Plant Health Care report May 4, 2012
Tagged as: juniper scale, Alder leafminer, Arborvitae leafminer, ash-lilac borer, Black Knot, brown rot of stone fruit, elm leaf miner, four-lined plant bug, galls, honeylocust plant bug, Rose rosette, Spittle bug
May 4, 2012 issue 2012. 3_________________________________________________________________
Our report includes up-to-date disease and insect pest reports, as well as color images, for northeastern Illinois. You'll also find a table of accumulated growing degree days throughout Illinois, precipitation, and plant phenology indicators to help predict pest emergence. The report is published bi-weekly on Fridays in April and August, and weekly May-July.
Arboretum staff and volunteers will be scouting for insects and diseases throughout the season. We will also be including information about other pest and disease problems based on samples brought into the Arboretum's Plant Clinic from homeowners and professionals.
What indicator plants are in bloom at the Arboretum?
Horsechestnut (Aesculus hippocastanum), last issues plant is still in bloom
Cranberrybush Viburnum (Viburnum opulus var. americanum-figure 1) is beginning to bloom.
Accumulated Growing Degree Days (Base 50): 306 as of May 3
Accumulated Growing Degree Days (Base 30): 1498 as of May 3
It is interesting to note that the growing degree days were accumulating rapidly in March and now they are creeping along since the weather cooled down. In the last two weeks of March we accumulated 173 growing degree days (base 50). By comparison, during the last two weeks of April we accumulated only 34 growing degree days. So we are ahead of ‘normal’, but not as much ahead as we were. This means that we will need to be diligent in scouting and looking for pests. They may arrive earlier than ‘normal’, but not as early as we previously predicted. Careful observation will be important this year.
|Figure 1 Viburnum opulus var. americanum|
- Arborvitae leafminer
- Ash-lilac borer
- Juniper scale
- Four-lined plant bug
- Hoeylocust plant
- Elm leafminer
- Spittle bug
- Alder leaf miner
- Black knot
- Brown rot of stone fruit
- Rose rosette
Events of interest:
- Monitoring and Managing Insect Pests
Degree Days and Weather Information
As of May 3, we are at 306 base-50 growing degree days (GDD), which is 228 GDD 50 ahead of 2011 at this time. In April, it rained 2.29 in., which brings us to 6.93 in. through the end of April.
|Location||B50 Growing Degree Days
Through May 3, 2012
|Crystal Lake, IL*||318||--|
|The Morton Arboretum||306||.99|
|Northbrook**||326 (as of May 2)||.35" from April 25-May1|
**Thank you to Mike Brouillard, Northbrook Park District for supplying us with this information.
*We obtain most of our degree day information from the GDD Tracker from Michigan State University web site. For additional locations and daily degree days, go to http://www.gddtracker.net/
Pest Update: Insects
|Figure 2 Arborvitae leafminer|
Arborvitae leafminer (Argyresthia thuiella) larvae are becoming active and feeding. (Figure 2). The larvae are an eighth of an inch long and pale yellowish-green with dark brown to black heads. They tunnel into the tips of needles where they will remain and feed for most of the year. The heaviest feeding occurs in fall and early spring resulting in browning of needle tips (Figure 3). After pupation, adult moths normally begin to appear in late May to early June (400-600 GDD). Eggs are laid during late summer, and, upon hatching, the tiny caterpillar tunnels into the arborvitae scales.
|Figure 3 Arborvitae leafminer damage|
Management: In light infestations, prune off infested tips. With heavy infestations, chemical treatments are effective in controlling larvae and should begin 150-260 GDD (we have surpassed this aready). There are over 25 parasites (natural enemies) that have been recovered from arborvitae leafminer larvae and pupae. The use of insecticides may actually increase the leafminer numbers by destroying these natural enemies. Use chemicals sparingly.
An arborvitae leafminer feeding preference study performed at the Arboretum by Donna Danielson, Lisa Nakomoto, and Dr. Fredric Miller found that generally, the shorter, denser arborvitae cultivars such as 'Hetz Midget' were attacked less than the taller cultivars or the straight species.
|Figure 4 Spindle galls on Prunus|
Galls are irregular plant growths that occur on leaves, buds, bark, twigs, roots, and flowers of many plant species. Most galls are caused by irritation or stimulation of plant cells due to feeding or egg-laying by insects such as mites, midges, aphids, and wasps. Some galls are the result of infections by bacteria, fungi, or nematodes. There are numerous types and forms of gall. So far this year, we have seen maple bladder gall on maple, erineum gall on bur oak (Quercus macrocarpa ), spindle gall on linden (Tilia sp.) and the oak apple gall that we reported in the last issue. The galls listed below are caused by eriophyid mites that overwinter in bark crevices or wounds. The mites become active in spring and migrate to feed on expanding leaf buds.
|Figure 5 Erineum gall|
Spindle galls (figure 4) generally appear as small red bumps or spindle-like protrusions on leaf surfaces. They are very interesting to look at.
Erineum galls (figure 5) look like velvety red patches and are found on the underside of the leaves, while the upper surfaces show slight disfiguring due to feeding damage. Erineum galls are found on several plant species including maples, beech, and birch, even though the mites are host specific.
Maple bladder gall (figure 6) is showing up on the upper leaf surface of silver maple (Acersaccharinum). The galls look like small round red beads
|Figure 6 Maple bladder gall|
Management: Although the leaves may seem unsightly, and there may be some early leaf drop, these galls do not affect tree health so control is not required.
Good websites: http://www.ipm.iastate.edu/ipm/hortnews/node/2105
|Figure 7 Ash-lilac borer adult|
The first ash-lilac borer (Podosesia syringae) adult (figure 7) was caught in our pheromone traps last week. This is NOT the emerald ash borer, but is the native borer. The adults are wasp-like clear-wing moths with a 1/2 inch long brown body, brownish-black forewings, and transparent hind wings with a brown border. Sometimes they have one or more yellow stripes around their bodies. The insect overwinters as a partially grown larva within the host tree and emerges as an adult in late spring. The female lays her eggs in the bark of stressed plants in the Oleaceae family, especially lilac, ash, and privet. After hatching, brown-headed, creamy white larvae tunnel into wood and feed on phloem and then move into the sapwood. Exit holes are about ¼ inch in diameter and circular. Frass and sawdust is pushed out of the exit holes and may accumulate under the exit holes. Sometimes pupal skins can be seen emerging from exit holes. Branches can be severely damaged by this borer, and severely infested trees may die.
Management: Stressed plants are particularly vulnerable. Keep trees mulched and watered during dry periods. Prune out heavily infested stems. Since the borers are attracted to the larger lilac canes, keep lilacs rejuvenated by making basal cuts and letting new trunks grow.
Good websites: http://www.ipm.uiuc.edu/fruits/insects/ash_lilac_borer/
|Figure 8 Juniper scall|
Juniper scale (Carulaspis juniperi) (figure 8) has been found on Rocky Mountain Juniper (Juniperusscopulorum 'Pathfinder'). This scale, native to Europe, prefers junipers, but attacks eastern red cedar and cypress. Ornamental junipers most commonly attacked include eastern red cedar, Irish juniper, Savin juniper, and Chinese juniper.
Adult female scales overwinter on needles. They are circular, tan, and about 1.5 mm in diameter. In mid-to-late May about 40 eggs are laid beneath the female scale. Hatching occurs about 1 to 2 weeks later, and the yellow crawlers begin feeding soon after hatch. These insects, like all scales, suck the plant juices and cause the foliage to turn yellow to brown in color. Needles in the area of feeding become yellowish or straw colored and die. Severe infestations can cause plant death.
Management: Reduce the scale population by pruning out heavily infested branches now. Large infestations can be controlled with summer oils, insecticidal soaps, and insecticidal sprays. Beneficial insects (e.g. ladybird beetles and parasitic wasps) help control this pest so use insecticides sparingly and only when infestations are severe. Applications should be made when young crawlers emerge (normally in June; possibly a little earlier this year). Dormant oil sprays can be applied next year in early spring, prior to leaf emergence, to control overwintering females.
Four-lined plant bug
|Figure 9 Four-lined plant bug adult|
Be looking for the four-lined plant bug (Poecilocapsus lineatus) (figure 9). Leaves showing damage from this pest were submitted to the Plant Clinic last week. This insect feeds on 250 species, including many kinds of perennials, vegetables, and shrubs such as bluebeard, forsythia, and sumac. Feeding injury is frequently mistaken for leaf spots (figure 10). Four-lined plant bugs have a piercing, sucking mouthpart which they use to break plant cells and then flush the feeding wound with digestive juices. Damage appears as dark leaf spots which subsequently turn translucent. The damage they do is more serious on herbaceous plants than on woody plants. Sometimes by the time the damage is noticed, the insect isn't there anymore. Both nymphs and adults feed on leaves, creating the spots.
Nymphs are bright yellow to red with rows of black spots on the abdomen. The adult stage is 1/4" to 1/3" long and has four longitudinal black lines on its yellow or green back, thus the
|Figure 10 Four-lined plant bug damage|
name. It's quite a shy insect that scurries away when you try to find it. The insect overwinters as eggs laid in slits that are cut into plant shoots. There is one generation per year.
Management: Some people try to hand-pick these insects, but their timidity makes them difficult to catch. Chemical insecticides may be needed for serious infestations.
Good web sites:
Honeylocust plant bug
Honeylocust plant bug (Diaphnocoris chlorionis) nymphs (figure 11) are currently feeding on newly-emerging
|figure 11 Honeylocust plant bug nymph|
honeylocust leaves (Gleditsia triacanthos). The easiest way to find these and other plant bugs is to shake a branch over a white piece of paper. When you see a tiny green insect crawling on the paper, look at it through your hand lens. Honeylocust plant bugs have a pair of four-segmented antennae, although the antennae are probably too small at this stage to see without a microscope. Older nymphs also have yellow spots on their backs. This plant bug overwinters as an egg under the bark of two- and three-year-old twigs. The eggs hatch soon after bud break, and the nymphs crawl to unfolding leaves to feed. The insects are very small, and in May to early June the plant bugs become adults. Both nymphs and adults feed on foliage until early summer and can cause severe leaf distortion, dwarfed leaflets, chlorosis, and yellow-brown leaf spots. A heavy plant bug infestation may cause a failure to leaf out or premature leaf drop. In the past, our heavily infested trees were able to leaf out again.
Management: Young nymphs can be knocked off leaves of small trees by spraying them with a strong stream of water. In severe infestations, insecticidal soaps, summer oils, and insecticides may be warranted. Resistant cultivars can be planted such as 'Skyline' and 'Shademaster'. In general, yellow-leaved cultivars are more susceptible to this pest.
|Figure 12 Elm leafminer damage|
Elm leafminer (Fenusa ulmi) larvae are forming mines (figure 12) on David elm (Ulmusdavidiana var. mandshurica). The adults emerge in spring to lay eggs in elm leaf tissues. After about a week, the eggs hatch and young larvae begin to make mines in the leaves. The sawfly larvae are feeding on the leaf tissue between the upper and lower epidermis of the leaves. The mines at first look like U-shaped brown spots between veins in the leaf. Eventually the insects will eat a hole through the leaf epidermis, fall to the ground, and excavate a hole in the soil to overwinter. Severe damage can result in defoliation. To test a leaf for miners, hold the leaf up to the light. If the insect is still in the leaf, you can see it. You will also be able to see frass (insect feces) which looks like pencil shavings within the mined area. Other susceptible elms include the American elm (U. americana), English elm (U.procera), and Armenian elm (U. elliptica). They spend most of their life cycle burrowed about an inch in the ground.
Management: We are unaware of any nonchemical control. There is only one generation per year, and the leaves that emerge later will not be infested.
Good website: http://www.ext.colostate.edu/pubs/insect/05548.html
|Figure 13 Spittle bug froth|
We're starting tp see spittle bug eggs and expect to soon see the frothy white mass (figure 13) found they produce on foliage and twigs. The spittle, consisting of plant juices, is made by the immature bug to keep it moist and protect it from its enemies. Spittlebugs suck plant sap but inflict little damage on mature plants. There are a number of species of spittlebugs that feed on both deciduous and evergreen plants in our region.
Management: Control is rarely necessary, but hosing the plants down forcefully with water is usually sufficient to remove most of the insects. This may need to be repeated a few times.
Good website: http://urbanext.illinois.edu/focus/spittlebug.cfm
|Figure 14 Alder leafminer damage|
European alder leafminer (Fenusa dohrnii) adults (figure 14) were seen last week on the Arboretum grounds. These adults are looking for sites in which they can lay eggs. The miners begin mining along the midvein, but the insect will eventually mine entire leaves (figure 15). If you hold the leaf up to the light, you can see tiny larvae and frass in the mines. There are two generations per year in this area.
Management: In a severe infestation, The University of Illinois recommends that a systemic insecticide be used to obtain control of the larvae within the leaves. Acephate has traditionally been the insecticide of choice although imidacloprid is becoming more popular.
|Figure 15 Alder leafminer adult|
Suggested reading: http://www.ext.colostate.edu/pubs/insect/05548.html
Pest update: diseases
|Figure 16 Black knot infection; old (left) and new (right)|
Black knot (Dibotryon morbosum) (figure 16) is a serious and widespread problem of treesin the genus Prunus, especially plums and cherry trees. Right now we're seeing the abnormal swellings on branches of cherry plum (Prunus cerasifera). The fungus overwinters in the hard, brittle, rough, black "knots" on twigs and branches of infected trees such as wild black cherries in the woods or abandoned cherry orchards. These knots may be small or may be several inches long and wrap around the branch.
In the spring, the fungus produces spores within tiny fruiting bodies on the surface of these knots. The spores are ejected into the air after rainy periods and infect succulent green twigs of the current season's growth. The newly infected twigs and branches swell. The hypertrophied growth of bark and wood is a response to hormones and produces the swellings that we are now seeing. Frequently these swelling are not noticed the first year. The swellings become dormant in winter. But the following spring, velvety, green fungal growth will appear on the swelling. The swellings darken and elongate during summer and, by fall, turn hard, brittle, rough and black. The black knots enlarge and can girdle the twig or branch, eventually killing it.
Management: This is a difficult disease to manage. Prune and discard, burn or chip and compost all infected wood during late winter or early spring before growth starts and when new swellings appear. Pruning cuts should be made at least four to eight inches below any swellings or knots. In advanced cases with many knots, pruning out branches may not be feasible as it may destroy the shape of the tree. Chemical recommendations include a dormant fungicide spray.
Good web sites: http://www.ag.uiuc.edu/~vista/abstracts/a809.html
Brown rot of stone fruit
|Figure 17 Brown rot oozing|
Oozing of brown rot (figure 17) has been reported on Prunus this spring. Brown rot is caused by the fungus Monilinia fructicola that infects peaches, plums, cherries, apricots, and other Prunus species. The disease is first seen as blossom blight – the browning and sudden collapse of blossoms. Leaves are not directly infected. The infection spreads into shoots and twigs during the next several weeks resulting in shoot and twig blight. Cankers, which may be accompanied by a gummy exudate at their margins, form on twigs often causing twig dieback. Powdery-gray masses of spores (conidia) may be observed under wet, humid conditions. The conidia are responsible for fruit infections later in the summer. Infections of fruit start as brown spots that rapidly consume the entire fruit. Infected fruits (mummies) decay and shrivel and generally remain attached to the tree throughout the winter, providing inoculum for the following spring.
Management: Sanitation is crucial to control of brown rot. Prune out active infections immediately during dry weather. Don't forget to disinfect pruning tools. Rake and clean up debris under the tree during the summer to remove fallen leaves and fruit. Prune to promote good air circulation through the tree canopy. Wild or neglected stone fruit trees (e.g., wild plum and cherry) in the area are likely to have the disease and be sources of inoculum that should be removed. Later in the year remove rotted fruits (mummies) that are persistent, prune out cankers and infected twigs, and rake and clean up infected fallen leaves and fruit. If damage is severe, fungicides need to be applied when blossoms first open in early spring.
Good websites: http://ohioline.osu.edu/hyg-fact/3000/pdf/HYG_3009_08.pdf
|Figure 18 Rose rosette symptoms|
A couple of samples of rose rosette has come into the Plant Clinic in the last ten days. Rose rosette is believed to be caused by a virus or virus-like organism and is vectored by a small eriophyid mite. It can also be spread through grafts. Rosa sp. are the only known hosts, and all types of roses are infected, though multiflora is the most common host. Plants often die within one to two years after infection.
It is not always easy to diagnose this disease as symptoms vary depending on the species or cultivar infected. When all of the symptoms listed below are present, diagnosis is relatively straightforward. However, a diseased plant usually exhibits just a few of these symptoms, especially in the early stages of the disease. Symptoms (figure 18) include rapid elongation of new stems, followed by development of witches' brooms that appear as numerous red side shoots growing in different directions. Tiny and distorted leaves often, though not consistently, have a red coloration or a mosaic of green, yellow, and red. Thorns are much more abundant than normal, often giving a somewhat hairy appearance to the cane. Canes are thicker than the parent cane from which they emerged. Short, deformed shoots, often with red blotches, and distorted flowers with fewer petals than normal and abnormal coloration appear. Aborted buds, deformed buds, or buds are converted to leaf-like tissue.
Management: Infected plants cannot be cured and should be dug up and destroyed (including roots) when symptoms first appear.
Good website: http://hyg.ipm.illinois.edu/article.php?id=101
Events of Interest
MONITORING AND MANAGING INSECT PESTS
Learn the life cycles, signs and symptoms, and methods of control for the most common insects in our landscapes. Get up-to-date information on easy, less toxic strategies for managing insects and when treatment would do more harm than good. In the classroom portion of each section, you will become acquainted with current seasonal insect threats; then spend a morning identifying them in the field. Different insects will be covered in each section – register for both sections for a full picture of spring insect pests.
Recommended Text: A list of recommended references will be distributed in class.
Certificate Information: Home Landscape Gardening Certificate elective, Naturalist Certificate elective (6 hours); if both sections are completed, this class may be used to fill a Home Landscape Gardening Certificate Requirement.
♦H424. Wednesday, 6:30 – 9:30 pm & Saturday, 9 am – Noon. Thornhill Education Center. $69 (non-members $82). Limit 16. Donna Danielson, Arboretum Instructor
Section a: May 2 & May 5 Section b: May 30 & June 2
The Plant Health Care Report is prepared by Sharon Yiesla, M.S., Plant Clinic Assistant and edited by Stephanie Adams, M.S. Research Specialist (Plant Heath Care); Fredric Miller, Ph.D., research entomologist at The Morton Arboretum and professor at Joliet Junior College; Doris Taylor, Plant Information Specialist, and Carol Belshaw, an Arboretum Volunteer. The information presented is believed to be accurate, but the authors provide no guarantee and will not be held liable for consequences of actions taken based on the information.
Thank you...I would like to thank the volunteers that scout for us and who found most of the insects and diseases that are in this report. The Scouting Volunteers include: Mary Carter Beary, Davida Kalina, Ann Klinglele, LeeAnn Cosper, Kathy Stephens, and Loraine Miranda. Your hard work is appreciated.
Indicator plants are chosen because of work done by Donald A. Orton, which is published in the book Coincide, The Orton System of Pest and Disease Management. This book may be purchased through the publisher at: http://www.laborofloveconservatory.com/
The 2010 Commercial Landscape & Turfgrass Pest Management Handbook (CPM), for commercial applicators, and the Home, Yard & Garden Pest Guide (HYG) for homeowners from the University of Illinois, are available by calling (800-345-6087).
This report is available on-line at The Morton Arboretum website at http://www.mortonarb.org/tree-plant-advice.html
Copyright © 2012 The Morton Arboretum
Not printed on recycled paper, or any paper for that matter.
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