking from landfills (gradual damage). The extent of damage depends on the size of the leak, when it occurs (summer is worse), soil type (heavier is worse) and the amount of paving surrounding the plants. Gas injury due to atmospheric gas leaks usually stems from vents, chimneys, smokestacks or industrial equipment, and may or may not be phytotoxic. These releases are usually accidental and short-lived. - Girdling ()
Decline and dieback caused by girdling, either by roots or man-made objects, usually affect mature trees moreso than young ones. Symptoms may include: thinning crown, leaf scorch, sparse foliage, leaves in tufts, branch dieback, early fall color, and leaf drop. - Herbicide Damage ()
Herbicides can damage any type of plant and injury usually happens as a result of drift, careless application or evaporation during hot weather. Symptoms of herbicide injury may include: twisted plant stems; stem fasciation; narrow, curling or leathery leaves; or excessive callus formation on roots and stems along with secondary root growth. At extremely low application rates, broadleaf herbicides such as 2,4-D, MCPP or dicamba usually will not kill plants, although they will act as growth regulators. - Planting Too Deeply ()
Trees planted too deeply in the soil exhibit a gradual decline in their growth and development. Deep planting acts as a primary stress factor and can lead to stem girdling roots which will eventually choke the trunk. It can also make trees more susceptible to disease and insect pests, and frost cracks; can cause roots to grow up toward the surface where they will have to compete for nutrients and water; and can activate suckering shoots or adventitious roots that grow from the underground part of the trunk. If you cannot see the root flare of your woody plant, then it is planted too deeply. - Seasonal Needle Drop ()
Evergreen needles naturally discolor and drop off after one or more years on the plant, and interior needles are affected. Seasonal needle drop may be gradual or all at once and can be mistaken for disease or insect damage. Each species tends to keep their needles for a specific period of time, varying slightly between trees and from year to year. Pinus strobus is the most dramatically affected. Third year needles turn yellow throughout the tree and will usually drop by winter. It may look as if yellowed needles outnumber green ones, but this is natural. P. nigra and P. sylvestris usually retain needles for three years and drop them in their fourth year. Thuja occidentalis usually turn brown rather than yellow and remain attached much longer than mature pine needles. Taxus spp. needles turn yellow and drop in late spring or early summer of their third year. Abies and Picea spp. yellow and drop with age, but because of their branch arrangement, it's often difficult to tell unless you part the branches to look at the interior. - Soft scale (Coccidae family)
Soft scales are usually broadly oval becoming larger and more humped as eggs mature underneath the protective cover. Look for adults on twigs or small branches and immature stages on leaves or needles. - Sooty molds (Several)
Sooty molds are dark fungi that grow on plant surfaces covered in honeydew excreted by insects with piercing/sucking mouth parts such as aphids, scale, mealybugs and whiteflies. It is generally harmless to plants, except when it is prolific, preventing light from reaching leaf surfaces, causing plants stress. This stress may make the plant more susceptible to other diseases or problems. - Sunscald ()
Often the first symptom of sunscald is the reddish-brown discoloration of bark. Then, the bark shrinks, appearing sunken, splits and peels back in chunky patches exposing sapwood underneath. Often cankers develop. Severe sunscald may cause the entire trunk to be girdled, or only individual branches. Look for sunscald on the south, southwest or west side of trunks or branches. It most commonly affects trees suffering from water stress or young trees with thin bark. Newly planted or transplanted are most susceptible and container-grown plants are more likely to get sunscald than field-grown ones. Species particularly prone to sunscald include: Liriodendron, Acer, Tilia, Prunus, Pyrus, Malus, Juglans, and Ulmus. - Winter salt injury ()
De-icing salts accumulate in the soil along streets/sidewalks or may be dispersed in an aerosol spray by fast-moving traffic and high winds along wet, salted roads. Salt spray can travel hundreds of feet from the roads where it originated. Symptoms can be similar to other abiotic plant problems, but there are tell-tale indicators including: Damage is more severe on sides of plants facing roads/sidewalks; severity of damage increases with volume/speed of traffic and amount of salt used; plants downwind from roads show more damage than those upwind; most damage occurs within 60' of road and decreases with distance; branches covered by snow or otherwise sheltered show no damage; branches growing above spray drift zone show no damage. Symptoms in deciduous plants include: delayed budbreak; reduced leaf size/stem growth; off-colored foliage; scorched leaves; no flowering; bud/twig death; and branch-tip dieback leading to 'witches' broom' growth below the dead area. Symptoms on conifers include: tips of mature needles turn brown or yellow, discoloration moves down needle eventually killing all of it, then needles fall off; twig dieback; and symptoms manifest only on sides of plants facing roads/sidewalks.
Hemlock (Tsuga)
- Cytospora canker (Cytospora species)
A stem and branch disorder affecting many different types of conifers. In Wisconsin, Colorado Blue Spruce is the main species that is affected.
Pine (Pinus)
- Cytospora canker (Cytospora species)
A stem and branch disorder affecting many different types of conifers. In Wisconsin, Colorado Blue Spruce is the main species that is affected.
Spruce (Picea)
- Cytospora canker (Cytospora species)
A stem and branch disorder affecting many different types of conifers. In Wisconsin, Colorado Blue Spruce is the main species that is affected.