Conifer Tree Diseases, Disorders, Insect, and Mite Treatment Options

gardens

SOUTH DAKOTA STATE UNIVERSITY® JANUARY 2021 AGRONOMY, HORTICULTURE & PLANT SCIENCE DEPARTMENT Conifer Tree Diseases, Disorders, Insect, and Mite Treatment Options – 2021

John Ball | Professor, SDSU Extension Forestry Specialist & South Dakota Department of Agriculture Forest Health Specialist

Any management options, including those identifying specific active ingredients, are for the convenience of the reader. The bolded active ingredients mentioned in this publication are those that are most commonly available in pesticides used in South Dakota for Turf & Ornamentals and the inclusion of an active ingredient shall not be taken as an endorsement or the exclusion of one labeled for use a criticism regarding effectiveness. Please read and follow all label instructions and the label is the final authority for a product’s use on a particular pest or plant. Not all active ingredients listed are available to the public and some require a commercial pesticide license. It is the reader’s responsibility to determine if they can legally apply any product identified in this publication.

Conifer Diseases and Disorders Name Species Symptoms Management Cedar-apple rust - Primarily eastern redcedar, The reddish-brown galls Treatments are not applied Gymnosporangium juniperi- and Rocky Mountain form on twigs over two since the disease usually virginianae, cedar-hawthorn juniper. Some creeping years. The mature galls does little harm to its juniper rust – G. globsum. a fungus. juniper cultivars are also produce orange-gelatinous host and the treatment susceptible. tendrils (horn) during moist window too wide. spring weather. Infested Occurs throughout the state. cedar stems may become swollen and the branch dies above the infected point. The galls from cedar-apple rust persist for one season while those from cedar-hawthorn rust may last for many years. Cytospora canker – Valsa Primarily blue spruce. Black The needles on the infected Prune out all infected kunzei, a fungus. Hills spruce may also be lower branches turn brown in branches before the infected. the spring. These branches spring rains or postpone generally have spots or till summer. Disinfect Occurs throughout the state streaks of bluish white resin pruning tools between cuts. and is more common during (black fruiting bodies may Maintain health by mulch and following droughts. be found beneath the resin and irrigation. Cambistat patches). The disease is as a soil drench can reduce generally limited to branches symptoms. and is most common in trees over 15 years old. Phomopsis twig blight of spruce presents similar symptoms.

Page 1 © 2020, South Dakota Board of Regents Name Species Symptoms Management Diplodia tip blight – Diplodia Primarily Austrian pine, but Symptoms occur in late Chlorothalonil, copper, pinea (Sphaeropsis pinea), a also found on ponderosa, spring with new shoots and mancozeb, myclobutanil fungus. Scots, and mugo pine. needles becoming stunted. or thiophanate-methyl In the fall, small black fruiting applied just as the buds are Occurs throughout the state. bodies may be found at the opening (usually early May) needle base beneath the and repeat just before the papery sheaths and on cone needles completely emerge scales. and again in 10 days. Trees may be infected Propiconazole can be without showing symptoms injected into trunks in late fall until they are affected to protect the new candles by drought, hail or other the following spring. stressors. Dothistroma needle blight Austrian and ponderosa Symptoms occur in late Copper or mancozeb – Dothistroma septospora pine are the most common summer or fall and are first fungicides applied as (Mycosphaerella pini) a species affected by this seen on the lower crown and the new growth expands fungus. disease. older needles. Needles have (mid-May) and repeated in yellow and tan spots that late June. Ponderosa and Occurs throughout the state. become red to brown bands Austrian pines should also with yellow halos. The base receive a third application in of needle remains green mid-July. though small black fruiting bodies may be seen in the spring erupting through the needle. Elytroderma needle cast – Ponderosa and lodgepole Symptoms occur in the No effective chemical Elytroderma deformans, a pine. spring when groups of year- treatments. Remove heavily fungus. old needles turn reddish- infested trees. Occurs in the Black Hills. brown except for the base. Needles usually drop by October. Often confused with Diplodia but can be separated by the brown lesions that often occur in the inner bark of twigs infected with elytroderma. The formation of witches’ brooms is a common occurrence. Juniper blight - caused Phomopsis and kabatina are Cercospora blight Copper or mancozeb by one of three fungi: found on eastern redcedar symptoms occur in late applied three times - mid Phomopsis juniper-ovora, and Rocky Mountain juniper summer with the oldest June, early July and mid-July Pseudo-cercospora juniperi as well as the Chinese and needles on the lower, inside for Cercospora. Phomopsis or Kabatina juniperi. creeping junipers. Rocky branches turning bronze can be treated with copper, Mountain juniper is most or red and the symptoms mancozeb, propiconazole, susceptible to kabatina. are limited to the interior or thiophanate-methyl at Cercospora is generally needles. 14-day intervals beginning found on eastern redcedar in mid-May and continuing and Rocky Mountain juniper. Phomopsis and Kabatina until growth ceases or dry blight affects shoot tips and weather begins. these turn yellowish-brown to red, eventually becoming Kabatina is difficult to brown. effectively control as it enters through a wound, typically Kabatina symptoms occur on those caused by insects, previous season’s shoots in and infection occurs in the April and May with the brown autumn. Thiophanate- tissue dropping by June. methyl is labelled for Phomopsis symptoms occur treatment of Kabatina during the growing season from May to July as the newly expanding shoots become infested.

Page 2 © 2020, South Dakota Board of Regents Name Species Symptoms Management Lirula needle cast – Lirula Black Hills spruce is the A common symptom is A treatment of macrospora, a fungus. most susceptible. black bands on 2nd or 3rd chlorothalonil when the year interior needles that new needles are about half- Rarely found in state. late turn purplish-brown size, repeat 3 weeks later. and this extends over the entire needle by fall. Despite the name, needecast, the infected gray needles may remain attached for several years due to the fungus disrupting the abscission zone. Pine wilt – Bursaphelenchus Scotch, mugo and Austrian Symptoms begin in Sawyer beetles carry the xylophilus, a nematode. pines. midsummer with foliage nematode to host trees yellowing then browning. hence remove and burn Currently found along or Infected trees generally die infested trees before the south of US Hwy 212. that same fall with the gray beetles emerge, usually early needles hanging from the April. Infected trees must branches. The wood in the be cut level to the ground dead, infected trees will often as even a slight stump may be blue-stained. Typically harbor the nematode. High infects trees more than 10 value trees can be injected feet tall. with abamectin in early spring (April). Rhizosphaera needle cast Primarily Colorado blue Symptoms occur in Chlorothalonil, with the – Rhizosphaera kalkhoffii, a spruce. midsummer with the previous first application when new fungus. season needles on lower needles are half-size and Common throughout state. branches turning yellow then repeat 2 weeks later. purplish brown by late winter. Small black fruiting bodies with smooth margins emerge from the needle stomates in the spring. SNEED, (Sudden Needle Primarily Colorado blue The 1st and 2nd year This disease may only be a Drop) Setomelanomma spruce. needles turn a brown to secondary stressor, present holmiii, a fungus. purple-brown and drop on trees already declining Found across the state. prematurely. One branch from other stresses. may be affected or all the branches. Small dark fruiting bodies can be found on the affected twigs. Positive identification will require a sample to be sent in. Sirococcus shoot blight, Primarily Colorado blue The young shoots are killed, Chlorothalonil applications Sirococcus strobilinus, a spruce. the needles are shed and the when new needles are 1/2 fungus. tip of the bare shoot droops to 1-inch long (late May) and Found across the state. to form a curve. repeat 3 to 4 weeks later. Stigmina needlecast, Primarily Colorado blue Symptoms are like Chlorothalonil applied Stigmina lautii, a fungus. spruce. Rhizosphaera needlecast, when the new needles are purpling and loss of older half-size then every 2 weeks Found across the state. needles, usually beginning through August or until with the lower branches but weather turns dry. Treat the symptoms spread to upper entire canopy, not just the canopy. Small dark fruiting lower branches. bodies with spider-like margins can be found on the needles. This disease is becoming more common than Rhizosphaera.

Page 3 © 2020, South Dakota Board of Regents Name Species Symptoms Management Western gall rust – Primarily ponderosa and A round gall on the branches Resistance varies from tree Endocronartium harknessii, Scotch pine are infected. of the tree. The woody gall to tree. The galls may be a fungus. Primarily in the Black Hills will produce masses of pruned from small, infested but found across the state. orange spores each spring. trees but once a tree is infected, repeated infections are very likely. Weir’s cushion rust – Occurs on both Black Needles on the current Chlorothalonil applied at Chrysomyxa weiri, a fungus Hills and Colorado blue year’s shoot develop yellow bud-break and repeated two spruce. The disease is bands by late summer. The more times about 10 days more common in the Black following year the infected apart. Hills but now can be found needles have gold and throughout the state. yellow banding. Tiny yellow blisters also are found on the needles. Winterburn (browning) All evergreens but Needles turning brown Plant susceptible plants such arborvitaes, firs and yews or reddish brown. This as yews in areas where they are most susceptible. is desiccation due to the will not be exposed to winter needles transpiring during sun or wind. Make sure that mild, windy winter conditions evergreens do not undergo when water uptake is limited moisture stress in late by cold or frozen stems or summer/early fall. soils. Winter kill All evergreens. Needles turning brown or none reddish brown. The inner bark of twigs and branches may also have brownish streaks.

Page 4 © 2020, South Dakota Board of Regents Conifer Insects and Mites Name Species Symptoms Management Cedar bark beetle - Primarily junipers but Foliage on individual twigs Remove and burn infested Phloeosinus spp. some species may infest wilts, dies, and breaks off, branches and trees. Treat arborvitae. occasionally may affect trees with carbaryl or entire tree. Small holes found permethrin by early June. Found throughout the state. in the trunk with galleries Treat the trunk and all beneath. Larvae are white branches larger than 1-inch and legless, galleries are like in diameter. those of elm bark beetles. Pine bark beetles – Engraver Ponderosa pine. Engraver beetles: these Treat tree susceptible to beetle Ips calligraphus, I. insects typically infest the engraver beetle attack, grandicollis and I, pini. All pine bark beetles occur in canopies of pines so usual typically drought-stressed the Black Hills region. symptoms are browning or fire-scarred trees with Mountain pine beetle needles in the upper canopy. bifenthrin, carbaryl or Dendroctonus ponderosae Engraver beetles may be found throughout the state. During droughts, entire trees permethrin (note these and red turpentine beetle D. may become infested and must be labeled specifically valens. Mountain pine beetle does small pitch tubes may be for bark beetles) in mid-April NOT occur outside of the associated with the attack, about the time apple leaf Black Hills region. boring dust is commonly buds are opening. seen. If appropriate, treat trees for Mountain pine beetle: mountain pine beetle attack needles on infested trees with the same chemicals but turn reddish-brown, boring by early June. Note: once a dust may be found at base tree has been attacked, it is of tree. Pitch tubes (small too late for treatment. masses of pitch) can be found along the trunk from 3 No treatments are necessary to 40 or 50 feet for mountain for turpentine beetles. pine beetle attacks. Trees die within a year of attack by mountain pine beetle. The mountain pine beetle epidemic ended by 2016 and there is no need for preventative spraying of pines at this time. Red turpentine beetle: pitch tubes are found on the lower trunk from ground level to 3 to 5 feet. In the Black Hills, infested trees usually are already stressed by construction or fire. Pine needle scale – All pines and spruce. Look for white flecks on Treat with horticultural Chionaspis pinifoliae (an discolored needles. Heavy oil, insecticidal soap armored scale) Found throughout the state. infestations give the needles (note: oil and soap a pale “snowy” look. can discolor Colorado Crawlers are very small spruce) or dinotefuran or (need 10x lens) and are pyriproxyfen one week after reddish-brown. Tatarian honeysuckle blooms and another application when smooth hydrangea blooms with a third application in mid-July. Pine sawfly – Neodiprion Ponderosa, Scots and Tufts of dry, straw-like Azadirachtin, carbaryl, spp. Austrian pine. needles or only stubs of insecticidal soap or needles. Larvae found in Spinosad when larvae seen, clusters on the previous usually late April. season’s foliage.

Page 5 © 2020, South Dakota Board of Regents Name Species Symptoms Management Pine tip moth – Rhyacionia Ponderosa, Austrian, or Symptoms are dead and Treat with imidacloprid or spp. Scotch pine. dying new shoots with permethrin or Spinosad expanded needles. Brown to just as needles begin to Found throughout the state. orange larvae (3/8”) found in expand in May. pitch masses near the tips of shoots during the summer. Several generations per year so additional treatments may be needed in late June and July. Pine tortoise scale – All pines but most common Look for sooty mold, a black Imidacloprid as a soil Toumeyella parvicornus, a on mugo and Scotch pines. powdery substance, on drench in mid- September. soft scale needles and twigs. At the Acephate or malathion Striped pine scale is also base of the needles there applied in late June when A related species, striped found on ponderosa pine. will be small reddish-brown mockorange are in bloom pine scale Toumeyella pini, is global insect. and repeated 10 days later to found in the Black Hills. kills the hatched crawlers. Spruce bud scale – All spruce but most common Small reddish-brown globular Treat trees when lindens Physokermes piceae, a soft on Black Hills and Norway scales found in clusters begin to bloom (mid- scale spruce. at the base of twigs. They June) with carbaryl or resemble buds so are often dinotefuran. Imidacloprid Occurs throughout the state. overlooked. Often associated can be used as a soil drench with dying lower branches. in early fall for control the following season. Spruce needleminer – All spruce, but most common Small clusters of discolored Treat trees with carbaryl or Endothenia albolineana on Colorado blue spruce. needles webbed tightly permethrin in early April together and flattened and late June. Can use high- Occurs throughout state. against the branch. Needles pressure water to knock the are hollowed-out with nest off in early spring then small hole near the base. rake and burn debris. Symptoms usually begin on the lower 1/3 of the tree. Spruce spider mite - Primarily spruce, especially Yellowish to rusty-brown Treat with abamectin, Oligonychus ununguis the dwarf Alberta spruce, but needles are a common bifenazate, hexythiazox, also a problem on junipers. symptom of an infestation or spiromesifen, two and usually do not appear applications 6 to 10 days until mid-summer after the apart beginning when silver mite has become inactive. maples leaves begin to Silken webs may also be form. Pesticides containing seen lacing across needles. tau-fluvalinate may be also be used for suppression Mites may be detected early only. Horticultural oil also in the season by shaking a shows promise (but will branch over a white sheet of remove the blue coloration paper; the tiny slow-moving on spruce). Insecticidal black or gray-green spots soaps may be used but have are most likely spruce spider limited effectiveness against mites. this mite as soaps rarely Spruce spider mite is a cool penetrates the web and this season mite, so it starts can also be a problem with becoming active when silver oils. maple leaves are expanding. Another period of activity is when the maples begin their fall color change.

Page 6 © 2020, South Dakota Board of Regents Name Species Symptoms Management Twospotted spider mite – Primarily junipers but also on Chlorotic and stippled Treat with abamectin, Tetranychus urticae pine and spruce. needles are a common bifenazate, hexythiaox, symptom of an infestation. or spiromesifen two Foliage may drop applications 6 to 10 days prematurely. Silken webs apart in late June and early may also be seen lacing July. Pesticides containing across needles. tau-fluvalinate may be also be used for suppression Mites may be detected early only. Horticultural oil also in the season by shaking a shows promise (but will branch over a white sheet of remove the blue coloration paper; the tiny slow-moving on spruce). Insecticidal black or gray-green spots soaps may be used but have are most likely spruce spider limited effectiveness against mites. this mite as soaps rarely Twospotted spider mite is penetrates the web and this a warm season mite so is can also be a problem with active during the summer. oils. Zimmerman pine moth – Austrian, ponderosa, Infested branches bend or Drench trunk and branches Dioryctria spp. and Scotch pine. D. break at the trunk. Masses with bifenthrin or ponderosae found mostly of reddish pitch near where permethrin. D.tumicolella in the Black Hills region branch attaches to the trunk. and D. zimmermani should while D. zimmermani and Larvae creamy white for D. be treated during the middle D. tumicolella are found ponderosae, D. zimmermani of August and the end of statewide. larvae are greenish-brown April. Treatment for D. while D. tumicolella is ponderosae is first week in brownish. Larvae overwinter June and repeat 4 weeks beneath the bark for only for later. D. ponderosae, the others hibernate in a web on the bark over the winter

SDSU Extension is an equal opportunity provider and employer in accordance with the nondiscrimination policies of South Dakota State University, the South Dakota Board of Regents and the United States Department of Agriculture. Learn more at extension.sdstate.edu.