Bacterial leaf scorch confirmed in Arizona pecan, Disease found in New Mexico pecan

Bacterial leaf scorch confirmed in Arizona pecan, Disease found in New Mexico pecan Western Farm Press By Cary Blake 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.”