MELeaf: A Newsletter From the Horticulture Program, March 24, 2021

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MELeaf: A Newsletter From the Horticulture Program, March 24, 2021

In this issue:

Invasive Plant Checkup

Every year we see a few invasive plants offered for sale. The vast majority of nurseries and garden centers are doing a great job making sure none of the 33 prohibited plants are in their inventory. If you haven’t reviewed the list of plants and compared it to your current inventory or checked it again as new plants are received, we hope you will take a few minutes to make sure you are not selling prohibited plants 

We recently received an email with a picture of a box with burning bush and honeysuckle bare root plants for sale at a Sam’s Club in Bangor (pictures below). It is very difficult to manage the offerings of national chain stores and we rely on the help of engaged citizens to alert us to potential problems. Fortunately, the Sam’s Club manager was quick to remove the boxes from the shelves and to alert his corporate managers about the problem. Subsequent inspections of additional Sam’s Club and sister Walmart stores did not discover any more of these highly invasive plants. We continue to work with the corporate offices to make sure they stay on top of this issue and don’t end up with any of the 33 plants that are currently prohibited for sale or import in our state on their shelves or available on their websites. We are asking their corporate offices to also help us locate any of the purchased items so they can be returned and to prevent them from being planted in Maine. 

Invasive plants are a huge concern for many land managers and can significantly impact native plant populations. If we all work together we can prevent new introductions of these plants of concern. 

Steps you can take to prevent the spread of invasive plants in Maine:

Burning bush and honeysuckle boxes

Phytophthora ramorum - a good reason to buy local

Spring is finally here, and with it comes shipments of early flowering shrubs such as andromeda, witch hazel, scotch heather and rhododendrons to Maine nurseries. Before you move them into sales or holding areas, take care of the first order of business, a thorough scout for pests and diseases. One disease that nursery owners should be familiar with if they are buying plant material from the west coast is Phytophthora ramorum aka sudden oak death.

This often frustrating disease has a wide host range, over 100 species, including those mentioned above. Other important hosts are magnolia, viburnum, dogwood, lilac, fir, rugosa rose and oak. Symptoms of P. ramorum look similar to sunburn and other disease. Scout for leaf spots with a water-soaked appearance and indistinct edges that can be seen on both upper and lower leaf surfaces. On stems look for blackened or necrotic stem tips which stop water from reaching leaves and cause wilting.

In the right environment, such as coastal California and Oregon where it is established and kills native oaks, P. ramorum can survive in soil and water. These are also areas with large production nurseries that distribute plant material all over the country. P. ramorum is federally regulated, which requires nurseries in quarantine areas to be surveyed for the disease to make sure infected host plants are not moved to uninfected areas. If the disease is found at a nursery in the quarantine area, all host plants that were shipped that year must be tracked down to their end destination, a process called a trace-forward. A trace back is the reverse, when the disease is initially discovered on shipped plants and the movement of those plants is tracked back to the place where they were originally grown.   

If a P. ramorum infected plant is found at a Maine nursery, the federal quarantine dictates a protocol that must be followed to be sure the disease does not become established in the environment. P. ramorum is not possible to diagnose visually, the symptoms are too similar to plant damage from other causes. Suspect plants must be tested to confirm infection. Consider plant symptoms suspect if they meet ALL of these criteria:

If you have plants that meet these criteria, take pictures and send them to and include information on the species and variety of plants that are affected, where the plants were purchased, when they arrived in Maine and how many plants were in the shipment. Once we have this information we will contact you with further information about collecting a sample for testing. Reporting suspect plants is essential because this disease could be a disaster for Maine's forests. Early detection and proper destruction of infected plants is paramount.

Ways to reduce the risk of importing Phytophthora ramorum infested plant material:   

  • Know where your plant material is coming from, especially if buying through a broker.  
  • If host plants are ordered from within the quarantined area, ask the nursery of origin if P. ramorum has ever been found at their growing location.   
  • Be wary of especially good deals on host material coming from quarantine areas.   
  • Make sure any out of state plant material you purchase is coming from a licensed nursery with a certificate of inspection including certification for freedom of P. ramorum, if required. 
  • Buy local, where the native or established pests are more likely to be the same as in your area. 
  • Scout incoming plant material for symptoms and know when and how to report plants with suspicious symptoms.
Symptoms of Phytophthora ramorum

Some possible symptoms of Phytophthora ramorum

Current COVID-19 Guidelines for Greenhouse and Nursery Businesses

If you are anticipating brisk spring sales this year, you are not alone. After an entire year of pandemic restrictions and work from home’ schedules, customer demand for locally grown plants, seeds and gardening supplies is likely to be even bigger than last year. Is your operation ready for customers? Have you trained your staff to follow appropriate guidelines to protect themselves and customers and prevent the spread of COVID-19? 

Although we know more about COVID-19 than we ever wanted to, US CDC provides detailed guidance for preventing its spread in workplace settings which is appropriate and applicable to Maine greenhouses and nurseries. These strategies can be categorized as Engineering, Administrativeand Training. 

Engineering StrategiesThe greatest risk of disease spread is among people sharing indoor air, especially in close contact, or for prolonged periods (more than a few minutes)To reduce the risk, open screened windows and doors or use fans to ensure good ventilation indoorsMove displays and sales areas outdoors when possibleInstall a Plexiglas shield or move the card reader away from the cashier at the checkout station. Use directional markers, signs, floor stickers, or hay bales and flagging to create one-way customer flow, online sales and curbside delivery are likely to remain popular and also reduce the risk of disease spread. Good hand hygiene is another essential tool for reducing spread of illness, so providing convenient hand-washing facilities for workers is critical. Regularly clean and sanitize frequently touched surfaces such as card reader machines, keyboards, cart handles and door knobs.

Administrative Strategies: Require all employees, customers, and visitors to wear face coverings. Monitor state and local public health communications about COVID-19. Limit the use of shared work spaces by relocating work stations or using staggered schedules to reduce the risk of contagion among employeesActively encourage sick workers and those exposed to COVID-19 to stay home and follow CDC guidanceAdditional guidance on how long workers should stay home, get tested or stay isolated

Training Strategies: Provide employees with training on workplace policies and procedures including general hygiene, cleaning and disinfection protocols, proper use of face coverings and PPE, and what to do if sick or exposed to COVID-19.


Kathy Murray is Retiring!

Kathy Murray, entomologist extraordinaire, Horticulture Program IPM Specialist and all around great person is retiring at the end of April. Many of you have gotten to know Kathy as she planned, organized, presented and moderated various meetings and events for the Department of Agriculture, Conservation and Forestry including the Greenhouse Best Practices Workshop and the Tristate IPM Program. Kathy has been an invaluable resource for nurseries, greenhouses and us here at the Horticulture Program and helped identify and solve countless pest problems, while always promoting the use of IPM. We will certainly miss her, but hope you will join us in wishing her well in her retirement. If you'd like to sign Kathy's electronic retirement card,  contact

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