Rain makes grain, but it can also ramp up disease pressure. In areas such as Iowa, where 2015 precipitation totals have been consistently well above normal, potential yield loss from corn disease could shape up to be a real concern. Iowa State University plant pathologist Alison Robertson says she has her eye on three diseases in particular that could prove problematic.
1. Northern corn leaf blight. This disease has already been reported in several fields in southern iowa, Robertson notes.
“You will remember that this disease was widespread in Iowa in 2014, and severe on susceptible hybrids,” she says. “Since the fungus survives the winter in corn residue, we will likely have above normal inoculum present.”
Cool, wet weather is the recipe for making big batches of Northern corn leaf blight, Robertson adds.
“It will be very important this growing season to scout fields that are planted to NCLB-susceptible hybrids,” she says. “If 2015 remains cool and wet, NCLB will win the ‘Disease of the Year’ award for a second consecutive year.”
Where disease has infected at least 50% of plants, foliar fungicides can have a positive impact. Robertson says 2014 trials showed that applications at V5-V6 can reduce NCLB, and R1 applications are more effective protecting the canopy through dent stage.
2. Anthracnose leaf blight. Interestingly enough, research at Iowa State University and the University of Wisconsin shows anthracnose leaf blight and anthracnose stalk rot are caused by the same pathogen, but no relationship otherwise exists between the two. (In other words, you can get one but not the other, and one does not cause the other.)
There’s not an urgent need to manage this disease, Robertson says.
“Corn will rapidly grow out of the disease, and the affected lower leaves, which do not contribute to yield, will die and fall off the plant within a couple of weeks,” she says.
3. Common rust. This disease has also already been spotted in Iowa corn fields, Robertson says. However, most hybrids are already equipped with ample common rust resistance, she says – but inbreds do not.
“Thus, seed production fields should be scouted, and a fungicide [should be] applied if disease is present,” she says.
In May 2015, practically all of the western Corn Belt received between 100% and 300% of normal monthly rainfalls. While central Nebraska was one of the few exceptions, the eastern part of the state saw a repeat of 2014’s soggy field conditions.
In the video below, Tamra Jackson-Ziems, University of Nebraska-Lincoln Extension plant pathologist, discusses scouting tips on several other potential early season pests, including Goss’s wilt and corn nematodes, as well as the extreme care farmers should give to samples they send off to be tested.
“Treat it like you would the produce you purchase at the grocery store,” she says. “Bag it in plastic, keep it cool if possible, and ship it early in the week so it doesn’t sit over the weekend.”