Xylella Fastidiosa

Xylella fastidiosa is not a new name in the world of plant diseases, but its presence in Illinois is raising more and more concern. This bacterium, known for blocking the water transport system of trees and causing Bacterial Leaf Scorch (BLS), has now been confirmed in several areas across the state. In this blog post, we’ll go over detailed findings from seven different studies that confirm its spread in Illinois, what it’s doing to our local trees, and what people can do about it.

What is Xylella fastidiosa?

Xylella fastidiosa is a bacterium that lives in the xylem (the water-carrying tissue) of plants. It causes Bacterial Leaf Scorch in trees like oaks, sycamores, and maples. The disease spreads slowly and can eventually kill the tree. Insects like sharpshooters and spittlebugs carry the bacteria from one tree to another when feeding on sap.

Once infected, trees show symptoms such as leaf browning, wilting, and branch dieback. Over time, the entire tree can decline and die. Because the bacteria stay hidden inside the plant's tissue, testing is often the only way to know for sure what’s going on.

 

How Xylella fastidiosa is Affecting Illinois Trees: Study-Based Evidence

Let’s look at what different studies say about how Xylella fastidiosa is spreading in Illinois:

Study 1: University of Illinois Extension Newsletter (Pataky, 2005)

This study shows BLS confirmed in oaks in Champaign, Vermilion, and St. Clair counties. From 2000 to 2005, 28 positive BLS cases were recorded, mostly in red oaks, pin oaks, and white oaks. The study explains how the disease progresses over time and spreads via leafhoppers.

Study 2: Bugwoodwiki (Leininger et al., 1999)

This study focuses on sycamores and confirms that BLS is affecting both planted and wild sycamores in Illinois. Symptoms start with leaf discoloration and end in full scorch and dieback. It emphasizes that Illinois is a key area in tracking how the disease is spreading into northern states.

Study 3: Illinois Extension, "Bacterial Leaf Scorch Infecting Illinois Oaks" (Pankau, 2020)

Oak species, especially red oaks and pin oaks, are most affected in Illinois. The study mentions that the disease often begins in small sections of the tree canopy, slowly taking over. It also highlights how climate change might make things worse by helping the bacteria survive and spread.

Study 4: Progressive Tree Service (n.d.)

This detailed breakdown explains how the disease affects trees over time. Red oaks, white oaks, and maples are heavily impacted in Illinois. The study also mentions that cold winters don’t kill the bacteria — it survives in protected areas of the plant, only to come back strong in spring.

Study 5: Forest Health Monitoring (Adams et al., 2010)

This study found Xylella fastidiosa in two out of 18 tested trees in Illinois, confirming the bacterium’s presence. The study connects BLS with certain plant hardiness zones, showing how warmer weather could help the disease spread faster in the future.

Study 6: Journal of Integrated Pest Management (Overall & Rebek, 2017)

Here, the focus is on crops like peaches and plums, but it also confirms that the bacterium has spread into Illinois. The study explains how peach orchards in Illinois are affected by the disease and how researchers are working on vector control and resistant varieties.

Study 7: University of Illinois Extension, "Lawn & Garden" (Plewa & Cleveland, 2017)

This article talks about how the disease mostly affects urban shade trees like oaks, elms, sycamores, and maples. It explains how symptoms can look like drought stress, which makes it hard for homeowners to identify. Testing at the University of Illinois Plant Clinic is recommended.

 

Table: Summary of Xylella fastidiosa Presence and Impact in Illinois

Study	Area/Tree Affected	Presence Confirmed	Main Impact	Notable Notes
Pataky (2005)	Champaign, Vermilion, St. Clair	Yes (28 positive BLS cases)	Oaks (decline, death)	Spread via leafhoppers
Leininger et al. (1999)	General Illinois	Yes	Sycamores (scorch, dieback)	Infected trees die in 5-7 years
Pankau (2020)	Illinois Oaks	Yes	Oaks (decline, death)	Testing method developed
Progressive Tree Service (n.d.)	Illinois	Yes	Red/white oaks, maples	Disease survives winter
Adams et al. (2010)	Illinois	Yes (2 positive out of 18 samples)	Oaks, maples	Risk increases with warmer climate
Overall & Rebek (2017)	Peach orchards, sycamores	Yes	Crop loss, early leaf drop	Subspecies multiplex active in IL
Plewa & Cleveland (2017)	Urban landscapes	Yes	Oaks, maples, elms	Testing available for $25

 

Why This Matters for Illinois

If you have trees in your yard or manage public or private green spaces, this isn’t just some academic issue. It’s happening here and now. Oaks and other trees play a big role in air quality, property value, and wildlife support. Losing them slowly to a disease like BLS is not just a plant problem — it’s a community problem.

 

What Can Be Done?

There is no cure for BLS. But here’s what homeowners and land managers can do:

·         Get your trees tested if you see leaf browning that isn’t normal. The University of Illinois Plant Clinic offers testing.

·         Water and mulch your trees to reduce stress.

·         Remove dead or severely infected trees to stop the disease from spreading.

·         Avoid pruning during insect activity seasons unless tools are sterilized.

·         Watch for leafhoppers and other insect vectors.

 

Final Thoughts

The presence of Xylella fastidiosa in Illinois is no longer just a possibility — it’s a fact backed by years of research. With multiple reports confirming its impact on oaks, sycamores, and even fruit crops, it’s important for homeowners, landscapers, and researchers to stay informed and act early.

Testing, care, and proper management may not completely stop the disease, but they can help reduce the damage. With changing weather patterns and rising temperatures, early action is more important than ever.

 

References

• Adams, G. C., Catall, M., Walla, J., & Gould, A. B. 2010. "Bacterial Leaf Scorch Distribution and Isothermal Lines (Project NC-EM-08-02)." In Forest Health Monitoring, Chapter 10.
• Leininger, T.D., Solomon, J.D., Wilson, A.D., and Schiff, N.M. 1999. "Bacterial Leaf Scorch (Xylella fastidiosa Wells et al.)." Bugwoodwiki. http://wiki.bugwood.org/index.php?title=Archive:Sycamore/Xylella_fastidiosa&oldid=31636.
• Overall, L. M., & Rebek, E. J. 2017. "Insect Vectors and Current Management Strategies for Diseases Caused by Xylella fastidiosa in the Southern United States." Journal of Integrated Pest Management 8(1): 12. https://doi.org/10.1093/jipm/pmx005.
• Pankau, Ryan. 2020. "Bacterial Leaf Scorch Infecting Illinois Oaks." The Garden Scoop, Illinois Extension, University of Illinois. https://extension.illinois.edu/blogs/garden-scoop/2020-08-29-bacterial-leaf-scorch-infecting-illinois-oaks.
• Pataky, Nancy. 2005. "Bacterial Leaf Scorch Progress." Home, Yard, and Garden Pest Newsletter, University of Illinois Extension, September 28, pp. 2–4.
• Plewa, Diane, and Cleveland, Travis. 2017. "Lawn & Garden: Test Now for Bacterial Leaf Scorch." University of Illinois Extension. https://newherald.news/lawn-garden-test-now-for-bacterial-leaf-scorch-p3275-103.htm.
• Progressive Tree Service. n.d. "Bacterial Leaf Scorch." Retrieved from Progressive Tree Service website.