Plant Health Care Report June 22, 2012
Tagged as: Wooly alder aphid, tuliptree, thyronectria canker, sycamore lace bug, Squirrel damage, Spruce Gall Adelgid, diplodia tip blight, Diplodia (Sphaeropsis) tip blight on pine, ailanthus webworm, physiological yellowing, blossom end rot, stink bug, milkweed beetle
June 22, 2012 Issue 2012.10
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?
Smooth hydrangea (Hydrangea arborescens) (figure 1) is blooming.
Accumulated Growing Degree Days (Base 50): 1027 (as of June 20)
Accumulated Growing Degree Days (Base 30): 3179 (as of June 20)
Insects:
- Woolly alder aphid
Figure 1 Smooth hydrangea (Hydrangea arborescens) - Eastern spruce gall
- Ailanthus webworm
- Sycamore lacebug
- Milkweed beetle
- Stink bugs
Diseases:
- Diplodia/Sphaeropsis
- Thyronectria canker
Miscellaneous:
- Blossom end rot
- Physiological yellowing of tulip tree
- Squirrel damage
Degree Days and Weather Information
As of June 20, we are at 1027 base-50 growing degree days (GDD), which is 310 GDD 50 ahead of 2011 at this time. We have had .48" rain since the last PHCR so we have had 1.37" for June and 10.94" for the year (compared to 19.89" last year at this time).
| Location | B50 Growing Degree Days Through June 21, 2012 |
Precipitation (in) |
| Aurora, IL* | 1254 | -- |
| Carbondale, IL* | 1931 | -- |
|
Champaign, IL* |
1554 | -- |
| Chicago Botanic Garden** | 963 (as of 6/18) | 1.11" (6/12-18) |
| Crystal Lake, IL* | 1179 | -- |
| Harvard, IL* | 1149 | -- |
| Kankakee, IL* | 1382 | -- |
| The Morton Arboretum | 1027 (as of 6/20) |
.48" (6/15-20) |
| Northbrook** | 1134 (as of 6/20) | 1.35" (6/13-19) |
| O'Hare* | 1240 | -- |
| Peoria, IL* | 1585 | -- |
| Quincy, IL* | 1708 | -- |
| Rockford, IL* |
1246 |
-- |
| Springfield, IL* | 1721 | -- |
| Waukegan, IL* | 1045 | -- |
**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
Woolly alder aphid
 |
| Figure 2 Woolly alder aphids |
The Plant Clinic has received a sample of woolly alder aphids (Paraprociphilus tessellatus) (figure 2). The aphids were found in colonies on the branches of European alder (Alnus glutinosa). Aphids are small (about 1/12 of an inch long) and are identified by their sucking mouthparts, long, thin legs, long antennae, pear-shaped body, and pair of tube-like structures (called cornicles) emerging from their abdomen that look somewhat like tailpipes. Two hosts are needed to complete their life cycle: alders and silver maples. The eggs are usually laid in fall in the bark of the maples. When the young hatch in spring, they collect on leaves and reproduce. Their offspring fly to alders and collect on the twigs where new generations develop. They are small and covered with white waxy hairs. In fall, they will fly back to the silver maples to lay eggs. They do little damage.
Management: Aphids can be dislodged from plants using a strong jet of water from the hose. Doing this periodically will keep the aphid populations low and allow the parasites and predators to build up to effective control levels.
Good web site:
Eastern spruce gall
How can we get through an issue of the Plant Health Care Report without a gall? The Plant
 |
| Figure 3 Eastern spruce gall |
Clinic received a sample of Eastern spruce gall (figure 3) from northern Wisconsin. This gall is caused by an aphid-like insect called an adelgid (Adelges abietis). These insects were active in the spring and caused the gall to begin forming at that time. These galls are often mistaken for small cones. With Eastern spruce gall, the gall forms at the base of the new growth. (There is another gall known as Cooley spruce gall which has a similar shape, but forms on the tip of the new growth). The galls mature in midsummer and slits appear that allow the mature adelgids to leave the gall.
Management: While the galls will kill the new growth on which they form, infestations in our area are seldom heavy enough to require any type of management. Galls can be removed by hand before the slits open. Insecticides are seldom warranted but can be applied in early spring right before bud break or in late September and October.
Good websites: http://www.hort.uconn.edu/ipm/homegrnd/htms/59spgall.htm
http://ohioline.osu.edu/hyg-fact/2000/2550.html
Ailanthus webworm
 |
| Figure 4 Ailanthus webworm larva |
Ailanthus webworm (Atteva aurea) caterpillars (figure 4) were found on corkwood (Leitneria floridana). The caterpillars have sparse light hairs, a broad stripe down their backs that has been described as olive-green, and alternating black and white stripes along their sides. They cluster together in a loose web and feed on leaves from within the web. This insect is usually seen on tree-of-heaven (Ailanthus altissima), one of our least favorite trees. This is the well-known tree in the popular book A Tree Grows in Brooklyn. But tree-of-heaven is a weak-wooded, weedy, smelly tree.
Management: Here at the Arboretum, we cut the nests out of the tree. Bacillus thuringiensis var. kurstaki (Btk) could also be used to control young larvae, but the spray needs to penetrate the nest to be effective. Btk is not as effective against older larvae. Although ailanthus webworms are capable of defoliating their host, they rarely do.
Sycamore lacebug
 |
| Figure 5 Sycamore lacebug adult |
Sycamore lacebug (Corythucha ciliata) (figure 5) have been found feeding on American
sycamore (Platanus occidentalis). Lacebugs are a common pest of ornamental trees and shrubs, and most lacebug species are host specific. An exception is the hawthorn lacebug (C.cydoniae) that attacks several species within the Rosaceae family including cotoneaster, flowering quince, crabapple, mountain ash, Pyracantha, and hawthorn. Most lacebug species have two or more generations per year. The hawthorn lacebugs have only one generation per year.
The sycamore lacebug overwinters as an adult under loose bark of its host and becomes active in early spring as leaves begin to develop. Soon afterwards, the female lays eggs on the undersides of leaves. Eggs hatch within a few days and spiny, wingless, black nymphs begin feeding. Within 4 to 6 weeks the nymphs pupate, and the next generation of adults emerge (this is the generation we are now seeing). Adults are 3 to 6 mm long (1/8 to 1/4 inch) with lacy wings.
Sycamore lacebug adults and nymphs live on the lower surfaces of leaves and feed on leaf sap causing yellow and white stippling on the upper leaf surface. As the insects feed, they deposit a brown varnish-like excrement on the underside of leaves. Heavy infestations may lead to complete stippling of the leaf and premature leaf drop.
Management: There are several naturally occurring predators including green lacewings, mites, and assassin bugs. A forceful spray of water will dislodge newly hatched nymphs, and they will often die before they find their way back to suitable leaves. Plant site selection is also important as lace bugs prefer bright, sunny locations. Insecticides generally are not necessary except for severe infestations. Avoid using insecticides if natural predators are present.
Good website:
Milkweed beetle
 |
| Figure 6 Milkweed beetle |
Red milkweed beetles (Tetraopes tetraophthalmus) (figure 6) were found on common milkweed (Asclepias syriaca) this week. The beetles are 1/2 to 3/4 inch long and red with black spots and long black antennae. Adults feed on milkweed leaves, while in the larval stage they bore into and feed on milkweed stems and roots.
Management: They usually do not cause enough damage to require control.
Good websites: http://www.duke.edu/~jspippen/naturephotos/milkweedbeetle.htm
Stink bugs
There are a number of different species of stink bugs that feed on a wide range of host
 |
| Figure 7 Stink bug nymphs and their egg cases |
plants. Many of their hosts are wild plants, but they can also be found on cultivated crops and ornamental plants as well. Some stink bugs are predatory on other insects. Our scouts at The Morton Arboretum found stink bugs feeding on bald cypress (Taxodium distichum) this week. The stink bugs that feed on plants suck out sap from leaves, flower buds, and developing fruit. This may cause the plant tissues to be deformed or distorted. Adult stink bugs are shield-shaped and true to their name, they can produce an odor to repel predators. Young stink bugs (nymphs, figure 7) are more rounded in shape and have coloration similar to their adult counterparts.
Management: Stink bugs have a number of natural predators, so control is not always needed. While most stink bugs are not a big problem, we are on the lookout for a potentially serious stink bug, the brown marmorated stink bug (Halyomorpha halys). The brown marmorated stink bug is a pest that can do serious damage to agricultural crops, fruit and ornamentals. They have distinct antennae which have alternating dark and light bands at the end. There are also bands along the back end of the wings where they overlap on the abdomen. Go to http://ento.psu.edu/extension/factsheets/brown-marmorated-stink-bug for more information on this pest.
Pest update: diseases
Diplodia/Sphaeropsis
 |
| Figure 8 Diplodia tip blight |
We have found symptoms of Diplodia tip blight (Diplodia pinea) on current year needles of pine (Pinus sp.). This disease was Diplodia, then became Sphaeropsis and now is called Diplodia once again. We prefer to call it tip blight. It is a common disease of two- and three-needle pines in our region. Austrian, mugo, red and Scots pines seem to be a magnet for this disease, especially if they are stressed by insufficient water. The fungus infects needles as they are expanding, thus causing stunting and turning the needles straw-colored or brown (figure 8). Some "bleeding" or resin may appear dripping from infected needles. The disease frequently starts on lower branches and moves upward as spores are spread by splashing rain and wind. The fungus can also invade woody tissue and cause branches to die. Dead shoot tips and needles from previous years are often found throughout the canopy of larger trees. Black pepper-like fruiting bodies form at the base of the needles (look underneath the needle sheath) soon after the needles die.
Management: Most of the pines that get this disease are no longer recommended for use in the landscape. Managing the disease on existing trees is possible through sanitation, cultural, and chemical control practices. Rake up and discard infected cones and needles to remove immediate inoculum sources. The spores are moved on air currents, so sanitation will never be 100%. Also, keep trees mulched (do not use diseased pine needles as mulch) and watered during dry periods. Avoid overhead irrigation which helps spread spores, and do not prune susceptible trees in wet weather. As soon as tip blight is noticed, prune out and destroy diseased tissue. Sterilize tools between pruning cuts. Fungicides are effective if applied when needles are first emerging.
Good websites: http://www.ag.uiuc.edu/~vista/abstracts/aSPHAERO.HTML
http://na.fs.fed.us/spfo/pubs/factsheets/sphaeropsis/shootblight.htm
Thyronectria canker
 |
| Figure 9 Cankered stem |
We found branch dieback symptoms of Thyronectria canker on honeylocust (Gleditsia triacanthos var inermis). This disease, caused by the fungus Nectria austroamericana (Thyronectria austroamericana), is a common and serious canker disease of honeylocust. It is a major cause of decline of thornless honey-locusts in urban plantings in Illinois and is currently killing large specimens. The disease is minor in natural woodland areas.
Thyronectria canker causes girdling branch and trunk cankers that result in branch dieback (figure 9), reduced foliage, yellowing and wilting of foliage, premature fall coloration, and early leaf drop. Cankers are elongated and slightly sunken with callus ridges sometimes developing with age. The surface of killed bark may have a red-yellow discoloration. Reddish-brown discoloration develops in sapwood beneath and near the cankers and may extend to the heartwood. Note that the reddish color associated with the center of honey-locust stems is not related to this disease.
Management: Prune out dead branches to a branch junction in dry weather and at least one foot below the visible margin of the canker. Clean pruning tools between cuts to reduce spread of the fungus. Eliminate drought stress by mulching trees and watering during dry periods. Avoid physical damage to the trees.
Honey-locust cultivars vary in susceptibility to Thyronectria canker. An Illinois test found that canker incidence on inoculated stems was least on cultivars 'Holka', 'Imperial', and 'Shademaster'; greatest on 'Sunburst'; and intermediate on 'Moraine' and 'Skyline'.
Good websites: http://www.ext.colostate.edu/pubs/garden/02939.html
Miscellaneous
Blossom end rot
We continue to see problems related to low rainfall. One of these problems is blossom end
 |
| Figure 10 Blossom end rot (early stage) |
rot, which is common on tomatoes, peppers, and eggplant. Occasionally it will also show up on watermelon. Blossom end rot is a symptom of calcium deficiency, but it is tied into watering and rainfall. Generally, we do have enough calcium in the soil, but it needs to be transported up to the developing tomato in the water taken up by the roots of the plant. In times when rainfall in inadequate or the gardener is not supplying enough water, the calcium does not make it all the way to the developing tomato. If the calcium does not make it to the tomato, the blossom end (the bottom of the tomato) starts to break down. This often starts as a small blacked area (figure 10). In some cases the spot will enlarge, sometimes covering the entire lower end of the tomato. The affected area may become sunken and leathery.
Management: One of the most important management techniques is to avoid fluctuations in water supply. Keep soil consistently moist, providing about one inch of water per week. In very hot weather that may need to be increased to one inch every five days. Use mulch to conserve water. Remove affected fruit to allow water and calcium to go to developing fruit that have not been affected. When fertilizing use the nitrate form of nitrogen rather than the ammonia form. Excess ammonia can reduce the uptake of calcium.
Good websites: http://ohioline.osu.edu/hyg-fact/3000/3117.html
http://www.aces.edu/pubs/docs/A/ANR-1059/ANR-1059.pdf
Physiological yellowing of tulip tree
Physiological yellowing of tulip tree (Liriodendron tulipifera) is another problem related to the dry weather. We often see this problem start up in July. This year it is getting an early start due to the very dry spring we have had, coupled with the recent extreme heat. With this problem you will see completely yellow leaves scattered throughout the crown of the tree. They will soon fall off the tree. Some leaves may also show small black spots.
Management: This type of leaf yellowing does not have any real long term effect on the health of the tree. It does, however, indicate that the tree needs water. Water tulip tree weekly (one inch of water per week) to alleviate drought stress.
Good website: http://www.ppdl.purdue.edu/ppdl/hot07/7-24.html
Squirrel damage
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| Figure 11 Stems cut by squirrels |
We're receiving reports of small branches dropping out of trees (figure 11). This is caused by squirrels chewing on the twigs. The cut end is usually rough and shows signs of chewing. Later in the season we may see damage by twig girdlers and twig pruners, but that damage will be much tidier. Squirrel damage can happen on a variety of trees (we have seen chewed branches from ash and oak in the Plant Clinic in the last week). Squirrels chew on tree branches to sharpen and clean their teeth and gather seeds. They also use branches to line their nests. The harm to the tree is insignificant.
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 "> 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 "> This e-mail address is being protected from spambots. You need JavaScript enabled to view it .
Copyright © 2012 The Morton Arboretum
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