North Dakota Tree Handbook
Sapsucking Insects and Mites
Ash Plant Bug
R1-P402, R3-P36, R5-P119, R8-P134
Damage by the ash plant bug was noted in planted and native ash statewide. Moderate to
heavy damage was noted in all size classes of ash, but the most serious consequence were
to young trees, especially those stressed by other factors.
Honeysuckle Witches'-broom Aphid
R1- P314, R3-P34, R5-P107.
Honeysuckle aphids seriously damaged Tatarian honeysuckle statewide, effectively
stopping new growth and reducing the usefulness of Tatarian honeysuckle. The seriousness
of the damage makes further usage of Tatarian honeysuckle questionable, except the
resistant cultivars `Arnold red' and `Honey Rose.'
Many species of trees and shrubs
Severe damage was noted on quaking aspen, hybrid poplars, bur oak, chokecherry,
boxelder, green ash, American elm, snowball Viburnum, spruce and Scotch pine. Aphid
populations can rise very quickly and then, oftentimes, abruptly decline usually from
predation, especially by ladybird beetle and its larvae. Detection of aphids requires
close inspection on a regular basis. The presence of ants on the foliage generally means
aphid infestation of the plant. Treatment may be required on young trees, especially if
new growth is being affected and feeding damage threatens the form or vigor.
Giant Conifer Aphid
Scotch pine and ponderosa pine
The giant conifer aphid was locally abundant on Scotch pine in south central and
southwestern North Dakota. The insect was also present on Scotch and ponderosa pine,
primarily in the western half of the state.
Pine Needle Scale
Pine and spruce, especially mugo pine
R1-P108, R3-P38, R5-P41, R8-131, R9-P85.
The highest populations of pine needle scale were in the north central and south
central areas of the state on mugo pine and Black Hills spruce. Infestations are often
missed or mis-diagnosed because of the difficulty of associating the tiny white specks
with insect damage.
Spruce Spider Mite
Spruce, juniper and arborvitae
R1-P118, R3-P38, R5-P31.
High populations of mites were found in scattered locations throughout the state. Heavy
rain and cool weather reduced populations in 1993. Generally, mites are restricted to
localized protected areas and are not likely to be found uniformly over an entire large
tree. Smaller trees are more likely to be seriously infected. Rain and high winds often
dislodge the mites and their eggs. Open grown trees and shrubs are seldom seriously
infested. Foundation shrub plantings are the most seriously affected, especially those
sheltered by buildings or other types of structures. A separate species, the two-spotted
mite, is often found on hardwood shrubs.
Diagnosis can be difficult and spider-mite damage is often confused with winter drying,
drought stress, or other factors. Due to mis-diagnosis, much needless spraying is done.
This spraying may actually contribute to population buildups by eliminating predators.
Gall Making Insects and Mites
Ash Flower Mite Gall
Occurs on ash trees statewide, very noticeable in the winter when the galls turn
blackish and persist on the trees. Although unsightly, the galls cause little, if any,
actual damage to the trees. Male flowers are attacked with only occasional damage to
female flowers or leaves.
Honeylocust Pod Gall Midge
Locally abundant in Bismarck and Dickinson. Where it occurs it is persistant and
numerous, causing new foliage to be re-infested repeatedly over the season.
Poplar Bud Gall Mite
Cottonwoods and other poplars
Occurs statewide; found primarily on cottonwood and northwest poplars and is
particularly abundant on the later. The poplar bud gall mite may cause stunting, crooked
growth and can contribute to the death of younger stressed trees.
Poplar Vagabond Aphid
Cottonwoods and other poplars
R3-P30, R5-P209, R7-P95.
Occurs statewide, primarily objectionable because the relatively large galls persist
throughout the season and are very noticeable after leaf drop. The trees suffer little, if
any, actual physiological damage.
Oak Bullet Gall
R3-P30, R5-P213, R8-P74.
This gall was discovered to be abundant in Williston and sporadically in other areas
primarily on small to medium sized oaks. Some individual trees had large numbers of galls
on nearly every branch. Because the galls persist on the trees for up to five years, the
resulting accumulation of galls is very unsightly. This gall is a potentially serious pest
of bur oak in ornamental plantings.
Dutch Elm Disease
Dutch Elm Disease has spread to all of our major native stands of elms in the state.
Only a few small pockets of elms have escaped. The fate of planted elms is largely
dependent on their proximity to infested native stands where the disease is easily
transported to healthy trees by elm bark beetles. Once a tree is infected the disease can
spread to healthy trees via natural root grafts. In cities, elm firewood piles that harbor
bark beetles carrying DED spores are one of the most common means of spreading DED.
However, the incidence of disease was stable and, in some instances, even declined among
cities with active sanitation and other management programs. As the disease runs its
course in native elm stands, the risk of infection to nearby elms decreases.
X-disease is caused by a phytoplasma which occurs on native and planted chokecherry
across the state. Symptoms include leaves that turn red in mid-summer, the lack of fruit
or fruit which does not ripen normally, and a distinct rosette of leaves on branch tips
with reduced growth and eventual death. Symptoms are present on chokecherry in nearly
every county, and also are found on the ornamental Schubert chokecherry, often called
Canada red cherry. While many factors can cause chokecherry to exhibit some of the
symptoms characteristic of X-disease, the presence of all of the above described symptoms
on the same stem indicates a very high likelihood that X-disease is present. Laboratory
tests have now been developed to allow diagnosis of X-disease. The disease has been
confirmed in 15 counties.
Apple, crabapple, pear and Cotoneaster
R2-P162, R4-P76, R6-P99.
Fireblight is present statewide and remains a serious threat to susceptible cultivars
of apples and ornamental crabapples. A trend towards planting less susceptible cultivars
has reduced the severity of injury by restricting it to the fruit spurs instead of killing
entire branches. All of the major cities in North Dakota experienced high infestation
rates. The more isolated plantings in small towns, parks or farmsteads are not as likely
to be seriously injured. Siberian crabapple trees in windbreaks may be seriously affected.
Fire-blight is found on cotoneaster statewide. An insect (see pear slug) causes symptoms
which are often confused with fireblight. In the case of pear slug infestation, a close
inspection will reveal skeletonizing on the upper surface of the leaf and the possible
presence of larvae. While treatment with an insecticide is an effective control for pear
slugs, no pesticide is currently registered for fireblight control on cotoneaster.
Cottonwood and hybrid poplars
Septoria; R2-P74, R4-P50, R7-P37.
Cytospora; R2-P200, R4-P48, R7-P40.
Dothichiza sp.; R2-P184, R4-P54, R7-P40.
Phomopsis; R2-P142, R7-P40.
Cankers are an important cause of branch and stem mortality in hybrid poplars. Poplar
clones vary widely in their genetic resistance to these canker diseases. Ironically, the
native cottonwood that the hybrid poplars were meant to replace, is the most resistant.
Siberian Elm Cankers
Tubercularia; R2-P208, R4-P40.
Botryodiplodia sp.; R2-P182, R4-P38.
Many shelterbelts, especially single-row, have been infected by cankers and are in a
state of serious decline. These cankers are playing an important role in the deterioration
process. Many miles of single-row Siberian elm shelterbelts are being removed each year,
but few are being replaced.
Botryodiplodia; R2-P180, R4-P42.
Tubercularia; R2-P208, R4-P40.
Phomopsis; R4-P140, R4-P44.
Russian-olive, especially in shelterbelts in cultivated areas, continue to be plagued
by branch dieback from cankers. Cankers seem to be more numerous on trees near cereal
crops. This higher incidence may be related to more frequent direct exposure of trees to
herbicides such as 2,4-D. Many healthy trees, some of them large and obviously quite old,
continue to thrive in cities and parks where they have more room to grow and their
exposure to crop sprays is lessened.
Chokecherry, Plums and May Day Tree
R2-P152, R4-P70, R6-P101.
Black knot appears to be on the increase on ornamental Prunus. Canada red cherry
is often attacked. When the diseased branches are not trimmed out, the incidence of
disease increases year to year. The May Day tree seems to be particularly vulnerable and
many have been removed because of deformities caused by black knot.
Native chokecherry is infested with black knot disease statewide. Some chokecherry
clones are heavily infected with one or more knots present on nearly every branch. Where
heavily infected chokecherry are in close proximity to ornamental Prunus, diseased
plants should be removed.
Wetwood (Slime Flux)
Cottonwood, hybrid poplar and elm
R2-P382, R4-P64, R7-P52.
A high percentage of cottonwood, hybrid poplar and elm trees over 30-years old are
infected with bacterial wetwood. Outward signs of the disease are not always obvious. When
wetwood toxins are transported into the branches of a tree's crown, wilting of the leaves
may occur. Branch dieback and general tree decline can result. In some instances, wetwood
has been judged to be the primary cause of decline or death of trees.
Rhizosphaera Needle Cast
Rhizosphaera needle cast on spruce increased largely because of the cool wet weather in
1992 and 1993 which favored spore production and germination. Historically Rhizosphaera is
most prevalent in the eastern regions of the state, probably because of higher rainfall
and humidity in the east. Spruce grown in crowded conditions are the most seriously
Lirula Needle Blight
White spruce and Black Hills
Lirula needle blight was found primarily in north central, northeastern, and
southeastern portions of North Dakota. A planting on the Wakopa Game Management area in
Rolette County sustained light to moderate damage. Needle diseases of spruce are more
likely to affect sheltered trees (see Rhizosphaera).
Unknown Tip Dieback
Scotch, mugo and Ponderosa pine
Cenagium Dieback; R2-P230
In 1988, 1989 and 1990, a characteristic tip dieback symptom was found on pines in the
state. Damage occurred on the current year's growth. In some cases, the entire year's
growth was dead. In other cases, all needles and bark tissue beyond a certain point were
dead. No sign of insect activity or disease damage could be found. The symptoms closely
resembled Cenangium dieback of pines, but cultures were negative. With the return
to normal moisture conditions in 1991, this type of injury was rarely observed. A weak
opportunistic fungus was believed to be involved, but the mystery remains.
Sphaeropsis Shoot Blight (syn. Diplodia Tip Blight)
R2-P136, R4-P128, R9-P65, R10-P54.
In 1988 and 1989, Sphaeropsis shoot blight was identified in McHenry, Morton, Stark and
Slope Counties. Since 1991 Sphaeropsis has become much less prevalent.
R2-P196, R4-P132, R10-P53.
Cytospora canker caused damage to spruce across the state. Older trees or trees
stressed by sod competition, drought or root injury are especially susceptible to this
disease. Any serious decline in the health of a tree may allow invasion of the organism.
Infestations generally start with branches near the bottom of the tree. Crowding trees has
been implicated as a predisposing factor.
Western Gall Rust
Ponderosa and Scotch pine
R2-P282, R4-P126, R6-P51, R9-P27, R10-P73.
Western gall rust was found in pine plantations in McHenry, Bottineau, Pembina, Mercer
and Morton counties; several shelterbelts scattered throughout the state; and in native
ponderosa pine in Slope County. The incidence of this disease is on the rise in planted
R2-P456, R4-P33, R6-P118.
Herbicide injury has become an increasing problem for many tree species during recent
years. In addition to the more "traditional" phenoxy herbicide injury (2,4-D
drift), there has been increased damage from pre-emergent sprays. The list of approved
herbicides for use on trees, shrubs, field crops and ornamentals grows every year. In some
cases, injury symptoms of these herbicides on tree species is unknown. Potentially harmful
herbicides are sometimes added to "weed and feed" type lawn fertilizers. They
may leach into the root zone of trees from nearby crops. Where variable soil and weather
conditions exist, the application of herbicides according to label recommendations may
cause injury to nearby trees.
Boxelder, Siberian elm, Amur maple and grape are particularly sensitive to 2,4-D
injury. Direct herbicide application is not always necessary for these plants to show
damage symptoms. Phenoxy herbicide injury has been implicated in the decline of Siberian
elm, notably in single-row belts. Cottonwood seems to be especially sensitive to root
injury by Tordon and other soil-applied chemicals. Extreme care and constant vigilance is
needed to prevent herbicide and other chemical damage to trees and shrubs.
Conifers, especially spruce and pine, seem to be more prone to winter damage in
highly-fertilized lawns. Late summer or early fall applications of nitrogen may hinder
conifers from going dormant when they should. The same type of damage may occur on
deciduous trees and shrubs, but is not as recognizable as damage to conifers.
R2-P340, R2-P476, R4-P88, R9-P98.
Effects of the severe drought in 1988-1991 will continue to affect North Dakota trees
for several years to come. Trees were severely stressed and stressed trees are more prone
to attack by insects and disease. Boring insects and bark beetles increase during dry
periods and on weakened trees. Stressed trees are less able to resist invasion by canker
causing fungi. In spite of better growing conditions since 1991, many trees will continue
Sapsuckers and other Woodpeckers
Sapsucker damage occurs most commonly on medium to large trees, but small pines are
also commonly injured. Open areas of bark between whorls of branches are most often
attacked. Damage consists of evenly spaced rows of holes which may extend all the way
around the trunk. Because the holes are close together, sap flow may be interrupted and
the stem girdled above the point of injury. Sapsuckers are known to nest in the Turtle
Mountains, Pembina Hills and other large tracts of native woodlands in the state. Damage
may occur any time during the migration or breeding period in these regions. In the
remainder of the state injury occurs only during the migration period.
Other species of woodpeckers excavate holes when they attempt to reach insect larvae
that are tunneling in the wood or under the bark. These efforts, when noticed by humans,
are often not appreciated and misinterpreted as willful damage by woodpeckers to trees. If
woodpeckers are tunneling in your tree, insects are present. The exception is when
woodpeckers are excavating their nest holes usually in trees with heart rot. Woodpecker
activity may indicate trees are severely stressed and wood boring insects are present.
All species of trees, especially those in urban and suburban settings are prone to
mechanical injury caused by lawn mowers, line trimmers, rototillers, etc. Often these
injuries occur at the base of the tree where the presence of soil bacteria, moisture and
shade provide an ideal environment for diseases to proliferate and infect the tree. Human
or animal activities will compact the soil over the tree roots reducing air exchange and
water infiltration which reduces tree vigor. Improper pruning and jagged, broken limbs may
provide an avenue for disease infection and loss of vigor. Negative effects of these
activities accumulate over time. The low vigor resulting from these cumulative effects
predispose the tree to death when exposed to drought, insect infestation or disease
|Ash borer (lilac borer)
Ash and privet borer
Ash flower gall mite
Ash plant bug
Blackheaded ash sawfly
Ashgray blister beetle
Caragana blister beetle
Boxelder twig borer
Bronze poplar borer
Bronze birch borer
Caragana blister beetle
Cottonwood leaf beetle
Eastern ash bark beetle
Eastern spruce gall adelgids
Early aspen leaf roller
Elm lace bug
Elm leaf beetle
European elm scale
European fruit lecanium
European pine sawfly
Forest tent caterpillar
Giant conifer aphid
Great ash sphinx
Hackberry nipplegall maker
Honeylocust pod gall midge
Honeysuckle witches broom aphid
Introduced pine sawfly
Metallic pine pitch nodule maker
Native elm bark beetle
Oak bullet gall
Oak lace bug
Peach bark beetle
Pear slug or sawfly
Pine cone willow gall
Pine engraver bark beetles
Pine needle scale
Pine needle sheathminer
Pine tip moths
Poplar and willow borer
Poplar bud gall mite
Poplar petiolegall aphid
Poplar vagabond aphid
Prairie tent caterpillar
Red humped oakworm
Red turpentine beetle
Rose twig gall
San Jose scale
Scotch pine tip borer
Smaller European elm bark beetle
Ips calligraphus & I. pini
Malacosoma californicum lutescens
||Oligonychus species, Tetranychus
species & Eotetranychus species
Spruce gall midge
Spruce spider mite
Two-lined chestnut borer
Variable oakleaf caterpillar
Western ash bark beetle
Western pine tip moth
White-banded ash bark beetle
Woolly elm aphid
Yellowheaded spruce sawfly
Zimmerman pine moth complex
Dioryctria ponderosae, Dioryctria
tumicolella, Dioryctria zimmermani
Black rot (frogeye leafspot)
Cedar apple rust
Cytospora canker (spruce)
Sphaeropsis tip blight (pines)
Dutch elm disease
Kabatina tip blight
Cyclaneusma (syn. Nemacyclus)
Sphaeropsis sapinea (syn. Diplodia pinea)
|Rhizosphaera needle cast
|Siberian elm cankers
Western gall rust
Phytoplasma (formerly MLO)