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Hort Notes 2022 Vol. 33:2

April 1

A monthly e-newsletter from UMass Extension for landscapers, arborists, and other Green Industry professionals, including monthly tips for home gardeners.

To read individual sections of the message, click on the section headings below to expand the content.

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Hot Topics

Landscape Message Resumes for the 2022 Season

UMass Extension's LANDSCAPE MESSAGE is a regular update to inform and help guide Green Industry professionals in the management of our collective landscape. Each message includes valuable information from sites throughout Massachusetts: growing degree day accumulation, soil temperature, precipitation amounts, and plant phenology.

Detailed reports on cultural practices and the status of insects, diseases, and weeds of interest to landscapers, arborists and turf managers are also regular features. New messages are available weekly during the heart of the growing season, bi-weekly in mid to late summer, and monthly during the fall. 

For both the current and archived past messages, go to https://ag.umass.edu/landscape/landscape-message.


Sales of Creeping Jenny

As we move into the retail sales season, a reminder about creeping Jenny from the Massachusetts Department of Agricultural Resources (MDAR): creeping Jenny is prohibited from sale in the Commonwealth of Massachusetts.

Creeping Jenny ‘Aurea’ (Lysimachia nummularia) Creeping Jenny (Lysimachia nummularia) is a low-growing, creeping perennial plant that has long stems with pairs of round green leaves, and yellow flowers in summer. It is often touted as a good ground cover for wet areas, and its trailing foliage is used for decoration in hanging baskets and other planters. But creeping Jenny is also one of more than 100 invasive species on the Massachusetts Prohibited Plant List, meaning it cannot be sold, imported, or propagated in our state. With so many species on that list, this is one that sometimes sneaks by unnoticed in nursery and garden retail settings. This post is a reminder that you should not buy or plant this invasive species.

Creeping Jenny loves moist habitats and was once commonly recommended for planting in these areas. Unfortunately, the same properties that make it a desirable ground cover for gardeners and landscapers turn it an effective invader in natural wetland ecosystems. It is known to escape from cultivation into forested floodplains and other wetlands, where it often forms dense mats. It is also a prolific producer of seeds. For these reasons, creeping Jenny has been prohibited from sale in Massachusetts since 2009, after a review by the Mass. Invasive Plant Advisory Group (MIPAG).

MDAR has an active consumer reporting system in place, and you could be reported if you offer creeping Jenny for sale in Massachusetts. The most common cultivars are probably the yellow-leaved ‘Aurea’ and ‘Goldilocks’. If you are a retailer and have been shipped this species from out of state, please contact the originating producer to return the plants, or contact MDAR at jennifer.forman-orth@mass.gov for assistance.

Reports of creeping Jenny for sale can also be reported at MDAR's Plant Pest reporting web page.

Featured Plant

Rhododendron ‘PJM’

PJM Rhododendron in flower ‘PJM’ represents a group of rhododendrons; the original was named after Peter J. Mezitt and was bred by his son Ed Mezitt in 1943. The Mezitt family is known for breeding rhododendrons, but also as the originators of the family-owned Weston Nurseries in Hopkinton, MA.  ‘PJM’ was the result of a cross between a pink flowering selection of Rhododendron minus (R. carolinianum) and Rhododendron dauricum. The resulting hybrids are vigorous, compact, round, small leaved evergreen rhododendrons with exceptional winter hardiness. The rhododendron is hardy to at least -25oF.

'PJM' rhododendrons are one of the earliest blooming rhododendrons, typically blooming in mid-April to early May, and bloom often coincides with the arrival of hummingbirds in southeastern MA. The bloom color is lilac purple to pink, depending on the cultivar. Plant size ranges from 3-6’ tall and wide depending on cultivar. The foliage of 'PJM' rhododendrons is tidy and rarely has imperfections. The foliage is dark green in summer and turns a purplish hue in winter; the winter color often referred to as mahogany. 

'PJM' rhododendrons are relatively carefree, being well adapted to most suburban landscapes. Ideal site selection would include protection from exposure, acidic soil, consistent soil moisture and a mulched root zone. Damage from lacebugs has been observed on plants in full sun, but other than that, these rhododendrons are relatively pest free.

Cultivars of note include:

  • ‘Amy Cotta’ – compact, mature size 3’ tall and wide, lavender pink flowers
  • ‘Compacta’ – compact, mature size 4’ tall and wide, lavender flowers
  • ‘Elite’ – vigorous, mature size 6’ tall and wide, lavender pink flowers
  • ‘Regal’ – vigorous, mature size 6’ tall and wide, lavender pink flowers

Russ Norton, Agriculture & Horticulture Extension Educator, Cape Cod Cooperative Extension

Trouble Maker of the Month

Hemlock Woolly Adelgid (Adelges tsugae, HWA)

Overview & Recent Events:
The hemlock woolly adelgid is a non-native insect that has been found in much of Massachusetts since it was first detected here in 1989. The first record of this insect in the United States was in Richmond, Virginia in 1951. 

This tiny, aphid-like insect uses a long piercing-sucking type mouthpart (stylet) to feed at the base of eastern (Tsuga canadensis) and Carolina hemlock (T. caroliniana) needles. These insects feed on the nutrients found in the xylem of their hosts. Feeding from HWA causes discoloration, desiccation, needle loss, and dieback of branches in susceptible hosts. As the infestation progresses, crown vigor declines, leading to branch dieback and tree death. Research has shown that HWA can be fatal to hemlocks of all ages in 4-15 years, depending upon moisture availability and other factors influencing tree stress at the site. However, in the Northeastern US, historically, some hemlock trees have been able to persist at the higher end of that range or more, possibly due to winter mortality of the adelgid. 

Billions of hemlock woolly adelgid sexuparae (winged individuals) wash up on the beaches in York County Maine in June 2021. Images courtesy of Steven Porter, Camille Fine, and April Schneider (Portsmouth Herald, June 8, 2021).  In their native Japan, hemlock woolly adelgids alternate between southern Japanese hemlock (Tsuga sieboldii) and tiger-tail spruce (Picea torano). On the alternate tiger-tail spruce host, there is a sexual generation that creates a gall. Without the presence of this specific spruce host, HWA can have continuous asexual generations on hemlock. This is what happens in eastern North America - hemlock woolly adelgids are all females that reproduce parthenogenetically on hemlock. However, that is not the entirety of the story. The sexual (winged) generation, known as sexuparae, that migrate to tiger-tail spruce in the native range of the hemlock woolly adelgid, still occurs in the US. It is just a “dead-end”, as it perishes when no appropriate host is found. In June of 2021, beach-goers in Maine and the media saw a spectacular, perhaps never-before-seen, extreme example of this when billions of HWA sexuparae washed up on Maine beaches and dyed beach visitor’s feet black! For more information about this unique occurrence, visit the following Maine Forest Service Bulletin (Under Insects, Hemlock Woolly Adelgid): https://content.govdelivery.com/accounts/MEDACF/bulletins/2e96444 .

Hemlock woolly adelgid at the base of eastern hemlock needles. (Photo: Tawny Simisky) The overwintering hemlock woolly adelgid generation (sistens) is present through mid-spring and produces the spring generation (progrediens) which is present from early spring through mid-summer. HWA, unlike many other insects, does most of its feeding over the winter. Eggs may be found in woolly masses at the base of hemlock needles beginning in mid-March. Each woolly mass is created by a female who may then lay 50-300 eggs. Eggs hatch and crawlers may be found from mid-March through mid-July. From mid-July to mid-October, hemlock woolly adelgid nymphs (immatures) are found settled on the stems of their hosts, at the base of the needles. Nymphs are very small, flat, black, oval, and ringed with a fringe of white waxy strands (magnification from a hand lens is required to see them). During this timeframe, the nymphs enter a summertime dormancy, or aestivation, where they neither feed nor develop. It isn’t until mid-October that they resume feeding on the xylem ray cells of their hosts. New woolly masses appear again the following March, after the insects spend the winter feeding.

Management of the Hemlock Woolly Adelgid:
Hemlock grown on stressful sites (ex. compacted soils, poor drainage, drought prone sites) are much more apt to succumb to HWA infestation within 3-5 years. Research has shown that nitrogen fertilizer applications may make hemlock woolly adelgid infestations worse. 

Infested trees may be treated with foliar applications in late April to early May. Systemic applications can be made in the spring or fall, or when soil conditions are favorable for translocation to the foliage (high relative humidity, adequate soil moisture, etc.). 

Reduced-risk options include springtime dormant oil applications according to label instructions to prevent phytotoxicity and to increase efficacy. Verdant horticultural oils (lighter oils) can be used when dormant oils are no longer an option. Multiple applications may be necessary, according to label instructions. Thorough application is necessary for contact insecticides to be effective. 
Systemic applications with neonicotinoids (such as imidacloprid or dinotefuran) are effective at managing the adelgid for multiple seasons, according to research (5 years and 2 years, respectively - dinotefuran tends to act quickly and results may be noticed sooner than with imidacloprid, although both are effective at managing hemlock woolly adelgids). Neonicotinoids are lethal to pollinators, either through direct treatment or residues on or in plants (such as in nectar and pollen). Hemlock, however, is wind pollinated and as such the risk to pollinators from systemically treated hemlock may be lower than in more attractive, flowering and nectar producing plants. Nonetheless, the risks to pollinators should be considered when making any insecticide application or management decision.

As with any pesticide application, be sure to follow all label instructions for safety and proper use to protect the health of the applicator and the environment.

Change in Neonicotinoid Uses in Massachusetts:
The Massachusetts Department of Agricultural Resources (MDAR) has previously announced that the registration status of products containing neonicotinoid active ingredients (acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam) with certain use patterns are changing from general use to state restricted use. Products containing these active ingredients for the management of insect pests on lawns, trees, shrubs, home vegetable gardens and ornamentals (including hemlock woolly adelgid) will be state restricted use beginning July 1, 2022

On and after that date, only licensed dealers will be able to sell the products that have become state restricted use, and only individuals with the proper license or certification will be able to purchase (and apply) these products in Massachusetts.

For professionals: After July 1, 2022 you will need a commercial certification license (such as Category 36 – Shade Trees and Ornamentals or Category 37 – Turf) or a commercial applicators license (core license) and be working under the direct supervision of a certified applicator (ex. Category 36) to apply products containing these neonicotinoids in Massachusetts. 

For homeowners: After July 1, 2022 you will no longer be able to apply certain products containing acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam on your own property unless you become licensed through MDAR’s Pesticide Program. These products will no longer be available for sale to homeowners. If you still have these products that you purchased when they were general use (prior to July 1, 2022 for most), after July 1, 2022 they are considered hazardous waste and need to be disposed of. MDAR recommends not purchasing these products in bulk, so that this issue can be avoided. 

For more information about this change, please visit the neonicotinoid FAQ from MDAR at: https://www.mass.gov/service-details/pesticide-newsupdates 

Tawny Simisky, UMass Extension Entomologist

Q&A

Q. When is the best time to prune my shrubs?

A. Late winter/early spring is the best time to prune summer and fall flowering shrubs such as panicle hydrangea, butterfly bush, buttonbush, summersweet clethra, sweetspire, and summer flowering spirea. These shrubs form their flower buds on new wood that grows in the spring of the current year. Pruning these in late winter or early spring leads to vigorous stem growth in spring and summer that contain buds that will flower in summer and early fall.

The best time to prune spring flowering shrubs such as big leaf hydrangea (H. macrophylla), forsythia, viburnum, honeysuckle, and lilac is in the spring soon after flowering. These shrubs form their flower buds in mid to late summer and flower the following spring on one-year old shoots that grew the previous summer. Pruning live wood of these in early spring removes the flower buds and reduces the number of flowers that spring. However, if a full display of flowers is not important to you, then spring pruning is not a problem. 

DO NOT prune spring- or summer-flowering shrubs in late summer or early fall since this will stimulate new growth that may not harden off before winter and may lead to winter cold injury. However, you can prune off dead, diseased or damaged branches or shoots at any time. Newly planted shrubs should not be pruned unless branches are damaged since they need all their leaves to photosynthesize the food needed to encourage root growth.

Q. Is April a good time to divide perennials?
A. Spring is one of the best times to divide perennials and most perennials respond best when divided in early spring. In early spring, the weather is cool and there is usually adequate moisture in the soil. Roots have a lot of stored energy that helps the divisions recover from being cut apart and replanted. The new emerging shoots are likely to suffer less damage than fully developed growth and will also lose less water through evapotranspiration. Spring divisions also have the entire season to recover from the stress of division. Start by digging around the plant and then lift the entire clump out of the ground. Then, using a spade or sharp knife, cut the clump up to separate smaller pieces. Discard the old, dead center and trim off any damaged roots. Keep the divisions moist and shaded while you prepare the new planting site. After replanting, keep plants well watered.

Q. Should I plant trees and shrubs now or I should wait until later?
A. Early spring is also a great time to plant trees and shrubs. Summer planting when plants are in full leaf can be stressful and should be avoided if possible. Fall is also a good time to plants trees and shrubs, but the risk of plant failure increases with how late you plant in the fall. Spring is a good time of the year to plant trees and shrubs because this gives roots time to grow into the surrounding soil before stress due to high summer temperatures occurs. During the spring, there is usually adequate moisture in the soil from spring rains to enable plants to grow and establish without moisture stress. 

Geoffrey Njue, UMass Extension Sustainable Landscapes Specialist

Garden Clippings Tips of the Month

April is the month to . . . .

  • Sow seeds of cool season vegetable crops such as peas, kale, chard, cauliflower, spinach, carrots, beets, radishes, leaf lettuce, and green onions as soon as the soil is workable. A quick way to test if soil is “workable” is to pick up a handful and squeeze it. If the resulting clump falls apart with gentle prodding, the soil is ready to be prepared for planting. After sowing crops, cover seeded rows with floating row cover fabric to speed germination and protect seedlings from harsh spring winds.
  • Sow tomato seeds indoors for later transplanting into the garden after the danger of frost has passed. After reviewing decades of tomato studies, researchers at the University of Florida, Penn State, and Rutgers concluded that while fruit yield ultimately depends on cultivar and growing conditions, transplanting tomato seedlings into the garden when they are 6 to 8 weeks old is ideal for subsequent plant growth and development. 
  • Divide and replant late summer blooming perennials such as aster, daylilies, and phlox for the purpose of renovating older plants, keeping large clumps under control, and increasing the number of plants to grow or share. When dividing older perennials, discard the center of each clump and replant sections from the outer areas where shoots are more vigorous.
  • Monitor boxwoods around the property for leafminer larvae, which may be active and feeding. Small bumps on the undersides of leaves are evidence of the larvae inside; the tiny greenish or yellowish worm-like larvae are visible when affected leaves are peeled apart. Pruning larva-laden boxwood foliage now will reduce the number of adults hatching out in May.
  • Divide the crowns of rhubarb plants that have become crowded. Incorporate a liberal amount of compost or rotted manure into soil when replanting divisions. Rhubarb plants perform best when given plentiful moisture throughout the growing season. Remember to let the divisions grow for a year before harvesting stalks again.
  • Cut back the stem tips of houseplants to control leggy growth or make plants bushier. Houseplants are beginning to put on new growth now that they are getting more sun, more natural humidity, and increased warmth.
  • Rake lawns to remove debris as well as some of the dead grass or thatch that has accumulated since last year. Thatch removal permits better water and fertilizer movement into the soil, and soils with less thatch warm up rapidly to stimulate grass growth.
  • Plant dahlia tubers indoors to give them a headstart on the growing season. Fill pots halfway with an all-purpose potting mix, set in a tuber, and cover it with another 1 to 2 inches of potting mix. Place pots in a warm location and water carefully, allowing soil to dry somewhat between waterings, as tubers are prone to rotting in overly damp soil. Once tubers have sprouted, grow plants under lights set 6 inches above the pot or in a sunny window to keep them from becoming spindly.
  • Consider which perennials will need support during the growing season, and install support structures while plants are still small. Supports can range from purchased stakes, hoops, and netting to foraged branches. Whatever the chosen structures, getting them in place early will reduce the chance of fragile plants breaking while they’re being wrestled into their “girdle” and allows the plants to look more natural as they grow rather than appear forced into a frame after they’ve matured.
  • Mulch garden beds, both ornamental and vegetable, with 2 to 3 inches of an organic material (such as bark, wood chips, cocoa hulls, or straw). A generous layer of mulch can reduce the garden workload in terms of weeding, watering, and soil conditioning. Mulching prevents annual weed seeds from receiving the sunlight necessary for germination and weakens perennial weeds, making for easier removal. Mulch conserves moisture in the soil layer around plant roots, and improves both soil structure and nutrient availability as it breaks down and is worked into the soil over time.  

Jennifer Kujawski, Horticulturist

Have You Seen Me?

Deer Tick (black legged tick) adult Chances are you have…this is an adult stage female deer tick. These ticks in this life stage have been with us since last September and they will be active into May. We have received a number of calls from people who ventured out on some of those warmer January/February days who were totally surprised that they were bitten by ticks. One of the first questions they have is, why didn’t the freezing temperatures kill them? Well, ticks are able to make a chemical called glycerol - basically they make their own antifreeze. So, whenever temperatures are above freezing and there’s a break in the snow cover, the adults are active.

It's not just about Lyme disease anymore. If misdiagnosed and not treated properly, some people wind up with long term consequences. Other diseases transmitted by these ticks include babesiosis, anaplasmosis, relapsing fever and Powassan virus. So, what do we do to improve our odds of preventing getting a tick-borne disease?

For starters, wearing long pants and shoes, not sandals, helps. Pants should be a light color, which makes it easier to see the ticks. Treat exposed skin with a repellent like DEET. Clothing can be treated with a repellent that contains the active ingredient permethrin, which we find to be the most effective tool in the box. When I started doing research with this product, I found that if a tick gets exposed to a permethrin treated fabric surface for 60 seconds, it is guaranteed to die. Finally, when you come in from an outdoor activity, put your clothes in the dryer for 20 minutes.

Cape Cod Cooperative Extension has produced a series of videos on everything you need to know about the prevention of tick-borne diseases which you can find at Capecodextension.org/ticks

So, as the weather warms up, enjoy the outdoors. Don’t be tick afraid…be tick aware.

Larry Dapsis, Entomologist, Tick Project Coordinator, Cape Cod Cooperative Extension

Upcoming Events

For more details and registration options for any of these events, go to the UMass Extension Landscape, Nursery, and Urban Forestry Program Upcoming Events Page.

  • Apr 7, 2022 - Developing an Invasive Plant Management Program (B). Last class in the Invasive Plant Certification Program for 2022. Live via Zoom.
    Four pesticide contact hours in categories 29, 36, 37, 40, 48, and Applicator's License.

Pesticide Exam Preparation and Recertification Courses

These workshops are currently being offered online. Contact Natalia Clifton at nclifton@umass.edu or go to https://www.umass.edu/pested for more info.

InsectXaminer! 

Episodes so far featuring gypsy moth, lily leaf beetle, euonymus caterpillar, imported willow leaf beetle, and spotted lanternfly can be found at: https://ag.umass.edu/landscape/education-events/insectxaminer 

TickTalk with TickReport Webinars

To view recordings of past webinars in this series, go to: https://ag.umass.edu/landscape/education-events/ticktalk-with-tickreport-webinars


Additional Resources

For detailed reports on growing conditions and pest activity – Check out the Landscape Message

For professional turf managers - Check out our Turf Management Updates

For commercial growers of greenhouse crops and flowers - Check out the New England Greenhouse Update website

For home gardeners and garden retailers - Check out our home lawn and garden resources


Diagnostic Services

Landscape and Turf Problem Diagnostics - The UMass Plant Diagnostic Lab is accepting plant disease, insect pest and invasive plant/weed samples . By mail is preferred, but clients who would like to hand-deliver samples may do so by leaving them in the bin marked "Diagnostic Lab Samples" near the back door of French Hall. The lab serves commercial landscape contractors, turf managers, arborists, nurseries and other green industry professionals. It provides woody plant and turf disease analysis, woody plant and turf insect identification, turfgrass identification, weed identification, and offers a report of pest management strategies that are research based, economically sound and environmentally appropriate for the situation. Accurate diagnosis for a turf or landscape problem can often eliminate or reduce the need for pesticide use. See our website for instructions on sample submission and for a sample submission form at https://ag.umass.edu/services/plant-diagnostics-laboratory. Mail delivery services and staffing have been altered due to the pandemic, so please allow for some additional time for samples to arrive at the lab and undergo the diagnostic process. 

Soil and Plant Nutrient Testing - The lab is accepting orders for Routine Soil Analysis (including optional Organic Matter, Soluble Salts, and Nitrate testing), Particle Size Analysis, Pre-Sidedress Nitrate (PSNT), and Soilless Media (no other types of soil analyses available at this time). Testing services are available to all. The lab provides test results and recommendations that lead to the wise and economical use of soils and soil amendments. For updates and order forms, visit the UMass Soil and Plant Nutrient Testing Laboratory web site. 

Tick Testing - The UMass Center for Agriculture, Food, and the Environment provides a list of potential tick identification and testing options at: https://ag.umass.edu/resources/tick-testing-resources.