Scouting Report—Conifers::Arborvitae Leafminer, Balsam Twig Aphid, Cooley Spruce Gall Adelgid, Eastern Spruce Gall Adelgid, Larch Casebearer, Pine Bark Adelgid, Pine Eriophyid Mite, Pine Needle Scale, Rhabdocline, Spruce Spider Mite, Taxus Bud Mite, Rusts on Pines, Woolly Larch Adelgid
Broad-leaved Trees and
Shrubs:Azalea
Whitefly, Cankerworms,
Gymnosporangium Rusts,
Gypsy Moth, Honeylocust
Plant Bug, Imported Willow Leaf Beetle,
Linden Borers, Privet Rust
Mite, Snowball Aphid,
Viburnum Leaf Beetle
The Scouting Reports list chemicals registered for control of specific pests. Our recommendations are taken from the 1998 Pest Management Recommendations for Ornamental Trees and Shrubs. These recommendations apply to New York State.
The recommendations given in Branching Out are not a substitute for pesticide labeling. Read and follow the label before applying any pesticide!
Conifers |
Arborvitae Leafminer (14)–The larvae of this leaf mining moth were seen on our last scouting trip on Long Island. They are 1/4 inch long, green with black heads, and located in the shoot tips. For most of the year, they are located in the tips of the leaves. They mine the interior portions and cause affected areas to turn yellow then brown. Hold suspect leaves up to the light, and you'll see the larvae at work. If the infestation is light, prune off infested tips. There are many effective larval and pupal parasites that suppress the populations. However, the parasites are usually not abundant in specimen trees. Acephate foliar sprays control the larvae. These applications should be made now (150-260 GDD50.) and again in mid-August (1800-2200 GDD50.). Two pesticide treatments may be required for the first year of treatment.
Balsam Twig Aphid (33)–In Middletown (Orange County) last week, balsam twig aphids were moving onto the newly expanding growth of balsam fir and already causing characteristic curling and twisting of expanding 1998 needles. Christmas tree growers to the north with balsam or Fraser fir should begin to scout for this pest in earnest. In plantations with a history of the pest, crop trees may have to be sprayed with an appropriate insecticide to preserve their quality. Survival and growth of younger specimens are usually not greatly affected, and one can afford to wait for natural predators to build up.
Cooley Spruce Gall Adelgid (49)–Crawlers of this adelgid were observed on Douglas-fir in Orange County. Hatching generally begins right around the time that Douglas-fir is breaking bud. The crawlers may hatch out over a range of time so be ready to look for them when the new growth appears. On Douglas-fir, treat in early May 120-190 GDD50, but only on trees destined for market in the next two years. Younger trees can tolerate the feeding and there is little to be gained by spraying them.
Eastern Spruce Gall Adelgid (5)–Overwintering stem mothers had begun to initiate gall formation on our latest scouting trip to Long Island. Stem mothers are brown to black and should have white wax coverings and a full complement of eggs by this time. They can be found at the base of buds of Norway, white and red spruce and rarely on blue spruce. Gall formation begins even before the eggs begin to hatch. By the time you receive this newsletter the crawlers should be active and moving into the galls as they develop. Horticultural oil, insecticidal soap, carbaryl, or chlorpyrifos or imidacloprid may be applied up to 170 GDD50.
Larch Casebearer (11)–The damage from the larch casebearer is readily evident at this time. Infested trees have needles that are brown at the tips or bleached. The needles have an almost scorched like appearance. The larvae are camouflaged inside mined out needles. These needles are the color of dead needles. With a heavy infestation, premature defoliation is possible. With repeat defoliation, the growth of the tree is retarded, branches die, and the tree may be killed. In the Northeast, natural enemies attack this pest but don't keep them in check. Therefore, if the population of larch casebearer is cause for concern, a pesticide application may be warranted. To manage this pest, apply cyfluthrin or methoxychlor (Rockland 25 WP) through early May (363-618 GDD50).
Pine Bark Adelgid (31)–The pine bark adelgid crawlers are becoming active on white pines in Orange County. The insect usually causes little damage to healthy trees. The insects on the trunk can be removed with a high pressure spray of water if infestations are light. Alternatively, horticultural oil, insecticidal soap or chlorpyrifos may be applied from 56 to 618 GDD50 to kill the crawlers where large numbers of these pests are found on the shoots.
Pine Eriophyid Mite (54)–Pine eriophyid mites were found on Scots pine in Orange County during our last scouting trip. We also occasionally see damage from them on mugo pine. You will need a powerful hand lens and good eyesight to see the mites. They are very tiny, pink, and elongate. Pine eriophyid mites can stunt needles and cause them to be distorted and chlorotic. Landscape plants usually aren't threatened enough by this pest to justify management activities, but Christmas tree growers should be aware of it and examine unthrifty looking pines carefully to determine whether mites are there.
Pine Needle Scale (47)–Adult covers of this armored scale were found on white pine during the last scouting trip. Overwintering eggs are found underneath these covers. These eggs will hatch sometime in May until mid-June. When they hatch, small reddish nymphs will emerge from underneath. They may be dispersed by the wind to other trees or crawl to other nearby branches. The feeding from this insect causes the needles to turn yellow and then brown. From a distance the foliage may look white to gray. When a heavy infestation occurs, the affected branches or entire tree may die. White, mugo and Scots pines are often attacked. Austrian and red pines, spruces and Douglas-fir and cedars are also reported as occasional hosts.
Treat affected trees and shrubs with a horticultural oil, insecticidal soap, acephate, carbaryl, chlorpyrifos,cyfluthrin, diazinon, malathion,or bifenthrin. A treatment should be applied late May (298-448 GDD50) and in July (1290-1917 GDD50).
Rhabdocline Needlecast (15)–Rhabdocline needlecast fruiting bodies have split open so spore dispersal is all set for the new needles when they emerge. If your Douglas-fir (the only host) had problems with Rhabdocline needlecast last year you may need to apply chlorothalonil after budbreak but before new growth is 1/2 inch long. Repeat applications at 10-14 day intervals until July 1. This disease was once only a problem for Christmas tree growers but with each passing year, we see more of it on landscape specimens.
Spruce Spider Mite (52)–We are now entering another window of opportunity to treat this pest. If after scouting you judge it necessary to treat, apply a registered miticide in mid to late May (192-363 GDD50). Keep in mind that spruce spider mites are primarily cool season pests, and they will be causing their damage now before the warm weather hits.
Taxus Bud Mite (230)–The immature taxus bud mite, an eriophyid mite, has been reported in Rockland County. These eriophyid mites can be found on yew. You will need a 20X hand lens and very good eyes to see the mites. Eriophyid mites are 0.2-0.5 mm long, wormlike, and carrot-shaped. The feeding of the mites causes the buds to enlarge and die. If the infestation is severe, apply carbaryl, dimethoate, endosulfan, fluvalinate, or oxythioquinox in early to late May (148-448 GDD50). Shear off distorted growth and collect and destroy the trimmings.
Rusts on Pines:White Pine Blister Rust (131) and Pine-Pine Gall Rust (136)–Diagnosis of these rust diseases on pines is easiest in the spring when the cankers are sporulating. Sporulation of both of these rusts has begun in plantings south of the NYS Thruway. White pine blister rust cankers on eastern white pine produce spores in bright, yellow orange blisters. Look for the disease on stems and lower branches of smaller trees (mostly less than 6 inches diameter). Branches with cankers can be pruned, but there is little hope for trees with stem cankers other than to try to excise visibly diseased tissue and 1-2 inches of surrounding "healthy" bark. Pine-pine gall rust occurs on two and three needle pines, especially Scots and occasionally Austrian and mugo. Most galls vary in size from that of a golf ball on small branches to as large as a softball when developing on the stem. When mature, these galls split open to reveal masses of bright orange powdery spores that may easily be dispersed by the wind. Pruning before sporulation begins will reduce inoculum for future infections. Salvageable specimens may be treated with mancozeb or maneb 3 times at 2 week intervals when sporulation begins to prevent additional infections from getting started.
Woolly Larch Adelgid (32)–The woolly larch adelgid feeds on foliage, buds, and cones of larch. The newly hatched nymphs were detected last week on new larch growth on Long Island. Foliage affected by this insect has a white fluffy residue covering it. Where the infestations are moderate to heavy sooty mold and needle distortion are other symptoms that are likely to be seen. If this insect is a problem, apply insecticidal soap, horticultural oil, chlorpyrifos or imidacloprid during early to mid-May (121-192 GDD50) on larch.
Broad-leaved Trees and Shrubs |
Azalea Whitefly (151)–Adult whiteflies,
resembling tiny white moths, have been detected on azalea on Long
Island. Hosts of this insect include azalea,
rhododendron, mountain laurel, and andromeda. Medium infestations may produce
noticeable levels of honeydew and sooty mold. Heavy infestations can cause
leaves to turn yellow and drop prematurely. All stages feed on the undersides
of leaves. If honeydew or damage are easily identifiable, spray the undersides
of the leaves with insecticidal soap or horticultural oil. Predators and
parasites are frequently effective in keeping these pests at low levels.
Rake up and destroy fallen leaves from infected plants. If infestations are
intolerable apply acephate (PT 1300 DS), bifenthrin, chlorpyrifos, cyfluthrin,
diazinon, dimethoate, endosulfan, fluvalinate, horticultural oil, imidacloprid,
or malathion in early June to Mid-July (448-700 GDD50) and again
at 1250-1500 GDD50 and at 2032-2150 GDD50.
Cankerworms (63, 64)–Rockland County Cornell Cooperative extension staff report that second and third instar cankerworm larvae are active. These larvae chew shotholes in the leaves of deciduous trees such as apple, beech, birch, linden, maple and oak. The spring and fall cankerworms have green and brown to gray caterpillar forms. If the infestations are heavy, acephate, Bacillus thuringiensis subsp. kurstaki, bendiocarb (spring cankerworm), bifenthrin, carbaryl, chlorpyrifos, cyfluthrin, fluvalinate, permethrin, or phosmet (for spring cankerworm) can be used throughout May (148-290 GDD50).
Gymnosporangium Rusts (118,119)–Orange spots have begun to appear on the leaves of crabapples. On the upper surface of the leaves, tiny black pustules are located within the spots. Circular lesions can be seen, on the lower surface of the leaf, with the aid of a hand lens. Nothing can be done to treat this disease now. However, be prepared to treat infected trees next spring. In the future, try to avoid planting junipers and eastern red cedar near hawthorn, flowering crabapple, or quince. Plant rust resistant varieties of juniper to avoid this disease.
Gypsy Moth (61,62)–Reports from Nassau County's Cornell Cooperative Extension indicate the first instar gypsy moths are out and crawling on Long Island. If populations are not being controlled by natural enemies apply Bacillus thuringiensis subsp. kurstaki when the larvae are first detected. Alternatively, bendiocarb (Turcam), bidrin (on birch, maple, oak), carbaryl, chlorpyrifos, cyfluthrin, diflubenzuron, fluvalinate, phosmet, or permethrin are registered for use from 90-448 GDD50.
Honeylocust Plant Bug (194)–The
pale green nymphs have just emerged and are beginning to cause
damage to honeylocust. These nymphs have short wing
buds that do not reach to the end of their bodies. You will really have to
examine the foliage closely because the nymphs are inside the folded leaves
and are tiny (less than 3/16 of an inch long). The unfolding leaflets are
very susceptible to damage. The feeding of the nymphs and adults causes these
leaves to become stunted, deformed, and chlorotic. With a large population
of plant bugs, defoliation is possible. If the growing conditions are adequate,
honeylocusts will be able to recover from early damage and refoliate.
Imported Willow Leaf Beetle (106)–On
a recent scouting trip, we found adult leaf beetles feeding on
willows in Middletown. In addition to most species
of willow this beetle also feeds on Lombardy poplar and eastern cottonwood.
The adults are metallic blue to greenish blue in color, oval, and less than
1/5 inch long. Their feeding causes holes and notches in the leaves. With
a heavy infestation, the tree becomes unsightly and may turn brown as early
as mid-June. A management measure may not be needed since a parasitic wasp
(Schizonotus sieboldi) and low temperatures keep the populations down.
However, if the population is unacceptably high, several alternatives exist.
Severely infested willows and poplars may be treated with Bacillus
thuringiensis var. san diego (M-Trak), bendiocarb, carbaryl, or chlorpyrifos
in the last half of May and in early June (192-448 GDD50).
Linden Borers–Arborist Dick Johnson reports unusually high populations of small, 1/4 inch long, white borer larvae on little leaf linden in the Albany area. Information provided us by Greg Hoover, entomologist at Penn State, indicates what is described is the larval stage of a small moth known as the linden bark borer, Chrysoclista linneella (Clerck). This nut and fruit borer is an introduced European species. It was first reported in this country in 1928 when it was found infesting basswood near New York City.
In and of itself, their damage may not be sufficient to affect tree health. However, the larvae are attracting woodpeckers and by the time they are done, trees have sustained considerable damage. Adults are active from late May to mid-June therefore we expect the woodpecker activity to cease as the larvae transform into adults in the next few weeks. We will continue to search the literature for an effective and registered pesticide.
Privet Rust Mite (231)–We saw this eriophyid mite on our last scouting trip in Rockland County. These mites are white to yellow and spindle shaped with four short anterior legs. Even when viewed with a hand lens, they are so small that they appear as specks of dust or pollen. The host plants of this pest are the amur privet and the California privet and regal privet. The immature mites suck leaf juices and introduce toxins that cause leaves to cup downwards and turn olive green. Premature leaf drop and silvery stippling of foliage are also symptoms. Predaceous mites are the most effective natural enemies to these pests, but carbaryl, fluvalinate, horticultural oil, or oxythioquinox can be used to fight these pests in the last 10 days of May through Mid-June (298-802 GDD50).
Snowball Aphid (142)–Snowball aphids have been detected on some viburnums in Orange County. Viburnum opulus, V. prunifolium, and V. acerifolia are most damaged. They are only found in the spring on this host. However, their feeding may cause foliage to become severely distorted. Predators seem to keep most populations in check but where they have become intolerable, you can treat with acephate, bifenthrin, cyfluthrin, diazinon, endosulfan, fluvalinate, imidacloprid, horticultural oil, or permethrin from early to mid-May.
Viburnum Leaf Beetle (104)–The larvae are active now and causing extensive damage on various viburnums in Monroe county. The larvae are pale and covered with tiny dots. Its preferred hosts are Viburnum opulus, V. lantana, V. dentatum complex, V. rafinesquianum, V. acerfolium, and V. lentago. They feed gregariously on the undersurfaces of leaves and eventually will eat all but the midrib and major veins of the leaves. Adult emergence occurs in mid to late July. Adults continue feeding and can cause almost as much damage as the larvae. It is similar in appearance and habits to the elm leaf beetle. Horticultural oil (leaf beetle larvae), insecticidal soap, and chlorpyrifos are registered for treatment of leaf beetles.
Note:This information is valid for New York. It may or may not apply in your area.
This publication contains pesticide recommendations. Changes in pesticide regulations or human errors are still possible. Some materials may no longer be available, and some may no longer be legal. These recommendations are provided only as a guide.
All pesticides distributed, sold, or applied in New York State must be registered with the Department of Environmental Conservation (DEC). Questions concerning the legality and/or pesticide use in New York State should be directed to the appropriate Cornell Cooperative Extension office or regional DEC office. Read the label before applying any pesticide. If any information in these recommendations disagrees with the label, the recommendation must be disregarded.
Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by Cornell Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical.
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