Southern rust has been confirmed in approximately 40 counties in Nebraska in the last several weeks. Most recently, positive samples have been collected from Buffalo, Hall and surrounding counties. While pressure might be low in some fields and not present in others, it’s still a good idea to keep this disease on the radar in the coming weeks as kernels start to fill.
There are two main types of corn rusts in Nebraska: common rust and southern rust. Common rust tends to come in earlier and usually does not warrant a fungicide application. Common rust pustules are spaced out on both the upper and lower leaf surface and produces spores that are brick red in color. Southern rust can be more damaging to yield potential depending on how much disease is present, hybrid sensitivity and time of year when infection occurs. Southern rust pustules usually develop on the upper leaf surface in tight clusters. These pustules then release orange or tan spores.
The easiest way to tell these rusts apart is to look at the spores using a microscope. Neither pathogen overwinters in Nebraska as it gets too cold. Typically spores blow up from southern states.
The “perfect storm” for southern rust development is:
» High relative humidity.
» Warm temperatures in the upper 70s or 80s.
» Susceptible hybrids.
» Rust spores capable of infecting the plant.
Many hybrids are susceptible to southern rust, so scouting is essential. Monitor fields to determine if a foliar fungicide treatment is necessary. There is currently no economic threshold for foliar fungicide applications to manage southern rust in corn. However, paying close attention to crop stage of development, environmental conditions, irrigation and the potential risk for southern rust to develop in the region needs to be taken into account when deciding to manage this disease.
Studies have shown that if southern rust is confirmed, fungicide applications between silking (R1) and milk (R3) stages is most beneficial to protect yield. However, check how long the residual lasts on these products as late season infection may still occur, and a second application may be required. Applications at dough stage (R4) may still be beneficial if disease pressure is quite severe. Fungicide application made within two weeks, or 50% starch line, of physiological maturity is not as likely to give an economic return on your investment.
The weather will also play a huge role in determining if applications need to be made later in the growing season. If a field sample is found that looks questionable or could potentially be southern rust, contact the local Extension office or submit a sample to University of Nebraska-Lincoln’s Plant and Pest Diagnostic Clinic in Lincoln for confirmation.
More information about this disease can be found at cropwatch.unl.edu/2019/southern-rust-corn-confirmed-southeast-nebraska.
Virtual field days
Many field days this summer have been modified or canceled due to the COVID-19 pandemic. Nebraska Extension hosts several in-person field days during the summer months under normal circumstances where producers and ag industry professionals can learn about research projects conducted across the state.
Due to the pandemic, these field days have been modified into a “virtual field day” format so growers and industry professionals can still receive updates on research efforts conducted across Nebraska. The Extension Weed Scientists at UNL put together two virtual field days on weed management and herbicide resistance updates.
The first virtual field day covers weed management strategies in Xtend Flex Soybeans, Enlist Soybeans, white corn and popcorn varieties and herbicide options for terminating cover crops in soybeans. More information can be found at go.unl.edu/2020weedfieldday.
A second virtual field day was produced on atrazine, glyphosate and ALS inhibitor-resistant Palmer amaranth. This virtual field day looks at row spacing and herbicide programs for managing resistant weeds in Enlist E3 corn and herbicide options to control resistant Palmer amaranth. More information can be found at go.unl.edu/palmer-amaranth2020.
Finally, the Extension was not able to host the Wheat Field Days across the state this summer, so this information is also being shared virtually. Two videos were produced to share this research. The first video looks at production and background information on the plots grown, which can be found at mediahub.unl.edu/media/13563, and the second looks at different varieties grown within these trials across Nebraska, and can be found at mediahub.unl.edu/media/13564. More information on these virtual field days can be found on UNL’s CropWatch website.
Virtual Nebraska Grazing Conference
Nebraska Extension is offering the Nebraska Grazing Conference in a virtual format this year. This free virtual conference will be held from 11:30 a.m. to 5 p.m. on Aug. 11 and 12. While this conference is free, registration is required for each day attended. Registration opened on Aug. 1 at grassland.unl.edu. Themes for this year’s virtual conference include “Weather Ready Ranches,” “Ranch of the Future” and “Invasive Woody Plant Management.” This conference also includes podcasts and “watch parties” where Extension professionals will share updates of what’s going on in their part of the state pertaining to grazing systems. Conference details and a full schedule can be found online at grassland.unl.edu/ngc-virtual.