Roots, Shoots, Fruits & Flowers: Potato Wart Disease, Blossom End Rot X2, Hydrangea Leaf Spot & Louisiana Super Plants

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A potato infected with a fungal wart disease. Photo: Andrea Wilson.

Potato Wart Disease

Andrea recently harvested some vegetables from her garden and saw something of concern, “I attached some pictures of the potatoes we grew. First batch we dug up and I have never seen this before. What is it and are they still edible? Thank you.”

AHA send this image to the Plant Diagnostic Lab in Baton Rouge, and the diagnosis came back as “potato wart disease” or PWD. PWD is a fungal disease and according to the USDA, “The disease appears mainly on stolons and tubers. Symptoms on above ground growth are not often visible.” The USDA website also shares this information, “[The fungal pathogen] loves wet conditions. It produces a thick-walled structure known as a winter sporangium which can remain viable for up to 30 years. It can survive at depths of 50 cm [ or almost 19 inches] in the soil.”

Where does PWD come from? The answer is: “Infected seed tubers, infected soil, machinery and implements used in infested potato fields and potato cultivation, footwear, and manure from animals that have fed on infested tubers can spread this disease.”

The fungus has no health effects to people. The deformed potato is unmarketable, so this disease hurts the potato farmer economically and upsets the gardener.

Some states regulate PWD with quarantines, but Louisiana does not regulate this disease. One measure to contain this disease includes using PWD resistant varieties of potatoes. Prevention of PWD is more practical than control.

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Banana peppers with blossom end rot. Photo: Justin Ballew, Clemson Extension.

Blossom End Rot X2

Kimberly, another gardener, saw a condition on some of her vegetables, “What is on my hot banana peppers and how do you correct it?”

Like tomatoes, peppers can have blossom end rot or BER. This condition is the result of a lack of calcium in the soil. For the long term, soil testing and then fertilizing according to recommended rates in the analysis will resolve this deficiency. For the short term, a level teaspoon of calcium nitrate per plant will help salvage the rest of the gardening season.

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A small squash with blossom end rot and another infection. Photo: Peggy Kessler, Master Gardener.

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Blooms of the limelight hydrangea. Photo: Dan Gill, LSU AgCenter.

Hydrangea Leaf Spot & Louisiana Super Plants

Gayle wrote about her hydrangea, “Can you possibly give me some direction based on these pictures?”

Gayle has a fungal leafspot disease. An AgCenter horticultural agent wrote about some control measures, “It is highly important to remove any diseased leaves that have fallen from the plant as well as hand picking highly infected leaves from of the plant. Be sure to discard these disease leaves in the trash, and do not put into the compost bin.

Chemical control options of Cercospora leaf spot include spraying regularly with a product containing chlorothanil, such as Bonide Fung-onil™, Ortho MAX Disease Garden Control™ or Daconil™. Spraying will not take away the damaged area of the foliage but will prevent the spread to new foliage. Lastly, fertilize lightly with a nitrogen fertilizer to help encourage the new disease-free growth.”

Another option may include a new type of hydrangea. The limelight hydrangea is a Louisiana Super Plant (LSP). Dr. Jeb Fields, a horticultural specialist, shared this guidance about the limelight hydrangea, “In general Limelight does not have major issues with leaf spot like some other hydrangeas on the market. We see Cercospora [a fungal disease] on [regular garden] hydrangea much more often than [the limelight] Hydrangea. [None] of [the hydrangeas] are completely resistant, and any of the hydrangeas can have Cercospora problems. Limelight [hydrangeas] are also generally planted in the sun so the foliage will dry out much more quickly.”

If you are unfamiliar with the Louisiana Super Plant program, The LSU AgCenter identifies ornamental plants which consistently resist diseases and insects and maintain their attractiveness. They tend to be lower maintenance and keep the color of both their blooms and foliage over the growing season. The plants that perform the best are recognized as Louisiana Super Plants.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or khawkins@agcenter.lsu.edu. Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

7/9/2020 4:48:07 PM
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