Update on Bacterial Leaf Streak of Corn in Nebraska

Feb. 23, 2017

http://cropwatch.unl.edu/2017/update-bacterial-leaf-streak-corn-nebraska

Terra Hartman – Graduate Research Assistant
Tamra Jackson-Ziems, Extension Plant Pathologist

Bacterial leaf streak disease of corn is caused by the bacterium Xanthomonas vasicola (syn. X. campestris pv. zeae). It was previously only reported on corn in South Africa, and had not been reported in the United States until August 2016.

Nebraska map showing counties with bacterial leaf streak.
Figure 1. Distribution of bacterial leaf streak in Nebraska in 2016. The pink color indicates that bacterial leaf streak was confirmed in at least one sample received from that county. Unshaded counties indicate a lack of samples submitted or that those submitted tested negative.

This bacterium is most noted for causing gumming disease, a leaf blight and vascular wilt that affects sugarcane. The vascular wilt phase has not been observed in corn.

Bacterial leaf streak has been confirmed in Nebraska, Colorado, Kansas, Iowa, Minnesota, South Dakota, Illinois, and Texas. A 2016 survey funded by the Nebraska Corn Board confirmed that bacterial leaf streak was present in at least 51 Nebraska counties (Figure 1) across much of the state. The pathogen was not detected in samples from some extreme eastern and western counties. These results don’t necessarily indicate its absence, but rather may be due to a lack of representative samples from those areas, especially considering the disease has been confirmed in several adjacent counties in neighboring states.
Symptoms

Sampling of bacterial leaf streak lesions of corn

Figures 2-4. Bacterial leaf streak lesions may vary in color and length, but will be between veins and often have wavy margins.

Symptoms include yellow, tan or dark to light brown striped lesions with wavy margins that can appear on the leaf blade (Figures 2 and 3) or be concentrated around the midrib (Figure 4).
bacterial leaf streak lesions
Figure 5. Lesions may appear bright yellow when backlit.

These lesions can appear yellow when backlit (Figure 5). Symptoms have been observed on the lower leaves as early as the beginning of June in Nebraska on V7 corn, and tend to move up the plant as the infection progresses. While this seems to be the normal pattern for disease development, there have been cases where symptoms first appeared in the mid-canopy or upper leaves during mid-season.

Bacterial leaf streak and gray leaf spot are often mistaken for each other due to their similar appearance and behavior. There are two key differences to look for when trying to distinguish between these diseases:

First, consider the time of year when the symptoms develop. If the symptoms first developed in June, it is likely bacterial leaf streak, as cooler weather conditions in Nebraska are not often favorable for gray leaf spot development.

Second, examine the margins of the leaf lesions. Bacterial leaf streak typically has a wavy margin, whereas gray leaf spot lesions usually have smooth, linear margins (Figures 6 and 7).

Gray leaf spot and bacterial leaf stripe

Figures 6 and 7. Gray leaf spot lesions (left) versus bacterial leaf streak lesions (right) on corn. Note the wavy margins of the bacterial leaf streak lesions versus the smooth, linear margins of the gray leaf spot lesions.

While these considerations can be useful, neither can be used exclusively to diagnose these diseases every time, especially when both diseases are present on the same leaf.

Be sure to observe many lesions on several plants and always submit a sample for diagnosis if you’re unsure of a diagnosis or if you suspect the bacterial leaf streak has developed in a new area.

Epidemiology

Xanthomonas vasicola is capable of overwintering in infested residue, where it can survive until environmental conditions become favorable for it to infect the next year’s crop. This bacterium does not require wounds to establish an infection, and it is believed to enter the plant through natural openings, such as the stomata.

Center pivot irrigation and wind-driven rain may increase the severity of infection by creating conditions that allow the pathogen to enter the plant’s natural openings, such as stomata. Bacterial leaf streak has been confirmed in dent (field) corn, popcorn, seed corn, and sweet corn.
Favorable Conditions

This pathogen is favored by warm, humid conditions, and is thought to be spread by wind-driven rain.
Management

When making management decisions, it is important to verify the diagnosis. Bacterial leaf streak and the common fungal disease, gray leaf spot, can appear very similar in some hybrids and the fungicides used to treat gray leaf spot are not expected to be effective against bacterial leaf streak.

Resistance to the bacterial leaf streak pathogen has not been confirmed in corn, so resistant hybrids are not available. Crop rotation to a non-host crop may help reduce disease severity in future corn crops, however disease development has been observed after one-year rotations to soybeans, wheat, and after fallow. Rotation alone won’t prevent bacterial leaf streak.

Tillage may reduce disease severity by promoting degradation of the infested crop debris source, but it will not eliminate the disease. Cleaning equipment when moving from an infested field to a disease-free field may slow the spread of the disease. These are standard practices for mitigation of bacterial diseases, but none of them will eliminate the pathogen and some may be impractical in some production systems.
For More Information
Nebraska Extension Plant Pathologist Tamra Jackson-Ziems talks with Market Journal host Jeff Wilkerson about bacterial leaf stripe in corn.

If you have questions about bacterial leaf spot, please contact Nebraska Extension Plant Pathologist Tamra Jackson-Ziems at 402-472-2559 or tjackson3@unl.edu.

Additional resources include:

Bacterial Leaf Streak of Corn Confirmed in Nebraska, Other Corn Belt States
Bacterial Leaf Streak in the CropWatch Plant Disease Management section
Corn Disease Management: Bacterial Leaf Streak published by the Crop Protection Network in December 2016.

About Robert Wright

Robert Wright is a Professor and Extension Entomologist at University of Nebraska-Lincoln. You can reach him by email at rwright2@unl.edu. Follow him on Twitter @BobWrightUNL
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