6/20/2020

Bacterial Leaf Streak of Corn

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Disease Facts

Caused by the bacterium Xanthomonas vasicola pv. vasculorum.
First detected in North America in 2014 in a Nebraska corn field.
Currently confirmed in 11 states: Nebraska, Colorado, Illinois, Iowa, Kansas, Minnesota, Missouri, South Dakota, Oklahoma, Texas, and Wisconsin.
Can be found in field corn, seed corn, popcorn, and sweet corn.
Plant does not have to be injured for disease to enter the plant. Bacterium can enter plant through stomatal openings.
Bacterial inoculum overwinters on plant residue and causes symptoms on several host plants.
Many diseases look similar to bacterial leaf streak, so it is recommended to confirm disease through a diagnostic laboratory.
A different but closely-related pathogen affects sorghum; Xanthomonas vasicola pv. holcicola.

Global Distribution and Spread

Bacterial leaf streak of corn was first detected in 1948 in South Africa.
The first confirmed case in the United States was in Nebraska in 2014, although there is evidence it may have been present as early as 2010.
Bacterial leaf streak has also been confirmed in Argentina (2017) and Brazil (2018).
It is not known how the pathogen was spread to North and South America.

Disease Cycle

X. vasicola pv. vasculorum appears to overwinter in infected crop residue from the previous growing season.
Bacteria move from residue onto living plant tissue via rain splash. Bacteria can enter the plant through stomata or wounds.
Symptoms often appear on the bottom leaves of a plant and spread upwards.
Spread of secondary infection upwards through the canopy, from plant to plant, and into adjacent fields is facilitated by overhead irrigation or wind-driven rain.

Symptoms and Impact on Crop

Bacterial leaf streak produces narrow tan, yellow, brown, or orange lesions that have a bright yellow halo when backlit.
Lesions can extend to several inches long and stay in between leaf veins (interveinal).
Edges of the lesions are wavy and have a jagged appearance, which is a key distinguishing feature.
Lesions can also appear greasy or water-soaked.
Symptoms have been observed as early as the V4 growth stage in the field.

Preliminary observations suggest that severe infestations can impact corn yield. The extent of yield reduction in these cases and the frequency with which severe infestations capable of reducing yield occur are not well-understood at this point.
Generally, yield losses appear to be minimal as long as extensive symptoms are not present before or during grain fill.
The presence of other foliar diseases, such as gray leaf spot, in combination with bacterial leaf streak can result in more yield loss due to greater leaf area loss. Fungicides do not control bacterial leaf steak, but can help protect yield by managing accompanying fungal diseases.

Bacterial Leaf Streak Symptoms Compared to Other Diseases

Fungal
Rectangular lesions that have very straight sides.
Light does not shine through easily (more opaque).
Can have dark, fungal structures which produce clear spores characteristic of gray leaf spot.
More on Gray Leaf Spot.

Fungal
Often more oval or circular in shape.
Appears dark when leaf is backlit.
Pustules are raised above the leaf surface and are orange to reddish-orange from rust spore production.
More on Common Rust.

Fungal
Lesions are mostly oval to elongated.
Lesions may have bright yellow edges, especially when backlit.
Often contains black pycnidia (fungal fruiting structures) imbedded in leaf tissue.
More on Diplodia Leaf Streak.

Fungal
Lesions are rectangular to oblong in shape.
Appears tan in color.
Lack of uniformity makes it difficult to identify. Laboratory testing can help differentiate.
More on Southern Corn Leaf Blight.

Factors Favoring Bacterial Leaf Streak

Warm conditions with a high relative humidity.
Can withstand cooler temperatures (different from gray leaf spot) and can be found as early as V4 in corn.
Thought to be spread by wind-driven rain and irrigation.

More common in continuous corn fields but has been found in other rotation systems, particularly those that include another host crop.
Favored by minimum tillage systems where inoculum can remain on residue.

Disease Management

Proper identification of the disease is crucial since it cannot be treated by chemical controls unlike many similar-appearing diseases.
Minimize continuous exposure to the crops and weeds that have been identified as susceptible hosts.
- - Control volunteer corn which can serve as a host.
- - Proper weed management and pasture grass control.
Harvest infected fields last to reduce the spread of inoculum.
Tillage and residue management are possible considerations.
There appears to be some variability among corn hybrids in susceptibility to bacterial leaf streak.

Crops: Corn, oats, rice
Prairie Grasses: Orchard grass, Indiangrass, big bluestem, little bluestem, timothy, sand bluestem, green foxtail, bristly foxtail
Weeds: Johnsongrass, yellow nutsedge

References

Castro, M.O., T. Hartman, T. Coutinho, J.M. Lang, K. Korus, J.E. Leach, T. Jackson-Ziems, and K. Broders. 2020. Current understanding of the history, global spread, ecology, evolution, and management of the corn bacterial leaf streak pathogen, Xanthomonas vasicola pv. Vasculorum. Phytopathology. 110:1124-1131.
Robertson, A., K. Broders, R. French, T. Jackson-Ziems, D. Jardine, K. Korus, J. Lang, J. Leach. 2017. Bacterial Leaf Streak. Corn Disease Management. Crop Protection Network.
Schlund, S., T. Hartman, T. Jackson-Ziems. 2017. Bacterial Leaf Streak of Corn. CropWatch. Univ. of Nebraska-Lincoln.
Smith, D.L., C. Groves, B. Hudelson, and S. Lueloff. 2018. Bacterial Leaf Streak of Corn Confirmed for the First time in Wisconsin. Wisconsin Crop Manager Newsletter. Univ. of Wisconsin-Madison.