trees and shrubs

Q&A: What is this white growth on my cherry laurel shrub?

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white prunicola scale on cherry laurel
An infestation of white prunicola scale on cherry laurel. Photo: University of Maryland Extension

Q: We have cherry laurel shrubs that were growing very well for a few years. Yesterday, I noticed some of the leaves on one side of a laurel were brown. When I looked closer, I found that all of the branches inside were covered with a white substance. What is it? What can I do about it?

Answer: The white substance on the branches is an infestation of white prunicola scale. Scales are very tiny insects that feed on plant sap. Their feeding leads to leaf yellowing, browning, and eventual dieback of branches.

Scale insects are challenging to manage. The waxy white substance they produce provides a form of protection from desiccation and predators. They produce three generations each year, so if a population is not controlled all at once, they can continue to reproduce and be a persistent problem.

When there is a heavy infestation of white prunicola scale and dieback is severe, it may be best to remove the shrub altogether rather than try to treat it. Depending on where the infestation is located, you may be able to prune out branches selectively and discard them.

Fertilized female scales overwinter on the bark of the branches, so another step in management is to apply a dormant rate of horticultural oil during the dormant season (when deciduous plants have lost their leaves). You can first use a soft-bristled brush to scrub off the scale patches gently. Then apply the horticultural oil.

white prunicola scale
White prunicola scale covering (female) and eggs. Photo: Brian Kunkel, University of Delaware, Bugwood.org

If female scales remain on the shrub, juveniles (called “crawlers”) will emerge in the spring. Crawler periods vary from year to year depending on temperatures. For this species, new generations may be out in May, mid-July to mid-August, and September.

The tiny juvenile crawlers are salmon-colored. You can place a simple trap to detect their activity; wrap a piece of double-sided tape around a few branches. When you see crawlers stuck to the tape, that is the ideal time to apply horticultural oil. Oil spray is the least harmful to beneficial insects such as ladybird beetles, which you want to keep in your landscape because they help tamp down on other pests.

White prunicola scale is a fairly common problem on cherry laurels. Residents who have these shrubs should check them periodically for leaf yellowing and white spots on lower branches. Scales are easier to manage if you catch them early.

By Christa K. Carignan, Maryland Certified Professional Horticulturist, Coordinator, University of Maryland Extension Home & Garden Information Center

More on this topic: Cherry Laurel: Identify and Manage Problems, from the University of Maryland Extension (February 2024)

Have a plant or insect question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask Extension.

Dealing with standing water in your yard

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standing water in the yard
Deal with standing water by adding topsoil or planting vegetation that prefers boggy areas. Photo: UME / Ask an Expert

Q: Our backyard has very low spots where the water ends up after heavy rains. How do I deal with this? I would like to plant a garden of shrubs and perennials but don’t think many can take that much water. Red maples and birch seem happy, but the hydrangeas I planted last year all died. It gets quite a bit of sun.

Answer: Most plants will not tolerate sitting in standing water or saturated, soggy soil for long periods. You may be able to add one to two inches of soil to fill in low spots or raise the grade enough so that water will run off better or at least not accumulate there. A steep grade is not necessary or desirable because in dry years you do want the water to sink into the soil and down to plant roots.

This past year we had abnormal rainfall — about twice the average. Many people lost plants in areas where they had grown for years but were now under water too much for the plants to survive. The maple you have may be red maple, which is happy even in a bog; the birch is probably a river birch. Hydrangeas love moist soil, but cannot tolerate standing water. In saturated soils, the water pushes out the oxygen roots need. Eventually, the plant drowns, unless it is a plant adapted to saturated soil, i.e. a bog.

You may have a good location for a rain garden. Many plants love this environment — some stunning natives in particular, such as button bush and clethra. (Both are also butterfly magnets!) Take a look at the University of Maryland Extension webpage on stormwater practices.

Don’t get bogged down (no pun intended!) with details. Just plant what likes “wet feet.” Native plants are the best. For more plant choices, look at the U.S. Fish & Wildlife Service’s excellent publication, “Native Plants for Wildlife Habitat and Conservation Landscaping: Chesapeake Bay Watershed.” In the lists, ‘Plants for Freshwater Wetlands and Other Wet Sites’ should be helpful. (There is also the equivalent online database, http://www.nativeplantcenter.net/.).

You may not have standing water continuously in the future. However, it is predicted that we can expect a lot more wet years and extreme weather ahead because of climate change. A rain garden is a smart way to handle this, as long as this spot does not hold water all summer (and breed mosquitoes). When you install a rain garden, the plant roots will be pulling in the water and drying up the low area, too.

By Ellen Nibali, Horticulturist, University of Maryland Extension Home and Garden Information Center. Ellen writes the Garden Q&A for The Baltimore Sun.

Have a plant or insect question? University of Maryland Extension’s experts have answers! Send your questions and photos to Ask Extension.

Boxwood Blight in Maryland

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Until last summer most people in Maryland weren’t aware of the new fungal disease infecting boxwood called boxwood blight. In 2011 professionals in the green (landscape and greenhouse) industry were informed of the disease but the outbreaks were scattered and insignificant. However, the rainy 2018 season greatly increased the spread of the disease. It has now become more noticeable in Maryland landscapes. In addition, on a few occasions, it has been observed on Japanese spurge (Pachysandra terminalis) in Connecticut and on sweetbox (Sarcococca sp.) in Maryland and Virginia. Essentially, boxwood blight occurs up and down the east coast.

Boxwood blight will infect all boxwoods grown in landscapes. However, some cultivars, especially English and American, are more susceptible than others. See the following photos for symptoms of boxwood blight.

boxwood blight leaf lesions
Dark leaf spots are a symptom of boxwood blight. Photo: Dave Clement

boxwood blight stem lesions
Narrow black lesions (cankers) on green stems are a key symptom of boxwood blight. Photo: Dave Clement

boxwood blight lesions on dead stems
Black lesions on stems of boxwood. Photo: Dave Clement

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So the question is what to do if your shrubs are diagnosed with boxwood blight? The best information for homeowner action is located on the Virginia Boxwood Blight Task Force website: Best Management Practices for Boxwood Blight.

Here is a quick summary of what to do in the landscape:

  • A strong suggestion is to avoid planting any new boxwood plants in your existing landscape or bringing in boxwood greenery, including holiday boxwood wreaths.
  • If planting, inspect your plants carefully and ask if the plants have been raised in a certified “cleanliness program.”
  • Observe and watch any newly planted boxwoods carefully for disease symptoms.
  • Send photos of suspicious symptoms to the Home & Garden Information Center’s Ask Extension service.
  • If disease symptoms are diagnosed, immediately bag and remove infected plants along with fallen leaves. Mulch the area to bury remaining debris. Do not compost infected boxwood material. Launder all clothing, gloves, and shoes, and sanitize gardening tools.  Removal will not guarantee eradication of the boxwood blight pathogen since it can survive in resting structures in the soil for many years.
  • Fungicide sprays have shown some disease suppression in limited situations. However, these treatments do not eradicate boxwood blight and need repeated applications throughout the growing season.
  • Consider replacement of boxwoods with non-susceptible plants such as hollies and conifers.

By Dr. Dave Clement, Principal Agent, University of Maryland Extension, Home & Garden Information Center. 

For those who are looking, there are sycamores

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sycamore tree
American sycamore tree in winter. Photo: Paul Wray, Iowa State University, Bugwood.org

I knew I had to go back to school to study horticulture when I was in my mid-twenties. Every day on my way to work I found myself looking out the windows at trees instead of watching the road. The Catoctin mountain forest was particularly enticing. Route 15 was a much quieter road then, and fortunately, there were no mobile phones to provide additional distractions. Although I admired the landscape in general, there was one tree that stood out amongst the others: the sycamore. Against a blue daytime sky or a sunrise dancing with pink and purple hues, its white bark was remarkable. The shape of this towering tree with its dazzling bark and color contrast inspired me to leave a secure job in search of knowledge for the things that ignited curiosity in me. Continue reading →

Q&A: What’s wrong with my cherry laurel shrubs?

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cherry laurel
Cherry Laurel with Leaf Scorch Symptoms and Holes. Photo: University of Maryland Extension / Ask an Expert

Q: My cherry laurels do not look good. There are brown spots and holes on the leaves and white stuff on the trunk. What can I do?

A: First, there is a lot to like about cherry laurels (Prunus laurocerasus). They are popular evergreen screening and foundation plants, deer-resistant, and pretty tough once established. Cherry laurels make their best growth in moist, well-drained soil in full sun to partial shade. They even tolerate full shade.

We receive numerous questions about problems with these shrubs. They can have multiple issues that are attributed to environmental, climate, or site conditions. When the plants are stressed, they weaken and become susceptible to diseases and/or insect pests. It is helpful to be aware of these issues before planting them. Continue reading →