Diseases – Maryland Grows

Boxwood Blight in Maryland

April 1, 2019June 15, 2021Maryland Grows2 Comments

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.

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

January 7, 2019April 7, 2021Maryland Grows6 Comments

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 →

2018 vegetable garden re-cap

November 16, 2018January 11, 2022Maryland Grows1 Comment

This is a good time to think about what worked and what didn’t work so well in our 2018 garden spaces. What was unexpected, which weeds and diseases were challenging, how can we prevent problems and have greater success next year? In that spirit, and before they become dim memories, I’ll share a few observations from the past growing season.

Weather

No two years are alike when it comes to weather and food gardening, but wow, 2018 was unusual! We had a slow spring warm-up and record rainfall in Maryland for the May-July period with multiple 2+ inch rain events (NOAA, 2018; Baltimore Sun, 2018). Unfortunately, extreme weather events and above-average rainfall is consistent with the climate change models for the mid-Atlantic region.

The combination of environmental factors- excess rain, wet soils, wildly fluctuating spring temperatures, and high heat and humidity through much of the summer- contributed to a lot of plant stress, leached nutrients, soil erosion, increased disease and weed pressure, and decreased yields.

Learn more about climate change and how gardeners can meet the challenge on HGIC’s climate change page. Also, at the bottom of the page you will see Climate Change in Your County. This little gem is from the Climate Smart Farming program at Cornell University and presents data graphs of temperature and precipitation changes since 1950 in all Northeast counties.

Edema (burst plant cells) of tomato seedlings

Too much water inside the home! Jerry Brust, Ph.D., Vegetable IPM Specialist, identified excessive watering as the cause of these tomato transplant symptoms. “Loving them to death” is a common gardening disorder. Let the top of the growing medium dry a bit before watering.

Leaf spot diseases on Roselle hibiscus

Roselle sabdariffa is a fabulous plant grown by many gardeners of Indian and West African descent. It has a lemon-sour taste similar to French sorrel. There are several leafy types that are harvested throughout the growing season.

I’ve observed these plants in community gardens in Central Maryland for many years and saw no disease problems. This year, leaf spot symptoms appeared late summer in Howard Co. I sent a sample to the UM Plant Diagnostic Lab. Three different fungal pathogens were found on the sample and the symptoms are most consistent with Cercospora leaf spot, a disease known to infect Roselle. The lab provided excellent recommendations for preventing or minimizing the problem next year: keeping the foliage dry (no overhead watering), remove infected debris at the end of the season to reduce inoculum, and plant it in a different part of the garden next year.

Rainstorms washed away precious soil

Torrential July downpours washed unprotected soil onto streets and down storm drains across the region. Clay and organic matter particles were washed away with the rain leaving silt, sand, and stones in the road. Negative environmental effects at one location affect the ecosystem downhill and downstream.

All boys (for a while) club

This young zucchini plant produced 12 male flowers (on straight stalks known as pedicels) before the first female flower (undeveloped fruit, the ovary, forms below the un-opened flower). Be patient- this is normal for most species and varieties in the Cucurbitaceae family.

Must prevent tomato diseases, must prevent tomato diseases, must prevent…

The principal fungal leaf spot diseases of tomato, early blight (above) and Septoria leaf spot, can be effectively managed so that decent crops are harvested each year. Reduce infection and spread by planting clean seed and transplants, 2 ft. minimum spacing, removing lower leaf branches, watering at plant base, removing all plant debris at season’s end.

Go deep for dependability

Photo: Jon Traunfeld

I love these examples of deep and productive raised bed gardens at the Friends House community garden in Sandy Spring.

Life is impermanent (including blackberry)

The excavated crown of an 8-year old blackberry plant that was infested with rednecked cane borers. The plants were also infected with spur blight, a fungal disease and possibly other pathogens. HGIC strongly recommends bramble fruits because they are dependable and can be grown organically. But they are susceptible to many insect pests and diseases and may become so weakened that they need to be removed.

Enjoy your Thanksgiving and start dreaming about next year’s garden!

By Jon Traunfeld, Extension Specialist

Q&A: What’s wrong with my hydrangea flowers?

August 6, 2018March 11, 2022Maryland GrowsLeave a comment

Q: My hydrangea bloomed white but instead of turning red it turned brown. What is happening to the petals and what can be done?

A: A disease called Botrytis blight can cause spots and browning symptoms on the flower petals of Hydrangea and other types of flowers as well. Extended periods of cloudy, rainy weather like we had recently can favor the development of this fungal disease. Botrytis first appears as water-soaked spots that gradually expand into brown blotches. There is no remedy for this damage. Prune out and dispose of the damaged flower parts.

The spotting on the leaves is common on Hydrangeas in late summer, especially in our humid climate. Leaf spots can be caused by fungal and bacterial pathogens. The leaf spots are mainly a cosmetic problem. They will not kill the plant. Chemical control is not recommended in most home garden situations.

Keep Hydrangeas watered regularly during drought periods and avoid overhead watering to minimize wetness on the flowers and foliage. Clean up and dispose of symptomatic leaves at the end of the growing season.

Visit the Home & Garden Information Center website for more information on common problems of trees and shrubs.

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

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

What causes holes in my cherry tree leaves?

August 28, 2017April 7, 2021Maryland GrowsLeave a comment

Q: I have a cherry tree that has been in the ground for three years and has grown well. This year, the leaves have holes and they are falling to the ground already. The tree was sprayed twice with an insecticide and a fungicide. All sprays have been at the recommended dilutions. The leaves continue to fall. What is the problem?

A: The foliage of your tree looks like it was subject to cherry shot hole disease. Infected leaves will turn yellow and drop from the trees in mid-summer, if the infection is severe. This disease can be common when we have wet spring weather. The pathogen may continue to infect leaves throughout the growing season if rainy weather persists. In most cases, trees recover from this disease and no treatment is necessary. Rake and dispose of fallen leaves in the fall to reduce overwintering pathogens.

In addition, be sure to identify a pest or disease before you decide to spray. Some insecticides are “broad-spectrum” products which will also harm many beneficial insects. Also, an insecticide will not do anything to treat a fungal or bacterial disease.

Learn more about cherry shot hole on flowering cherries and how to manage it.

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

Tomato problems? You’re not alone!

August 18, 2017February 25, 2022Maryland Grows6 Comments

We are at the peak of tomato harvesting and enjoyment time in Maryland. But many gardeners are unhappy, to varying degrees, with the quantity and quality of the fruits of their labor. Those tomatoes we waited so patiently for may have disappointing spots, rots, cracks, and holes.

Before we get into the specific problems, let’s agree that we cannot expect all of our fruits to be perfect, no matter how much time, money, and effort we invest. It’s a garden, not a climate controlled factory. Weather and climate change, soil and sunlight, cultivars and spacing are just some of the many factors affecting plant growth — and they change every year.

This is a good time to think about what we can do next spring to get more out of our tomato plants next year. Picking fruits when they begin to change color from green will increase the number of usable fruits. It allows you to get your fruits off the vine before problems strike. Ripen them indoors on a counter or in a box, basket, or bag. I think you’ll find they taste just as good as their “sun-ripened” sisters.
Continue reading →

Wilted Plants? Check for Signs of Southern Blight

August 7, 2017August 7, 2017Maryland GrowsLeave a comment

Southern blight on sage. Photo: Dave Clement

Southern blight is a plant disease that is active now in hot summer weather. It is caused by a fungus called Sclerotium rolfsii. This fungus has a wide host range including woody plants, vegetables and herbs, and ornamental perennials such as coneflower, peony, and hosta.

Signs and Symptoms of Southern Blight

The first symptoms seen are wilting and collapse of individual stems or entire plants.
Close inspection of the stem at the soil line reveals white mycelium (strands of fungus growing on the stem and/or soil surface), and small, white or tan spherical sclerotia that resemble mustard seeds.
Roots of infected plants are unaffected. Decay of the stem at the soil line is common during hot, humid weather.
Southern blight on banana pepper. Photo: Gerald Holmes, Bugwood

How to Manage Southern Blight

The cornerstone for control of southern blight is clean-up of diseased plants in the garden.
Wilted and blighted plants and plant parts should be promptly removed from the garden.
Do not compost material killed by southern blight because the resting spores (sclerotia) of these fungi may survive the composting process.

Visit the Home & Garden Information Center for more information on Southern blight.

Have a question about ornamental plant care? Submit your question to Ask an Expert.

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