Plant Health Update, September 2025 Summary

In the early part of 2025, many trees developed a large canopy due to abundant rainfall and moderate temperatures. By late summer (August, September), the temperatures were generally above average, and many areas of the state were on the dry side. These weather conditions are conducive for the expression of bacterial leaf scorch disease symptoms, and samples were submitted to the PDIDL from many areas of central Oklahoma during September. As symptoms of bacterial leaf scorch can be confused with marginal discoloration due to drought and high temperatures, a diagnosis requires laboratory testing.

 

Bacterial leaf scorch is caused by Xylella fastidiosa. Although the bacterium is found throughout the US and includes hundreds of hosts, the number of reported hosts in Oklahoma is limited (Table 1).

 

 

Infected trees develop yellowing and browning foliage from late summer to early fall (Figure 1). Close inspection of affected leaves shows that the margins are brown, and a yellow halo is generally present in the transitional zone between brown and green (Figure 2). Perennial and woody plants show progressive decline, and the disease is eventually fatal.

 

Figure 1. American elm with premature yellowing and browning of leaves due to bacterial leaf scorch disease. Image taken in early September.

 

Figure 2. Typical marginal discoloration (browning and yellowing) of American elm leaves with bacterial leaf scorch.

 

In 2024, an American elderberry with bacterial leaf scorch symptoms was observed in Payne County, Oklahoma (Figure 3). Symptomatic leaves were tested by the PDIDL and found positive for X. fastidiosa. This was a first report for the bacteria affecting this host and it was published in November 2025.

 

Figure 3. American elderberry with marginal leaf discoloration due to bacterial leaf scorch disease.

 

In September 2025, symptoms of bacterial leaf scorch were observed on an Eastern redbud (Cercis candensis) in Oklahoma City (Figure 4). The tree exhibited premature defoliation and marginal leaf discoloration (Figure 5).

 

Figure 4. Eastern redbud in Oklahoma City with yellowing and browning of leaves due to bacterial leaf scorch. The disease also causes premature defoliation and branch dieback.

 

Figure 5. Marginal browning and yellowing of Eastern redbud leaves due to bacterial leaf scorch disease.

 

There is no cure for bacterial leaf scorch disease, and the disease can be spread by xylem-feeding insects. The insects may spread the bacteria to other plants in the area when they feed on infected plants. Both American elderberry and Eastern redbud are native plants in Oklahoma. Pecan trees are also hosts of this bacterium. To date, the disease has not been found to affect pecans in Oklahoma, although it is found in nearby states (Louisiana, Texas). Recognizing new hosts allows growers to better scout unmanaged areas around orchards for potential bacterial leaf scorch symptoms. Elimination of any plants harboring the disease can prevent its spread into pecan orchards. This practice is already employed by grape growers since the bacterium has been found in grape vineyards in our state.

 

A summary of all submissions in September to the PDIDL by Oklahoma specialty crop growers is provided in Table 2. Look for additional plant health updates from the PDIDL in the next few weeks for our remaining 2025 submissions. If you have suggestions for future topics, please contact jen.olson@okstate.edu or call the PDIDL at (405) 744-9961.