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Hort Notes 2022 Vol. 33:4

June 1

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

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Hot Topics

Volutella Blight of Pachysandra

Volutella blight is a common disease of plants in the Buxaceae, a family that includes pachysandra, boxwood (Buxus species), and sweet box (Sarcococca species). The fungus Coccinonectria pachysandricola causes Volutella blight on pachysandra and sweet box, while Pseudonectria buxi and Pseudonectria foliicola cause Volutella blight on boxwood. Originally, all of these fungi belonged to the genus Volutella, hence the common name of the disease they cause.

The fungi that cause Volutella blight are opportunistic pathogens that take advantage of wounded or weakened plants. Drought stress and winter injury are among the most common factors that make plants more susceptible to Volutella blight. 

Symptoms of Volutella blight on pachysandra include tan to brown leaf spots, sometimes with concentric rings, sometimes with a yellow halo. Dark brown lesions may girdle the stems, causing defoliation, dieback, and thinning of the stand. The conidia (asexual spores) of the causal fungi are borne on structures called sporodochia, which are cream-colored to light orange or pinkish and are sometimes visible in lesions. In summer, reddish-brown fruiting structures called perithecia may be observed in lesions.

Sanitation is important for Volutella management in pachysandra plantings. Remove all diseased plant tissues on a sunny day when foliage is dry. Provide irrigation during dry periods. Water in the morning so that foliage will dry as the day warms. Drip irrigation is preferable to overhead watering. Do not overwater. Protect plants from winter injury with a light mulch such as straw. Control insects that feed on pachysandra. Pachysandra procumbens (Allegheny spurge) is reported to be less susceptible to Volutella blight than P. terminalis (Japanese spurge); consider replacing P. terminalis with P. procumbens or another genus of groundcover if problems persist. Fungicides are available for management of Volutella blight on pachysandra, but few are available to homeowners, so it is best to consult with a landscaping company. 

Since Coccinonectria pachysandricola does not affect boxwoods, there is no risk of Volutella blight spreading to boxwoods from pachysandra. That said, the environmental and cultural conditions that are conducive to disease development are the same for all three species of fungi that cause Volutella blight, so it is possible for disease to occur on both pachysandra and boxwood at the same time.

Angela Madeiras, UMass Extension Plant Pathologist


State Agricultural Officials Ask Public to be on Alert for Hatching of Invasive Spotted Lanternfly Eggs

Spotted lanternfly egg mass; Source: MDAR staff The Massachusetts Department of Agricultural Resources (MDAR) is asking the public to keep an eye out for the invasive pest known as spotted lanternfly (Lycorma delicatula) during the spring planting season due to the risk of egg masses being accidentally brought in on shipments of trees imported from other states. MDAR recently received reports that nursery stock from SLF-infested areas may have been sent to Massachusetts growers. Due to this, anyone who has recently purchased trees or shrubs or had them planted on their property, particularly maple or crabapple trees, is being asked to inspect the trunk and branches to ensure there are no SLF egg masses or any hitchhiking nymphs, and to report any finds to MDAR. For more details, go to https://www.mass.gov/news/state-agricultural-officials-ask-public-to-be-on-alert-for-hatching-of-invasive-spotted-lanternfly-eggs.

Earlier this spring, the MA Department of Agricultural Resources (MDAR) also released a Notice to the Nursery and Landscape Industry reminding growers and landscapers to inspect any material coming from states where the spotted lanternfly has been found. To read the full notice, go to: https://massnrc.org/pests/blog/?p=2933.

Spotted lanternfly nymphs (Photo: Richard Gardner via bugwood.org) Established spotted lanternfly populations have (to date) only been detected in Worcester County, MA in the communities of Fitchburg and Shrewsbury, MA. Professionals and residents working and living in those areas should be vigilant and report anything suspected to be the spotted lanternfly to the MA Department of Agricultural Resources at https://massnrc.org/pests/slfreport.aspx . Everyone in Massachusetts should be looking for and reporting this insect if it is found.

Now is the time when spotted lanternfly egg masses will have hatched and nymphs (immatures) will be active.

For More Information about the Spotted Lanternfly

From UMass Extension:

From the MA Department of Agricultural Resources:

Trouble Maker of the Month

Spongy Moth Update for Berkshire County, MA!

NOTE: Central and eastern Massachusetts Lymantria dispar (formerly known as gypsy moth) populations have not been elevated in the last couple of years; this is specific to Berkshire County for 2022.

Spongy moth (Lymantria dispar) caterpillar activity in Berkshire County

Egg hatch was first reported to UMass Extension by arborists in Great Barrington, MA on 5/5/2022. Since then, the MA Department of Conservation and Recreation (MA DCR) has seen eggs hatching in Williamstown, Hancock, Pittsfield, Erving, and Wendell, MA. Ballooning spongy moth caterpillars were seen shortly thereafter, dispersing on fine strands of silk using the wind to move them, as is typical for this species. MA DCR and others also saw caterpillars resting on their egg masses, and some of them dying there (such observations have been seen in previous years in other locations). Surviving caterpillars are now feeding on their host plants, including but not limited to: oak, maple, birch, poplar, willow, apple, hawthorn, and many others.

Here are a few important points to remember about spongy moth if you are in Berkshire County, MA

  • In 2021, many in Berkshire County experienced elevated Lymantria dispar (spongy moth) caterpillar populations for the first time since the 1980’s. Berkshire County was largely spared (until now) in the most recent outbreak that for central and eastern MA peaked in 2017, where over 920,000 acres of defoliation occurred in those areas. Locations in Berkshire County with many overwintered egg masses (that have now hatched and caterpillars ballooned and settled to feed) may have noticeably elevated populations of this insect again in 2022.
  • Most otherwise healthy trees can withstand a single year of defoliation from this insect. Tree mortality may happen when multiple years of defoliation occur in a row.
  • While many birds do not like to feed on hairy spongy moth caterpillars as they grow in size, species such as blue jays, orioles, and certain towhees like them! Black-capped chickadees are known to feed on egg masses too.
  • Shrews, mice, voles, chipmunks, and other small mammals feed on spongy moth caterpillars and pupae.
  • Ground beetles such as those in the genus Calosoma feed on spongy moth caterpillars and pupae.
  • Ooencyrtus kuvanae is a tiny parasitoid wasp that will lay its eggs in the eggs of the spongy moth. It is capable of killing approx. 20-30% of the eggs in spongy moth egg masses. It is already known in much of Massachusetts.
  • Cotesia melanoscelus is another parasitoid wasp that will attack very young Lymantria dispar caterpillars.
  • Compsilura coccinnata is a parasitic fly that was released many years ago to manage spongy moth caterpillars. While it does indeed do this, it unfortunately also attacks more than 100 other moth and butterfly species (this was before it was widely known that generalist parasitoids should not be used for biological control efforts; that lesson is well learned now and biocontrol is conducted differently by scientists to avoid this).
  • Heavy-hitters: The NPV virus (nucleopolyhedrosis virus) that is specific to Lymantria dispar caterpillars is excellent at killing many of them, especially as populations increase. Entomophaga maimaiga, a fungal pathogen of the spongy moth, is also highly effective at killing their caterpillars, even when populations are low. This fungus may do well with cool, rainy weather in the spring and early summer.

There are reduced risk insecticide options available for managing spongy moth on individual trees. One example, Bacillus thuringiensis Kurstaki (Btk), is a reduced risk insecticide derived from a soil dwelling bacterium that is specific to the Lepidoptera (including spongy moth) that can be used on host plant leaves while caterpillars are actively feeding, but before they are over ¾ inch in length. If caterpillars are longer than ¾ inch, other active ingredients such as spinosad (also reduced risk) may be more effective. Professional arborists can help homeowners manage this insect if populations are high for the second year in a row on individual specimen trees. However, once caterpillars are very large (2-3 inches long), they are much more difficult to kill and will have already done much of their feeding. Management is no longer necessary in July once caterpillars pupate and stop feeding. 

Otherwise, hang in there, and eventually the natural enemies listed above will reduce the population again below noticeable levels. As always, the question is…when?

    Tawny Simisky, UMass Extension Entomologist

    Q&A

    Q.  Our company is working on a plan to control a sizable population of Japanese knotweed along a riverbank.  Since the location is near water, the Massachusetts Wetland Protection Act 310 CMR 10.00 comes into play. During the Notice of intent hearing, the Conservation Committee approved the management plan and the use of glyphosate as you prescribed. This approval requires that we use a glyphosate formulation that does not contain POEA. What is POEA and what glyphosate formulation(s) should we be using?

    A. POEA (polyoxyethylene tallow amine) is a non-ionic surfactant used in herbicide formulations to increase their efficacy by promoting the penetration of the herbicide into plant leaf cuticles. POEA is known to have toxic effects on aquatic organisms, so formulations of glyphosate that contain POEA are not labeled for near or in water applications. Formulations of glyphosate that don’t contain POEA are labeled for the management of vegetation that is near or in water. When glyphosate is the best choice for managing a specific weed or invasive plant, you will need to use a POEA-free formulation. Below is a table of some of the more common POEA-free glyphosate formulations.

    TRADENAME MANUFACTURER EPA REG #
    Rodeo Corteva Agriscience 62719-324
    Roundup Custom for Aquatic and Terrestrial Use Bayer CropScience 524-343
    Glyphosate 5.4 Alligare 81927-8
    Aqua Neat Nufarm 228-365

     

    Q.  We have been seeing an increase in lesser celandine on some of the properties we manage. We are interested in some information on species characteristics and management options.

    A.  In the May edition of Hort Notes 2022, volume 33:3, there is an article on lesser celandine - click on the “Trouble Maker of the Month” section of the newsletter.

     

    Q.  We have been trying to select an herbicide for the control of white clover in turf. We understand that clopyralid and quinclorac both provide good to excellent control. Which should we use?

    A.  Selecting which of these two herbicides depends on the site and what other weeds that you might want to control. Clopyralid products have a residential turf restriction on the label, but can be used in all other areas including golf, athletic fields, cemeteries, and commercial turf. Clopyralid is a broadleaf herbicide and will not control grassy weeds. Quinclorac is labeled for all turf sites and will control grassy weeds such as smooth and large crabgrass. In addition, quinclorac products (single herbicide products only) are safe for over-seeding of existing turf while clopyralid has a 3 to 4 week after seeding restriction.

    Randy Prostak, UMass Extension Weed Specialist

    Garden Clippings Tips of the Month

    June is the month to . . . .

    Lawns

    • Consider allowing your lawn to go summer dormant. Cool season grasses naturally go dormant during the hot and dry parts of summer. When cool temperatures return in late summer, cool season grasses will resume growth.  
    • Raise the lawn mower height to 3-4”. Raising mower height will reduce stress during the hottest, driest months.
    • Keep mower blades sharp, return clippings to the lawn, and avoid mowing when wet.
    • When watering lawns, water deeply and infrequently. Water in the early morning when the grass would naturally be wet with dew. Most lawns require about an inch of water each week.  

    Ornamentals

    • Pinch back perennials like asters and chrysanthemums. Pinching helps produce nicely mounded plants and reduces lodging.
    • Remove foliage from bulbs like tulips, daffodils, and hyacinths only after the foliage has begun to yellow. Removing the foliage earlier will reduce bloom potential in subsequent years by decreasing the amount of food stored in the bulk produced by photosynthesis.
    • Remove spent flowers. Dead flowers can be a source of botrytis, especially on plants like peony and New Guinea impatiens.
    • Now is the time to prune those spring blooming shrubs not pruned during the dormant season.
    • Make sure to continue watering newly planted trees, shrubs, and herbaceous plants.
    • Consider installing drip irrigation. Drip irrigation is easy to install, conserves water, and does not wet foliage, potentially reducing disease.

    Fruits and Vegetables

    • Use mulches to reduce evaporative loss of moisture from soil and reduce weeds. Natural mulches such as straw and leaves will keep soil cool. Black plastic mulches will warm soil.
    • Stay vigilant with weeding. Use shallow cultivation on seedlings to minimize soil disturbance and avoid bringing new weed seed to the surface.
    • Stake, trellis or cage tomatoes. Remove suckers (the shoot that forms in leaf axils) on larger fruiting tomato cultivars weekly.
    • June drop is a phenomenon in fruit trees often related to poor pollination or carbohydrate regulation .
    • Thin peaches and nectarines to about 6 inches between fruits. This will allow fruits to become larger and avoid breakage of limbs as a result of overbearing.

    Other

    • Take the time to identify the plants in your yard. Do the research and find out what native plants already exist and/or what invasives need to be managed.
    • Take the time to monitor plants for pests and damage. Timely identification will allow intervention before pests get out of hand. When monitoring, look carefully over the entire plant from the base to the top, also looking at the undersides of leaves. A magnifying glass can help make out anything the naked eye can’t.
    • Pay attention to watering needs. Install a rain gauge so you know exactly how much precipitation has fallen.  

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

    Tick season is in Full Swing…

    Deer tick size comparison of life stages.It is nearly summer and people are engaged in a lot of outdoor activities, particularly as we navigate out of the pandemic. And in New England, we have to be mindful that there is a continuous exposure risk for a tick bite. Check out the family portrait on the left. On the far right is an adult female deer tick and an adult male is in the center (adult stage tick season finished in late May in Massachusetts).

    On the left is a nymph stage tick and these will be active into August. Nymphs are the size of a poppy seed, which means they can easily elude a tick check. This is reflected in the case data shown in the chart below (MA Dept. Public Health). This stage is responsible for 85% of tick-borne diseases. Note however that there are cases of Lyme disease every month of the year.Number of confirmed and probable Lyme disease cases reported in MA by month in Onset, MA 2014

    And it’s not just about Lyme disease anymore. Other significant diseases carried by deer ticks are babesiosis and anaplasmosis.  We see a certain level of co-infection where ticks are causing more than one pathogen.

    A personal protection plan is very straightforward. When you are in tick habitat, which could be in the woods or at the edge of your backyard, wearing light-colored long pants and shoes, versus sandals, is a start. When you come back indoors, be sure to do a tick check and throw the clothes you were wearing in the dryer for 20 minutes.

    Repellents are important - skin repellents like DEET or picaridin are effective. Avoid “all natural” products - there is no testing that shows these products are safe or effective.

    From my standpoint, the most effective tool in the box is permethrin treated clothing and footwear. It not only repels but actually kills the ticks. You can find this product at garden centers and sporting good stores. I have prepared a video on the ins and outs of using permethrin, part of our ten part Tickology series. 

    Enjoy the outdoors, be tick aware, and stay tick safe.

    Larry Dapsis, Entomologist, Cape Cod Cooperative Extension

    Upcoming Events

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

    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.