Plant Health Care Report June 29, 2012
June 29, 2012 Issue 2012.11
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?
Bottlebrush buckeye (Aesculus parviflora) (figure 1) is in bloom.
Accumulated Growing Degree Days (Base 50): 1201 (as of June 28)
Accumulated Growing Degree Days (Base 30): 3513 (as of June 28)
- Pine needle scale
- Genista caterpillar
Figure 1 Bottlebrush buckeye (Aesculus parviflora)
- Oak slug sawfly
- Spiny elm caterpillar
- Second generations
- Rust on lawns
- Walnut anthracnose
- Botryosphaeria canker
- Entomosporium leaf spot
- Mulch volcanoes
- Remontant flowers
Degree Days and Weather Information
As of June 28, we are at 1201 base-50 growing degree days (GDD), which is 371 GDD 50 ahead of 2011 at this time. We have had .02" rain since the last PHCR so we have had 1.39" for June and 10.96" for the year (compared to 20.84" last year at this time).
|Location||B50 Growing Degree Days
Through June 28, 2012
|Chicago Botanic Garden**||1145 (as of 6/25)||.01 (6/19-25)|
|Crystal Lake, IL*||1345||--|
|The Morton Arboretum||1201||
|Northbrook**||1282.5 (as of 6/27)||No rain (6/20-26)|
**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
Pine needle scale
|Figure 2 Pine needle scale|
The second generation of pine needle scale (Chionaspis pinifoliae) adults (figure 2) is present on pines (Pinus species). The scale eggs overwinter beneath a waxy, white female adult that looks like a white, tear-drop shaped fleck on an infested pine needle. After the eggs hatch, the tiny crawlers move to a new site on the host plant to feed. They suck juice from needles. As the crawlers develop, they secrete a white, waxy covering over their bodies. By late June or early July, they reach maturity and second generation eggs are laid. Second generation crawlers begin to appear in late July to early August. A heavy infestation will cause needles to turn yellowish brown.
Heavy infestations can give trees a flocked appearance. After multiple years of severe infestation, branches, and sometimes trees, can be killed. Pine needle scale prefers Scots and mugo pines and occasionally infests Austrian, white, and red pines.
Management: Several species of ladybird beetles and parasitic wasps are important natural predators of this scale. Insecticidal sprays and soaps are effective only when crawlers are active. Use insecticidal soap instead of a chemical spray as the latter will more readily kill natural predators and beneficial insects.
Genista caterpillars (Uresiphita reversalis) (figure 3) have been found defoliating false indigo
|Figure 3 Genista caterpillar|
(Baptisia australis) at The Morton Arboretum and in some other suburban sites. The larvae are pale yellow-green with black spots, black heads, and white hairs protruding from their bodies. The only hosts are legumes. In the south, genista caterpillars have two generations, but in New York, there is only one. In Illinois we sometimes see one generation and sometimes two. This is one of those pests that shows up on Baptisia in some years and not in others. This year our horticulture staff reports at least one Baptisia plant was completely defoliated. In other years, genista caterpillar has been reported on dyers greenwood or dyers greenweed (Genista tinctoria), which is less commonly planted.
Management: The caterpillars can be handpicked. Bacillus thuringiensis var. kurstaki (Btk) can also be used to control young larvae. Btk is not as effective on mature larvae.
Good website: http://www.entomology.ksu.edu/doc5018.ashx
|Figure 4 Bagworm|
The Plant Clinic has had a call on bagworms (Thyridopteryx ephemeraeformis). Bagworms overwinter as eggs inside the female bag that contains between 300 and 1,000 eggs. The eggs hatch in early summer and the young larvae suspend from a silk string and are often "ballooned" by wind to nearby plants. When a suitable host plant is found, larvae begin to form bags over their bodies. By mid-August the larvae have matured and are 1 to 1-1/2 inches in length, and their completed bags are 1-1/2 to 2-1/2 inches long (figure 4). They move to a sturdy branch, attach the bag with a strong band of silk, and then pupate. About four weeks later, adults emerge and mate. The sedentary female, which has no eyes, wings, legs, antennae, or functional mouthparts, lays eggs and is then mummified around the egg mass within the bag.
The tiny cone-shaped brownish bags are constructed from silk and camouflaged with bits of twigs and foliage. Larvae stick their heads and front legs out of the top of the bags to feed and move. The feeding by young larvae results in brown spots and holes in the foliage. As the larvae grow, they enlarge their bags and feed on the entire leaf leaving only veins. Bagworm populations can build rapidly and quickly defoliate their hosts. Healthy deciduous trees can usually tolerate three consecutive years of severe defoliation before they are killed. Evergreen trees, on the other hand, are frequently killed by just one year of severe defoliation. Bagworm larvae feed on over 120 species of trees and shrubs. Their bags are made of the foliage they're feeding on, so a bagworm feeding on pine will have pine needles in its bag, while a bagworm feeding on a crabapple will have pieces of crabapple leaves decorating its bag.
Until a few years ago, bagworms were generally considered more of a problem south of Interstate 80. They can now be found in the Chicago area. They have survived in this area in the last few years due to the warmer winter temperatures. Once a plant is infested, populations can grow quickly on that plant.
Management: Bagworms can be a serious problem. Bacillus thuringiensis var. kurstaki (Btk) and insecticidal sprays are effective but need to be used on young larvae. It is best to wait until they have stopped ballooning before applying insecticide. Handpicking bags in winter and early spring will also help control populations.
Good web sites:
Oak slug sawfly
|Figure 5 Oak slug sawfly|
We've found oak slug sawfly (Caliroa quercuscoccineae) larvae (figure 5) feeding on white oak (Quercus alba). The sawflies feed on the lower layer of the leaf, leaving behind the upper epidermal layer and creating a 'window pane' effect. The larvae are about 3 mm (1/8 inch) long, pale yellow-green, and slimy; they will reach about 12 mm (1 inch) when mature. There are two to three generations per year.
Completely skeletonized oak leaves drop prematurely. Pin oak and scarlet oak are preferred hosts, but this insect will feed on white and black oaks as well. Normally, damage is an aesthetic problem.
Management: This pest is generally kept in check by parasites, microbial disease, and other natural enemies. Even noticeable outbreaks are generally not dangerous to the health of the host oaks.
Spiny elm caterpillar
Spiny elm caterpillars (Nymphalis antiopa) (figure 6) are feeding on the leaves of sugar
|Figure 6 Spiny elm caterpillar|
hackberry (Celtis laevigata). This caterpillar is the larval form of the familiar mourning cloak butterfly. Mourning cloak butterflies spend the winter as adults and are frequently seen out flying on the first sunny days of early spring. The caterpillars are purplish-black with white specks and a row of orange to red spots along the back with branched spines circling the body, and ultimately grow to 2 inches long at maturity. They often feed in large groups. It is common for these caterpillars to defoliate one branch first before moving to the next one. Spiny elm caterpillars prefer to feed on the leaves of elm and willow, but you may also find them on a variety of other hardwood trees including birch, hackberry, sugarberry, linden, cottonwood, and poplar. There are two generations per year.
Management: Although common, these caterpillars usually do not develop in high enough numbers to cause much damage. Numerous parasites and predators, including parasitic wasps and some birds, help keep spiny elm caterpillar populations under control. Bacillus thuringiensis var. kurstaki (Btk) is effective against young larvae, but is not as effective against older larvae.
A couple of pests that were reported earlier this year are producing a second generation. Alder leafminer (Fenusa dohrnii), reported in issue 3 is being found feeding on Ohio buckeye (Aesculus glabra). Balsam twig aphid (Mindarus abietinus), reported in issue 5 is feeding on balsam fir (Abies balsamea).
Pest update: disease
Rust on lawns
|Figure 7 Spores of rust on turf|
Orange spores are coming to a shoe near you, courtesy of rust on turfgrass. We generally don't see this disease until mid-July when the grass slows its growth due to heat and dryness. The slow growth of the turf allows the disease to attack the grass. The heat and dryness came early this year and so did the rust. Turfgrass rust is caused by a Puccinia sp. All turfgrasses can be infected by many different species of rust fungi, and Kentucky bluegrass is one of the more rust-susceptible grass species.
|Figure 8 Rust spores on shoes|
Initial symptoms of rust disease include yellow lesions on grass blades that enlarge over time and rupture to release orange spores (figure 7). When you walk across the lawn, your shoes pick up the orange spores and turn orange (figure 8). The spores are wind-blown and splashed by rain to new infection sites on grass.
Management: There is no permanent shoe damage, and the orange spores can be easily wiped off. Grass rust is usually not severe enough to warrant use of fungicides, and sound management practices will keep this disease in check. Management practices that spur a little growth will minimize rust. These practices include watering and fertilizing with nitrogen. While these practices may apply to a highly managed lawn, they may not be great for the average home lawn. Watering the lawn in summer is not really a priority since the lawn can go dormant and come back when the rain and cooler temperatures return. Fertilizer may be harmful to an unwatered lawn. When the rain returns and the grass grows again, the rust usually diminishes. Some management techniques that apply to any lawn include mowing at the height recommended for the particular turf species and using rust resistant varieties or blends of turfgrass when starting new lawns. For the most part, turfgrass rust is a relatively minor disease that we can live with.
We are seeing the first symptoms of walnut anthracnose. Symptoms are small leaf spots with
|Figure 9 Walnut anthracnose|
pale centers and dark-brown margins (figure 9). The spots are somewhat circular and first appear on the underside of leaves, eventually becoming apparent from both sides. They range in size from pinpoints to about 6 mm (1/4 inch) in diameter. When numerous, they cause leaf yellowing, curling, and margin browning. In addition, sunken necrotic (dead) spots develop on the husks of infected nuts. Infection of immature nuts may result in their premature drop. Occasionally, lesions appear on current year's shoots. Walnut anthracnose may cause premature defoliation and diminish nut quality, but is not considered a major problem in ornamental walnuts.
Management: Gather and destroy fallen leaves to reduce inoculum. Reduce tree stress by watering during periods of drought and through proper fertilization in fall.
|Figure 10 Wuilted branch caused by Botryosphaeria|
We are seeing branch wilting symptoms of Botryosphaeria canker, caused by the fungus Botryosphaeria ribis, on eastern redbud (Cercis canadensis). This common canker disease causes branch wilting and dieback (figure 10). Sunken areas with swollen ridges (cankers) form on infected bark (figure 11). These cankers cut off sap flow (girdle branches) and cause leaves to turn yellow, brown, and then wilt. Branches die beyond the point of girdling. Botryosphaeria cankers are usually cracked, dry, discolored, and covered with small black fruiting bodies that can be seen with a hand lens. The sapwood beneath a canker dies and is discolored brown.
|Figure 11 Botryosphaeria canker on trunk|
The disease is also common on many trees including apple, birch, dogwood, elm, hickory, horsechestnut, linden, oak, and sycamore. Botryosphaeria infects both healthy and stressed trees, but the disease is more severe on plants stressed by drought, heat, freezing, defoliation, and planting outside native ranges.
Botryosphaeria and Verticillium both attack redbud and cause similar wilt symptoms from afar. To differentiate the two, peel back the bark of a wilted branch. Streaked sapwood is a symptom indicative of Verticillium wilt and not the canker. The canker disease will also have sunken cankers on the bark and the black fruiting bodies present.
Management: Prune infected branches during dry weather to keep spores from spreading. Prune at least 6 to 8 inches below affected tissue. To prevent the spread of the disease, clean pruning tools between cuts. Remove diseased branches from the site since the fungus can persist and sporulate in dead plant material. Keep trees healthy by watering during drought periods and mulching properly. Avoid wounding the tree since the fungus can enter through tree wounds.
Good websites: http://www.ag.uiuc.edu/~vista/abstracts/a813.html
Entomosporium leaf spot
We found early symptoms of Entomosporium leaf spot on quince (Cydonia oblonga f.
|Figure 12 Entomosporium leaf spot|
maliformis) caused by the fungus Entomosporium mespili. Leaf spots first appear as minute, circular, red-purple spots on either surface of the leaf (figure 12). When fully developed, the lesions are irregular spots 2-5 mm (1/12 to 1/5 inch) in diameter with ashen gray centers and dark purple borders. Tiny black, blister-like specks (fruiting bodies) form in the center of the lesions. Numerous lesions may coalesce into large blotches on heavily diseased leaves.
Symptoms first appear on new growth on lower branches and gradually spread upward. Infection is mostly limited to the leaf blade, but occasionally spots occur on petioles and tender young shoots. Severe infections can cause premature defoliation. E. mespili also infects other rose family members including serviceberry, apple, crabapple, hawthorn, mountain ash, chokeberry, cotoneaster, and pear.
Management: Avoid summer pruning or frequent pruning or fertilization as this encourages flushes of new growth that are susceptible to attack. Increase air circulation around the tree by avoiding overhead watering and providing enough spacing between plants for good air circulation. Chemical controls are rarely justified except when plants are stressed or recently transplanted, or when repeated defoliations occur. Fungicides can be used preventatively but must be applied on a regular basis throughout the season to be effective. Like many leaf spot diseases, the inoculum overwinters in fallen leaves so rake and discard fallen leaves in the fall.
Good websites: http://www.aces.edu/pubs/docs/A/ANR-0392/ANR-0392.pdf
No mulch volcanoes
We talk a lot about proper mulching and avoiding mulch 'volcanoes'. To address this issue, we are reprinting an article written by Dr. George Ware of The Morton Arboretum several years ago. The article is entitled Keep the Base of the Tree Trunk Dry, and it appeared in The Illinois Arboriculture Newsletter:
"The response to continuous contact with moisture is quite different for trunks and tree roots. Buttress roots of trees in a woodland environment are usually exposed and visibly distinct. In urban situations trunks sometimes appear to emerge from the soil as cylinders, a strong indication of deep planting or perhaps some other aspect of management such as settling root balls in poorly tamped planting-hole bottoms. Widespread prevalence of mounded pikes of mulch around tree trunks prompted this report on situations where trunk-base wetness exists.
A study in Madison, Wisconsin provided a great deal of information and insight on problems of deep planting. Sugar maple was commonly the replacement tree following the loss of American elm to Dutch elm disease in the 1960's and 1970's. A study showed that more than two-thirds of young urban sugar maples in Madison showed decline. There were debilitation symptoms in the crowns but also obvious was deterioration of bark and wood in the root-collar zone. Two kinds of fungi, collar-rot (Phytopthora citricola) and basal canker (Fusarium sp.), were found to be associated with this decline. Collar rot appeared to be the most destructive. Buried buttress roots and emergent cylindrical trunk bases were common. Some upper-level buttress roots were found to be buried 6 to 10 inches. The appearance of the crowns declining trees correlated well with the degree of damage produced by collar rot and basal canker, both strongly associated with deep planting and almost continuously wet bark.
The placement of mounds or cones of mulch around trees may also keep trunk bases nearly continuously moist, a condition that may be conductive to collar rot, basal canker or other fungi. Though properly applied mulch may nurture and regulate favorable conditions that somewhat resemble the forest floor, excessively deep mulch may be detrimental to near-surface roots, creating low oxygen levels and excessive moisture at soil-mulch interface. Avoidance of mulch touching the tree trunk is embodied in the procedure producing what is sometimes known as mulch "donut". The use of tub-ground mulch, ground into fine fragments, produces faster decomposition and a faster blending of organic material with soil, creating a favorable environment for earthworms, which increase superficial soil porosity, a boon to development of fine roots. In forest situations, earthworms are known to accelerate decomposition of organic matter, releasing nutrients too rapidly. In urban situations, additional mulch facilitates a continuing breakdown process. It is likely that prolong bark wetness may also be produced by vegetation closely surrounding the trunk, such as hosta and small plants of buckthorn and honeysuckle.
Rapidly growing young trees in a meadow situation are often enclosed by grass. "Girdling soil" is associated with rapid trunk diameter expansion that compacts and presses soil outward and upward. The trunk may emerge from the grass as a cylinder. Grass and soil around basal bark appear to initiate bark decay, sometimes leaving exposed wood. Partial girdling of the trunk may be associated with wetness of soil and closely enclosing vegetation. Spreading grass roots and rhizomes seem to be a significant part of this problem. Ultimately, expansion of diameters of buttress roots appears to elevate the trunk base.
Construction Site Changes
Grade changes with soil fill are associated with suffocation of near-surface roots, but such fill may also surround the trunk, enclosing basal bark with continuously moist fill material. It is too important to protect from modification, a long existing soil-air interface within the "drip-line" off a tree, and desirably, even a larger area.
Armillaria Root Rot
Armillaria is the moist common root-rotting fungus in northern hardwood forests. It is also common in urban landscapes, orchards, and gardens. Damage is difficult to estimate because Armillaria often follows other malefactors and is often associated with root-infecting fungi and with secondary insect infestations. Thus, "volcano" mulching and deep planting may introduce precursors responsible for stress that lessen resistance to Armillaria. Therefore, keeping the trunk base dry may indirectly reduce activity of Armillaria. Indeed, in regions with hot summers, in some instances, diseased trees appear to have been saved by removal of soil around the root collar and root buttresses."
|Figure 13 'Ann' Magnolia blooming in summer|
We're seeing a few magnolias such as Ann magnolia (Magnolia 'Ann') (figure 13) with flowers on them. Since magnolias are spring-flowering trees, what's going on? Actually, it is not unusual for magnolias to do this. Sometimes a few flowers on magnolias get tricked into blooming at the wrong time. Since only a few flowers on each tree are blooming, the remaining flower buds will remain dormant and should bloom at the normal time next spring.
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
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
. Inquiries or comments about the PHC reports should be directed to Sharon Yiesla at
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