Plant Health Care Report June 15, 2012
June 15, 2012 Issue 2012.9
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?
Elderberry (Sambucus canadensis) (figure 1) is in full bloom.
Accumulated Growing Degree Days (Base 50): 869 (as of June 14)
Accumulated Growing Degree Days (Base 30): 2901 (as of June 14)
- Cedar quince rust on serviceberry
- Bacterial blight or fireblight?
- Mosaic virus on Katsuratree
- Watering reminder/fertilizer warning
- Drought tolerant trees
At the Sterling Morton Library
- The Pioneering Prairie Spirit in Landscape Design
Degree Days and Weather Information
As of June 14, we are at 869 base-50 growing degree days (GDD), which is 258 GDD 50 ahead of 2011 at this time. We have had no additional rain since the last PHCR so we remain at 10.46 in. for the year (compared to 18.75 in. last year at this time).
|Location||B50 Growing Degree Days
Through June 14, 2012
|Chicago Botanic Garden**||815 (as of 6/11)||No rain (6/5-11)|
|Crystal Lake, IL*||969||--|
|The Morton Arboretum||869||
|Northbrook**||961.5 (as of 6/13)||No rain (6/6-12)|
**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/
Special note: The search is on for Gypsy moth. Gypsy moths traps were put out this week.
Pest update: Insects
|Figure 2 Japanese beetle adults|
We are sorry to announce that Japanese beetle (Popillia japonica) adults (figure 2) have been seen. Our volunteersand staff reported them in Joliet, Naperville and Long Grove this week. Japanese beetles are up to 1/2 inch long, and have oval, metallic green bodies with coppery brown wing covers. They appear to have five white spots along each side and two additional white spots behind their wing covers. Upon examination under a hand lens, the spots are actually tufts of white hair.
Adult beetles feed on nearly 400 different species of ornamental plants with about 50 species being preferred. Highly preferred hosts include rose, crabapple, cherry, grape, and linden. The adults feed on leaf tissue between veins, resulting in skeletonized leaves (figure 3) that soon wither and die. Severely infested plants may be almost completely defoliated.
|Figure 3 Japanese beetle damage on linden|
Japanese beetles overwinter as larvae (grubs) about four to eight inches beneath the soil surface. In spring, as the soil temperatures warm to about 55° F (usually mid-April), the grubs move upward and feed on plant roots. Adults normally emerge from late June through July. Due to the strange weather, they are making an early appearance this year. Within a few days after emergence, females mate and burrow into the soil to lay eggs at a depth of two to four inches. Nearly all eggs are laid by mid-August. In sufficiently warm and moist soil, eggs will hatch in about ten days (in this situation, our low rain fall may actually be a benefit, making egg laying more difficult). Larvae feed on plant roots until cold weather forces them to greater depths in the soil for the winter. There is one generation of this beetle per year.
Management: Adult Japanese beetles can be handpicked. It is easiest to catch them by placing a soapy-water filled container directly under the leaf that they are chewing on and then shaking the leaf. The soapy water ensures that the beetles die while you're collecting them. The beetles generally fly straight down into the collecting container. Sometimes Japanese beetle pheromone traps are used to trap them. This is not recommended as you will be attracting even more beetles to your property (more than the trap can collect). Insecticides can be used in the case of valuable plants.
Japanese beetle larvae (grubs) have a different management strategy. If areas of turfgrass are dying, peel the lawn back and look underneath to assess the population. Treatment for grub infestations in lawns is not considered necessary unless the population exceeds 10 to 12 grubs per square foot. Eggs and first instar larvae require moisture to survive; therefore, the easiest way to reduce grub populations is to limit lawn irrigation during the egg-laying period when beetle populations peak (mid-July through early August). Japanese beetles also avoid laying eggs in shade, which is another great reason to plant more trees and shrubs. Insecticide applications are effective in controlling young larvae. To achieve the most effective control, insecticides should be applied when grubs are small and feeding near the soil surface (from early August until cold weather drives them deeper into the soil). Insecticide applications in spring are often ineffective since the grubs are quite large or in late spring, they could be pupating.
We receive a lot of questions about the use of the biological control milky spore disease (Bacillus popilliae). This is a bacterium that is specifically toxic to the grub stage of the Japanese beetle and is applied to the soil. This is a slow method at best in the warmer southern states and is often not very effective at all in colder, northern states. Also if you have grubs that come from another beetle, it won't work on them at all.
Beneficial nematodes are now available that can be watered into turf where they infest and kill grubs. Products containing Heterorhabditis bacteriophora nematodes are recommended by the University of Illinois. Beneficial nematodes are not always available in stores; they are available through mail order/internet sources. Ohio State University keeps a web site listing good mail order sources of beneficial nematodes at:
Figure 4 Euonymus scale males (white)
Euonymus scale (Unaspis euonymi) is one of the most common insects that we see in the Plant Clinic, especially on ground cover euonymus. We are seeing scale and crawlers at this time. The crawler stage is the only life stage vulnerable to insecticides. Scale insects have piercing/sucking mouthparts. Feeding by euonymus scale causes small yellow or white spots (mottling) on the upper leaf surfaces. Moderately to heavily infested plants grow very slowly, if at all. Heavy infestations can cause branch dieback and may even kill some plants. Euonymus (Euonymus spp.), pachysandra (Pachysandra spp.), and bittersweet (Celastrus spp.) are the principal hosts. Stressed plants are most susceptible to attack. Plants growing adjacent to foundations with poor air circulation are more severely damaged.
Male adult scales are white and the females are dark brown and oystershell-shaped (figure 4). Euonymus scales are armored scales, meaning they have a protective covering over their bodies. The crawlers are tiny and yellow; you definitely need a magnifier or hand lens to see them. Euonymus scales can be found on leaves as well as stems. Euonymus scale overwinters as mated females on plant stems. Eggs develop beneath the scale and hatch during late spring. The tiny yellow crawlers move to new succulent leaves to feed. This is the stage that we are seeing now. As they mature, they secrete a waxy protective coating or "armor." There are usually two generations per year in our area. We'll expect to see the second generation in late July/early Aug.
Management: Pruning out heavily infested branches can help to reduce the number of scales. Insecticidal soaps, summer oils, or other insecticides should be applied only when crawlers are visible on the plant. Additional applications are typically recommended.
Good web sites:
Yet another gall
|Fiogure 5 Maple gouty vein gall|
The galls just keep on coming this year. We have a report of maple gouty vein gall (figure 5) on black maple (Acer nigrum). This gall is caused by a gall midge. This is another interesting gall that does no real damage. No management is needed.
Pest updates: diseases
Cedar quince rust on serviceberry
|Figure 6 Spore horns of cedar quince rust on fruit|
That's right; the title says serviceberry (Amelanchier species). We usually see this disease most commonly on hawthorns, but this year it is showing up on serviceberry. Serviceberry is a host for this disease, but in most years we do not see infection on it. There are no symptoms on the leaves, but long aecial tubes have formed on the fruit (figure 6), and aeciospores are being released. These spores will infect nearby junipers. Cedar quince rust does not cause galls on juniper foliage; rather, spindle shaped swellings form on the twigs and branches. It can also form swellings on the stems of the deciduous host.
Management: It is too late to treat the deciduous hosts at this time. This fall , clean up and discard all debris. For next season, protect emerging leaves and succulent shoots of deciduous hosts that have had rust problems in prior years with an appropriate fungicide.
Bacterial blight or fireblight?
|Figure 7 Fireblight|
For the last month or so we have had reports of bud, leaf and shoot blight symptoms on ornamental pears. The University of Illinois Plant Clinic reported these as symptoms of bacterial blight caused by Pseudomonas syringae (go to http://hyg.ipm.illinois.edu/article.php?id=362 for their full report on this problem). The symptoms are similar to those of fireblight (figure 7) (another bacterial disease caused by Erwinia amylovora). If you need to know if your pear has fireblight or bacterial blight, you may need to have a sample cultured in a lab.
Management: Some of the management techniques used for fireblight also can be used for bacterial blight. When fertilizing, avoid excessive nitrogen applications that might lead to succulent growth that is more susceptible to infection. Cankered branches should be cut out during dry weather and tools should be cleaned between cuts. To ensure that all of the infected tissue is being removed, make pruning cuts 8-12 inches elow the last symptoms. The University of Illinois is recommending regular pruning be done in January or February.
Mosaic virus on Katsuratree
|Figure 8 Mosaic virus on Katsuratree|
The galls are running rampant this season and so are the viruses. The increase in these problems is due to the fact that they are caused by insects (galls) or insect-vectored (viruses). The drier weather is favoring insect populations while suppressing severe fungal problems. A mosaic virus has been found on Katsuratree (Cercidiphyllum japonicum). Many viruses have the word 'mosaic' in their name. This term refers to the main symptom where the leaf seems to be composed of variously colored mosaic tiles (figure 8).
Management: There is no chemical management of viruses. Once the plant is infected it cannot be 'cured'. There are two options for dealing with viruses. First, you can keep the plant and live with the fact that it has the virus. For some plants this is an acceptable option, especially if it does no serious damage to the plant or there are no other plants of the same species nearby to become infected. The second option is to destroy the plant. This is a good idea with small plants like roses, hostas or raspberries where there are other plants of the same species nearby that might become infected.
Watering reminder/fertilizer warning
Back in issue 5 (May 18), the newsletter included an article on proper watering. Now almost a month later we find ourselves still very dry. In the last month we have only had about one inch of rain. This article serves as a quick reminder that watering is very important in this time of very little rain. Our plants are under a lot of stress. We are seeing trees showing symptoms of wilting, early fall color and leaf drop. These are signs of stress. Drought stress may also lead to poor fruit formation and poor bud formation for next year.
A question that we receive in the Plant Clinic fairly regularly is "Should I be fertilizing?" It is really getting too late in the season to be fertilizing trees and shrubs. Don't fertilize woody plants until they go dormant in fall. Annual and perennial flowers can still be fertilized, but fertilizer should not be applied unless the soil moisture is good. Fertilizer can be damaging to drought stressed plants.
|Figure 9 Chlorosis on oak|
Chlorosis is showing up on a number of plants including river birch (Betula nigra), oakleaf hydrangea (Hydrangea quercifolia) and sweetspire (Itea virginica). Chlorosis is a yellowing of the leaf due to low levels of chlorophyll (the green pigment in leaves). In mild cases, leaf tissue appears pale green but the veins remain green (figure 9). Leaf tissue becomes progressively yellow, and may turn white in advanced cases. Leaf margins may become scorched or develop symmetrical brown spots between veins. Trees that commonly show chlorosis include pin oak, red oak, red maple, white oak, river birch, tulip-tree, sweet gum, bald cypress, magnolia, and white pine.
There are many causes of chlorosis. The most common chlorosis in our area is due to iron and manganese deficiencies resulting from alkaline soils. High pH causes iron and manganese that is present in the soil to become unavailable to the plant. Anything that negatively impacts the root system (physical damage, flooded soils, and dry soils) can also lead to chlorosis. There may be more than one possible cause. Take river birch for example. It is fairly common to see chlorosis from lack of iron. In this case, we see the typical yellow leaf with green veins. River birch also suffers when the soil is too dry. In that case, we tend to see leaves turn all yellow and fall off (sometimes as many as half the leaves may drop). Determining the cause helps us to determine management practices.
Management: In dry seasons, be sure to provide enough moisture to plants. Where soil pH is alkaline (northern Illinois), avoid planting trees that do not tolerate alkaline soils. If leaves do become chlorotic, first determine the pH of the soil by doing a soil test or sending a sample of soil to a laboratory. Regional laboratories include:
• A & L Great Lakes Laboratories in Fort Wayne, Indiana (260-483-4759)
• Alvey Laboratories in Belleville, Illinois (618-233-0445)
• Kane County Farm Bureau in St. Charles, Illinois (630-584-8660)
• University of Wisconsin Cooperative Extension Service in Madison, Wisconsin (608-262-4364)
Take the necessary steps to remedy the situation based on the results of the test.
• Fertilizing soil with a nitrogen- and sulfur-based fertilizer in early spring through mid-May.
• Use chelated iron which is not affected by soil pH.
• Place iron or manganese implants in the trunk of the tree.
Good websites: http://www.ag.uiuc.edu/~vista/abstracts/aIRONCHL.HTML
Drought tolerant trees
This seems like a good time to talk about drought tolerant trees. We are in the middle of an ongoing dry spell and this won't be the last one, so we might as well plan ahead. Also, with the removal of so many trees due to emerald ash borer, many homeowners are faced with finding a replacement tree.
Let's review some basics so we do this right. If you can, avoid planting in summer due to higher heat and lack of water. Use summer to plan and be ready to plant in fall when the weather is better (cooler at least). If you find that you absolutely must plant in summer, be prepared to water your new tree on a regular basis. Our goal is to keep the root ball and surrounding area consistently moist. If you can't commit to watering, don't put in a new plant.
Consider starting with a smaller specimen. Many homeowners are buying large trees hoping to get to a large mature size faster. Generally this does not happen. The time for recovery and establishment is often longer for a tree with 4" diameter trunk than it is for a tree with a 2" diameter trunk.
Now let's get down to the drought tolerant part of the conversation. Trees that are considered drought tolerant only become so after they have become established in the landscape. That means that for at least the first year or two, the homeowner will need to provide water on a regular basis. This time will be longer if you choose to plant a larger specimen. Once trees do become established and are considered drought tolerant, we must remember that drought tolerant does not mean drought-loving. In the case of a long or severe drought, even these trees may need supplemental watering from time to time.
Here are some trees that are considered drought tolerant (trees marked by * are native to northern Illinois):
Large deciduous trees (over 40') Small deciduous trees (15-25')
*Hackberry (Celtis occidentalis) *Eastern Redbud (Cercis canadensis)
Ginkgo (Ginkgo biloba) Smokebush (Cotinus coggygria)
*Kentucky Coffeetree (Gymnocladus dioicus) Thornless Cockspur Hawthorn
(Crataegus crus-galli var inermis)
*Black Walnut (Juglans nigra)
*Sycamore (Platanus occidentalis) Winter King Hawthorn
(Crataegus viridis 'Winter King')
*Northen Pin Oak (Quercus ellipsoidalis) Crabapple (Malus many cultivars)
*Shingle Oak (Quercus imbricaria) *Wafer-ash (Ptelaea trifoliata)
*Bur Oak (Quercus macrocarpa) Peking Tree Lilac (Syringa pekinensis)
Redmond Linden (Tilia x 'Redmond')
Hybrid Elms (Ulmus Hybrids)
Medium deciduous trees (25-40')
American Smoketree (Cotinus obovatus)
Persimmon (Diospyros virginiana)
Osage-orange (Maclura pomifera)
Lacebark Elm (Ulmus parvifolia)
Large evergreen trees (over 40') Medium evergreen trees (25-40')
Black Hills Spruce (Picea glauca var. densata) Lacebark Pine (Pinus bungeana)
Limber Pine (Pinus flexilus) Swiss Stone Pine (Pinus cembra)
Ponderosa Pine (Pinus ponderosa)
Small evergreen tree (less than 20')
Chinese Juniper (Juniperus chinensis cultivars)
Rocky Mountain Juniper (Juniperus scopulorum cultivars)
*Eastern Redcedar (Juniperus virginana cultivars)
At the Sterling Morton Library
The Pioneering Prairie Spirit in Landscape Design
Christopher Vernon & Robert Grese, Landscape Historians and Authors
Wednesday, June 20, 2012 - 6:30 p.m. - 8:30 p.m.
In the late 19th and early 20th centuries, landscape architects in the Chicago region changed the face of landscape design. Join landscape historians Christopher Vernon and Bob Grese to meet the pioneers of the native landscape movement. These experts will share the impact of important landscape architects such as Jens Jensen, O.C. Simonds, (the landscape architect who designed the Arboretum), Frederick Law Olmsted, and others. Join them to explore the research included in their new books, Graceland Cemetery: A Design History and The Native Landscape Reader, and to view and discuss the short film by Darrel Morrison, Designing in the Prairie Spirit, which will be shown at the event. This event is partially underwritten by the Library of American Landscape History and forms a part of the Sesquicentennial Celebration of the Founding of Graceland Cemetery.
Pre-registration is required for this evening event to be held in the Sterling Morton Library. Registration details can be viewed at:
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.
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
Copyright © 2012 The Morton Arboretum
Not printed on recycled paper, or any paper for that matter.
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