Its official – the Arizona pecan industry has a new plant disease, according to plant pathologist Mary Olsen.
Olsen of the University of Arizona told several hundred folks gathered at the Arizona Pecan Growers Association annual meeting in Tucson in August that pecan bacterial leaf scorch (PBLS) disease was confirmed in Arizona pecan in July with help from the Plant Diagnostic Lab at New Mexico State University (NMSU).
Two diagnostic methods were used to confirm the disease - DNA and ELISA, the latter an acronym stands for enzyme-linked immunosorbent assay.
“I think you’ve lived with this disease for a while,” Olsen told the standing-room-only crowd.
This finding is the first confirmed PBLS case in Arizona pecan. The disease was confirmed in New Mexico in mid-August, according to NMSU Plant Pathologist Natalie Goldberg.
Unknown is whether the disease is found in pecan in California.
PBLS is found in some southeastern U.S. pecan orchards in different pecan varieties.
In Arizona, PBLS has been confirmed in the Western and Pawnee varieties.
The disease is caused by a strain of the bacterium Xylella fastidiosa, which is carried from plant to plant by xylem-feeding insect vectors. Olsen says the vector in Arizona has not been identified.
In other pecan-growing states, PBLS vectors include members of the Cicadellidae (leafhopper) and Cercopidae (spittlebug) families. Studies by Louisiana State University suggest the vectors include the glassy-winged sharpshooter, leafhopper, and adult spittlebug.
Leaf scorch diseases caused by different strains of Xylella fastidiosa are found in other crops, including California-grown almonds, grapes, and olives causing reduced yield and often plant death.
This disease has had a devastating impact on residential oleander plants in the greater Phoenix area.
Olsen and UA Cooperative Extension Horticulture Agent Joshua Sherman are conducting an Arizona grower survey on the disease to determine its distribution in pecan throughout the state.
Symptoms of PBLS include terminal dieback in the early spring and leaf scorching. The UA says disease development and symptoms can occur on one or more limbs in the tree canopy.
In Arizona, symptoms are typically seen on terminal shoots but also secondary shoots, including curling leaflet margins which turn from tan to brown. The UA says necrosis progresses toward the midrib and petiolule, followed by the abscission of impacted leaflets and rachises.
The terminal shoot often turns black and dies.
Olsen notes that marginal necrosis can be confused with salinity issues, black aphid damage, and foliar fungal pathogens.
Research conducted at Louisiana State University suggests disease severity varies among pecan varieties, and the bacteria can be transmitted from infected rootstock or introduced in infected scion wood.
Olsen said, “We need to determine the vector, learn if there are alternative hosts, and whether the bacterial strain in Arizona pecan is the same or different from other states.”
Arizona is the fourth largest pecan producer in the nation behind Georgia, Texas, and New Mexico, respectively. The 2014 Arizona pecan crop was valued at $42 million, according to the National Agricultural Statistics Service.
True water needs
Water use in pecan was also discussed at the conference by Shirley Papuga, associate professor and chair of the UA’s Watershed Management and Ecohydrology Program.
Papuga says much of the pecan research in the nation’s Southwest is centered in Texas and New Mexico so there is little Arizona-specific water data for pecan production. Water data from the two other states may not be completely applicable for Arizona since, for instance, the pecan-growing season is longer in the Grand Canyon State.
To study Arizona pecan water needs, Papuga and colleagues received $90,000 funding from the Arizona Department of Agriculture through the specialty crops grant program to conduct a three-year water study at two Arizona commercial pecan operations located in Bowie (Cochise County) and Sahuarita (Pima County).
A 50-foot tower was built on each site and outfitted with key water and weather measurement instruments.
Last year, the researchers collected their first full year of data from the study. Papuga says perhaps the most interesting data gained in 2014 was that both sites used about the same amount of water – nearly 50 inches - despite an estimated 1,000 feet elevation difference between the sites.
Over the three-year study, Papuga will gauge how much water is required to keep commercial pecan trees healthy and produce high yields, including during the key growth stages.
“We want to determine the actual water needs in orchards and how water demands can vary during the season – during the fruiting and nutting periods, for example – and work with growers to help find irrigation strategies that minimize water use and maximize production,” Papuga said.
Federal marketing order
Pecan grower Bruce Caris of the Green Valley Pecan Company updated the crowd on the proposed federal marketing order (FMO) on pecans. Three public hearings have been completed and the industry-recommended FMO is now under review by USDA.
“We’re now in a ‘quiet period’ while USDA Secretary Tom Vilsack reviews the proposal and the feedback,” Caris said.
If Secretary Vilsack approves the FMO proposal, Caris believes a FMO grower referendum could be held next year.
According to the American Pecan Board, the FMO would help market and promote pecans to increase demand and prices; promote industry data; establish quality, size, and grade standards; plus coordinate and invest in pecan research.
Fried chicken feet
Tree nut export sales to China were discussed by Calway Foods President Jack Huang of Santa Clara, Calif. While China’s economy has slightly slowed, Huang believes the world’s largest populated country will remain a top market for tree nuts.
“The long-term outlook for China is that they will continue to grow and recover from the current (economic) setback,” Huang said.
Tree nut demand continues to increase globally as household incomes rise. Huang says about 20 percent of China’s 1.4 billion population are now in the ‘middle class’ and desire more protein in the diet from tree nuts.
Huang predicts China’s middle class will nearly double to about 630 million by 2022.
“Ten years ago no one in China knew about pecans. Now they all do,” Huang said.
While the Chinese have a hankering for nuts, Huang says the favorite food of the Chinese is fried chicken feet.
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