Bacterial Leaf Streak Disease (BLS) is caused by the bacteria Xanthomonas vasicola pv. vasculorum. The disease was officially confirmed to be present in fields in 2016 and symptoms were again observed during the 2017 growing season. Symptoms of the disease were first observed in fields in Southwest Nebraska in 2014. Confirmed diagnosis of the disease has now been officially documented in the following states of Nebraska, Colorado, Kansas, Iowa, and Illinois. Prior to this the disease had only been observed in areas of South Africa.
Other than the symptomology of Xanthomonas vasicola pv. vasculorum there is very little known about the bacteria. How the bacteria over winters is not known for sure, but are thought to survive on corn stover. How the bacteria actually infects or enters the plant is not for certain either. Unlike Goss’s Wilt Bacteria that generally infects the plant through a wound in the plant tissue, it appears as though Bacterial Leaf Streak may not need a wound to enter the plant, but can enter through the stomata of the leaf and move throughout the plant from there. It is also thought that the bacteria can be air borne and spread but no one is for certain how far it may be able to travel. Occurrence of Bacterial Leaf Streak often tends to be higher in areas where irrigation is widely used as water droplets splash the bacterium from the residue onto the plant. Also, it is currently unknown as to whether or not the bacteria are seedborne as research has not been done at the current time. There is just a lot to discover and learn about this new disease in corn.
My personal observation, from the last 3 years of seeing BLS, is that the disease appears to flourish in areas where spring weather tends to be wet with frequent or above average rainfall. In 2014 we saw BLS in an area in SW Nebraska that had received well above average rainfall during that spring. In 2015 BLS appeared in many areas of SW Nebraska again, because of above average precipitation in the spring. Same pattern appeared again in 2016 but was much more prevalent because it was showing up in fields earlier in the crop’s growth stage. Now in 2017, SW Nebraska was much drier throughout the spring and the disease was difficult to find. However, NW Kansas received well above average precipitation throughout the spring and summer and BLS is very prevalent. Same appears to be true as you move East across Nebraska where spring precipitation events were very frequent. I believe that frequent or above average rainfall early in the crops growth stage can greatly increase the chances of the crops infection by BLS.
Bacterial Leaf Streak most generally first appears on the lower to mid canopy. Symptoms somewhat resemble those of Gray Leaf Spot (GLS) which is a common fungal disease in corn. The difference in symptomology between GLS and BLS are distinct. GLS leaf lesions tend to be gray or brown in color and the margins of the lesions are most generally straight. BLS lesions are browner, reddish, and tan in color and the margins of the lesions are more wavy or uneven.
Unlike GLS which can be effectively controlled with the application of a fungicide. BLS is a bacterium and like Goss’s Bacterial Wilt there is currently no known control of the either corn leaf disease. The one good thing about BLS is that it is not apparent that there is any real significant yield loses associated with the disease except for in extremely severe cases.
Since there is no way to control BLS once it has infected a crop, some measures can be taken to help reduce the risk of getting the disease. Hybrid selection is one possible way. Since, BLS is so new to the scene there are really pretty few rating currently placed on hybrids. It does appear from my personal notes and experience that there are some hybrids that are more susceptible. We were fortunate this year to have gotten some natural infection of BLS at two AgReliant Genetics research locations where some ratings and notes could be taken. It does appear that there are some hybrids and lines that are more susceptible than others. When planting corn back into fields that have previously showed symptoms of having BLS, really consider your hybrid selection. Crop rotation may be the best way to limit exposure to BLS. As you move into the 2018 growing season growers need to be looking back at scouting or field notes from the 2017 growing season and decide if there is an issue that needs addressed.
Some personal experience I have had since 2014 when first seeing symptoms of BLS in Southwest Nebraska. In 2014 the symptoms were limited to just a couple fields. In 2015 the spread of symptoms of BLS spread to several counties within the same area. In 2016 the spread of symptoms and confirmation of the actual disease were in the States mentioned at the start of this article. So, BLS spreads quickly, but exactly how it is spreading is unknown at this time. I think there is a lot of misdiagnosis of BLS and people are mistaking BLS for GLS. BLS has probably been in several states for the last few years but was simply being misdiagnosed as GLS. Either way, the spread of BLS has been significant in just a few years. Yield reduction from my experience has been null to very minimal. I have personally not been in a field that any significant yield loss has occurred when the crop had been infected. But, severity of the symptoms have been trending in an upward fashion in some areas and to say we won’t see significant yield effects at some time would not be prudent. There is a lot to learn about this new corn disease BLS. Be sure you are getting correct diagnosis of any corn leaf diseases to be sure you are making solid agronomic decisions regarding the crop.
References and additional information:
Note: The information in this issue is based upon field observations and third party information. Since variations in local conditions may affect the information and suggestions contained in this issue, LG Seeds disclaims legal responsibility therefore. Always read and follow label instructions.
LG Seeds and design are trademarks of SCA Limagrain.
Download a copy of this Technical Bulletin: Tech_346 - Bacterial Leaf Streak of Corn - An Update