Xylella Fastidiosa

Xylella Fastidiosa in Arizona

Xylella fastidiosa (Xf) is a bacterial pathogen that affects plants by clogging their vascular system, leading to a variety of diseases. In Arizona, this pathogen has emerged as a significant concern for local agriculture, particularly in pecan orchards and vineyards. Over the years, Xf has been found to cause diseases like Pecan Bacterial Leaf Scorch (PBLS) and Pierce’s Disease (PD) in various crops. Recent studies reveal alarming insights into the spread of X. fastidiosa in Arizona, making it crucial for farmers and researchers to understand the pathogen's behavior and impact.

Infection due to Xylella fastidiosa leads to symptoms such as leaf scorch, branch dieback, and, in severe cases, plant death. X. fastidiosa is primarily spread by xylem-feeding insect vectors, such as sharpshooters and leafhoppers. While certain strains of X. fastidiosa are benign in native plants, others cause significant damage to crops and ornamental plants.

This pathogen has been responsible for devastating agricultural diseases, including:

·         Pierce’s Disease in grapevines

·         Citrus Variegated Chlorosis in citrus

·         Pecan Bacterial Leaf Scorch (PBLS) in pecans, as observed in Arizona and New Mexico .

The Spread of Xylella Fastidiosa in Arizona

Arizona has witnessed several outbreaks of Xylella fastidiosa, particularly in pecan trees, ornamental plants like Chitalpa tashkentensis, and grapevines. The pathogen's presence in these plants is concerning for Arizona’s agricultural industries.

Key Findings from Arizona Studies

1.      Pecan Bacterial Leaf Scorch (PBLS): PBLS, caused by X. fastidiosa, was first detected in Arizona in 2015. Symptoms such as leaf scorch, necrosis, and branch dieback have been observed in several pecan orchards across the state. The disease has severely affected the pecan industry, which contributes significantly to Arizona’s economy. The pathogen is primarily spread by insect vectors such as sharpshooters, with some studies indicating that grafting of infected plant material also contributes to its spread.

2.      Chitalpa and Other Ornamental Plants: X. fastidiosa has also been detected in Chitalpa trees, a popular ornamental species in Arizona. Chitalpa trees exhibit leaf scorch symptoms, which were initially thought to be due to environmental stress but were later linked to X. fastidiosa infection. This pathogen was also found in nursery stock, suggesting that it can spread through commercial plant trade .

3.      Genetic Analysis and Subspecies of Xylella Fastidiosa: Recent genetic studies have uncovered a novel subspecies of X. fastidiosa, known as X. fastidiosa subsp. tashke, which has been identified in Chitalpa trees in Arizona. This new subspecies is genetically distinct from other known strains and has been linked specifically to the southwestern U.S., including Arizona .

Impact on Arizona's Agriculture

The impact of Xylella fastidiosa in Arizona is far-reaching:

·         Economic Losses in Pecan Orchards: PBLS has led to declining yields and increased management costs in pecan orchards. The disease causes trees to suffer from poor water and nutrient transport, ultimately affecting tree health and productivity .

·         Threat to Vineyards: Pierce’s Disease, caused by X. fastidiosa, is a major threat to Arizona’s grape industry. The pathogen affects grapevines by blocking water transport, causing vine death, and reducing the quality of the grapes .

·         Spread through Nursery Stock: The discovery of X. fastidiosa in nursery stock emphasizes the risk of pathogen spread through the trade of plants. This can lead to the introduction of the disease into new areas, exacerbating the problem.

Table: Summary of Xylella Fastidiosa in Arizona

Region/Plant	Presence of X. fastidiosa	Disease Caused	Impact	Study Reference
Pecan Orchards	Positive for X. fastidiosa	Pecan Bacterial Leaf Scorch	Reduced tree growth, yield loss, economic impact	Study 2, Study 5
Chitalpa Trees	Positive for X. fastidiosa	Leaf scorch, dieback	Aesthetic and functional damage in landscapes	Study 3, Study 7
Vineyards	Positive for X. fastidiosa	Pierce’s Disease	Potential for grapevine death, loss of quality yield	Study 6

Prevention and Management Strategies

Managing Xylella fastidiosa in Arizona requires a multifaceted approach:

1.      Vector Control: Sharpshooters and other insect vectors play a key role in spreading X. fastidiosa. Using insecticides and implementing monitoring systems like sticky traps can help control vector populations .

2.      Improved Diagnostic Tools: Researchers are working on developing more reliable diagnostic methods, such as PCR-based tests, to detect X. fastidiosa early in infected plants .

3.      Tree Removal and Grafting Practices: Infected trees should be removed to limit the spread, and nurseries should ensure their stock is free from the pathogen. Additionally, using healthy scion wood for tree propagation can help prevent the introduction of X. fastidiosa .

The Pathogen’s Growing Threat in Arizona

Xylella fastidiosa presents a growing threat to Arizona's agriculture, particularly affecting pecan orchards and vineyards. The novel subspecies X. fastidiosa subsp. tashke, found in ornamental plants like Chitalpa, further complicates efforts to manage the pathogen. Ongoing research and proactive management strategies will be crucial in mitigating the impact of X. fastidiosa in Arizona and preventing its spread across the southwestern United States.

References

1.      Randall, J. J., Goldberg, N. P., Kemp, J. D., et al. (2009). "Genetic Analysis of a Novel Xylella fastidiosa Subspecies Found in the Southwestern United States." Applied and Environmental Microbiology, 75(17), 5631–5638.

2.      Hilton, A.E., Jo, Y-K., Cervantes, K., et al. (2017). "First Report of Pecan Bacterial Leaf Scorch Caused by Xylella fastidiosa in Pecan (Carya illinoinensis) in Arizona, New Mexico, California, and Texas." Plant Disease, 101(6), 1027. https://doi.org/10.1094/PDIS-02-17-0298-PDN.

3.      "Prevalence and strain characterization of Xylella fastidiosa causing grapevine and pecan diseases in Arizona." University of Arizona.

New Mexico, with its vibrant agricultural economy, is now grappling with an emerging threat to its crops: Xylella fastidiosa, a plant pathogen causing a range of diseases in various species. From pecans to peaches, the spread of this bacterium has raised alarm bells for farmers and agricultural experts alike. With the bacterium’s ability to infect diverse crops and its potential for devastating economic losses, understanding its presence, spread, and the diseases it causes has become a critical issue in the state.

This blog post will explore the growing presence of Xylella fastidiosa in New Mexico, its impact on plant health, and the research efforts aimed at controlling its spread. Drawing on studies and reports, we will highlight the specific plant diseases linked to the pathogen, with a focus on its presence in pecans, peaches, and grapes—three key crops for New Mexico’s agricultural sector.

 

What is Xylella fastidiosa?

Xylella fastidiosa is a gram-negative bacterium known for causing a variety of diseases in plants by inhabiting their xylem vessels, which are responsible for water transport. The bacterium disrupts this system, leading to symptoms like leaf scorch, stunting, dieback, and even plant death. It spreads primarily through insect vectors such as sharpshooters and spittlebugs that feed on infected plants and subsequently transmit the pathogen to healthy ones.

This pathogen is notorious for its impact on several crops, including grapes (causing Pierce’s disease), oleanders (oleander leaf scorch), and pecans (pecan bacterial leaf scorch). Its adaptability and ability to infect a wide range of plants make it a major concern for agricultural regions, particularly in the southwestern United States, including New Mexico.

 

 

Xylella fastidiosa in New Mexico: Recent Studies and Findings

Study 1: Pecan Bacterial Leaf Scorch in New Mexico

Pecan bacterial leaf scorch (PBLS), caused by Xylella fastidiosa, was first confirmed in New Mexico in 2015. The pathogen affects pecan trees, leading to symptoms like leaf scorch, reduced tree vigor, and in severe cases, tree death. The primary vectors for the disease are insects like leafhoppers and spittlebugs, which transmit the bacterium to healthy trees.

In New Mexico, PBLS has spread across both commercial and native pecan orchards, raising concerns about the future of the state’s pecan industry. The economic impact of this disease is significant, as New Mexico is a major producer of pecans, which are a vital part of the local agricultural economy.

Impact on Agriculture:

·         Symptoms: Terminal dieback, scorched leaves, necrosis, and eventual death of terminal shoots.

·         Economic Impact: Loss of yield, reduced quality of nuts, and increased management costs for growers.

Research and Management: Researchers are investigating the insect vectors involved in spreading Xylella fastidiosa in pecan orchards, with a particular focus on controlling the disease through insect management and optimizing irrigation practices to mitigate its effects.

Reference:
Olsen, Mary. "Bacterial leaf scorch disease confirmed in Arizona pecan." Farm Progress, September 7, 2015. Farm Progress Article.

Study 2: Peach Trees and the Spread of Xylella fastidiosa

In 2010, Xylella fastidiosa was detected in peach trees in New Mexico, marking the first instance of the pathogen in this crop in the state. The disease caused leaf deformities, dark green venation, stunted growth, and branch dieback in peach trees, similar to symptoms observed in other plants infected by the bacterium.

The discovery of Xylella in peach trees is particularly concerning because it expands the pathogen's host range, which now includes important crops like peaches and pecans. The potential for Xylella to spread across New Mexico’s agricultural landscape is alarming, given the economic importance of both crops.

Symptoms and Impact:

·         Symptoms: Leaf deformities, dark green venation, mottling, stunted growth, and branch dieback.

·         Economic Impact: Potential for severe yield loss in peaches, with concerns about the pathogen's impact on pecans as well.

Reference:
Randall, J. J., J. French, S. Yao, S. F. Hanson, and N. P. Goldberg. "First Report of Xylella fastidiosa in Peach in New Mexico." Plant Disease, June 14, 2011. Plant Disease Article.

Study 3: Pecan Bacterial Leaf Scorch in the Southwestern U.S.

A more recent study, published in 2017, further documents the spread of pecan bacterial leaf scorch in New Mexico. The research underscores the economic threat posed by Xylella fastidiosa to the state’s pecan industry, where the disease has already resulted in reduced yields and lower-quality nuts.

Transmission and Control Measures:

·         The disease is transmitted primarily through xylem-feeding insects, and its spread is exacerbated by infected grafts and rootstocks.

·         Current management strategies include insect control, pruning infected trees, and using resistant cultivars.

Reference:
Hilton, A. E., Jo, Y.-K., Cervantes, K., Stamler, R. A., Randall, J. J., French, J. M., Heerema, R. J., Goldbery, N. P., Sherman, J., Wang, X., and Grauke, L. J. 2017. "First report of pecan bacterial leaf scorch caused by Xylella fastidiosa in pecan (Carya illinoinensis) in Arizona, New Mexico, California, and Texas." Plant Disease, 101(11): 1949. Plant Disease Journal.

Study 4: Xylella fastidiosa in New Mexico Grapevines

Xylella fastidiosa was first detected in New Mexico grapevines in 2006, where it caused Pierce’s disease. This discovery was particularly significant because it marked the introduction of the pathogen to a region previously free from the disease.

Symptoms in Grapevines:

·         Symptoms: Leaf scorch, vine dieback, and eventual plant death.

·         Economic Impact: The grape industry in New Mexico, particularly its emerging wine industry, is at risk due to the presence of this pathogen.

Reference:
Randall, Jennifer J., Maxim Radionenko, Jason M. French, Natalie P. Goldberg, and Stephen F. Hanson. "First Report of Pierce’s Disease in New Mexico." Plant Health Progress, October 2, 2007. Plant Health Progress Article.

Study 5: New Subspecies of Xylella fastidiosa Identified

A recent genetic study of Xylella fastidiosa found a novel subspecies in New Mexico, linked to the Chitalpa tree. This new strain is genetically distinct and adds complexity to the challenges of managing Xylella in the region.

Pathogenicity and Genetic Diversity:

·         Genetic analysis showed that the strain infecting Chitalpa trees is distinct from other known subspecies.

·         This new strain may have different behavior and host specificity, adding new challenges for agricultural management.

Reference:
Randall, J. J., Goldberg, N. P., Kemp, J. D., Radionenko, M., French, J. M., Olsen, M. W., & Hanson, S. F. (2009). "Genetic analysis of a novel Xylella fastidiosa subspecies found in the southwestern United States." Applied and Environmental Microbiology, 75(17), 5631–5638. Applied and Environmental Microbiology Journal.

Study 6: Chitalpa as a Reservoir for Xylella fastidiosa

The detection of Xylella fastidiosa in Chitalpa trees in New Mexico in 2006 highlighted the tree's role as a potential reservoir for the pathogen, facilitating its spread across agricultural crops like grapes and pecans.

Potential for Spread:

·         Chitalpa trees, often used as ornamental plants, may act as reservoirs for Xylella, spreading the pathogen to nearby crops.

Reference:
Randall, J. J., M. Radionenko, J. M. French, M. W. Olsen, N. P. Goldberg, and S. F. Hanson. "Xylella fastidiosa Detected in New Mexico in Chitalpa, a Common Landscape Ornamental Plant." Plant Disease, 91, no. 3 (2007): 329-330. Plant Disease Article.

Study 7: Xylella fastidiosa and Its Spread in Southwestern U.S.

This study further explores the spread of Xylella fastidiosa in New Mexico and surrounding regions, including Arizona and Texas. It examines the potential for cross-regional spread and its effects on various crops, including grapes and pecans.

Research Implications:

·         The pathogen’s spread across southwestern states is becoming more widespread, and it poses a significant economic risk to New Mexico’s agricultural sector.

Reference:
Goldberg, N. 2015. "Pecan bacterial leaf scorch in New Mexico and Arizona (presentation)." New Mexico Pecan Growers Conference. October 21, 2015. Accessed April 20, 2025. NM Pecan Growers Conference.

 

Table: Summary of Xylella fastidiosa Presence and Impact in New Mexico

Region	Crop Affected	Symptoms	Economic Impact	Study Outcome
Northern New Mexico	Peach Trees	Leaf deformities, branch dieback	Potential yield loss	First report of Xylella in peach trees. Concern for pecan industry.
Southwestern New Mexico	Pecan Trees	Leaf scorch, reduced vigor	Yield loss, lower-quality nuts	Xylella fastidiosa causing Pecan Bacterial Leaf Scorch. Major economic threat.
Southern New Mexico	Grapevines (Chardonnay)	Leaf scorch, vine dieback	Threat to grape production	Xylella identified in grapevines, posing risk to the local wine industry.
Las Cruces	Chitalpa Trees	Leaf scorch, branch dieback	Potential risk to ornamental plants	Xylella detected in Chitalpa trees. Potential for broader spread to crops like grapes and pecans.

 

The Pathogen’s Growing Influence

Xylella fastidiosa has firmly established itself in New Mexico, affecting a range of important crops. The discovery of the pathogen in pecans, peaches, grapes, and ornamental plants underscores the need for increased monitoring and management strategies to protect the state’s agricultural economy. Ongoing research is crucial for developing effective control measures to prevent further spread and mitigate the economic consequences of this devastating pathogen.

 

References

• Olsen, Mary. "Bacterial leaf scorch disease confirmed in Arizona pecan." Farm Progress, September 7, 2015. Farm Progress Article.
• Randall, J. J., J. French, S. Yao, S. F. Hanson, and N. P. Goldberg. "First Report of Xylella fastidiosa in Peach in New Mexico." Plant Disease, June 14, 2011. Plant Disease Article.
• Hilton, A. E., Jo, Y.-K., Cervantes, K., Stamler, R. A., Randall, J. J., French, J. M., Heerema, R. J., Goldbery, N. P., Sherman, J., Wang, X., and Grauke, L. J. 2017. "First report of pecan bacterial leaf scorch caused by Xylella fastidiosa in pecan (Carya illinoinensis) in Arizona, New Mexico, California, and Texas." Plant Disease, 101(11): 1949. Plant Disease Journal.
• Randall, Jennifer J., Maxim Radionenko, Jason M. French, Natalie P. Goldberg, and Stephen F. Hanson. "First Report of Pierce’s Disease in New Mexico." Plant Health Progress, October 2, 2007. Plant Health Progress Article.
• Randall, J. J., Goldberg, N. P., Kemp, J. D., Radionenko, M., French, J. M., Olsen, M. W., & Hanson, S. F. (2009). "Genetic analysis of a novel Xylella fastidiosa subspecies found in the southwestern United States." Applied and Environmental Microbiology, 75(17), 5631–5638. Applied and Environmental Microbiology Journal.
• Randall, J. J., M. Radionenko, J. M. French, M. W. Olsen, N. P. Goldberg, and S. F. Hanson. "Xylella fastidiosa Detected in New Mexico in Chitalpa, a Common Landscape Ornamental Plant." Plant Disease, 91, no. 3 (2007): 329-330. Plant Disease Article.