for Arborists, Landscape Managers & Nursery Managers

Commercial Horticulture April 20, 2012Coordinator Weekly IPM report: Stanton Gill, Extension Specialist, IPM for Nursery, Greenhouse and Managed Landscapes, sgill@umd.edu. 301-596-9413 (office) or 410-868-9400 (cell)

Regular Contributors: Pest and Beneficial Insect Information: Stanton Gill and Paula Shrewsbury (Extension Specialists) and Brian Clark (Extension Educator, Prince George’s County)Disease Information: Karen Rane (Plant Pathologist) and David Clement (Extension Specialist)Weed of the Week: Chuck Schuster (Extension Educator, Montgomery County)Cultural Information: Ginny Rosenkranz (Extension Educator, Wicomico/Worcester/Somerset Counties)Fertility Management: Andrew Ristvey (Regional Specialist, Wye Research & Education Center)Design, Layout and Editing: Suzanne Klick (Technician, CMREC)

In This Issue...

If you work for a commercial horticultural business in the area, you can report insect, disease, weed or cultural

plant problems found in the landscape or nursery to

sklick@umd.edu

TPM/IPM Weekly Report

- Season update- Locust leafminer and emerald ash borer - Inkberry leafminer- European pine sawfly- Wool sower gall- Brown marmorated stink bugs- Photinia leaf spot- Insects on boxwood- Azalea lace bugs- Insect traps- Scale reports- Pearleaf blister mite- Gymnosporangium rusts- Slugs- Rose aphids

Beneficial of the WeekWeed of the WeekPlant of the WeekPhenologyDegree DaysConferences

Integrated Pest Management for

Commercial Horticulture

www.ipmnet.umd.edu

How Far Are We Ahead In The Season?We continue to be about 3 weeks ahead in the season when comparing bloom time of plants and degree days. I spoke with University Extension friends from the mid-West and the far West at a training session at the University of Delaware last week. The mid-West is in the same boat as us with the very early season. Unfortunately they had several cold snaps in the last 2 weeks and it looks like the cherry crop in Michigan was severely damaged. One Extension friend was from Oregon and he is reporting a cooler than normal spring and they are actually about 3 weeks behind their normal plant development and insect activity times. They are also getting plenty of water in the far West this spring.

This brings up an interesting point the drought this spring is causing plants to look wilted and stressed. I visited several sites last week and saw trees that had been transplant 4 weeks earlier and they were under severe stress. It is supposed to ran this weekend and let’s hope we start to get some little more rain this spring or we will feel the impact in plant loss of newly transplanted trees and shrubs.

The NOAA long-term (summer) forecast is projecting above-average temperature and below-average precipitation for mid-Atlantic regions. The rain next week will help but we may be in for a dry summer – so plan to provide lots of watering to newly transplanted trees and shrubs.

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Inkberry LeafminerInkberry holly has been used in many commercial planting sites as a hedge plant. The inkberry leafminer has increased as a problem along with the increased use of this plant. The inkberry leafminer adults just emerged in the areas of Olney and Brookeville on April 14. Control: This leafminer can be controlled by soil applications of dinotefuran (Safari, Transtect) or imidacloprid (Merit, Mallet).

Locust leafminer adult

Wool sower gallPhoto: Ginny Rsoenrkanz

European Pine Sawfly (Neodiprion sertifer)The European pine sawfly hatched last weekend in the Gaithersburg area. Look for the larvae on mugo, Scotch, red, white, and jack pines. The sawfly will feed for the next 6 weeks on pine foliage. The eggs were embedded in the pine needles. The larvae tend to feed together (gregariously) so they should be easy to spot.Control: Acelpryn, Acephate or bifenthrin are a few materials that will control the larvae of pine sawfly.

European pine sawfly larvaPhoto: Steven Katovich, USDA Forest Service, Bugwood.org

Wool Sower Galls Ginny Rosenkranz sent in a photo of wool sower gall on water oak (Quercus nigra). The wool sower gall is commonly reported each year and is caused by the tiny cynipid wasp, Callirhytis seminator. This gall is specific to oaks and is only found in the spring. The galls drop from the tree after the adult wasp emerges. They are seldom abundant enough to cause significant damage to the oaks. Control is not necessary.

Black Locust Trees, Locust Leafminer and Emerald Ash BorerPaula Shrewsbury is reporting that black locust is now in bloom in College Park which means we should be expecting / monitoring for emerald ash borer adult activity.

We are also receiving reports of locust leafminer adult activity. The adults overwintered in bark crevices or leaf litter and have started to feed on recently emerged black locust leaves. Look for skeletonization and shothole damage on the foliage which is caused by the feeding of the adults. Later in the season is when the more significant damage will be evident by the feeding of the larvae.Control: Not necessary. Both the leafminer and black locust are natives and the trees manage to recover from the damage year after year.

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Brown marmorated stink bugs hiding under tubing (above) and in tree crevice (right)

Brown Marmorated Stink BugsThe warm weather of Sunday, April 15, caused stink bugs to become very active and start buzzing around inside your customers’ houses. They are very attracted to fluorescent lights, especially the light spectrum slightly below the blue spectrum, at this time of year. Cool fluorescent bulbs tend to be plentiful in this light spectrum. I (Stanton) am starting to pick them up in the Westminster area in my outdoor black light traps. I have not found feeding on any of the early forming fruit, but they are being found flying around the orchard. On Thursday, I was visiting a nursery and saw brown marmorated stink bugs hiding on various parts of yellowwood and zelkova. They were not feeding but were finding places to hide during this brief cool period.

Insects on Boxwood Paula Shrewsbury reported that boxwood leafminers are active on boxwood in College Park this week. We are also seeing adults flying around boxwood here at the research center and there are several clusters of adults that have been caught in spider webs. Paula noted that boxwood spider mites are active in College Park as well.

Photinia leaf spotPhoto: Steve Cohan, UMD

Photinia Leaf SpotSteve Sullivan, The Brickman Group, found photinia leaf spot last week on photinia on campus in College Park. He noted that it has not been good weather (until this week’s rain) for it as of yet, but there was still some fungal spots on new growth. The spots are circular, with a brown center and bright red margin. The spots show up on new growth in mid-May and later, but infection occurs earlier. The fungus that causes this troublesome disease (Entomosporium maculatum) over-winters on spotted leaves on the plant and on the ground. Under wet conditions, the new growth can be infected by spores washed or splashed onto them.Management and Control: Plant photinia in a sunny spot that has good air circulation. During the growing season, and especially for fall cleanup, use a leaf blower to blow out the spotted leaves. They may be composted. Chemical control can be used to prevent infection on new growth if the disease has been severe, resulting in heavy leaf blight and drop. Many fungicides are registered including: propiconizole (BannerMaxx); and Triadimefon (Bayleton, Strike); and thiophanate-methyl (Cleary’s 3336); and Heritage and Compass and many others.

Boxwood leafminer adult (left) and many leafminer adults caught in spider web (right)

Stink Bug

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Cottony camellia scale on Foster hollyPhoto: Dave Freeman, Oaktree Property Care

Azalea Lace BugsGinny Rosenkranz found azalea lace bugs active in Salisbury on April 17. High populations of azalea lace bugs develop when plants are planted in sunny locations. Look for white stippling damage on the top side of the foliage and lace bugs and black fecal spots on the underside of the foliage. Research by Paula Shrewsbury and her graduate students showed that spiders are one of the major predators of lace bugs. There are two to three generations per year in Maryland. Control: Planting azaleas in shady locations helps keep lace bug numbers low. Control options include imidacloprid (Merit), thiamethoxam (Flagship) and dinotefuran (Safari, Transtect).

Reports of Scale

European Elm Scale: Marie Rojas, IPM Scout, is reporting European elm scale on Ulmus p. ‘Dynasty’ ‘Patriot’ and ‘Allee’ in Laytonsville and Dave Freeman, Oaktree Property Care, is finding them on elms in Springfield, Virginia. No crawlers were reported so far, but they usually go to crawler in early May so they should be active soon in the area.

Cottony Camellia Scale: Dave Freeman is finding them on Foster hollies and burford hollies in Northern Virginia. He turned some over and eggs are present, but no crawlers yet.

Calico Scale: We have received samples of female calico scale that are swelling up now. So far, no reports of crawlers, but it is getting close. Additional Scale: Marie Rojas is finding white prunicola scale on Prunus x yedoensis, oystershell scale on Fraxinus p. ‘Patmore’, European fruit lecanium scale on Carpinus b. ‘Fastigiata’ and pretty high numbers of Japanese maple scale on in a landscape on Acer palmatum var. dissectum and ‘Thundercloud’ plums in Laytonsville.

Calico scale photographed this week that is close to crawler stage

Walnut Tree Borer and Ambrosia Beetle Traps: ReportTony Murdock, Fine Pruning, sent in samples from the two traps he is monitoring in Frederick County. There were no ambrosia beetles or walnut twig beetles in these samples this week.

Damage from azalea lace bugs

We are tracking crawler activity so please let us know if you see any scale in the crawler stage. You can also send us samples and we can check for the stage of insect development.

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Gymnosporangium RustsSteve Black, is reporting heavy sporulation of cedar apple rust on Eastern red cedars (Juniperus virginiana) in a landscape in North Potomac. The rain this week provided good conditions for the quick development of this disease. The gymnosporangium rusts require two kinds of plants to complete their life cycle. They overwinter on junipers such as the Easter red cedar as leaf galls or shoot cankers. In cool, wet periods in the spring these galls produce orange gelatinous tendrils upon which the teliospores are found. The teliospores germinate to produce colorless basidiospores. The basidiospores are carried on air currents to infect the pomaceous hosts (apple, Amelanchier, some pears).

• Cedar-apple rust is caused by the fungus: Gymnosporangium juniperi-virginiana. The fungus alternates between many species and varieties of cedar, (Juniperus species) and many pomaceous plants such as apple, pear and hawthorn. Leaf spots are produced on the pomaceous plants. • Cedar-hawthorn rust is caused by the fungus: Gymnosporangium globosum. Small galls are seen on the junipers, and leaf spots are seen on the pomaceous plants.• Cedar-quince rust is caused by the fungus: Gymnosporangium clavipes. Shoot cankers are seen on the juniper and fruit and twigs are infected on the apples and hawthorns. This is considered the most destructive of the gymnosporangium rusts because of the damage to twigs and fruit.

Control: Timing is critical for good control on the pomaceous hosts (apple, hawthorn, etc). The sprays have to be applied when spores are being shed from the junipers, usually starting in mid-March. No chemical control is usually advised to prevent infection of the junipers. Infection of the junipers is happening all summer and into the fall from spores produced on the apples which would require many sprays all season. The period during which the pomaceous plants are infected is short (March through May). Spray susceptible crabapples, apples, quince and hawthorn with a labeled fungicide.

Pearleaf Blister MiteMarie Rojas reported pearleaf blister mite on Pyrus c. ‘Aristocrat’ this week in Laytonsville. Pear leaf blister mite is an eriophyid mite that was first found in the United States in 1902. Pearleaf blister mite females overwinter under bud scales and become active in the early spring. If thorough sprays are not made before bloom then pear blister mite populations can increase and become a problem. In the spring, the mites migrate to the new foliage and start feeding which causes the gall which looks like a “blister”. These mites reproduce throughout the season. Look for brownish blisters on the undersides of pear and apple leaves. The pimple-like blisters start greenish and become red before finally turning brown on pears. The blisters on apples start yellow and never become as red as the ones found on pears. When massed together, these blisters can cover large areas of the undersides of leaves. Look at the undersides of leaves for the blister-like galls in the spring. Control: Nothing at this time of the year. If necessary, overwintering females can be controlled with applications of sulfur applied just after leaf drop in October.

Blistering on underside of foliage

Heavy sporulation starting on Eastern red cedarPhotos: Steve Black

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Flower flies feed on nectar when they are adults. These true flies mimic bees, but note only one pair of wings are present. Photo: M. J. Raupp, UMD

Flower fly larvae are voracious predators of aphids. Also note the aphid mummy (parasitized aphid) at the top of the image. Photo: P. Shrewsbury, UMD

Weed of the Week, Chuck SchusterThis week, I have received many calls about Japanese stiltgrass, Microstegium vimineum. This weed is a native of Asia, and first appeared in the U.S. in 1919 and spread rapidly throughout the eastern U.S. It is a shade tolerant, summer annual, and is most often found in moist, shady environments. Habitats include forests, turf, ornamental beds, ditches and damp fields. It will thrive in warmer, dry weather such as we have been experiencing as some of our desired cool season turf growth slows down due to are abnormal warm and dry spring. Japanese stiltgrass has a fibrous root system, with stems that are erect or reclining and it will root at stem nodes. Its leaves are up to four (4) inches in overall length and one half (.5) inches in width and have a white mid vein which divides the leaf into unequal halves. The seed head has 1 to 6 terminal spike branches. A prolific seed

Beneficial of the Week, Paula ShrewsburyRoses are eaten by aphids, aphids are eaten by flower flies: a small part of the circle of life

For the past few weeks I have been watching a few different beds planted with roses. The rose aphids on these roses have been quite happy… sucking sweet sap from the buds and building up their populations to pretty high densities. Many of you have likely noticed the large number of green colored aphids, and abundant white shed skins on the flower buds of roses. Well, the happy aphid story is changing this week to the story of the massacre of the aphids. In response to the building densities of aphids, many parasitoids and predators move on to the roses and begin to feast on the aphids. There is a suite of natural enemies that are very efficient at finding populations of aphids and knocking back their numbers to near zero. One example of this is the flower flies, also known as syrphid or hover flies. Flower fly adults, although they are true flies, are bee mimics and feed on the nectar and pollen of flowers. They cue in on branches infested with aphids and lay small white eggs individually on the leaves or buds. Once the eggs hatch the maggot-like larvae voraciously search for and consume aphids. Given a chance, flower flies along with other natural enemies, including lady beetles, parasitic wasps, fly midge larvae, will usually provide biological control of aphids. Once the aphid food is gone the natural enemies should move on to other herbivores in your landscapes and nurseries.

Rose AphidsPaula Shrewsbury and Brian Clark, UME, reported rose aphids on roses in Clinton and College Park. Paula was seeing the aphids and their complex of natural enemies for the last 2 to 3 weeks.

SlugsBrian Clark, UME-Prince George’s County, reported finding slugs on cannas this week. With this week’s rain and some rain predicted over the weekend, slug activity is likely to increase.

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Plant of the Week, Ginny RosenkranzThere are over 10,000 hybrids of Rhododendron created by many horticultural enthusiasts that are listed in the International Register and about 2,000 can be found for sale in nurseries all over the world. There are 6 different groups of deciduous azaleas including Ghent, Mollis, Knapp Hill-Exbury, Occidentale, Northern Lights, and Eastern American species and hybrids. The Exbury azaleas were hybrid crosses from the Ghent hybrids in 1870 with the Chinese azaleas and other species. Some of the seedlings from these crosses were acquired by Rothschild of Exbury.

These deciduous azaleas are 4-10 feet tall and 4-6 feet wide, with dark green foliage that shows reddish orange color in the fall. The Exbury azalea ‘Gibraltar’ is one of the most heat tolerant of this group and blooms early in the spring with bright flame orange colored flowers with ruffled petals. The flower cluster or trusses are 2-3 inches across, and the trumpet-shaped flowers are fragrant and attractive to butterflies. It grows 5-6 feet tall and 5 feet wide and has rich green leaves that turn yellow to orange and

Note the white midvein

Gilbraltar Exbury AzaleaPhoto: Ginny Rosenkranz, UME

Japanese stiltgrassPhotos: Chuck Schuster, UME

producer, each plant produces between 100 and 1,000 seeds annually. Pre emergent herbicide applications for larger areas are the recommended method of control. The seeds will germinate in late March to early April in the average year, which is before crabgrass. Flowering occurs in late September to early October in this region. Prevention of seed production is important for control of Japanese stiltgrass for the following year

Mowing can be used to limit the spread and development of this weed. It must be kept short from the beginning of the season to prevent seed head formation. Chemical control can be accomplished with the use of properly applied pre emergent herbicides. Pre emergent control of Japanese stiltgrass needs to be started very early in the season. Remember the early germination of this weed, before crabgrass, and note the rainfall during this period. Control options are similar to that of crabgrass, start early and reapply in wet years. Barricade has been applied in research plots in December, March and May provided the highest percentage of control at 86%, with a single treatment in March on the average providing 81% control. Acclaim Extra has been used successfully as a post emergent herbicide in turf with Envoy used in turf and selected ornamental beds. Use caution when using Envoy, as it has restrictions because of sensitivity of some ornamentals. Glyphosate products may be used for spot spraying in landscape beds, but remember to use caution as this product will damage ornamentals that come in contact with this product.

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PLANT PLANT STAGE (Bud with color, First bloom, Full bloom, First leaf)

LOCATION

Aesculus pavia Full bloom (April 16) Howard CountyAmsonia tabernaemontana (eastern bluestar)

Full bloom (April 16) Howard County

Calycanthus fertilis Full bloom (April 20) Silver RunDodecatheon (white flower) Full bloom (April 19) Howard CountyGeranium maculatum First bloom (April 16) ColumbiaHydrastis canadensis Full bloom (April 20) Silver RunIllicium floridanum Full bloom (April 16) Howard CountyPodophyllum peltatum (mayapple) First bloom (April 18) Ellicott CityPrunus serotina (black cherry) First bloom (April 20) Ellicott CityQuercus rubra (red oak) First leaf (April 20) Ellicott CityRhododendron ‘Klondyke’ First bloom (April 20) Silver RunRhododendron ‘Marydel’ Bud with color (April 20) Silver RunRhododendron atlanticum First bloom (April 20) Silver RunRhodendron flammeum ‘Double Pleasure’

Bud with color (April 20) Silver Run

Rhodendron vaseyi Full bloom (April 20) Silver RunRobinia pseudoacacia First bloom (April 18) College ParkSaruma henryi (upright wild ginger) Full bloom (April 20) Silver RunStewartia pseudocamellia Full leaf, Bud (April 20) Ellicott CityStyrax obassia First bud (April 16) Howard CountyUvularia sessilifolia Full bloom (April 20) Silver Run

Plant Phenology: What’s in bloom

Degree Days (As of April 19)Baltimore, MD (BWI) 333 Dulles Airport 324 Frostburg, MD 178 Martinsburg, WV 295 National Arboretum 412 Reagan National 459 Salisbury 513

Come Hang Out With UsThe Maryland Arborist Association and the University of Maryland Extension are going to conduct an evening in the landscape looking at insects and diseases. What could be more delightful? Brookside Gardens in Wheaton, Maryland, is opening their doors to us on May 17 from 5:00 – 8:00 p.m. Besides getting to see the coolest diseases and bugs of 2012 (we bring in most of the samples in secure containers) you will get a chance to see the gardens in their springtime glory. You get two pathologists, Karen Rane and David Clement, and two entomologists, Mary Kay Malinoski and Stanton Gill, to guide you through an evening of fun recognizing the hit list of bugs and disease of the season. As a extra bonus you get a great catered dinner. For a brochure, go to http://www.mdarborist.com/documents/PestWalkBrochure_May2012-final_000.pdf

red in the fall. The plants should be placed in acidic, moist, well drained soils away from winter winds and late afternoon sun. They are much more tolerant of bright sunlight than the evergreen rhododendrons. They should be planted about 1 inch higher than the surrounding soils and mulched lightly to retain soil moisture. Hardy in USDA zones 5-8, the plants bloom profusely in May and can last for at least 2 weeks. This variety is mildew resistant, although like all azaleas it is susceptible to Phytophthora root rot, Ovulinia petal blight, and Phomopsis twig blight. Azalea lace bug, scale, mite and the rhododendron borer are among the insect pests.

Stanton GillExtension Specialist

sgill@umd.edu

Paula Shrewsbury Extension Specialistpshrewsb@umd.edu

Ginny RosenkranzExtension Educatorrosenkrnz@umd.edu

Chuck SchusterExtension Educator

cfs@umd.edu

Karen Rane Plant Pathologistrane@umd.edu

Brian Clark Extension Educator bpclark@umd.edu

Andrew RistveyExtension Specialistaristvey@umd.edu

David ClementPlant Pathologist

hgic.umd.edu

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by University of Maryland Extension is implied.

CONTRIBUTORS:

University of Maryland Extension programs are open to all citizens without regard to race, color, gender, disability, religion, age, sexual orientation, marital or parental status, or national origin.

Thank you to the Maryland Arborist Association, the Landscape Contractors Association of MD, D.C. and VA, the Maryland Nursery and Landscape Association, Professional Grounds Management Society, and FALCAN for your

financial support in making these weekly reports possible.

Photos are by Suzanne Klick or Stanton Gill unless stated otherwise.

Upcoming Programs

MAA Pest WalkMay 17, 2012Location: Brookside Gardens, Wheaton, MD

Invasive Species Identification and Management SeminarMay 23, 2012 9:30 -3:15Location: 12055 Government Center Parkway, Fairfax, VACost: Free, but registration is required. To register please go to: http://ffxpest.eventbrite.comContact: Jack Baggett 703-324-5542, John.baggett@fairfaxcounty.gov

ASCFG Mid-Atlantic Regional MeetingJune 18, 2012Roost Flowers and DesignLocation: Virginia Beach, Virginiaascfg.org

MNLA Field DayJune 21, 2012Location: D.R. Snell Nursery, Union Bridge, MD

Maryland Christmas Tree Association’s Summer MeetingJune 30, 2012 (Saturday)Location: Taylor Sines Woodlake Tree Farm, Oakland, MDContact: 410-452-9793

2012 Perennial Plant SymposiumJuly 4 - 10, 2012Location: Boston, Massachusettsperennialplant.org

OFA Short CourseJuly 14 - 17, 2012Location: Columbus, Ohioofa.org

OFA Perennial Production ConferenceSeptember 10 - 12, 2012Location: Grand Rapids, Michiganofa.org