Plant Health Care Report July 13, 2012
Tagged as: leaf spots, slime mold, Borers, cytospora canker, milkweed bugs, pear leaf blister mite, rust mite, two spotted spider mite, viburnum leaf beetle
July 13, 2012 Issue 2012.13
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?
Chicory (Cichorium intybus) (figure 1) is blooming and has been blooming for several weeks.
Accumulated Growing Degree Days (Base 50): 1629.5 (as of July 12)
Accumulated Growing Degree Days (Base 30): 4221.5 (as of July 12)
Insects:
- New pest!: Viburnum leaf beetle
Figure 1 Chicory (Cichorium intybus) - Borers
- Pear leaf blister mite
- Milkweed bugs
- Bald cypress rust mites
- Two-spotted spider mites
Diseases:
- Cytospora canker
- Leaf spots
Miscellaneous:
- Slime mold
Degree Days and Weather Information
As of July 12, we are at 1629.5 base-50 growing degree days (GDD), which is 467 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 21.68" last year at this time).
| Location | B50 Growing Degree Days Through July 12, 2012 |
Precipitation (in) |
| Aurora, IL* | 1875 | -- |
| Carbondale, IL* | 2653 | -- |
|
Champaign, IL* |
2195 | -- |
| Chicago Botanic Garden** | 1582.5 (as of 7/9) | .15" (7/3-9) |
| Crystal Lake, IL* | 1790 | -- |
| Harvard, IL* | 1754 | -- |
| Kankakee, IL* | 1998 | -- |
| The Morton Arboretum | 1629.5 |
no rain (7/6-12) |
| Northbrook** | 1755 (as of 7/11) | .57 (7/4-10) |
| O'Hare* | 1877 | -- |
| Peoria, IL* | 2228 | -- |
| Quincy, IL* | 2411 | -- |
| Rockford, IL* |
1870 |
-- |
| Springfield, IL* | 2384 | -- |
| Waukegan, IL* | 1626 | -- |
**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
New pest: Viburnum leaf beetle
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| Figure 2 Egg laying damage (Photo credit: U of I Plant Clinic) |
The Viburnum leaf beetle (Pyrrhalta viburni) is native to Europe. In the United States it hasbeen found in only a few states, including New York, Ohio, Pennsylvania, Maine, Vermont and Massachusetts. The first confirmed occurrence of the beetle in Illinois was documented in 2009 in Cook County. A second occurrence was confirmed last week in DuPage County. Should we panic? No. Should we be alert and looking for this pest? Definitely! Early detection is important for management of any pest.
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| Figure 3 Feeding damage (photo credit: U of I Plant Clinic) |
This is a pest of concern because it has the potential to be a serious defoliator of viburnums. The beetle overwinters as eggs in the tips of stems (figure 2). The egg-laying damage usually occurs in rows. The eggs are laid in holes chewed by the adult. The holes are then covered by a cap of chewed bark. These caps are fairly easy to see as they are darker than the stem.
The eggs hatch into larvae in the spring, usually in May. The larvae vary in color. They may be pale green, pale orange or yellow. They do have a distinctive pattern of black spots along their sides and a row of black dashes running down their backs. At maturity, the larvae are a little less than half an inch long. The larvae chew on the undersides of new foliage, skeletonizing it.
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| Figure 4 Viburnum leaf beetle (photo credit: U of I Plant Clinic) |
When mature, the larvae crawl to the ground, usually in mid-June, and pupate in the soil. Adults emerge from the soil (early July) and also chew on the leaves (figure 3). Their feeding damage forms irregular round holes in the leaves. The beetles (figure 4) are about ¼ inch long and generally brown in color. On close inspection golden hairs can be seen on the wing covers of the adult beetle (figure 5). The adult beetles will be mating and laying eggs from summer into fall. There is one generation of the beetle each year.
Viburnum leaf beetle feeds only on viburnums. Several viburnums are susceptible, including arrowwood viburnum (Viburnum dentatum),
European cranberrybush viburnum (V. opulus), American cranberrybush viburnum (V. trilobum), and Rafinesque viburnum (V.rafinesquianum). Other hosts include Sargent viburnum (V. sargentii), wayfaring tree (V. lantana), nannyberry (V. lentago), and blackhaw viburnum (V. prunifolium). Resistant viburnums include Korean spice viburnum (V. carlesii), Burkwood viburnum (V. burkwoodii), doublefile viburnum (V. plicatum var. tomentosum), Judd viburnum (V. × juddii), lantanaphyllum viburnum (V. × rhytidiophylloides), and leatherleaf viburnum (V.rhytidiophyllum).
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Figure 5 Hairs on bivurnum leaf beetle |
Heavy and repeated defoliation by the viburnum leaf beetle can lead to death of the shrubs. Management of this pest can include several practices depending on the time of year. From October through April twigs with eggs in them can be pruned out and destroyed. Insecticides can be used on the larvae in May when they are feeding, and on the adults in summer when they are feeding. University of Illinois Extension suggests the insecticides containing one of the following ingredients: carbaryl, cyfluthrin and permethrin.
For more information and photos of beetle:
To report this pest: Illinois Cooperative Agricultural Pest Survey is interested in monitoring where this pest is found. To report the viburnum leaf beetle at your location go to their website http://www.inhs.illinois.edu/research/CAPS/ for instructions on reporting the beetle.
Help with identifying viburnum leaf beetle: There are some agencies that can help you with identification of the beetle. They include:
Morton Arboretum Plant Clinic (phone: 630-719-2424; email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it )
University of Illinois Plant Clinic (phone 217-333-0519; web: http://web.extension.illinois.edu/plantclinic/ )
You local University of Illinois Extension office (to find your local county office, go to http://web.extension.illinois.edu/state/findoffice.html
Borers
With all the stress the environment is putting on our landscape plants, this might be a go
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| Figure 6 Damage from viburnum borer |
od time to review wood-boring insects, often referred to simply as borers. We all seem to be aware of the emerald ash borer which is in the news constantly, but there are many other borers out in the landscape as well. Borers are generally attracted to stressed trees. Newly planted and drought stressed trees, as well as trees subjected to mechanical damage, such as being hit by a lawn mower or weed whacker, are prone to borer attack.
Borers, in their larval stage, feed just under the bark or sometimes deep in the heartwood of a wide variety of woody plants. Those that feed just under the bark will disrupt the flow of water to the upper portion of the tree or shrub. Even a moderate infestation can kill a tree. Look for off-color foliage or dying foliage, sawdust-like frass (insect excrement) in bark crevices and cracks and dead branches. Borers that tunnel deeper in the heartwood may do structural damage to the tree over time.
Wood-boring insects can often be identified by the species and location of the insect. Bronze birch borer, for example, attacks white-barked birches by tunneling under the bark of the trunk. Viburnum crown borer attacks viburnums near the ground, at the base of their stems (figure 6). Peach tree borer attacks peach trees and other trees in the genus Prunus. They also attack the tree low near the ground.
Management: Prevention is key. Trees should be sited properly, so they are growing in conditions conducive to good health. Keep trees healthy by watering them during droughts. A properly mulched tree will negate the need for a lawn mower or weed whacker and minimize injury, while conserving soil moisture. Chemical control is usually ineffective against borers already in the tree, but may prevent future attack. Therefore, the treatments must be timed to prevent newly hatched borer larvae from entering the tree. To do that we must be aware of the life cycle of each insect and also be looking for new borer holes. The appearance of new holes indicates that adult borers are exiting the tree and preparing to mate and lay eggs.
Good website:
http://www.mortonarb.org/component/content/article/193-insects-diseases/753-borers.html
Pear leaf blister mite
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| Figure 7 Pear leaf blister mite damage |
Pear leaves (Pyrus sp.) showing small blisters (figure 7) have been brought into the Plant Clinic. This often looks like a fungal leaf spot, but is not. The blistering is caused by the pear leaf blister mite (Phytoptus pyri), an eriophyid mite that is a pest of pear, apple, and European mountain ash. Blisters begin as small greenish to pale yellowish bumps that eventually turn brown and reach 1/8 of an inch in diameter. Heavily infested leaves become distorted and drop prematurely. Mites also feed on developing fruit, causing depressed brown spots surrounded by a halo of clear tissue. Often, fruit becomes deformed and misshapen. The adult mites overwinter in bud scales. They become active in spring as buds swell and migrate to emerging leaves, burrowing beneath the epidermis of the leaf underside. Their feeding induces blister formation. The eggs are laid in the fall, and the young remain in the gall until they mature. They then migrate to new leaves. There are 2 to 3 generations per year.
Management: This is only a cosmetic problem so controls are not warranted.
Good web site: http://www.ipm.ucdavis.edu/PMG/r603400511.html
http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls89eriophyidmites.pdf
Milkweed bugs
In the June 22 issue we reported on milkweed beetles, and now the milkweed bugs are
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| Figure 8 Small milkweed bug adult |
showing up. Our scouts have found the large milkweed bug (Oncopeltus fasciatus) feeding on butterfly weed (Asclepias tuberosa). It's probably safe to assume that the small milkweed bug (Lygaeus kalmia) (figure 8) is out there somewhere as well. These two insects look very much alike, both sporting bright orange-red and black colors. Young bugs (nymphs) also have these colors, but lack fully developed wings (figure 9). Both the adults and the nymphs will feed on the milkweed seeds, and it is not uncommon to see groups of them huddled together on the milkweed pods. These insects are often mistaken for boxelder bugs which are similar in color.
Management: None usually needed.
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| Figure 9 Milkweed bug nymphs |
Good websites: http://bugguide.net/node/view/504
http://insected.arizona.edu/milkinfo.htm
Bald cypress rust mites
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| Figure 10 Stippling from rust mites |
Bald cypress rust mites (Epitrimerus taxodii) were found feeding on bald cypress (Taxodiumdistichum). These rust mites are about the size of dust. They look like tiny, pale, wedge-shaped mites. They crawl over the surface of needles, rasping through the epidermis and extracting the cell contents. The resulting damage first looks like very fine spots called stippling (figure 10). Occasionally, leaf tips become dwarfed and distorted. Needles eventually become yellowish and then reddish brown. Inner needles are usually affected first. The mite population generally explodes with the onset of warm weather, and thousands can be found on a single leaf.
Management: Severe infestations can unduly stress trees and chemical control may be warranted. Bald cypress is sensitive to horticultural oils so these products should not be used for control.
Good web site: http://bygl.osu.edu/archive/bygl2009_864.html#5
Two-spotted spider mites
We are seeing the two-spotted spider mites (Tetranychus urticae) on false indigo (Baptisia
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| Figure 11 Two-spotted spider mite |
australis) and Chinese sumac (Rhus chinensis). Two-spotted spider mites (figure 11) are very small, about 1/60 of an inch long. You need a hand lens to see them clearly. Mites are not insects but insect relatives. Mites have eight legs and two body regions, while insects have six legs and three body regions. The two-spotted variety has two spots on their backs, which are composed of food contents. Two-spotted spider mites love hot, dry weather (and we've had plenty of that!!). Leaves attacked by spider mites show stippling or tiny, chlorotic flecks. If enough damage is done to a leaf, it begins to look bronzed and may drop prematurely. Spider mites attack many kinds of plants and are also very common on house plants, especially in winter when your house is warm and dry.
Management: First, you may want to determine what kind of mites are on your plant by holding a white sheet of paper under a branch and shaking the branch firmly. If you have mites, tiny specks will start crawling on the paper. Squish some of the moving specks. If the resulting streaks are green, you are seeing mites that feed on plants. If you see red or brown streaks, you probably have predatory mites that are the natural predators of spider mites (a good thing). Beneficial mites move faster than the pest mites. Pest mites don't have to move fast to catch their food; plants don't run too fast. But the beneficials have to move faster in order to catch their prey. Anyway, if you see lots of green spider mites, you may want to treat the plant.
There are several options. A forceful stream of water may knock mites off the plant. This should be repeated for three days. Predatory mites can also be purchased and released on the plants. Insecticidal soaps and other insecticides can be sprayed to control mites.
Good websites: http://entnemdept.ufl.edu/creatures/orn/twospotted_mite.htm
http://insects.ippc.orst.edu/pnw/insects?33MITE01.dat
Pest update: diseases
Cytospora canker
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| Figure 12 Dead branch from Cytospora canker |
Infections caused by Cytospora kunzei (Leucostoma kunzei) have been found on conifers on the Arboretum grounds. This is a common fungal disease of stressed conifers. Cytospora canker rarely affects trees that are younger than 15 to 20 years old or that are less than 20 feet tall. The disease usually starts on the lower branches of the tree and progresses upwards. Needles turn brown and finally drop, leaving dry, brittle twigs and branches (figure 12). The fungus enters the tree through wounds and creates cankers within the bark. A thin coating of white resin is often found on infected twigs and trunks (figure 13).
Another problem that can be confused with Cytospora canker is too much shade. Spruces
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| Figure 13 Sap flow from Cytospora canker |
need full sun, so when the bottom branches get shaded out by other plants, those bottom branches die. But an older spruce in full sun that has the lower branches die is most likely a victim of Cytospora canker.
Management: Cytospora canker is a stress-related disease, so, at minimum, trees should be kept mulched and watered well during dry periods. Remove infected branches promptly during dry weather to reduce the spread of the disease. It is imperative to disinfect pruning tools between cuts. Give spruces adequate space when planting as dense planting is another common predisposing stress factor. There is no effective chemical control.
Good web sites:
http://ohioline.osu.edu/hyg-fact/3000/3033.html
http://ipm.uiuc.edu/diseases/series600/rpd604/index.html
Leaf spots
Leaf spot is a fairly general category of disease. Let's focus in on something we start seeing in mid- to late summer- leaf spots on perennials like purple coneflower, black-eyed Susan and aster. There are a number of different fungi associated with the leaf spots found on these plants. A couple of these fungi have already been identified attacking smooth aster (Aster laevis). Leaf spots that show up on our late-blooming perennials are often found on lower leaves of plants that are being watered with sprinklers systems. Sprinklers are often set to run every day or two for a short time, wetting foliage on a regular basis and setting up good conditions for fungal growth.
Management: Avoid wetting foliage of perennials. Apply water to the soil instead, watering deeply and infrequently (1 inch per week). Remove infected leaves and space plants properly to provide good air circulation.
Miscellaneous
Slime mold
Fuligo septica, otherwise known as slime mold, is commonly seen on decaying wood material
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| Figure 14 Slime mold (fresh) |
(mulch, fallen logs) during periods of wet weather. We certainly haven't had any of that, but there is a lot of watering going on due to the dry weather. After rain events (or thorough watering) , F. septica is bright yellow and slimy in appearance (figure 14). As the mold dries, it becomes off-white and finally becomes a tan-brown crust (figure 15). Its pinkish-brown spores are dispersed by air movement when the dried mass is disturbed. The mass may get as large as 8 inches long and wide, but is relatively thin (0.5 – 1.5 inches).
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| Figure 15 Slime mold (dried) |
Management: This is more a novelty than a pest. When the slime mold has dried, slide the blade of a shovel under it and put it in the garbage. Don't break it up or you will just disperse the spores.
Good website: http://www.extension.iastate.edu/newsrel/2003/mar03/mar0303.html
________________________________________
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 .
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