CPN-2008 — December 2016
Bacterial leaf streak of corn is caused by the bacterium Xanthomonas vasicola. The disease has been observed on field corn, seed corn, popcorn, and sweet corn.
Bacterial leaf streak of corn was only recently identified in the United States. The identity of the disease was confirmed in 2016, but the symptoms of this disease have been present in Nebraska since at least 2014. To date, the disease has been reported in nine states, including Colorado, Illinois, Iowa, Kansas, Minnesota, Nebraska, Oklahoma, South Dakota, and Texas.
Bacterial leaf streak symptoms appear as narrow leaf lesions with wavy-edges that occur between the veins of corn leaves (Figure 1A-1D). The lesions range from less than an inch to several inches long. The lesions may be yellow, tan, brown, or orange and look greasy or water-soaked.
Figure 1. These photos show the narrow leaf lesions characteristic of bacterial leaf streak.
Lesions can appear anywhere on the leaf blade, sometimes close to the midrib (Figure 1D). Lesions appear translucent with bright yellow halos, which when backlit, are easy to see extending from the lesions (Figure 2).
Over time, lesions can expand to cover larger areas of the leaf (Figure 3). In extreme cases, lesions may extend along the entire length of the leaf and grow together to form large, necrotic areas (Figure 4).
Disease symptoms have been observed in corn as early as growth stage V7 — the lesions first appear on lower leaves (Figure 5). Under favorable conditions, the disease can spread up the plant canopy, but symptoms may also occur only in the upper canopy (Figure 6). Symptoms in the upper canopy are more common when the disease occurs after tasselling. Some reports indicate that bacterial leaf streak appears after high wind and rain events.
We know very little about the bacterial leaf streak disease cycle. Researchers presume that X. vasicola survives the winter in infected crop residue, because the disease has been observed in volunteer corn that was growing in a soybean field where the disease had been identified the previous year in corn.
Most likely, irrigation, splashing rain, and wind-driven rain spread the bacterium, but it is unclear how far the bacterium can travel. It does not appear that plants must be wounded for the bacterium to enter the plant.
It is unknown if the bacterium is seedborne or if weeds adjacent to cornfields are alternative hosts (as is the case with other bacterial diseases such as Goss’s wilt). Researchers are currently investigating each of these aspects of the bacterial leaf streak disease cycle.
Bacterial leaf streak is more common in fields under continuous corn production, but it has been observed on corn following soybeans, wheat, and fallow. Bacterial leaf streak occurrence appears to increase after overhead irrigation or rainfall during hot weather. Under these favorable conditions disease severity can approach 30 percent (Figure 7).
Not surprisingly, we only have limited information about bacterial leaf streak effects on yield. We expect losses will be minimal if symptoms develop late in the season, or if extensive leaf blight does not occur before or during grain fill. Similarly, we have no information how bacterial leaf streak affects grain quality.
Diagnosing bacterial leaf streak in the field can be difficult because it can resemble other corn diseases and disorders (see Diseases and Disorders with Similar Symptoms below).
A laboratory can easily distinguish bacterial leaf streak from fungal diseases by bacterial streaming. Bacterial streaming occurs when you put a small section cut from the edge of a leaf lesion in a droplet of water on a microscope slide. When you view the slide under a microscope, you can observe the bacterial cells streaming out from the cut edge of the lesion (Figure 8).
However, other bacterial diseases also produce this streaming, so you should confirm the presence of X. vasicola by sending a sample to a plant disease diagnostic laboratory. If you suspect bacterial leaf streak, send symptomatic plants to a diagnostic lab to confirm the cause before implementing a disease management program. An accurate diagnosis will allow you to determine the best management strategy.
Gray leaf spot (GLS) produces lesions that look similar to bacterial leaf streak (Figure 9). GLS lesions tend to be more rectangular than bacterial leaf spot lesions.
GLS lesions have straight sides while bacterial leaf streak lesion margins are wavy (Figure 10). Light does not easily pass through backlit GLS lesions, so they are more opaque than the translucent lesions of bacterial leaf streak. If you examine the undersides of GLS lesions with a hand lens, you will often see dark, finger-like fungal structures (condiophores) emerging through the stomata.
Common rust may be mistaken for bacterial leaf streak (Figure 11).
Common rust lesions have raised, blister-like structures (pustules) within the lesion. When backlit, the pustules appear as dark circles (Figure 12).
Early Diplodia leaf streak symptoms include dark, water-soaked, linear lesions that become tan with long, parallel sides and a bright yellow halo (Figure 13).
As Diplodia leaf streak lesions mature, they become more elliptical and look less like bacterial leaf streak. You will also observe small, black fungal reproductive structures (pycnidia) scattered within the center of most mature Diplodia leaf streak lesions (Figure 14).
Mature southern corn leaf blight lesions can have brown to tan lesions with wavy sides and yellow halos in the lower canopy that resemble bacterial leaf streak (Figure 15). Southern corn leaf blight lesions are generally 1/8 to 1 inch long, but lesion length depends on hybrid genetics.
Southern corn leaf blight lesions do not produce bacterial streaming the way bacterial leaf streak does.
Genetic disorders such as lesion mimic may resemble bacterial leaf streak (Figure 16).
Genetic disorders that produce lesion mimic symptoms usually occur on every leaf of a plant. Unless the disease occurred early during vegetative growth, it would be unusual to see bacterial leaf streak symptoms on every leaf of a plant. Plants with genetic disorders may occur singularly or in small areas of a field, while bacterial leaf streak occurs in localized or widespread areas of a field.
Leaf miner feeding may be mistaken for bacterial leaf streak.
When you backlight a leaf with leaf miner feeding, the injured tissue has a “window-pane” appearance (Figure 17).
Fertilizer burn and sunscald can cause symptoms that resemble bacterial leaf streak.
Leaf tissue that has fertilizer burn or sunscald symptoms will be white, even when backlit (Figure 18). Saprophytic fungi may colonize the leaf lesions abiotic disorders cause. The fungi will look like black specks.
Currently, there is little information available for managing bacterial leaf streak. Field observations suggest that corn hybrids differ in susceptibility. Once hybrids can be screened for resistance, using resistant hybrids will be the best way to manage bacterial leaf streak.
Like other bacterial diseases (such as Goss’s wilt) there are no effective chemical controls.
We do not recommend tillage to reduce the risk of bacterial streak due to the need to manage soil erosion. While bacterial leaf streak has been most commonly observed in overhead-irrigated fields, it is also known to occur under both flood irrigation and dryland conditions. Researchers are investigating possible effective management strategies and potential sources of resistance.
Alison Robertson, Iowa State University
Kirk Broders, Colorado State University
Ron French, Texas A&M University
Tamra Jackson-Ziems, University of Nebraska-Lincoln
Doug Jardine, Kansas State University
Kevin Korus, University of Florida
Jillian Lang, Colorado State University
Jan Leach, Colorado State University
Tom Allen, Mississippi State University
Gary Bergstrom, Cornell University
Carl Bradley, University of Kentucky
Emmanuel Byamukama, South Dakota State University
Marty Chilvers, Michigan State University
Alyssa Collins, Pennsylvania State University
John Damicone, Oklahoma State University
Nicholas DuFault, University of Florida
Travis Faske, University of Arizona
Andrew Friskop, North Dakota State University
Clayton Hollier, Louisiana State University
Tom Isakeit, Texas A&M University
Heather Kelly, University of Tennessee
Nathan Kleczewski, University of Delaware
Dean Malvick, University of Minnesota
Hilary Mehl, Virginia Tech University
Daren Mueller, Iowa State University
Anna Freije, Purdue University
Pierce Paul, The Ohio State University
Adam Sisson, Iowa State University
Damon Smith, University of Wisconsin
Kiersten Wise, Purdue University
All photos were provided by, and are the property of, the authors and contributors except Figure 5 by Larry Appel, Appel Crop Consulting; Figure 8 by Edward Zaworski, Iowa State University; Figure 18 by Jim Fawcett, Iowa State University.
This publication was developed by the Crop Protection Network, a multi-state and international collaboration of university/provincial extension specialists and public/ private professionals that provides unbiased, research-based information to farmers and agricultural personnel.
Learn more at cropprotectionnetwork.org.
Design and production by Purdue Agricultural Communication.
©2017 by the Crop Protection Network. All rights reserved.
The information in this publication is only a guide, and the authors assume no liability for practices implemented based on this information. Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Individuals using such products assume responsibility for their use in accordance with current directions of the manufacturer.
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or a part of an individual’s income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at (202) 720-2600 (voice and TDD). To file a complaint of discrimination write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.
©2016 by the Crop Protection Network. All rights reserved.