Plant Health Care Report July 6, 2012
Tagged as: abiotic leaf scorch, annual cicada, Anthracnose, bullseye leaf spot, drought, earwig, filbert blight, magnolia scale, Rose curculio, sooty mold, tar spot
July 6, 2012 Issue 2012.12
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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.
If you prefer a PDF version of the PHCR, please click here to download and print.
Quick View
What indicator plants are in bloom at the Arboretum?
Queen Anne’s lace (Daucus carota) is in bloom (figure 1)
Accumulated Growing Degree Days (Base 50): 1425.5 (as of July 5
Accumulated Growing Degree Days (Base 30): 3877.5 (as of July 5)
Insects:
- Earwigs
Figure 1 Queen Anne's lace (Daucus carota) - Annual cicada
- Magnolia scale
- Rose curculio
Diseases:
- Sooty mold
- Birch anthracnose
- Tar spot of maple
- Bull’s-eye leaf spot
- Eastern filbert blight
Miscellaneous:
- Abiotic leaf scorch
- Drought stress down the road
Degree Days and Weather Information
As of July 5, we are at 1425.5 base-50 growing degree days (GDD), which is 433 GDD 50 ahead of 2011 at this time. We have had .26 inches of rain so far in July and 11.61" for the year (compared to 20.84" last year at this time).
| Location | B50 Growing Degree Days Through July 5, 2012 |
Precipitation (in) |
| Aurora, IL* | 1661 | -- |
| Carbondale, IL* | 2405 | -- |
|
Champaign, IL* |
1973 | -- |
| Chicago Botanic Garden** | 1340 (as of 7/2) | .27 (6/26-7/2) |
| Crystal Lake, IL* | 1586 | -- |
| Harvard, IL* | 1547 | -- |
| Kankakee, IL* | 1787 | -- |
| The Morton Arboretum | 1425.5 |
.65 (6/29-7/5) |
| Northbrook** | 1521.5 (as of 7/4) | .31 (6/27-7/3) |
| O'Hare* | 1665 | -- |
| Peoria, IL* | 2002 | -- |
| Quincy, IL* | 2177 | -- |
| Rockford, IL* |
1654 |
-- |
| Springfield, IL* | 2156 | -- |
| Waukegan, IL* | 1437 | -- |
**Thank you to Mike Brouillard, Northbrook Park District and Mike Annes, Chicago Botanic Garden, 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
Earwigs
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| Figure 3 Earwig |
Earwigs (Forficula auricularia) (figure 2) are starting to show up both outside and inside. Earwigs generally feed on dead insects and rotting plant material; however, they are also known to feed on flowers, fruit, and foliage of vegetable, fruit, ornamental, and field plants when populations are numerous. Their feeding causes small, irregular holes, and can give foliage a ragged appearance in severe infestations. This insect, which is about an inch long, is easily identifiable by the prominent pair of pincers on the tip of the abdomen. Earwigs are nocturnal creatures and hide in dark, moist places under stones and in debris or sometimes in bark during the day. They may find their way into houses and garages—particularly during periods of prolonged warm, dry weather like we are having now. Inside they seek out moist areas such as basements, crawl spaces, and kitchens where they feed on sweet, oily or greasy foods, in addition to houseplants. Since they feed on insect larvae, they are considered beneficial.
Management: Removing plant debris from your garden will remove some of their hiding places. Place rolled up newspapers on the ground near problem areas. Check the "newspaper traps" in the morning for earwigs. Shake the earwigs into a pail of soapy water. For indoor control, eliminate damp conditions in crawl spaces, near faucets, around air-conditioning units, and along house foundations. Keep moist mulches three feet away from the house foundation, window wells, and doorways, if you have a serious earwig problem. Trim back vegetation and remove ground covers near foundations that contribute to moisture retention. Move wood piles away from the house.
Good web sites: http://learningstore.uwex.edu/pdf/A3640.pdf
http://umaine.edu/ipm/ipddl/publications/5017e/
Annual cicada
The songs of the annual dog day cicadas (Tibicen linnei) (figure 3) are starting to be heard
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| Figure 3 Annual cicada |
now. These are the insects that make the sound "weeeeeeeeeeeee", "weeeeeeeeeeeeeee" high in trees during the warm, dog-days of summer (the dog days are a bit early this year). This is the mating call of the male. They are about 1.75 inches long and are green to brown with black markings. The distinguishing factor between the annual and periodic cicada is the eye color. The periodic cicada has red eyes and the annual has black.
Like the periodical cicadas, females lay eggs by sawing a slit in the bark of twigs and placing the eggs in the twig. Egg-laying injury can cause some minor twig dieback. After the eggs hatch, the young nymphs drop down into the ground to feed on plant roots. They have large front legs used for digging in the soil. They live on tree roots as nymphs for two to five years with some adults emerging in late summer every year. The feeding on the roots doesn't cause much damage. As the insects grow larger, they break out of their old exoskeletons or skins.
Management: Control is not necessary since annual cicadas cause minimal damage to trees.
Good websites:
Magnolia scale
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| Figure 4 Magnolia scale |
The Plant Clinic is starting to get calls from homeowners with magnolia scale (Neolecanium cornuparvum) on their magnolia trees. This is an unusual scale insect because they're so big and easy to see! Magnolia scale has become an ongoing problem in northeastern Illinois. These insects have sucking mouthparts and extract sap from the host plant's branches and twigs. Badly infested branches and twigs are weakened and plant growth is slowed. When infestations are severe, branch dieback can result, and with repeated severe attacks, trees may be killed. As with most soft scale infestations, plant leaves are often covered with sooty mold, a black fungus that grows on the honeydew excreted by the scales. Sooty mold cuts down on photosynthesis because it blocks sunlight from the leaf.
Initially, magnolia scales are shiny, flesh-colored to pinkish brown, and smooth, but they become covered with a white mealy wax over time. This wax is lost at the time crawlers emerge. Right now we're seeing white, waxy female adults that are about 1/2 inch in diameter (figure 4). Adult females give birth to live young, called crawlers, in late August or early September. The crawlers are tiny, flattened, and vary in color from yellow to reddish-brown. The crawlers settle on one- to two-year-old twigs to feed and remain there through the winter.
Management: Before you buy a plant, check it carefully for scale. Beneficial insects, such as ladybird beetles, are frequently seen gobbling up crawlers. Fall and spring insecticide applications to control crawlers are suggested. To check for crawlers at the end of summer, put double-sided tape on each side of a scale colony. The crawlers will become stuck on the tape. This would not be used for control, just to check for the presence of crawlers.
Good web sites: http://ohioline.ag.ohio-state.edu/hyg-fact/2000/2003.html
http://woodypests.cas.psu.edu/FactSheets/InsectFactSheets/html/Magnolia_Scale.html
Rose curculio
Rose curculios (Merhynchites bicolor) were found on rugosa rose (Rosa rugosa) on our
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| Figure 5 Rose curculio |
grounds this week. This is a red weevil with a black snout, head, and legs (figure 5). The snout is ideal for drilling small holes into flower buds and rose hips for feeding and egg laying. The curculio is about ¼ inch long. Damaged flower buds that bloom will appear ragged and unsightly. Larvae that feed within rosebuds sometimes kill them.
Management: Adults can be handpicked. Like Japanese beetle, adults fall from the plant when they are disturbed. You may be able to catch many of the insects by shaking rose canes over a bucket. Remove spent flowers to eliminate larvae.
Good website: http://entomology.wsu.edu/outreach/bug-info/rose-curculio/
Pest update: diseases
Sooty mold
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| Figure 6 Sooty mold |
Sooty mold, caused by several species of fungi, is showing up around the area. This looks like a black coating and lives on the surfaces of leaves (figure 6). To be sure it is sooty mold, try rubbing it off the leaf. You should be able to. The black coating is actually a dark fungus. These are saprophytic fungi that live on honeydew, a sticky secretion of many sap-feeding insects like aphids and scale. If you see sooty mold, look for the insect that created the honeydew. Sooty molds harm plants indirectly by blocking out light and reducing photosynthesis. They have no host preference as far as we know. There are two types of sooty mold growth. The first is growth on leaves, which lasts for the life of the leaf. The second is a persistent growth on stems and twigs of woody plants and also on outdoor structures and furniture. They are normally considered an aesthetic problem.
Management: Sooty mold is best controlled by controlling the honeydew-producing insect. Remember, you need to identify the insect to control it. Ohio State University indicates that a strong spray of water can be used to dislodge the mold growth from many plants.
Good web sites: http://www.ag.ohio-state.edu/~ohioline/hyg-fact/3000/3046.html
http://www.ces.ncsu.edu/depts/ent/notes/O&T/houseplants/note41/note41.html
Birch anthracnose
Birch anthracnose was found this week. Symptoms are large brown blotches (figure 7) with
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| Figure 7 Birch anthracnose |
indefinite margins surrounded by yellow tissue. Black pepper-like fruiting bodies (pycnidia) can be found embedded within the brown blotches. Affected leaves often drop prematurely while part of the blade is still green. This common fungal disease is most prominent on lower branches and can progress up the tree. Gray, paper, and river birches are attacked. It is a little surprising to see this since cool, rainy summer weather promotes this disease.
Management: Birch anthracnose does not cause serious harm to the tree. Good sanitation is important, so rake up and destroy infected leaves. There are fungicides available in severe cases.
Good websites: http://www.ag.uiuc.edu/~vista/abstracts/a621.html
Tar spot of maple
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| Figure 8 Tar spot of maple |
Tar spot of maple was found sugar maple (Acer saccharum). The disease looks just like shiny black spots of tar flung about on the upper surface of maple leaves (figure 8). Several different fungi in the genus Rhytisma infect the leaves of maples and cause the spots. The spots range from 1/5 to 4/5 inch in diameter. Rhytisma spp. most commonly infects leaves of silver and Norway maples, although big leaf, mountain red, Rocky Mountain, and sugar maples are also susceptible. It does little harm to the trees, but is unsightly.
Management: Management is not necessary unless a tree is severely infected. To reduce inoculum, rake up and discard the leaves in fall. An appropriate fungicide may also be helpful in severe cases.
Good website: http://plantclinic.cornell.edu/factsheets/tarspotofmaple.pdf
http://www.ppdl.purdue.edu/ppdl/expert/Tar_Spot_on_Maple.html
Bull's-eye leaf spot
Cristulariella leaf spot or bull's-eye leaf spot was found on Bukhara fleece flower (Fallopia
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| Figure 9 Bull's eye leaf spot |
baldschuanica). This is called bull's-eye leaf spot because the grayish-brown leaf spots have alternating light and dark concentric rings that almost look like a target (figure 9). The spots have a light center and are up to an inch in diameter. This fungal disease kills plant tissue by creating toxic amounts of oxalic acid. Fluctuating summer temperatures and rainfall usually retard the growth of the fungus. There are many common hosts, including black walnuts, magnolias, maples, sycamores, tree-of-heaven, and tulip trees.
Management: Removing and discarding infected leaves will destroy inoculum to prevent secondary infections. Rake up and discard leaves in the fall.
Good websites: http://www.ppdl.purdue.edu/PPDL/weeklypics/10-30-02.html
Eastern filbert blight
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| Figure 10 Eastern filbert blight |
Eastern filbert blight has been found on Harry Lauder's Walking Stick (Corylus avellana 'Contorta'). This disease is caused by the fungus Anisogramma anomala infecting filbert (i.e. hazelnut) (Corylus) species. According to Sinclair and Lyons in Diseases of Trees and Srhubs, the disease is limited to North America and the genus Corylus. This pathogen is considered to be an obligate parasite, meaning that it must infect its host in order to complete its lifecycle.
This disease has largely been studied in Oregon, where they have cool wet winters, so the lifecycle may be different in other parts of North America (Sinclair and Lyon). The pathogen requires 2-3 years to complete its life cycle, the length depending on the host's susceptibility. The symptoms include longitudinal cankers (figure 10) that are pocked with single to multiple rows of black, raised, and oval perithecial stromata (spore-producing bodies, also known as black pustule-like bumps). The infected branches may have dead leaves attached. Although the cankers can grow 30 cm (nearly a foot) per year on susceptible hosts (Sinclair and Lyon), the tree may not die for several years.
The pathogen's life cycle begins in the fall during rainy periods. The ascospores are moved in water and wind to surrounding plants. Once the spores adhere to a branch, they germinate and infect the plant. The perithecial stromata mature and produce the ascospores before overwintering. It's these mature overwintered spores that spread during the spring rain and winds, and infect new growth.
Management: The most common management practice is planting resistant varieties of Corylus. The cankers can be pruned out of the tree successfully so long as all the infected tissue is removed. It may be moved around within an infected tree on pruning tools, so sanitizing pruning tools between cuts is imperative.
Good websites: http://oregonstate.edu/dept/botany/epp/EFB/index.htm
Miscellaneous
Abiotic leaf scorch
As is common during a drought, many trees have begun to show signs of abiotic leaf scorch
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| Figure 11 Abiotic leaf scorch |
(figure 11). This problem occurs during periods of drought because roots are unable to supply enough water to replace what is transpired by the leaves. Symptoms include interveinal and marginal leaf browning on many leaves scattered uniformly within the canopy. Severe abiotic leaf scorch causes leaves to drop prematurely.
Sometimes abiotic leaf scorch appears similar to bacterial leaf scorch caused by the bacterium Xylella fastidiosa. This disease occurs on many tree species including oak, elm, maple, mulberry, and sycamore. Trees infected with X. fastidiosa exhibit marginal leaf browning, but unlike abiotic scorch, the browning varies in color and is often bordered by a pale halo. Discoloration moves in irregular blotches toward the midrib. Older leaves are usually symptomatic first, and symptoms begin to show during early to mid summer. These symptoms will spread to younger leaves and will worsen until the leaves drop in the fall. Symptoms recur each year and eventually spread throughout the tree's crown. Reduced growth, dieback and even death are not uncommon.
Management: Abiotic leaf scorch can be reduced through proper management practices. Trees and shrubs should be irrigated during drought to a depth of 6 to 8 inches. Recently transplanted trees and shrubs should receive at least one inch of water per week. Heavily compacted soil will reduce water flow to the plants, so mulch, amend, and loosen surface soil in compacted landscapes.
Bacterial leaf scorch is transmitted by xylem-sap feeding insects such as spittlebugs and leafhoppers. Avoid wounding susceptible trees to prevent infection by these vectors. Infected trees should be removed to prevent spread to healthy trees. There is no known effective preventative treatment or cure for bacterial leaf scorch. Trunk injections with antibiotics have been shown to suppress symptoms and delay tree death. Pruning infected branches has met with limited success.
Good websites: http://www.ag.uiuc.edu/~vista/abstracts/a620.html
http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/PPFS-OR-W-12.pdf
Drought stress down the road
We are all dealing with too little rain and too much heat. The advice that gets repeated over and over is to water your plants to help them survive the drought. You may be saying to yourself "I think I can live with my plants wilting and turning brown, so I just won't water". The wilting and browning, however, are the short term problems. What about looking down the road a bit, especially on woody plants like trees and shrubs that stand in our yards for years and years?
There are long-term effects to a drought, and some of these can be minimized through proper watering. Summer is the time when many trees and shrubs are making their buds for next year. If the water supply is inadequate at this time, photosynthesis is decreased and the plant may make less food for itself. This can lead to fewer buds forming or smaller than normal buds, leading to poorer growth next year. If the tree is a flowering tree, the flower display may be reduced, and on fruit trees we may see smaller crops.
Drought stress can affect trees in another way. Trees undergoing drought stress may be less able to tolerate attack by insects and diseases. When trees are stressed they can emit volatile chemicals. Wood-boring insects are able to detect these volatile chemicals and use them to locate weakened trees. Most (not all) wood-boring insects attack weakened trees. Canker diseases may become more prevalent on drought stressed trees. The pathogens that cause canker diseases are not strong pathogens, so they need a host that is weakened in some way. Drought stressed trees are less resistant to these canker pathogens. Root rots may also become a problem down the line. During a drought, roots may be damaged and become open to attack by root rot organisms when the soil becomes wet again in the future.
Damage to the tree's root system can also have a lasting effect. A compromised root system will have trouble taking up water. This may last for some time, until new roots can grow. So don't put the hose away the minute the drought is over. Trees may need a little extra help for the rest of the season.
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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. Thanks also to Donna Danielson, who teaches at The Morton Arboretum and shares her findings when she scouts for her classes.
Literature recommendation:
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, for commercial applicators, and the 2012 Pest Management for the Home Landscape 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
For pest and disease questions, please contact the Plant Clinic at (630) 719-2424 between 10:00 and 4:00 Mondays through Saturdays or email This e-mail address is being protected from spambots. You need JavaScript enabled to view it . Inquiries or comments about the PHC reports should be directed to Sharon Yiesla at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Copyright © 2012 The Morton Arboretum
Not printed on recycled paper, or any paper for that matter.
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