College of Agriculture, Forestry and Life Sciences; Public Service and Agriculture

Clemson researchers say South Carolina peaches suffered minimal damage from freeze


CLEMSON – Clemson researchers report South Carolina peaches appear to have survived the recent cold snap, but growers shouldn’t let down their guard just yet.

Peach trees at Clemson's Musser Fruit Research Center in Seneca
Peach trees at Clemson’s Musser Fruit Research Center in Seneca survived the recent freeze.

The Clemson Peach Team and Cooperative Extension Service agents met this week to discuss the impact the recent freeze may have had on the state’s peaches.

“Based on what we’re seeing, there has been minimal damage in the Upstate and McBee area,” said Juan Carlos Melgar, a Clemson pomologist. “We saw only spotted damage on the Ridge, mostly on early varieties. For other varieties, it has been more of a light thinning. A mature tree can have a full crop even with 10 percent of all the flowers at bloom. So we’re still optimistic, although, at the same time, cautious as we are not still free from freeze risks.”

To help South Carolina peach growers produce bountiful yields, the Peach Team and Cooperative Extension Service agents met with growers during the 2019 Ridge Peach Producers meeting to provide growers with the latest, research-based information. Topics ranged from disorders to diseases and from pests to budget issues.

The Ridge — Edgefield, Saluda and Lexington counties — is South Carolina’s predominant peach-growing region.

Disorders and diseases

Streaking or “Tiger Stripes” is one disorder Guido Schnabel, a Clemson plant pathologist, discussed during the meeting. Tiger Stripes first were observed in Byron, Georgia, in 2003 and have since increased in importance. This disorder is associated with drought followed by “tiny rain” events.

“We don’t see this disorder every year,” Schnabel said. “But some years, this disorder is very significant, such as in 2018 when Tiger Stripes did severe damage to the South Carolina peach crop. We found susceptibility to streaking depends on cultivar, maturity stage and rainwater quality.”

Symptoms include streaks that can be up to 10 milimeters in diameter, increase slightly in intensity and diameter from top to bottom and reach maximum intensity and width near the bottom of the fruit. Streaked peaches can be found on all sides of a tree, top and bottom, as well as inside and outside the canopy.

Diseases the team is looking at include Armillaria root rot. This devastating soil-borne fungus costs growers millions of dollars in crop losses. There are no controls for Armillaria, which attacks almond, cherry and peach trees.

“This disease spreads via root grafts,” said Ksenija Gasic, a Clemson peach breeder and geneticist. “It can survive for decades in root pieces before becoming active. Right now, the best thing to do if Armillaria root rot is detected in an orchard is to remove all infected trees, including roots, and neighboring trees. To lessen the possibility of acquiring Armillaria root rot, growers should avoid planting in the same site year after year.”

Armillaria root rot is threatening the sustainability of the stone fruit (peach, cherry and almond) industry across United States. Finding a solution requires collective efforts of researchers from all affected states – South Carolina, Georgia, Michigan and California. The Clemson University Peach Team is leading an Armillaria root rot initiative with researchers from the University of Georgia, Michigan State University, the University of Kentucky, the University of California-Davis and the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS) to determine genetic control of the disease and help deliver resistant rootstocks. Currently just one peach rootstock, MP29, is resistant to Armillaria.

“But the supply is limited,” Gasic said. “This group will work together to find a solution to help growers in their fight against Armillaria root rot.”

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Above Ground Root Collar Excavation is one management tool the researchers have in their stockpile to use against Armillaria root rot. This excavation involves removing soil from around each tree’s root crown, or root collar, and exposing the primary roots to air and solar heating. While not “bullet proof,” this practice can reduce Armillaria colonization and prolong the productivity of infected fruit trees, Gasic said.

Pests, weeds and budgets

In addition to plant diseases, insect pests are another enemy growers must work to keep from attacking their orchards. Brett Blaauw, a peach entomologist from the University of Georgia who has a joint appointment with Clemson, talked about how to monitor for and destroy plum curculios,brown marmorated stink bugs and insects that crawl. To help growers determine when to look out for pests, Blaauw keeps updated information on his blog found at

Growers in the southeastern United States can learn more about pest management from the 2019 Southeastern Peach, Nectarine and Plum Pest Management and Cultural Guide. Current information about fruit crop diseases, pests and disorders also is available from Clemson’s MyIPM Smartphone App Series found in the Apple Store and Google Play at no cost.

Not only do diseases and insects create problems for growers, but weeds and other invasive plants can as well. Herbicides can be used to control weeds. For best control, Wayne Mitchem a horticulturist from North Carolina State University, advises growers to always read labels and apply herbicides between dawn and two hours before sunset.

“Timing is important,” he said. “Bright sunshine gets the best results. The activity of herbicides increases on all plants when temperatures are at their highest.”

Paraquat, also known as Gramoxone, is one popular herbicide that recently has undergone some label changes mandated by the Environmental Protection Agency (EPA). These changes include restricting use to just certified applicators. Applicators also must successfully complete a mandatory training program every three years when using this product.

Peach trees also should be given the proper amount of nutrients. Fertilizing is one method to ensure soil is properly nourished.

“Before applying any fertilizer, growers should first have soil tests done on their properties and consider leaf analyses, as well as other factors such as previous year crop load, intensity of pruning, ripening season and tree age,” Melgar said. “Having the proper amount of nutrients is very important for tree health and productivity.”

After an orchard has been established, creating and maintaining a budget is the next step in helping achieve success. Nathan Smith, a Clemson Extension economist housed at the Sandhill Research and Education Center, said he and his team are putting together an enterprise budget for peaches. Enterprise budgets are tools South Carolina growers can use for projecting costs and returns for their crops.

“Once this enterprise budget is completed, growers can use it to create their own budgets,” Smith said. “This budget should only be used as a general guideline. Each farm should develop a budget based on its specific situation.”

South Carolina is number two in United States peach production, second only to California, with Georgia and New Jersey following. This year’s meeting was organized by Sarah Scott, Clemson Extension area horticulture agent for Edgefield and Aiken counties. Scott noted the importance of field agents working with campus researchers to provide growers with the latest research-based information.

“These meetings are a great time for growers, researchers and industry professionals to network and discuss new technologies and information that may be helpful for the upcoming season,” Scott said. “Researchers from the main campus work closely with the peach industry and are able to share the latest information with growers. They also are able to give updates on trials and research that they have been working on which in many cases, growers have a hand in.”

Wally Yonce of Johnston grows 150 acres of peaches and attends this meeting every year to learn new information. He depends on information from Clemson Extension to help him grow a productive crop.

“I call my local Extension agent whenever I have a question about my peaches,” Yonce said. “If I see symptoms that I believe may be related to a disease, or if things appear abnormal, I call Clemson Extension agents and seek their advice. Someone will come out and look at whatever it is I have questions about, take samples if needed, have tests run and come back with information about what it is and how to take care of it.”

For more information about peaches, visit Clemson Extension’s About Peaches website.


Projects referred to in this article are supported by USDA-AMS-SCMP Grant No. 2015-10-70 and USDA-SCRI Grant No. 2018-51181-28378. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the view of USDA.

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