The 2018 corn-production season in Wisconsin has been challenging. Many farmers had what looked to be some of the best corn production ever. Then diseases arrived.

There have been numerous foliar diseases including a tar-spot epidemic in Wisconsin and surrounding states.

To add insult to injury, the University of Wisconsin has also confirmed bacterial leaf streak for the first time in Wisconsin corn. Corn producers and agronomists have been on the lookout for bacterial leaf streak for several seasons. But the disease wasn’t officially confirmed in the state until this year. A corn sample was received at the UW’s Plant Disease Diagnostic Clinic, from Pierce County, Wisconsin, with bacterial-leaf-streak symptoms.

Bacterial leaf streak of corn was reported for the first time in 2016 on corn in the United States. But it was likely present since 2014 in Nebraska. There have been subsequent reports from other states — Colorado, Illinois, Iowa, Kansas, Minnesota, Oklahoma, South Dakota, Texas and now Wisconsin.

Bacterial leaf streak is caused by the bacterium Xanthomonas vasicola pathovar vasculorum. It causes narrow leaf lesions with wavy brown marks. Lesions can appear translucent and have halos when back-lit. Symptoms on corn have been observed as early as the V7 growth stage, starting in the lower canopy and moving higher on plants if weather favors the disease. Wet weather and hot temperatures are conducive for bacterial leaf streak.

Little is known about the disease cycle. But it’s believed to overwinter on corn residue. The bacterium is presumed to be spread by irrigation as well as by splashing rain or wind-driven rain. No injury is needed for the bacterium to enter plants. It’s unknown if the bacterium can be spread with seed or if there are alternative weed hosts.

Most researchers believe yield loss is minimal if the disease manifests late in the season. If earlier and if it causes extensive leaf blight during grain fill, yield losses could be more substantial. Little is known about bacterial leaf streak’s impact on grain quality.

Some corn hybrids appear to have better resistance to bacterial leaf streak than others. Farmers should consult their seed dealers to find hybrids rated resistant. Hybrid resistance will be key to managing the disease.

Because bacterial leaf streak is caused by a bacterium, fungicides are not effective in controlling it. Withholding irrigation hasn’t been effective because the disease also occurs in non-irrigated fields. Managing corn residue via rotation may be helpful. Burying residue with tillage might also be an option. But greater priority should be given to managing soil erosion.

Farmers who suspect bacterial leaf streak in their corn can send leaf samples in sealed plastic bags with no added moisture to the University of Wisconsin Plant Disease Diagnostic Clinic. Visit pddc.wisc.edu for more information.

Damon Smith is a University of Wisconsin-Extension field-crops pathologist, Carol Groves is an associate researcher at UW-Madison, Brian Hudelson is a plant-disease diagnostician at UW-Madison and Sue Lueloff is an assistant plant-disease diagnostician at UW-Madison. Contact dlsmith26@wisc.edufor more information.