Plant Health Care Report

Scouting Report of The Morton Arboretum

July 8 – July 14, 2006 Issue 2006.13

Quick View

What’s in Bloom at the Arboretum?

We have come to the end of our phenological indicator plant list for the season. A weekly picture of perennials or annuals that are in bloom will be provided even though predictions of pests and diseases have not been calibrated to these plants.

Balloon flower

Growing Degree Days (base 50): 1,333

Insects Diseases

• Apple-and-thorn Skeletonizer on Lancelot® • Birch Anthracnose on Forrest’s Birch Crabapple • Melampsora Rust on Peach-leaved Willow • Bronze Birch Borer on Asian White Birch • Oak Wilt on Red Oak • Gypsy Moth Update • Mossy Rose Gall on Sweetbrier Rose

Degree Days and Weather Information

As of July 11, 2006 we are 3 growing degree days (base 50) (GDD) behind the historical average (1937–2005) and 135 GDD behind last year. Precipitation at the Arboretum, as well as some other locations in the area, has been an inch or more below our optimal weekly rainfall of one inch these past two weeks. Temperatures have been up to 10 degrees below our average which has helped soil moisture retention in some areas. Local forecasters are predicting temperatures for next week to be up to several degrees above our normal high of 87° F (31° C) and normal low of 63° F (17° C). At present, only isolated thunderstorms are expected next week; therefore, supplemental irrigation may be required. Check the soil moisture levels around trees and shrubs. The soil should be moist to a depth of 6 to 8 inches.

Precipitation Growing Degree July 5–July 11 Location* Days through July 11 mm inches The Morton Arboretum (Lisle, IL) 1,333 13 0.5 Chicago Botanic Garden (Glencoe, IL) 1,170 3 0.1 Chicago O’Hare Airport 1,347 8 0.3 Regent’s Park (Rockford, IL) 1,265 0 0 *Thank you to Derek Settle, Chicago District Golf Association; Mike Brouillard, Moore Landscapes, Inc.; Tom Tiddens and Chris Yooning, Chicago Botanic Garden; and Bill Kramer, University of Illinois Extension for supplying us with this information.

This Week’s Sightings

Bronze Birch Borer

We are finding D-shaped holes in Asian white birch (Betula platyphylla). The 3 mm (1/8 inch) holes are created by bronze birch borer (Agrilus anxius) adults when they emerge from birch trees. The adults are slender olive-bronze beetles somewhat flattened on top and about 12 mm (1/2 inch) long. Larvae are creamy white, segmented, legless grubs. They reach about 25 mm (1 inch) long and 3 mm (1/8 inch) wide at maturity.

Bronze birch borer ridges on bark from larva tunneling This insect overwinters in the larval stage in tunnels beneath the bark. Adults emerge in late May to early June and continue into August leaving characteristic D-shaped exit holes in the bark. About one week after emergence females begin laying eggs in crevices and cracks in the bark. The eggs hatch in 10 to 14 days and the larvae immediately bore into the cambium layer (and occasionally into the sapwood), where they feed and tunnel in a zigzag manner. Larva tunneling severely injures the tree’s vascular system disrupting the flow of water and nutrients. Girdling of the cambium of a branch or trunk by tunneling larvae results in sudden wilting and death of the branch or entire tree.

Early symptoms of infestation are sparse chlorotic foliage in the upper crown followed by leaf wilting and branch dieback. Ridges and bumps caused by tunneling can often be seen on branches.

The bronze borer is considered a secondary pest that attacks stressed trees. (Larvae have been reported to be unable to survive in healthy trees.) Our drought last summer caused significant stress to birches thus increasing their susceptibility to this insect. All birches can be attacked but paper, white, and water birch are among the preferred species.

Control: The most important factor in managing the bronze birch borer is to maintain tree vigor through proper fertilization, watering, and controlling aphids and leafminers. Do not prune susceptible birches during the adult flight period from late May through August since this may attract more egg-laying females. Prune off dead and dying branches in fall and winter. Systemic insecticides provide protection and should be applied in early spring. Refer to the 2005 Commercial Landscape & Turfgrass Pest Management Handbook (CPM) for commercial applicators and the Home, Yard & Garden Pest Guide (HYG) for homeowners for specific chemical recommendations.

In the future, plant resistant birches and site them properly. Birches should be planted in shady, cool, and moist wooded areas, otherwise they are more likely to become stressed, lose vigor, and succumb to attack. River, monarch, and heritage birch have shown resistance to this borer.

Good websites: http://ohioline.osu.edu/hyg-fact/2000/2018.html http://www.extension.umn.edu/distribution/horticulture/DG1417.html

Apple-and-thorn Skeletonizer

We are finding apple-and-thorn skeletonizer (Choreutis pariana) larvae on Lancelot® crabapple (Malus ‘Lanzam’). This is a pest of apple, birch, crabapple, cherry, hawthorn, willow, and mountain-ash. Larvae skeletonize and roll leaves causing leaf browning and premature drop. Larvae are pale yellow and develop dark tubercles (bumps) along their body as they mature. Fully grown larvae are approximately 12 mm (1/2 inch) long.

The apple-and-thorn skeletonizer overwinters as an adult. Eggs are laid in late spring to early summer on the undersurface of leaves near the midrib. After hatching, young larvae feed on the underside of leaves. Later they move to the upper leaf surface, tie the edges together with silk, and feed there until they pupate. Apple-and-thorn skeletonizer young larva (5 mm x 0.5 mm), frass, and feeding damage Control: Apple-and-thorn skeletonizer is usually kept in check by natural enemies. Handpick and destroy caterpillars when practical. Caterpillars inside rolled leaves can be squished and heavily infested twigs pruned.

Mossy Rose Gall

Mossy rose galls are developing on sweetbrier rose (Rosa eglanteria). The galls are caused by Diplolepis rosae, a cyanid gall wasp. The wasps lay eggs in one- year-old rose twigs, and the development of galls is stimulated by the presence of newly hatched larvae.

Galls are spherical hairy masses 25 to 50 mm ( 1 to 2 inches) in diameter. They are initially light green with pink and light green hairs, but turn brown with age. Galls encase the cyanid gall wasp larvae until adults emerge the following spring.

Control: The most effective control is to prune out galls before the wasps have matured and emerged from the galls. Adults emerge from the old galls in spring; Mossy rose gall therefore, prune out galls in the fall or winter cutting below the gall and above a bud.

Good website: http://www.extension.iastate.edu/Publications/IC417.pdf

Birch Anthracnose

Birch anthracnose has been found on Forrest’s birch (Betula forrestii). Symptoms are light to dark brown leaf spots or blotches with indefinite margins surrounded by yellow tissue. Black fruiting bodies (pycnidia) are embedded within the brown blotches. Affected leaves often drop prematurely while part of the blade is still green. This common fungal disease is most prominent on lower branches and can progress up the tree. Gray, paper, and river birches are also attacked. Cool, rainy summer weather promotes this and many other anthracnose diseases. Birch anthracnose does not cause serious harm to the tree.

Birch anthracnose on paper birch Control: Remove and destroy fallen leaves to reduce inoculum.

Good websites: http://www.ag.uiuc.edu/~vista/abstracts/a621.html http://www.mortonarb.org/plantinfo/plantclinic/disease_anthracnose.pdf

Melampsora Rust

We are finding Melampsora rust, caused by the fungus Melampsora sp., on peach-leaved willow (Salix amygdaloides). Small yellow spots have developed on upper leaf surfaces with corresponding small yellow-orange pustules on lower leaf surfaces. In late summer the pustules turn dark brown to black and become crust-like.

The fungus overwinters in fallen leaves. In spring spores are blown by air currents to alternate hosts (e.g., larch, Douglas-fir, and balsam fir) and infect expanding needles during wet periods. The needles of alternate hosts develop yellow spots on their upper surfaces. During the summer aeciospores are produced on the conifer needles and are dispersed by wind to willows where they cause the urediniospores we are seeing now. Melampsora rust on Populus sp. Severe infections may cause willow leaves to become distorted, wither, and drop prematurely. Repeated infections may slow the tree growth, but this slow growth is often masked by the normally rapid growth of willows. Usually melampsora rust is not a problem in landscape willows.

Control: Rake and destroy fallen leaves in the fall to reduce inoculum.

Good website: http://www.ipm.uiuc.edu/diseases/series600/rpd605/

What’s Our Plant Clinic Seeing?

Gypsy Moth Adult Emergence

Our Plant Clinic has received reports of adult gypsy moth emergence in Lisle. Adult males are brown with black markings and have a wingspan of 37 mm (1-1/2 inches). Female moths are white to cream-colored with black markings on their wings and have a wingspan of about 50 mm (2 inches). Although winged, the females are too heavy to take flight.

Females lay egg masses in July and August on branches and trunks of trees. They are also found in sheltered locations such as under loose bark, in woodpiles, on outdoor furniture, or the undersides of vehicles. The egg masses are buff colored, covered with hairs, and about 37 mm (1-1/2 inches) long.

Adult female gypsy moth

Adult male gypsy moth

Gypsy moth egg mass

See PHC 2006.03 (http://www.mortonarboretumphc.org/PHC%20report%20pdfs/050506%20Issue%203.pdf) for further information on this insect.

IF YOU SEE A GYPSY MOTH IN ANY OF ITS STAGES CALL TOLL FREE: 1-866-296-MOTH(6684)

More information can also be obtained by contacting: Illinois Department of Agriculture Des Plaines Office 9511 Harrison Street, Room A-169 Des Plaines, Illinois 60016 847-294-4343 TDD: 217-524-6858

Good websites: http://www.aphis.usda.gov/lpa/pubs/fsheet_faq_notice/fs_phgmprogress.html http://www.na.fs.fed.us/spfo/pubs/fidls/gypsymoth/gypsy.htm http://www.mortonarb.org/plantinfo/plantclinic/pests_gypsymoth.pdf

Sightings Elsewhere

Oak Wilt

Scott Haulton of the Forest Preserve District of Will County has reported finding oak wilt on red oaks (Quercus spp.) in the Will County forest preserves. Symptoms on red oaks include leaf wilting, bronzing, and premature leaf drop. Both the red and white oak groups are susceptible to oak wilt; however, the former is most susceptible. Symptoms between the two groups are different. In red oaks, death is rapid with wilt symptoms starting at the top of the tree and progressing inward and downward on the lateral branches within a few weeks. Leaves wilt from the leaf tip and margins to the bases and typically turn an off-green before showing bronze coloration. Near complete leaf drop usually occurs by the middle of

summer making infected trees stand out. Fallen leaves are often green at the base. There can be profuse suckering at the base of the tree. When an infected branch is cut in cross section, or bark peeled back, very light brown streaking or speckling can sometimes be seen in the outer ring of sapwood. Symptoms of the disease on white oaks are similar, but infected white oaks die slowly, a branch at a time, over a period of one to many years. Leaf discoloration of affected white oaks usually resembles autumn colors, and brown streaking in the outer growth ring of sapwood is often apparent.

The causal fungus, Ceratocystis fagacearum, invades the xylem and Leaf discoloration (left) induces the tree to clog its own vessels. Water flow is stopped and cells begin dying. Oak wilt can spread from infected trees to healthy trees through root grafts and by insects, especially picnic beetles, that carry spores of the fungus from one tree to another as they feed and visit wounds.

Control: Monitoring and rapid removal (sanitation) is key to controlling oak wilt. Remove trees as soon as you confirm the disease. Vector insects feed on fresh pruning wounds; therefore, oaks should not be pruned during the Sapwood streaking growing season when the nitidulid beetles are active. This disease can spread to other healthy oaks about 25 to 50 feet away (depending on tree size) via root grafts. To help halt the spread, dig a trench to a depth of approximately three feet between infected and healthy trees to break root grafting. Some systemic fungicides are labeled for controlling this disease. Refer to the CPM or the HYG for chemical recommendations.

Good websites: http://www.mortonarb.org/plantinfo/plantclinic/diseases_oakwilt.pdf http://na.fs.fed.us/spfo/pubs/howtos/ht_oaklab/toc.htm http://www.ag.uiuc.edu/~vista/abstracts/a618.html

What to Look for Next Week

Next week we will be looking for bald-cypress rust mites, leaf blotch of American linden, lecanium scale, Septoria leaf spot, and yellow-necked caterpillars.

In all things of nature there is something of the marvelous. —Aristotle

The Plant Health Care Report is prepared by Cindy Terrell of The Morton Arboretum and edited by Fredric Miller, Ph.D., Research Associate, Entomology at The Morton Arboretum. 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.

The Plant Health Care program is partially funded by grants from the Illinois Arborist Association (http://www.illinoisarborist.org/) and the Illinois Landscape Contractors Association (http://www.ilca.net/). 6

The 2005 Commercial Landscape & Turfgrass Pest Management Handbook (CPM), for commercial applicators, and the Home, Yard & Garden Pest Guide (HYG) for homeowners from the University of Illinois, are available by calling (800- 345-6087). You may also purchase them online at: https://webstore.aces.uiuc.edu/shopsite/browsecommhort.html. One further source is your local county extension office.

This report is available on-line at The Morton Arboretum Plant Health Care website: http://www.mortonarboretumphc.org/.

Please direct inquiries or comments about the PHC reports to Cindy Terrell (mailto:[email protected]).

Conversion Tables

Temperature Conversion

Fahrenheit 0 10 20 30 32 40 50 60 70 80 90 100

Celsius -18 -12 -7 -1 0 4 10 16 21 27 32 38