Plant Health Care Report June 8, 2012
Tagged as: poison hemlock, maple petiole borer, pipevine swallowtail, Apple Scab, Columbine leafminer, galls, Guignardia leaf blotch, leafhoppers, Lecanium scale, measles on peony, witches broom of hackberry
June 8, 2012 Issue 2012.8
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?
Northern Catalpa (Catalpa speciosa) (figure 1) is in full bloom.
Accumulated Growing Degree Days (Base 50): 751 (as of June 7)
Accumulated Growing Degree Days (Base 30): 2643 (as of June 7)
- Poison hemlock – danger
|Figure 1 Northern Catalpa (Catalpa speciosa)|
- Columbine leafminer
- More galls
- Witches’ broom on hackberry
- Lecanium scale
- Maple petiole borer
- Pipevine swallowtail
- Apple scab
- Guignardia leaf blotch
- Measles on peony
Degree Days and Weather Information
As of June 7, we are at 751 base-50 growing degree days (GDD), which is 259.5 GDD 50 ahead of 2011 at this time. So far in June it has rained .89 in., which brings us to 10/41 in. for the year (compared to 15.74 last year at this time).
|Location||B50 Growing Degree Days
Through June 7, 2012
|Chicago Botanic Garden**||671.5 (as of 6/4)||1.35 (5/29-6/4)|
|Crystal Lake, IL*||817||--|
|The Morton Arboretum||751||
|Northbrook**||813 (as of 6/6)||.87 (5/30-6/5)|
**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/
Poison hemlock – danger
Figure 2 Poison hemlock (Conium maculatum)
The Plant Clinic has received a number of reports on poison hemlock (Conium maculatum) popping up in yards and along roadsides. University of Illinois is reporting this across the state in greater abundance than in previous years. Poison hemlock is a member of the carrot family (which contains both edible and toxic plants, so beware!!). Most members of this family have the same type of umbrella-shaped flower cluster know as an umbel. So the flower cluster of Queen Anne's lace and the flower cluster of poison hemlock look similar. This can lead to incorrect identification and potential contact with a dangerous plant.
Figure 3 Stem of poison hemlock
Poison hemlock is a large, non-native plant (often 6 feet or more) (figure 2). The smooth stem is stout, has a ridged appearance and is marked with purple spots (figure 3). The stem is hollow. Leaves are laege and very ferny in appearance (figure 4). Poison hemlock is a biennial plant, which means it will form foliage in the first year and flower and set seed in the second year. Plants in their second year are flowering now and have the typical white flower cluster (umbel) of the carrot family. Queen Anne's lace has one red floret in the center of its flower cluster, poison hemlock does not.
|Figure 4 Leaves of poison hemlock
Photo credit: Sharon Yiesla
All parts of the plant are toxic and may lead to death if ingested. The plant's oil may be absorbed through the skin, so long sleeves and gloves will be needed when handling the plant.
Management: Plants can be cut down or dug out. This should be done before the plants go to seed and is most easily done when plants are small. Again cover your skin during this process. Do NOT burn the plants. In spring, smaller, actively growing plants may be treated with an herbicide containing glyphosate.
Good websites: http://hyg.ipm.illinois.edu/article.php?id=380
Pest Update: insects
|Figure 5 Leafhopper nymph|
Several species of leafhoppers are feeding on various woody plants. This week our scouts found nymphs (figure 5) and adults feeding on yellowwood (Cladrastis kentukea), and we have an unconfirmed report of them on red maple (Acer rubrum). This is just the beginning of a long season of leafhopper activity, as there are thousands of species that infest woody and herbaceous plants. They will be active throughout the growing season.
Leafhoppers have piercing/sucking mouthparts and feed on leaf sap, causing yellow-white stippling (figure 6) and leaf curling. The stippling is similar to spider mite damage but more noticeable. Damage on some plants shows up as stunted shoots and distorted leaves, while on other plants appears more like stippling on the leaves. Leafhoppers attack several host trees, with red maples showing the most damage. Feeding on maples produces stunted tree shoots and leaves with brown edges that curl downward. Sometime feeding leads to scorched-looking margins. This is referred to as 'hopper burn'. Leafhoppers can be vectors of several woody plant diseases including elm yellows, aster yellows, and bacterial scorch diseases. Controlling the vector helps to control these diseases.
Most leafhopper species overwinter as eggs in the bark of host plants or among fallen host
|Figure 6 Leafhopper damage on maple|
plant leaves. Eggs hatch in the spring and five nymphal stages are passed through before the adult stage is reached. Adults are generally less than 3 mm long.
Management: Remove and destroy leaf debris in the fall. Keep trees healthy and vigorous by keeping them mulched and watering during drought periods to lower tree stress. In severe infestations, insecticides can be used and should be applied when hoppers are visible on the foliage but before leaves begin to curl.
Good websites: http://www.inhs.uiuc.edu/~dietrich/Leafhome.html
|Figure 7 Columbine leafminer damage|
We are seeing mines in columbine (Aquilegia species and hybrids) leaves created by the columbine leaf miner (Phytomyza aquilegivora). Damage is serpentine or snake-like white mines (figure7) in leaves, usually after the plants flower. The adults are small flies that deposit eggs on the underside of leaves. After hatching, the maggots burrow into the leaves, creating the mines.
Management: Removing and destroying infested leaves early in the season will help reduce later infestations, because there are several generations.
Good web site: http://www.urbanext.uiuc.edu/focus/per_aquilegia.html
We have been reporting a variety of galls this year, and we continue to see more of them on
|Figure 8 Jumping oak gall|
a variety of plants. The oaks and hickories are getting their fair share of them now. The majority of galls are harmless and require no control measures. We present them here so you start to recognize them and know that you are basically looking at a cosmetic problem.
This week our scouts have found jumping oak gall (figure 8) on bur oak (Quercus macrocarpa). Jumping oak gall is caused by a gall wasp, Neuroterus saltatorius. Later in the season, the galls will fall to the ground, and the activity of the larvae inside will cause the galls to jump around. Great entertainment for all!
A couple of galls have been found on hickory (Carya ovata). One of the phylloxeran insects
|Figure 9 Phylloxera gall on hickory|
(there are at least 29 that attack hickory trees) has caused galls (figure 9) on the leaves of hickory. The galls are round, about 1/3 of an inch in diameter, hollow, and brown. The aphid-like insects overwinter as eggs in bark cracks and crevices and in old galls. When the tiny nymphs hatch in spring, they crawl into expanding buds and feed on bud tissue. The plant responds to the insect feeding by growing plant tissue around the insect. When the nymphs mature, they lay eggs inside the galls. More nymphs hatch, filling each gall with many insects. As the galls dry out, they darken and split open, releasing another generation of phylloxerans that emerge from the gall to lay eggs and continue the cycle.
We are also seeing an interesting gall caused by a hickory gall midge (Caryomyia species)
|Figure 10 Hickory gall caused by gall midge|
(figure 10). There are a number of galls produced by different species of hickory gall midge. The one we are seeing looks like a little volcano!
Witches' broom on hackberry
|Figure 11 Witches' broom on hackberry|
Witches' brooms (figure 11) were found on hackberry (Celtis occidentalis). This is a common disfiguring disease of hackberry caused by two organisms working together: a powdery mildew fungus and an eriophyid mite. In fact, some people think the witches' brooms are a characteristic of hackberry because it is so common. Each broom is a compact cluster of twigs caused by the repeated killing of twigs. They actually do look like an old fashioned broom stuck up in the tree.
Management: Pruning out the brooms is of limited value unless done before many brooms have developed. The brooms don't seem to hurt the tree but are unsightly. Or you could think of the brooms as winter interest. Chinese hackberry (Celtis sinensis) and Jesso hackberry (Celtis jessoensis) are resistant
Good website: http://www.ipm.uiuc.edu/diseases/series600/rpd662/
Lecanium scale (Lecanium sp.) adults (figure 12) and eggs are present on bald cypress
|Figure 12 Lecanium scale adults
Photo credit: Donna Danielson
(Taxodium distichum). Lecanium scales are common pests in North America and include about a dozen species that attack a wide variety of shade and fruit trees and ornamental trees and shrubs. They vary in size, color, and shape, depending somewhat on the host plant they attack. The adult scale length varies from 1/8 to 1/2 inch.
Most species of lecanium scales have similar life cycles. Eggs are laid beneath the females beginning in late spring to early summer. After egg laying, the female's body dries, becomes brittle, and turns brown. This "scale" covering provides protection to the developing eggs. Crawlers are expected to emerge at 900-1200 growing degree days (base 50), and we may reach that range this weekend if we get the heat that is predicted. After the crawlers hatch, they migrate to leaves to feed on plant sap. Infested plant leaves are often covered with sooty mold, a black fungus that grows on the honeydew excreted by the scales as they feed. In severe infestations, lecanium scales will cause some twig dieback and premature leaf drop.
Management: Hand removal is possible on small trees/saplings/plants. Heavily infested branches may be pruned out to reduce infestations. A summer oil or insecticidal soap can be sprayed when the crawlers are active.
Maple petiole borer
|Figure 13 Leaves that have fallen due to petiole borer|
We have seen maple petiole borers (Caulocampus acericaulis) on sugar maple (Acer saccharum). This time of year, when a sugar maple suddenly drops a lot of leaves (figure 13), it may be due to injury to the petioles by tiny wasps. The petioles on the fallen leaves have a darkened area at the base, but the fallen leaves are still green. In mid-spring adults lay eggs near the base of maple petioles. The resulting borer larvae hatch and bore the inside of the petioles. This weakens the stems and when the wind blows, the leaves fall off with the larvae usually left behind in the part of the petioles that remains on the tree. Eventually the rest of the petiole falls off the tree with the larvae in it. The larvae leaves the petiole stem and tunnels into the soil where it pupates until the following spring.
Management: None necessary. Leaf drop is rarely more than 20 percent of the canopy. A healthy tree can lose a significant number of leaves without harm.
Good web site: http://www.ca.uky.edu/entomology/entfacts/ef405.asp
Another one of our favorite insects has just been discovered. Pipevine swallowtail (Battus
|Figure 14 Larva of pipevine swallowtail|
philenor) larvae (figure 14) have been found feeding on the leaves of Manchurian pipevine (Aristolochia manshuriensis). Pipevine swallowtail larvae feed only on plants in the pipevine family.
These fascinating insects grow to two inches long, are black, and have dark outgrowths protruding from each segment. Each larva has long filaments coming out of its first segment which it uses to explore its path. It also has four longitudinal rows of bright orange projections along its body. The larvae are toxic and distasteful to animals. So you don't consider the guy pictured on the right to be a beautiful creature? Just wait a bit and you'll soon see a gorgeous black butterfly with blue-green metallic hind wings and a wingspan of about four inches.
Pest update: diseases
|Figure 15 Early symptoms of apple scab|
We are finally seeing symptoms of apple scab (figure 15) on Japanese flowering crabapple (Malus floribunda). Symptoms are showing up a bit later than usually due to our dry weather and early emergence of leaves. We are hopeful that infections will be less severe this year and possibly we will see less defoliation than usual.
The lesions look like velvety, olive-green leaf spots and will continue to develop into larger, irregular dark spots. Sunken spots may also appear later on fruits. Often lesions develop along the mid-veins of the leaves. Infected leaves eventually turn yellow and drop prematurely on susceptible hosts. The scab fungus (Venturia inaequalis) overwinters on fallen leaves and on lesions on twigs. Sunken spots may appear later on fruits, and susceptible crabapples can be defoliated in severe disease years. Scab severity is a product of hours of leaf wetness and temperature and host susceptibility. Scab severity is much less during dry springs.
Management: The best way to avoid apple scab is to plant resistant varieties. Resistance just means that in the typical year, a resistant plant won't suffer as much from the disease as a susceptible plant. However, it may exhibit symptoms in "bad" scab years. When shopping for new crabapples, ask your local nursery which scab-resistant varieties they stock.
Caring for your trees, such as watering during summer droughts, may moderate effects of defoliation and reduced photosynthesis in affected trees. As the fungus overwinters on fallen leaves and blighted twigs, collecting and destroying these tissues may help reduce the source of inoculum next year.
Guignardia leaf blotch
The initial stages of Guignardia leaf blotch (Guignardia aesculi) (figure 16) were found on
|Figure 16 Guignardia leaf bloth on Aesculus|
Ohio buckeye (Aesculus glabra). Right now we're seeing reddish brown to brown lesions with a yellow border that blends into the normal green leaf tissue. Upon closer inspection with a hand lens we have also seen the dark pycnidia (fungal fruiting bodies), which look like black pepper on the lesions on the upper surface of the leaf. The blotches will enlarge, coalesce, and may cover the entire leaf by the end of summer. Premature defoliation may follow on the most susceptible hosts. This disease eventually decreases a tree's ability to photosynthesize, but generally the disease doesn't become severe until the tree's annual growth has slowed or is complete. Therefore it does not do much harm to trees in the landscape, but it does make them unsightly.
In the last week, we have also had samples of Boston ivy (Parthenocissus tricuspidata) come
|Figure 17 Guignardia leafspot on Boston ivy (juvenile leaf)|
in to the Plant Clinic with a leafspot (figure 17) that is caused by Guignardia bidwellii. The spot is relatively round with a dark margin. The dark fruiting bodies can also be found in this leaf spot. This disease also affects Virginia creeper (Parthenocissus quinquefolia).
Management: Removing fallen leaves may help to destroy the overwintering inoculum. On Boston ivy and Virginia creeper, removing badly infected leaves may help. Pruning trees to improve air flow may also help, since the spores are spread and germinate under moist to wet conditions.
Measles on peony
|Figure 18 Measles on peony|
Cladosporium leaf blotch has been found on a few of our peonies. This disease is also known as measles. Symptoms are large, circular, dark purple-brown spots (figure 18) on the upper surface of the leaves and corresponding light brown spots on the lower surface of the leaves.
Management: Sanitation is important. Dispose of diseased plant parts at the end of the growing season to reduce inoculum. Avoid wetting the foliage during watering. Fungicides are available, but must be used early in the season as new foliage is emerging
Good website: http://www.ag.uiuc.edu/~vista/pdf_pubs/631.pdf
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.
- Plant Health Care Report July 1, 2011 (Issue 2011.11) 23%