Protecting Alabama Peaches
From climate change to soil-borne fungus, Alabama Extension horticulturists seek management options to protect against diverse challenges.

Emerging threats, from the climate to the soil, are making it harder to grow peaches in Alabama. Peach production came to Alabama in the early 1800s. Today, there are about 1,500 acres dedicated to commercial peach production, which is the equivalent of just over two square miles spread out over many farms. Much of it is in Chilton County. The average life of a peach orchard is about 12 years, but previously had been a good bit longer. Growers may plant 25 to 30 varieties in each orchard to produce early, midseason and late-season peaches that fill specific marketing spaces within the season.

In 1948, Auburn University developed the Chilton Research and Extension Center, a part of the Alabama Agricultural Experiment Station, with an initial research focus in support of Alabama’s peach industry.  Today, it also includes other fruit and agronomic crop research.  It is the home of Alabama Extension’s research efforts to help peach growers deal with problems that threaten the future of the crop.

Changing Climate

Peaches enjoyed in summer develop from the chilly temperatures from the previous winter.  Depending on the variety, peach development requires temperatures of 45 degrees Fahrenheit and below for anywhere from 600 to 1,000 hours, or chill hours.  Dr. Edgar Vinson, assistant extension professor of horticulture at Auburn University, believes global climate change has had a significant impact on the peach industry.

Dr. Edgar Vinson

“Changes in climate are making it increasingly harder to reach the required number of chill hours.  If your peach operation is in a region that received 1,200 chill hours historically, but due to warming trends now receives 750, high chill hour varieties that require 950 or 1,000 chill hours will really struggle to produce an ample number of quality fruit. Over time, these trees will become weak, and their longevity will be shortened. These factors place a significant strain on peach farmers,” Vinson said.

“Today, we recommend varieties that need no less than 600 chill hours, and no more than 800 chill hours, maybe 900 tops in the Chilton County region.  This ensures that you have trees that will get at least close to the recommended amount for the required amount of chilling, but it cuts out quite a number of trees with desirable traits. It affects the overall peach production stream.”

With warmer winters, chill hours are harder to predict.  Vinson said Auburn University is exploring chemical “rest-breaking” products.  One is hydrogen cyanamide, a substance that is sprayed on the developing buds of other crops to concentrate harvests. Another option is potassium nitrate, a fertilizer that is safer to use.

“These products create anaerobic conditions in the flower and leaf buds, which wakes the tree up, so to speak.  This can cover for a certain deficiency of chilling, but it cannot make up for everything,” Vinson said.

Vinson said the Alabama Extension commercial horticulture team is collaborating with horticulture specialists at Auburn and hopes to offer peach growers management options based on modeling predictions.

“The climate is what it is.  We just have to take what we get and work with it. It does help to be able to predict climate variables,” Vinson continued.  “There is a very strong Extension component to not only get the information out to growers, but to know if these new protocols will be adopted by growers,” he said.

Soil Fungus

The second major challenge faced by Alabama peach growers is a soil-born fungus called Armillaria root rot, or ARR. It is also known as Oak root rot.

“It begins to feed on the roots of the trees. It can attack multiple species of plants, not just peach trees. It is often found in forests, killing everything in its path. It attaches to the root and breaches the exterior of the root. The plant is not able to pick up the nutrients or water like it could previously.  Enough of the root mass can be compromised to the point that the tree will succumb to the disease,” he said. “The worst part is that once it is in the soil, Armillaria cannot be removed.”

In peach orchards, ARR can kill trees in five to seven years, and in some cases as little as three.  It can greatly reduce the longevity of the entire orchard.

“We’ve had intense peach cultivation for generations now. New land is becoming harder and harder to come by. Growers unfortunately have to go back into those same orchards and replant when necessary. After generations of doing that, the soil is full of fungus and those trees are often susceptible to those diseases,” Vinson said. “The fungus is in all peach producing states, including South Carolina and Georgia.

“It is soil limited but it can move. Especially if you are sharing equipment or if you have soil on your shoes and go to another orchard, you can spread it.”

Given the challenges faced by peach producers, Vinson feels the best path forward is to create varieties that are resistant to diseases and climatic conditions.  One promising variety is called MP29. It is tolerant or resistant to Armillaria.

The problem with MP29 rootstock is that it cannot be propagated by seed, and so it has to be grown primarily from clones or tissue culture. It is a dwarfing rootstock and does not grow fast, taking twice as long to get started in the orchard.

“Most nursery growers are hesitant to deal with MP29 rootstock, because it would essentially cause them to overhaul their industry to accommodate this one rootstock, and they would have to charge a pretty penny for the plants,” he said.

Because MP29 in its current form presents problems for the nursery industry, Vinson and colleagues are working to speed the initial growth of the plant.  One way is to plant in plastic mulch that reflects light up to the canopy of little trees to encourage more and faster growth. “We want to get the trees growing at a faster rate and reduce the growing time from two years to just one,” according to Vinson.

Another option, pioneered by Clemson University, is called root collar evacuation. It involves planting trees on berms and then removing the soil around the crown of the tree.

“The concept is to remove fungus-infested soil from the root crown. The tree will eventually succumb, but you have more years to reap profit from the investment that you put in those trees.