Extension Master GardenerSM Volunteers of Buncombe County

Plant Diseases

Southern Blight: Large Variety of Plants Vulnerable to This Disease

With summer coming, so are plant diseases. One that can affect an astonishing variety of plants—from apple trees to zinnias—is Southern blight, caused by the fungus Sclerotium rolfsii.

Southern Stem Blight_Sclerotium rolfsii_leaf wilt on pepper plant; courtesy of Chatham County NC State Extension
Leaf wilt on pepper plant, a sign of Southern blight

What to watch for
Southern blight thrives in hot, humid conditions. Although the fungus can infect many plant parts—including roots and fruits—it typically shows itself as wilt resulting from rotting stems at the base of the plant. Even before the plant wilts, you’ll often see water-soaked spots on the stems.

Common casualties
Some plants are particularly vulnerable. Hostas may succumb in your perennial garden. Many root crops are affected, including beets, carrots, Jerusalem artichokes, parsnips, radishes, sweet potatoes, and turnips. Other victims may be cantaloupe, eggplant, peppers, snap beans, sweet corn, and tomatoes.

SouthernBlight_Hosta_moccasinlanding_CC BY-NC-ND 2.0_Flickr
Southern blight on hosta

How it survives
One reason Southern blight can persist in soils is that it forms sclerotia: hard, rounded bodies that look like mustard or radish seeds. The disease is sometimes called Sclerotial blight for this reason. It can also remain in plant residue in the soil and spread through surface water.

What to do
As with all fungal diseases, prevention is key. Once the plants are infected, fungicides may help prevent the spread of the disease to other plants, but won’t reverse problems on plants already affected. Depending on the crop, fungicides used as soil drenches prior to planting may prevent infection. Different fungicides are recommended for different crops, however.

Sclerotia or hard nodules on pepper plant stem with Southern blight, Sclerotium rolfsii; courtesy of Chatham County NC State Extension
Sclerotia or hard nodules on pepper plant stem with Southern blight

Immediately remove infected plants along with their roots and the surrounding soil. Do not compost! If container plants are affected, do not reuse the potting soil. If Southern blight takes hold in your garden, solarizing for several weeks using plastic during the summer may kill the fungus.

For more information about recommended fungicides:
https://content.ces.ncsu.edu/north-carolina-agricultural-chemicals-manual/disease-control
(See page 498 for Southern stem blight, Sclerotium rolfsii)

Factsheet from the American Phytopathological Society:
http://www.apsnet.org/edcenter/intropp/lessons/fungi/Basidiomycetes/Pages/SouthernBlight.aspx

Article written by Debbie Green, Extension Master GardenerSM Volunteer.

Time to Maintain: Remove Leaf Gall from Azaleas and Camellias

I am fortunate to have many native flame azaleas growing on my property. But this time of year—April and May—just when they begin to bloom, I see abnormal growths at the tip of some stems. They look like little green apples and are slightly smaller than a ping pong ball. What are they?

Azalea Leaf Gall (Exobasidium vaccinii)
The growths are caused by a fungus that thickens the emerging foliage into these soft-tissue balls. The spores of the ripening fungus are spread by wind and splattering raindrops. They overwinter in the ground and on the plant’s branches and re-infect the azalea again in the spring. While the galls won’t kill the plant, they are unsightly. The best defense is to pick the galls while they are still small and green. Once they’ve turned white and begun to dry up, they release their spores and you’ll contend with even more galls next season. Exobasidium vaccinii primarily affects native azaleas, but it can spread to rhododendrons and hybrid azaleas, too.

Camellia Leaf Gall (Exobasidium camelliae)
I also have a beautiful stand of sasanqua camellias affected by leaf gall caused by a different fungus. The emerging leaves thicken and turn reddish. I check the shrubs every few days and clip off the affected leaves before the galls mature and release spores. Although Exobasidium camelliae mostly affects the sasanquas, other camellia species are also susceptible.

Camellia leaf gall (Exobasidium camelliae). Photo by Joey Williamson, courtesy of Clemson University Extension.
Camellia leaf gall (Exobasidium camelliae). Photo by Joey Williamson, courtesy of Clemson Extension.

Good practices
Be sure to sterilize your pruners between cuts so as not to spread the fungus to other branches. Dispose of the galls in a plastic bag and throw them in your trash—not the compost pile. Manual removal is usually the only treatment needed. Providing good air circulation minimizes the time rainwater stays on the leaves during rainy seasons, reducing the likelihood of fungal infections.

For more information about azalea leaf gall, view this publication from Cornell University: http://plantclinic.cornell.edu/factsheets/azaleagall.pdf

For more information about camellia leaf gall, check out this video from Clemson Cooperative Extension: http://www.clemson.edu/extension/hgic/videos_posters/videos/camellia_leaf_gall.html

Article written by Beth Leonard, Extension Master GardenerSM Volunteer.

Late Tomato Blight Is Here

Late tomato blight was discovered in Buncombe County last week. This is a reprint of a post written by Debbie Green, originally published two years ago.

Tomatoes should be reaching their prime, and if you have lush green plants with ripening fruit, enjoy your harvest. If your plants aren’t looking so good however, they may have one of the many tomato diseases that sometimes thwart even the most experienced vegetable gardeners. One of the most serious of these is late tomato blight, which typically affects plants later in the growing season, but has been confirmed on plants in West Asheville as of early July this year. This disease can spread spores as far as 20 miles, so identifying the disease and destroying the affected plants may spare others’ tomatoes from developing the symptoms.

The first symptoms of late blight on tomato leaves are irregularly shaped, water-soaked lesions.
The first symptoms of late blight on tomato leaves are irregularly shaped, water-soaked lesions.

Rain and high humidity are both favorable conditions for the spread of late blight. Once your plants are infected they can’t be cured; fungicides containing copper or chlorothalonil are currently the only treatments proven effective to prevent late blight. If you spray your plants, follow label directions. Take care to cover all leaf surfaces; use eye protection and other precautions to prevent contact with the spray.

The good news is there are less devastating diseases that are not late blight, so getting a positive diagnosis is important. The first signs are irregular dark spots that look water-soaked on the newer leaves at the top of the plant, often with a lighter-colored “halo” around them. As the spots enlarge, the leaves shrivel and die. You may also see white cottony growth on the underside of the leaves. Both ripening and green fruits are also affected, with greasy looking spots that turn brown and leathery.

During humid conditions, white cottony growth of P. infestans may be visible on the underside of affected leaves.
During humid conditions, white cottony growth of P. infestans may be visible on the underside of affected leaves.

There are many images available online to help you determine if you have late blight; one of the most comprehensive series of photos is this one prepared by Dr. Meg McGrath of the Long Island Horticultural Research and Extension Center: http://www.longislandhort.cornell.edu/vegpath/photos/lateblight_tomato.htm#images. If you are unsure about the diagnosis, you can bring photos and samples of your plants to the Master Gardener Clinic at the Buncombe County Extension Office.

If you do have late blight, bag up your plant as soon as you can, but do it on a sunny day to reduce further spread of the disease. You can salvage already ripened fruit or green tomatoes that don’t show symptoms; these are safe to eat. Take care to look for affected plants other than tomatoes, especially potatoes and petunias. Weeds in the nightshade family may also show symptoms and should be removed and bagged.

Infected fruit are typically firm with spots that eventually become leathery and chocolate brown in color.
Infected fruit are typically firm with spots that eventually become leathery and chocolate brown in color.

If you lose your plants, there is always next year. There is ongoing research on less susceptible varieties and some evidence that ‘Defiant,’ ‘Mountain Merit,’ ‘Mountain Magic,’ and ‘Plum Regal’ tomato varieties are resistant to late blight. Consider planting these varieties next season if you want to increase your chances of a blight-free crop.

For more information see http://content.ces.ncsu.edu/publication/tomato-late-blight/

Contact Us

Buncombe County Extension Office
49 Mount Carmel Road
Asheville, NC 28806
Helpline 828-255-5522

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