Woody Plant Pests

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 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.'

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.

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.

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.

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

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.

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.

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.

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.

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.

Diseases

Hardwood Diseases

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.

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.

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.

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.

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.

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.

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.

Conifer Diseases

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 affected.

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).

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.

In 1988 and 1989, Sphaeropsis shoot blight was identified in McHenry, Morton, Stark and Slope Counties. Since 1991 Sphaeropsis has become much less prevalent.

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 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 ponderosa pine.

Abiotic Factors

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.

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 to decline.

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 infection.

Common and Scientific Names of Woody Plant Pests

Insects	Scientific Name
Ash borer (lilac borer) Ash and privet borer Ash flower gall mite Ash plant bug Aspen leafminer Blackheaded ash sawfly Blister beetles Ashgray blister beetle Caragana blister beetle Boxelder twig borer Bronze poplar borer Bronze birch borer Caragana aphid Caragana blister beetle Carpenterworm Cecropia moth Chokecherry aphid Cottonwood borer Cottonwood leaf beetle Eastern ash bark beetle Eastern spruce gall adelgids Early aspen leaf roller Elm lace bug Elm leaf beetle Elm leafminer Elm sawfly European elm scale European fruit lecanium European pine sawfly Fall cankerworm Fall webworm Forest tent caterpillar Fruittree leafroller Giant conifer aphid Grasshoppers Great ash sphinx Hackberry nipplegall maker Honeylocust pod gall midge Honeysuckle witches broom aphid Introduced pine sawfly Lace bugs Larch casebearer Larch sawfly Leaf crumpler Lecanium scale Linden looper Metallic pine pitch nodule maker Mourningcloak butterfly Native elm bark beetle Oak bullet gall Oak lace bug Oystershell scale Peach bark beetle Peachtree borer Pear slug or sawfly Pigeon tremex Pine cone willow gall Pine engraver bark beetles Pine needle scale Pine needle sheathminer Pine tip moths Poplar and willow borer Poplar 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 Scurfy scale Shothole borer Smaller European elm bark beetle	Podosesia syringae Tylonotus bimaculatus Eriophyes fraxiniflora Tropidosteptes amoenus Phyllocnistis populiella Tethida barda Epicauta species Epicauta fabricii Epicauta subglabra Proteoteras willingana Agrilus liragus Agrilus anxius Acyrthosiphon caraganae Epicauta subglabra Prionoxystus robiniae Hyalophora cecropia Aphis cerasifolia Plectrodera scalator Chrysomela scripta Hylesinus aculeatus Adelges abietis Pseudexentra oregonana Corythucha ulmi Pyrrhalta luteola Fenusa ulmi Cimbex americana Gossyparia spuria Parthenolecanium corni Neodiprion sertifer Alsophila pometaria Hyphantria cunea Malacosoma disstria Archips argyrospila Cinara species Melanoplus species Sphinx chersis Pachypsylla celtidismamma Dasineura gleditschiae Hyadaphis tataricae Diprion similis Corythucha species Coleophora laricella Pristiphora erichsonii Arobasis indigenella Lecanium corni Erannis tiliaria Retinia metallica Nymphalis antiopa Hylurgopinus rufipes Disholcaspis quercusmamma Corythucha arcuata Lepidosaphes ulmi Phloetribus liminaris Synanthedon exitiosa Caliroa cerasi Tremex columba Rhabdophagus strobiloides Ips calligraphus & I. pini Chionaspis pinifoliae Zelleria haimbachi Rhyacionia species Cryptorhynchus lapathi Saperda calcarata Aceria parapopuli Pemphigus populitransversus Mordvilkoja vagabunda Malacosoma californicum lutescens Symmerista albifrons Dendroctonus valens Diplolepsis spinosa Quadraspidiotus perniciosus Dioryctria species Chionaspis furfura Scolytus rugulosus Scolytus multistriatus
Spider mites	Oligonychus species, Tetranychus species & Eotetranychus species
Spring cankerworm Spruce budworm Spruce needleminer Spruce gall midge Spruce spider mite Tip moths Two-lined chestnut borer Tussock moth Uglynest caterpillar Variable oakleaf caterpillar Warty leafgall Western ash bark beetle Western pine tip moth White-banded ash bark beetle White-spotted sawyer Woolly elm aphid Yellowheaded spruce sawfly Zimmerman pine moth complex	Paleacrita vernata Choristoneura fumiferana Endothenia albolineana Mayetiola piceae Oligonychus ununguis Rhyacionia species Agrilus bilineatus Parorgyia grisefacta Archips cerasivorana Heterocampa manteo Aceria negundi Hylesinus californicus Rhyacionia bushnelli Hylesinus fasciatus Monochamus scutellatus Eriosoma americanum Pikonema alaskensis Dioryctria ponderosae, Dioryctria tumicolella, Dioryctria zimmermani

Diseases	Scientific Names
Anthracnose (ash) Anthracnose (oak) Black knot Black rot (frogeye leafspot) Cedar apple rust Cytospora canker (spruce) Sphaeropsis tip blight (pines) Dutch elm disease Fireblight Kabatina tip blight Cyclaneusma (syn. Nemacyclus) needle cast	Gnomoniella fraxini Apiognomonia errabunda Apiosporina morbosa Botryosphaeria obtusa Gymnosporangium species Cytospora kunzei Sphaeropsis sapinea (syn. Diplodia pinea) Ophiostoma ulmi Erwinia amylovora Kabatina juniperi Cyclaneusma minus
Poplar cankers	Cytospora species Phomopsis species Dothichiza populea Septoria musiva
Rhizosphaera needle cast Russian-olive cankers	Rhizosphaera kalkhoffii Botryodiplodia theobromae Tubercularia ulmea Phomopsis arnoldiae
Siberian elm cankers Sooty mold Valsa canker Western gall rust Wetwood X-disease	Botryodiplodia hypodermia Tubercularia ulmea Various species Valsa species Peridermium harknessii Enterobacter cloacae Phytoplasma (formerly MLO)