for Arborists, Landscape Managers & Nursery Managers

Commercial Horticulture July 28, 2017Coordinator 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 Nancy Harding, Faculty Research AssistantDisease 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 (Extension 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

- Mimosa webworm- Caterpillars- Japanese maple scale- Ideas for biocontrol conference- Filbert blight- Powdery mildew- Pear trellis rust- Tiger bee fly- Bagworm update

Beneficial of the WeekWeed of the WeekPhenologyDegree DaysAnnouncements

Pest Predictive Calendar

IPMnetIntegrated Pest Management for

Commercial Horticulture

extension.umd.edu/ipm

Mimosa Webworms: Dropping From TreesBy: Stanton Gill

I received an email from an arborist who reported larvae dropping from silken threads from honeylocust trees. They were dropping onto a customer’s deck over the weekend during a cookout. They certainly gave the guests something to talk about. These are the larvae of mimosa webworm (Homadaula anisocentra). This pest was introduced from China back in the 1940s. The mimosa webworm feeds primarily on the leaves of mimosa and honeylocust trees. Since there are not too many mimosa trees left around, this pest shows up mainly on honeylocust.

There are two generations of this pest in Maryland. The larvae dropping down in late July from the foliage is part of the first generation. The adults were out in early June. Females laid eggs on the terminal leaves and small twigs. Larvae hatched back in mid- to late June and immediately began to feed on the lower surface of leaflets. Mature larvae from the first generation pupate in late July and the second generation of adults appear again in early August. Second generation larvae are active

The first generation of mimosa webworm is finishing now; look for early instar second generation caterpillars as we move into August

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Orange-striped oakworms are gregarious feedersPhoto: Rich Beere, Scientific Plant Service

Orange-striped Oakworms and Catalpa Sphinx Moth CaterpillarsRich Beere, Scientific Plant Service, found orange-striped oakworms on July 27 at the Emmitsburg welcome center. Marie Rojas, IPM Scout, found these caterpillars (large and small) on Quercus palustris and Q. phellos this week. There is one generation. It is common to see the orange-striped oakworm on paved paths as they search for places to pupate. Caterpillars can be found from mid to late July through early fall. Marie Rojas and Steve Clancy, Country Springs Nursery, are also seeing catalpa sphinx moth caterpillars (aka catalpaworms) on catalpa this week. With multiple generations, look for this caterpillar from June through early fall. Control: Parastic wasps help keep caterpillar populations in check. Bt can be used for small larvae and other labelled insecticides for larger caterpillars if needed.

There is one generation of orange-striped oakworm per yearPhoto: Marie Rojas, IPM Scout

during August and early September. Larvae from this generation may be so abundant that they web leaves throughout the entire crown of the tree causing it to look completely brown. This situation happens in some years, but not all years. Pupae from this second generation act differently in that they overwinter inside cocoons within the web or in bark crevices.

Control: It is too late for the first generation, but the second generation can be controlled with Acelepyrn, Mainspring or Spinosad (Conserve) applications.

If you have catalpa, the catalpa sphinx moth caterpillar is one of the easier caterpillars to spotPhoto: Marie Rojas, IPM Scout

Japanese Maple ScaleBy: Stanton GillWe took the first counts on our 2017 trials to evaluate new materials for Japanese maple scale on Wednesday. We are at the start of the second generation crawler stage on the Eastern Shore of Maryland. Meanwhile, Distance or Talus, which are insect growth regulators, are the best materials that we have previously tested for Japanese maple scale control. For those of you with customers with fruit trees infested with this scale, you can use the same product that is in Distance, but under the trade name Esteem.

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Filbert Blight Damage Evident in JulyBy: Stanton Gill

I was in Delaware working on a thrips trial on Thursday when I noticed a Harry Lauder’s walking stick plant with severe dieback. The dieback is from filbert bight and you can see the cankers forming on the stems. With the hot weather of July, the dieback becomes more noticeable on infested plants. This plant is a favorite of many of your customers and is used as a specimen in the landscape. You need to let your customers know that it is highly susceptible to filbert blight. There is not much you can do at this time of year. Often, it takes two or three years before the plant is completely dead, and it is sad to watch it decline each season.

Look for longitudinal rows of black stromata made up of elliptical masses of fungal tissue on the surface of branches that were infected up to 18 months earlier. The cankers that are filled with the stromata persist and enlarge yearly. As the branches become girdled by the cankers, leaves and branches die, and the problem becomes more noticeable with the flagging of dead tissue in the canopy.

Infections begin in the spring: New, rapidly growing shoots are most susceptible. Spores enter the elongating cells directly, and are actively promoting infection over a wide range of temperatures when accompanied by high humidity. Once inside the tissue, the fungus will grow within the phloem and outer areas of xylem until, 12 to 18 months later, the stromata appear on the surface of the branch. Reproductive structures, the perithecia, form within the stromata, and within the perithecia, ascospores – the reproductive cells – develop. By the next spring, ascospores shoot out from the perithecia, and may be observed by the milky ooze they form on the surface. They are spread by wind and rain to create new infections.

Control: Sanitation is important in managing this disease. Remove diseased branches well below the edge ofthe canker in order to stay ahead of the disease. To prevent further spread, compost or burn these branches.Protectant fungicides can be applied in the spring to protect new shoots from infection.

Looking for Feedback - A Biocontrol ConferenceBy: Stanton Gill

I am in the early stages of developing a Biological Control conference for the greenhouse and nursery industry for December 4, 2017. I would like feedback from people in the nursery and greenhouse industry on potential topics and speakers. Send these suggestions to me at sgill@umd.edu.

If filbert blight disease is allowed to continue on this Harry Lauder’s walking stick, the plant will die within a few seasons

If you a observe Harry Lauder’s walking stick declining, check stems for these longitudinal rows of black stromata

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Powdery Mildew on MonardaBy: Stanton Gill

While on the Eastern Shore this week, I visited a greenhouse operation that was growing Monarda. It has been the perfect weather over the last couple of weeks for powdery mildew. Mt. Cuba Center (Hockessin, DE) has a list that includes resistant cultivars at the end of their Research Report on Monarda. If possible, plant resistant cultivars in the landscape to reduce the incidence of powdery mildew disease.

Powdery mildew is infecting many plants, not only Monarda plants at a greenhouse, but a variety of plants in landscapes

Pear Trellis RustBy: David Clement, UME-HGIC

Marie Rojas, IPM Scout, is reporting pear trellis rust on 'Aristocrat' pears in Montgomery County. Pear trellis rust symptoms are very visible now on pear trees. This disease is caused by the rust fungus, Gymnosporangium sabinae, and has a complex life cycle between several species of juniper (Juniperus sp.) and ornamental (Pyrus calleryana) and orchard pears (Pyrus communis). Leaf spots on pear turn bright reddish orange by mid-summer. By late summer, brown, blister-like swellings form on the lower leaf surface just beneath the leaf spots. These spores are blown by wind to susceptible juniper species from late summer through fall where they cause infections on young juniper shoots.

This rust produces bright reddish orange leaf spots on upper and lower leaf surfacesPhoto: Marie Rojas, IPM Scout

Junipers and ornamental and orchard pears are alternate hosts for pear trellis rust Photo: David Clement, UME-HGIC

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Bagworm UpdateBy: Stanton Gill

We conducted insect field trials this week on the Eastern Shore. While there, I looked at some large 30 ft tall Thuja ‘Green Giant’ trees that were heavily damaged by bagworms. We have had several landscapers report that bagworms do not like this plant. This is not so, as evidenced by this feeding injury. We are now late into the life cycle of bagworms and they will be feeding for only another week or so. At this point the damage is pretty much done for the season. Next year you can apply Spinosad (Conserve ), Bt, Acelepryn or Mainspring for control. Watch for next season when we announce the hatch out.

Tiger Bee FlyMeipo Martin, Montgomery County Master Gardener, found this tiger bee fly on her deck. The larvae are parasites of carpenter bees. These flies lay eggs at the opening of carpenter bee holes.

The larva of tiger bee fly is a parasite of carpenter beesPhoto: Meipo Martin, Montgomery County Master Gardener

Thomas Joyce, Manassas City, reported that “bald cypress were treated for bagworms earlier in the season and I have found that they moved onto oaks trees that are beside them.” The photo shows how heavily the bagworms are feeding on one of the oaksPhoto: Thomas Joyce, Manassas City

Beneficial of the WeekBy: Paula Shrewsbury, University of Maryland

Silphium perfoliatum (cup plant) is in peak bloom: a plant that hums from insect activity!

Plants provide resources in the form of nectar and pollen for beneficial insects such as pollinators and omnivorous natural enemies. Over the years we have repeatedly discussed the importance of conserving beneficial insects and the services that they provide, and that the best way to do this is to include a diversity of flowering trees, shrubs, and herbaceous plants in our nurseries and landscapes. However, not all plants are created equal in the amount and nutritional value of their nectar and pollen. Back in the March 24 IPM Newsletter – Beneficial of the Week I provided a list of web sites that have been shown through research to provide optimal floral resources for pollinators and/or natural enemies as references for you to use when selecting plants.

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Although there are many plant species, both native and non-native on those lists, today I want to talk about one species of plant and the amazing insect activity it supports – Silphium perfoliatium (common name: cup plant). Silphium came into full bloom in my home garden about 10 days ago and there has been insect and bird activity all day long. Silphium is an herbaceous perennial in the Asteraceae family that is native to most of the U.S. that is east of the Rockies. It is a very tall plant (4-8’ is reported, mine is 7-8’) so you need to have the right location for it to work aesthetically in the garden. It is a mid-late season (July – September) bloomer and with clusters of bright yellow flowers (~3-4”diam.) near the top of the plant. This plant is sunflower-like in its habit and appearance. It does well in full sun to partial shade and prefers moist to wet soils. Silphium also has large opposite leaves (up to ~12” long) that attach at their base to the sturdy stem creating a “cup” (hence the common name of cup flower) that collects water.

So what is attracted to and uses the resources provided by Silphium? As I have watched the plants in my yard grow taller and taller, the many “cups” produced by the vegetative development attract song birds, in particular gold finch, who drink water from the cups, and later should feed on seed from the flowers. I have also seen predatory wasps drinking from the cups. Now that the flowers are in bloom the plant literally hums from the sounds of the many insects feeding on the nectar and pollen. I have seen yellow and black tiger swallowtails, at least 3 species of skippers, and cabbage butterflies. The plant is reported to be the host food for caterpillars of silvery checkerspot, Gorgone checkerspot, bordered patch and painted lady butterflies. Hymenoptera are also going crazy on this plant! I have seen honey bees, bumble bees (at least 3 species), and halictid bees. Other bees reported on this plant include sweat bees, leafcutter bees, small carpenter bees and digger bees. In addition to the many birds and pollinators this plant is documented to attract, it also attracts a diversity of natural enemies. These include several species of parasitic wasps, larger predatory wasps, minute pirate bugs, soldier beetles, predatory plant bugs, lady beetles, lacewings, long–legged and dance flies (predators), and jumping and crab spiders. Wow!

Silphium perfoliatum or cup plant is ranked high on many plant lists for its ability to attract pollinators, natural enemies, and birds. It also ranks highly on my list as a must for the garden and conservation strips. Go to Silphium Flower to see a YouTube of the impressive insect activity on Silphium perfoliatum flowers from my yard this week.

For more information on Silphium perfoliatum (cup plant) go to: http://www.canr.msu.edu/nativeplants/uploads/files/1Native_Plants_reupload/Cup_plant.pdf.

Silphium perfoliatum flowers support a diversity of insect fauna. Note that almost every flower head has at least one insect on it! Photo: P.M. Shrewsbury, UMD

Silphium perfoliatum plants provide resources used by a diversity of insects and birds. Note the height (4-8’, these are close to 8’) and be sure to find the right aesthetic location for these tall, dramatic plants. Photo: P.M. Shrewsbury, UMD

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Weed of the WeekBy: Chuck Schuster, University of Maryland

Mugwort: Artemisia vulgaris, also known as chrysanthemum weed, is a weed found throughout the eastern United States. This perennial, rhizomatous plant can be spread from nursery stock to the landscape. This weed is prolific once introduced into a landscape and may grow to a height of four to five feet. As the stems get longer they become woody, with a reddish brown color. Leaves are three to four inches in length, one to three inches in width, and are deeply lobed and alternate. Leaf undersides produce white or gray hairs and the upper side may have only a few hairs. The flowers are often not seen, will appear in small clusters at the top of the plant, and will be on short upright stalks. Seed from this plant is most often not viable.

Mugwort is a difficult to control weed. Pre emergent herbicides are not effective. Good sanitation is important to prevent the introduction of this into the landscape when adding new plant material. In turf, it will tolerate close mowing, and spreads through rhizomes 2,4D and dicamba work well on this weed in turfgrass. Use caution in warm weather for volatilization. Landscape post emergent products that are effective will be the glyphosate family, with applications in both May and August being effective.

Seed from mugwort is often not viablePhoto: Chuck Schuster, UME

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

LOCATION

Ceratostigma plumbaginoides (plumbago) First bloom Ellicott City (July 28)Eutrochium fistulosum (Joe pye weed) First bloom Ellicott City (July 25)

Phenology

Degree Days (As of July 27)Annapolis Naval Academy (KNAK) 2451 Baltimore, MD (KBWI) 2320 College Park (KCGS) 2289 Dulles Airport (KIAD) 2341Ellicott City (E247) 2240 Fairfax, VA (D4092) 2522Frederick (KFDK) 2284 Greater Cumberland Reg (KCBE) 2142 Gaithersburg (KGAI) 2213 Martinsburg, WV (C1672) 2153Natl Arboretum.Reagan Natl (KDCA) 2767 Rockville (C2057) 2366 Salisbury/Ocean City (KSBY) 2156 St. Mary’s City (St. Inigoes, MD-KNUI) 2584 Westminster (KDMW) 2430

Important Note: We are now using the Online Phenology and Degree-Day Models site.

Use the following information to calculate GDD for your site: Select your location from the mapModel Category: All models Select Degree-day calculatorThresholds in: Fahrenheit F Lower: 50 Upper: 95Calculation type: simple average/growing dds Start: Jan 1

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.

Stanton GillExtension Specialist

sgill@umd.edu410-868-9400 (cell)

Paula Shrewsbury Extension Specialistpshrewsb@umd.edu

Ginny RosenkranzExtension Educatorrosnkrnz@umd.edu

Chuck SchusterExtension Educator

cfs@umd.edu

Karen Rane Plant Pathologistrane@umd.edu

Andrew RistveyExtension Specialistaristvey@umd.edu

David ClementPlant Pathologist

clement@umd.edu

Nancy HardingFaculty Research

Assistant

Commercial Horticulture Conferences

Green Industry Summer PicnicAugust 19, 2017Location: Just This Side of Paradise Farm, Woodbine, MD

Cut Flower Tour - Eastern ShoreSeptember 12, 2017

Top Native Plants for the Mid-Atlantic RegionPresenter: Holly ShimizuOctober 11, 2017Location: Johns Hopkisn University, Rockville, MDRegistration Information