Stave Off Sweet Potato Disease

Bacterial soft rot has proven to be a challenge for southeastern growers. Photo credit: Jason Chandler
Bacterial soft rot has proven to be a challenge for southeastern growers. Photo credit: Jason Chandler

Several key diseases of sweet potatoes affect growers in the Southeast, and tactics such as variety selection, sanitation, and proper postharvest handling have proven to be effective control measures.

Chris Clark, Professor at Louisiana State University (LSU) Agricultural Center’s Department of Plant Pathology and Crop Physiology, shows how using these management tactics can help keep key diseases at bay.

Assess Your Conditions
The first thing to do before choosing your varieties is to determine what diseases may be potentially present in your fields, Clark says.

The selection of resistant varieties is most often used to control soilborne diseases, as opposed to diseases associated with propagation, which are typically controlled by using virus-tested seed or certified seed, he explains.

“In the case of soilborne diseases, a grower may conduct soil tests, particularly for root knot nematodes, a pathogen that is common in the sandier soils of the Southeast,” Clark says. “By soil sampling and getting test results in the fall, growers can know whether or not they’re going to have to deal with it. If so, there are some varieties that have pretty good resistance and there are some that are susceptible.”

Increased Varietal Diversity
While the sweet potato industry was dominated by a few standout varieties, Clark explains how things are changing.

“‘Covington,’ a variety developed by North Carolina State University, has been predominant for the last few years, but there are other varieties that are being grown more so than in the past. Now we have ‘Bayou Belle,’ ‘Orleans,’ ‘Evangeline,’ and the newest one, ‘Bellevue,’” he says. These foundation seed varieties were developed by LSU.

When evaluating resistance among varieties, Clark and his colleagues have a different rating system for each disease.

“We evaluate them in controlled tests, comparing them to something we know is susceptible and something we know is resistant,” he explains.

Because root knot nematode is more common in Georgia and the Carolinas, many varieties adopted in that region will have resistance, particularly varieties ‘Bellevue,’ ‘Evangeline,’ and ‘Bonita.’

While disease resistance is key, Clark explains that most growers will not select a variety unless it is high yielding and high quality.

“For many years, they grew things that were susceptible even though there were resistant varieties available. That’s one of the critical things for us — trying to get everything in the same package,” he says.

Key Diseases And Non Varietal Management Methods
Clark says the potyvirus complex, which is a group of viruses comprised of sweet potato feathery mottle virus, sweet potato virus C, sweet potato virus G, and sweet potato virus 2, is a major threat to growers in the Southeast.

The best and only way to manage this complex is to start out with clean seed, he says. To support the distribution of clean seed, a sweet potato network was added to the National Clean Plant Network in 2015.

“One of the activities of the National Clean Plant Network is to develop tissue culture techniques to produce plants free of viruses. We then increase the tissue culture in greenhouses and produce foundation seed so farmers can buy clean plants of each of these varieties,” he explains.

After buying clean foundation seed, most growers increase the seed on the farm for an average of one year so there is enough to plant a crop.

“During this time, we encourage them to isolate the seed from their old plantings as much as they possibly can to avoid infection,” he adds.

Another key disease that has made an appearance in recent years is black rot, which can be carried in on seed roots.

“If it’s brought in, it can then spread onto the sprouts that come up from those seed roots that are used to transplant the crop. Again, the advice is to start clean and stay clean,” Clark says.

Although there are few management methods after infection occurs, crop rotation for up to three years may help. Selected crops for rotation will vary by state, but as long as it is not sweet potatoes, and there aren’t too many morning glories (a close relative of sweet potatoes) in the field, it should help prevent infection, Clark says.

While not as consistent, bacterial soft rot also has proven to be a challenge for southeastern growers. Bacterial soft rot tends to occur whenever oxygen is limited in the environment.

“The bacteria grow equally well in the presence or absence of oxygen, but to defend itself, the plant needs to have oxygen,” Clark explains.

Symptoms can be seen if the grower seals the plant bed too tightly with plastic and there is no air exchange, if potatoes are in storage with high temperatures and limited air exchange, or if there is a layer of moisture left on the sweet potatoes for an extended period of time.

Postharvest Management
To help control postharvest diseases or diseases that occur in storage, Clark recommends curing sweet potatoes immediately after harvest.

“With the curing process, we generally hold the sweet potatoes at 85°F to 90°F at about 85% humidity for anywhere between four to seven days,” he explains. “That helps promote healing of the wounds that occur when the sweet potatoes are being harvested, and it prevents pathogens from getting in and causing disease. It also helps prevent them from losing moisture.”

Improve Your Sanitation Practices
Sanitation is key when managing disease. While growers may have different systems for cutting seed, if using knives, dipping the knives in sanitizing solution with 10% bleach is helpful, Clark says.

When it comes to machinery, if a disease such as black rot is present, it is critical to sanitize all surfaces, however difficult that may be.

“You have to think about sanitizing the digging equipment, the pallet boxes, the packingline, and so on, from start to finish. You have to clean every surface that comes in contact with the sweet potatoes,” Clark explains.

For more information on sanitation and other postharvest management practices, you can consult the Postharvest Management of Sweet Potatoes publication at https://is.gd/sweet_potatoes.

Topics: ,

Leave a Reply

One comment on “Stave Off Sweet Potato Disease

Crop Protection Stories
Crop Protection
August 9, 2017
Why Some of the Most Dangerous Potato Diseases are Successful
If you understand the role oxygen, and its lack, plays in potato diseases, you'll be better equipped to battle them. Read More
a freshly picked avocado cradled in hand
Crop Protection
August 3, 2017
Can Avocados Be Saved from Deadly Laurel Wilt Disease?
Scientists from Florida and California are on the case and collaborating. Read More
Crop Protection
August 2, 2017
Report: 90% of NY Beehives Had Varroa Mites in 2016
Cornell University's NYS Beekeeper Tech Team recent report also shows most hives are infected with Deformed Wing Virus (DWV), a disease linked to the mites. Read More
sprayer nozzles
Biocontrols Conference
July 31, 2017
11 New Biocontrol Products You Need to Know
One of the highlights of the Biocontrols Conference & Expo Series is getting an early look at some of the Read More
Citrus
July 28, 2017
Popular Herbicide Registered for California Bearing Citrus and Caneberries
The supplemental label for Valent’s Chateau herbicide is particularly welcome for California growers of bearing citrus fruit, as it’s a new use. Read More
Diamondback-Moth-adult-Stormy-Sparks
Crop Protection
July 25, 2017
Vegetable Field Scouting Guide: Diamondback Moth
Due diligence is needed to help take down this pest of biblical proportions. Read More
Disease Control
July 25, 2017
Brown Rot Sinks its Teeth into Michigan Cherries
Unseasonably wet weather causes outbreak, and growers are warned it can spread to peaches. Read More
Disease Control
July 24, 2017
Researchers Find Detection Method for Crown Gall Disease
Oregon State University researchers developed molecular tools to work with commercially available kits that allow the user to quickly and effectively test plants for the disease, using a dipstick that reveals the presence of the pathogen within minutes. Read More
Citrus
July 23, 2017
USDA Invests $7.6 Million toward Beneficial Insect Research
Projects to promote beneficial organisms as part of a pest control strategy. Read More
Fruits
July 14, 2017
Brown Marmorated Stink Bug Predator Egg Mass Found
Samuri wasp parasitized egg mass found in Southern New Jersey peach orchard. Read More
Beet-armyworms-on-a-tomato-plant
Citrus
July 12, 2017
Tomato Pests Can Be Induced to Cannibalism, New Study Shows
The University of Wisconsin's John Orrock says when beet armyworms are exposed to concentrations of methyl jasmonate, they will abandon eating tomatoes — and start eating one another. Read More
Citrus
July 12, 2017
USDA Pulls 8 Products from Approved Organic Production List
After a few months of speculation, the USDA's Agricultural Marketing Service has published its Sunset 2017 final rule on approved products for organic production and handling. Read More
darkwinged fungus gnat larvae
Fruits
July 12, 2017
How to Deal with Annoying Fungus Gnats on the Farm
Learn how to identify, the survival and spread, as well as management methods for this insect pest. Read More
Close-up of mature diamondback moth
Insect Control
July 7, 2017
Can Genetic Engineering Put an End to Diamondback Moth Plague?
USDA OKs field release of pest with self-limiting gene at Cornell research farm. Read More
Center pivot irrigation system at Florida research farm
Citrus
June 30, 2017
New Project to Promote Water Security for Florida and Georgia Farmers
With the help of five-year, $5 million USDA grant, stakeholders will learn what it takes to better preserve precious resource. Read More
The Latest
Crop Protection
August 11, 2017
Do Fungicide- and Insecticide-Treated Se…
The University of New Hampshire has received half a million dollars to investigate if seed treatments inadvertently protect weed seeds from its usual predators. Read More
Citrus
August 11, 2017
Field Scouting Guide: Common Lambsquarte…
Take a look at these tips for identifying and treating this pervasive weed. Read More
Crop Protection
August 9, 2017
Why Some of the Most Dangerous Potato Di…
If you understand the role oxygen, and its lack, plays in potato diseases, you'll be better equipped to battle them. Read More
Crop Protection
August 3, 2017
Can Avocados Be Saved from Deadly Laurel…
Scientists from Florida and California are on the case and collaborating. Read More
Crop Protection
August 2, 2017
Report: 90% of NY Beehives Had Varroa Mi…
Cornell University's NYS Beekeeper Tech Team recent report also shows most hives are infected with Deformed Wing Virus (DWV), a disease linked to the mites. Read More
Biocontrols Conference
July 31, 2017
11 New Biocontrol Products You Need to K…
One of the highlights of the Biocontrols Conference & Expo Series is getting an early look at some of the Read More
Crop Protection
July 25, 2017
Vegetable Field Scouting Guide: Diamondb…
Due diligence is needed to help take down this pest of biblical proportions. Read More
Citrus
July 23, 2017
USDA Invests $7.6 Million toward Benefic…
Projects to promote beneficial organisms as part of a pest control strategy. Read More
Citrus
July 12, 2017
Tomato Pests Can Be Induced to Cannibali…
The University of Wisconsin's John Orrock says when beet armyworms are exposed to concentrations of methyl jasmonate, they will abandon eating tomatoes — and start eating one another. Read More
Citrus
July 12, 2017
USDA Pulls 8 Products from Approved Orga…
After a few months of speculation, the USDA's Agricultural Marketing Service has published its Sunset 2017 final rule on approved products for organic production and handling. Read More
Crop Protection
June 25, 2017
Study Suggests Closer-Proximity Lures He…
Research shows single-trap locations are not as effective as those kept close together. Read More
Citrus
June 22, 2017
Technology Boom Boosting Farm Life to a …
Whether it is human genetics or genetics applied to plants, knowledge is growing at a dizzying pace. Read More
Crop Protection
June 21, 2017
Certis Bolsters Biopesticide Business Po…
Addition of LAM International to allow for expansion of product development. Read More
Crop Protection
June 21, 2017
Early-Season Scouting Tips for Sweet Cor…
Black cutworm and true armyworm have been caught in relatively high numbers across the Midwest, including Michigan. Learn more about determining risk and scouting in your sweet corn plantings. Read More
Citrus
June 15, 2017
Make Way for Life-Saving Science on Your…
While nature always finds a way to adapt, science continues to find other ways to cope. Read More
Crop Protection
June 12, 2017
Registration Open for Ag Innovations Con…
Event focuses on microbial control strategies. Read More
Crop Protection
June 7, 2017
Field Scouting Guide for Squash Powdery …
Learn how to spot and treat a pest that impacts all cucurbits. Read More
Crop Protection
June 1, 2017
Can Attract-and-Kill Technology Protect …
Since devastating many Mid-Atlantic farms in 2010, this Asian-borne pest continues to cause growers significant headaches. New research, however, may offer insights into treatment options that minimize the use of harsh chemicals. Read More