Causal organism: Erwinia amylovora

Hosts: Rosaceae family such as: apple, pear, cherry, plum, crabapple, hawthorne, amelanchier, strawberry, rose, mountain ash, spirea.... 

The bacterium is most destructive in apple and pear orchards. 

Symptoms: Wilting, shriveling, and blackening of blossoms, leaves and shoots. Cankering of branches. Stem cankers can girdle trees. 

Signs: Droplets of fluid containing bacteria that ooze from bark lenticels and wounds in moist weather. 

Bacteria overwinter in canker margins and are disseminated by insects, rainsplash, and wind during the warm, moist weather of spring. 

TO DO:

1. Be able to recognize the symptoms. 

2. Review your How-to.
 
 

BACTERIAL DISEASE 

Common name: Crown gall

Causal organism: Agrobacterium tumefaciens

Hosts: Fruit and nut trees and other ornamentals 

Symptoms: Basal stem and root galls; stunted growth. 

This bacterium lives in the soil and infects through lenticels or wounds. It may be dispersed in irrigation water or by movement of contaminated tools or plants. 

The bacterium carries a plasmid (extracellular DNA particle) which is released into a plant cell. The plasmid DNA redirects the plant cell DNA to replicate at an uncontrollable rate, resulting in increased cell growth and gall formation. The bacteria are then sloughed off into the soil where they overwinter. 

TO DO:

1. Become familiar with symptoms. 

2. Host cell multiplication continues even without the bacteria. Why?


 
 

VIRAL DISEASE 

Common name: Apple mosaic virus

Hosts: Members of the Rosaceae family; paper and yellow birch; horse-chestnut. 

Symptoms: Leaf chlorosis: 

interveinal

ringspot 

The virus is transmitted through infected nursery stock by grafting. Or it may be vectored by piercing-sucking insects such as aphids. 

TO DO:

1. Become familiar with the symptoms. Look for both types of leaf chlorosis. 

2. What host is present? 
 
 

MYCOPLASMA-LIKE ORGANISM CAUSED DISEASE 

Common name: Ash yellows

Causal organism: Unidentified mycoplasma-like organism

Hosts: Ashes, especially white ash, throughout northeastern U.S. and southern Canada. 

Symptoms: Reduced growth; tufted foliage; chlorotic, stunted leaves; twig and branch dieback; epicormic shoots at root collar and along trunk and limbs that become witches brooms. 

Probable vectors: Certain species of leafhoppers and spittlebugs 

TO DO:

1. Be able to recognize epicormic shoots and witches brooming on ash. See sample. 

2. Review your How-to. 
 
 
 
 

PARASITIC PLANT 

Common name: Leafy mistletoe

Causal organism: Phoradendron sp.

Hosts: Hardwoods (especially oak) and western conifers (especially junipers and cedars). 

Symptoms: Branch swelling and galls; dieback. 

Signs: Thick, often woody shoots of mistletoe growing from host branches. 

There are 12 species of leafy mistletoes in the U.S. ranging from southern NJ west to CA and south to FL. In the East, only hardwoods are infected, but in the West, both hardwoods and conifers are hosts. The leafy mistletoe has leaves and photosynthesizes to produce its own carbohydrates. But, the plant derives water and minerals from its host. Fruit-bearing branches of P. serotinum (eastern mistletoe) and P. tomentosum (a southwestern species) are collected and marketed as the holiday decoration. 

TO DO:

1. Be able to recognize a leafy mistletoe and to differentiate it from host tissue. 

2. Look for the fruits of the female plant in the mount. 

3. Why is this plant called a hemiparasite? 
 
 
 
 

PARASITIC PLANT 

Common name: Leafy mistletoe

Causal organism: Phoradendron juniperinum

Hosts: Junipers and incense cedar in the West 

Symptoms: Branch swellings and dieback 

Signs: Thick woody shoots with scalelike leaves growing in bushy clumps from host branches. This is the most widespread western Phoradendron. 

TO DO:

Become familiar with the scale-like leaves of this leafy mistletoe. 
 
 
 
 

PARASITIC PLANT 

Common name: Eastern dwarf mistletoe

Causal organism: Arceuthobium pusillum

Hosts: Black, red and white spruces 

Symptoms: Witches' brooms; dieback; growth loss; tree mortality. 

Signs: Small leafless shoots growing from host branches. 

Because the dwarf mistletoes do not have leaves for photosynthesis, they derive not only water and minerals from the host, but also carbohydrates. 

TO DO:

1. Be able to distinguish the dwarf mistletoe from leafy mistletoe. 

2. Check out the 3-parted male flowers in the mount. 

3. Review your "How to". 
 
 
 
 

PARASITIC PLANT 

Common name: Southwestern dwarf mistletoe

Causal organism: Arceuthobium vaginatum

Host: Ponderosa pine 

Symptoms: Witches' brooms; reduced growth; dieback 

Signs: Shoots of mistletoe growing from host branches. 

This is the most important and widespread disease of ponderosa pine in the Southwest. 

TO DO:

Note the mistletoe shoots on the pine branch. 
 
 
 
 

PARASITIC PLANT 

Common name: Lodgepole pine dwarf mistletoe

Causal organism: Arceuthobium americanum

Hosts: Lodgepole, jack and often ponderosa pines. 

Symptoms: Branch swellings; witches' brooms; dieback; growth reduction. 

Signs: Shoots of mistletoe growing from host branches. 

TO DO:

Note the mistletoe shoots on lodgepole pine in the mount. 
 
 
 
 

PARASITIC PLANT 

Common name: Beech drops

Causal organism: Epifagus virginiana

Host: Beech roots 

This plant is found beneath beech trees. It lacks chlorophyll in its scale-like, tan-colored leaves so derives carbohydrates from beech roots. 
 
 
 
 

PARASITIC PLANT 

Common name: Indian pipe

Causal organism: Monotropa uniflora

Host: Mycorrhizal fungi 

This plant is white or pink and lacks chlorophyll. It derives carbohydrates from tree roots by parasitizing the roots' mycorrhizal fungi. 
 
 
 
 

EPIPHYTIC PLANT 

Epiphytes are not parasitic. 

They are photosynthetic plants that attach to the bark of trees by means of roots or rhizomes. They gain support from the tree, but do not parasitize it. 

Water and minerals reach the epiphyte from rain and water leached from leaves above. 

Common examples are mosses in the North and Spanish moss in the South. 
 
 
 
 

ABIOTIC DISEASE 

Common name: Leaf scorch

Causal agent: Hot weather and drying winds, combined with excess salt, pavement or drought which can result in water shortage for the host. The leaves lose more water through transpiration than the tree can take up. 

Hosts: All trees; common in maple 

Symptoms: Chlorosis, necrosis of leaf margins 

TO DO:

1. Be able to recognize symptoms 

2. What host is present? 

3. Review your "How to". 
 
 

ABIOTIC DISEASE 

Common name: Winter burn or browning

Causal agent: In winter, a sudden drop in temperature at sunrise or sunset on the southside of the tree where host tissue is exposed to sun and becomes active. The rapid cooling injures activated foliage. 

Hosts: Ornamental conifers in northern latitudes. 

Symptoms: Reddish-brown (necrotic) foliage that remains attached to branch until summer. 

TO DO:

1. Be able to recognize symptoms. 

2. What host is present? 

3. Review your "How to". 
 
 
 
 

ABIOTIC DISEASE 

Common name: Frost injury

Causal agent: Late spring or early fall frost when tree foliage is succulent and actively growing. 

Hosts: All trees in northern latitudes. 

Symptoms: Drooping and eventually necrotic shoots or leaves. 

Most trees will survive but growth is reduced. This can be of concern to Christmas tree growers. 

TO DO:

1. Be able to recognize symptoms. 

2. What host is present? 

3. Review your "How to". 
 
 

ABIOTIC DISEASE 

Common name: Frost crack

Causal agent: A sudden drop in winter temperature causes the outer cells of the wood to contract faster than the inner cells. 

Hosts: All trees in northern latitudes. 

Symptoms: A long vertical crack or bulging seam along the stem. 

The term frost crack is misleading because the initial crack is usually caused by some other stress such as wounds or poorly healed branch stubs. Frost secondarily makes the crack continue or become longer. 

TO DO:

1. Be able to identify a frost crack. 

2. What fungus is fruiting in the frost crack on one of the samples? 

3. Review your "How to." 
 
 
 
 

ABIOTIC DISEASE 

Common name: Salt damage

Causal agent: Ocean salt spray or road salt, usually sodium chloride (NaCl). 

Hosts: All trees to some extent. Trees with low tolerance: apple, azalea, 

basswood, beech, black cherry, crabapple, dogwood, Douglas-fir, balsam fir, hemlock, hickory, holly, lilac, red and sugar maple, red and eastern white pine, rhododendron, white spruce.... 

Symptoms: Chlorosis, reddening, necrosis, and premature drop of conifer needles. Twig dieback on hardwoods. 

The salt spray may damage foliage directly as in the case of roadside pines or be taken up by the roots, causing symptoms, such as leaf scorch, to appear later in the summer, especially in hardwoods. 

TO DO:

1. Become familiar with symptoms on white pine. 

2. Be aware that salt accumulation in the soil has a long-term detrimental affect on roadside trees. 
 
 
 
 

ABIOTIC DISEASE 

Common name: Air pollution injury or Ozone damage

Causal agent: Ozone (O³) generated in polluted air by ultraviolet radiation and oxides or oxygen. It builds up to toxic levels for plants in urban areas during warm sunny weather. 

Hosts: All trees to some extent, especially white ash; trembling aspen; black cherry; lilac; eastern white, jack, loblolly and ponderosa pines; hybrid poplars; sumac; sycamore; tulip poplar.... 

Symptoms:Chlorotic spotting of conifer needles; tip necrosis of eastern white pine; reddish-purplish stipple of hardwood leaves. 

TO DO:

1. Become familiar with the symptoms of ozone damage on leaves and be aware that there are many other pollutants that cause tree damage, such as sulfur dioxide, hydrogen fluoride, nitrogen oxides, chlorine, hydrogen chloride, etc. 

2. What host(s) is(are) present? 
 
 

ABIOTIC CANKERS 

Can you find:

Branch rub? 

Beaver damage? 

Small rodent damage?

Porcupine damage?

Vine strangulation? 

Wire girdle? 

Buck rub? 

Woodpecker damage? 

Sapsucker injury?

Moose bark stripping?