Battle for the Belt: Season 2, Episode 16 – Corn Diseases and Ear Rots

Episode 16 of Battle for the Belt is now available: https://www.youtube.com/watch?v=Y325z4mIAXg

In Episode 16, we talk with Dr. Pierce Paul, the Ohio State University, CFAES Cereal Pathologist and State Extension Specialist, about the development of diseases and grain contamination with mycotoxins as influenced by planting date.

Planting date and disease
Altering a crop’s planting date directly influences the crop’s growing environment and consequently disease development. Early or late planting can coincide with different environmental conditions during critical crop growth stages. Most diseases that we deal with infect the plant at critical times during the growing season. The crop is more or less susceptible at certain growth stages, which vary depending on planting dates. If pathogen spores are available at the growth stage of greatest host susceptibility and the environment is favorable, infections will likely occur, and diseases will develop. Late planting does not always guarantee more disease, as it depends on which planting date receives the favorable conditions for the specific disease in question. There are some exceptions, tar spot seems to be a disease that develops best toward the end of the season. This is likely because tar spot is not endemic to Ohio yet, and spores have to blow in from outside. With late-planted corn, there are more opportunities for more spores to be blown in, infect, and damage plants at an earlier growth stages. Tar spot can have a greater impact on yield if it comes in well before grain fill is complete. The same can be said for gray leaf spot (GLS), but since it is endemic, lesion may show up early on lower, older leaves and quickly move up the plant as the season progresses, if weather conditions are favorable and the hybrid is susceptible.

For you to have disease epidemics, you have to have the “perfect storm”. (Figure 1.) Every side of the disease triangle needs to be present, a susceptible host, a virulent pathogen, and the right environment. With the range of five planting dates and four relative maturities in the Battle for the Belt project, you are more likely to see the coincidence of favorable weather, susceptible crop growth stage, and pathogen spores (inoculum) for one of more diseases to develop. As part of this project, disease monitoring and ratings are performed and results will be summarized after the end of this season.

Corn Ear Rots of Ohio
The main ear rots of concern in Ohio are Diplodia ear rot, Fusarium ear rot, Gibberella ear rot, and Trichoderma ear rot (Figure 2). Of these four, the most common are Diplodia and Gibberella ear rot (Figure 2). Diplodia is whitish mold growing on the surface of the ear and between the grain. If the ear is severely infected, is becomes lightweight and mummified. On the other hand, Gibberella ear rot (GER) is pinkish, with whiteish mold that develops mostly at the tip of the ear because the fungus infects via the silk. The latter is the single most important ear rot in Ohio, as it has increased in severity over the last decade or so and is associated grain contamination from mycotoxins, particularly deoxynivalenol (DON), also called vomitoxin, and zearalenone. GER, and DON in particular, could become a problem if harvest is delayed. This disease becomes worsened if harvest is delayed. Although infection does occur primarily during silking, corn stands in the field and exposed to late-season rainfall may still become infected and contaminated with high levels of DON. In recent years, grain loads have been turned away at the elevator for high DON levels, which has become a widespread concern. For more details on these ear rots, visit this link!

DON Screening of Corn Hybrids
In collaboration with Jason Hartschuh and Rich Minyo, last year the Cereal Pathology lab at Ohio State did a large-scale screening of several corn hybrids. There were 80 hybrids at three locations in Ohio, some were inoculated, and others were left not inoculated. This year they are screening some of the same hybrids. If you would like more information on the results of the screening, follow the link here.

DON Prediction Tool
The cereal pathology lab is working on a DON prediction tool. The goal is to be able to let a farmer know their risk of grain being contaminated with DON via a forecasting system. Currently the lab is testing different models developed by a PhD student who did preliminary screening of a small number of hybrids. He developed eleven different models by summarizing weather data before silking, at silking, during silking, and after silking. He evaluated weather data over 15-day time period, creating 300 different weather variables and then found the variables that had the strongest correlation with grain contamination of DON. Of those he created eleven different models to predict DON contamination. This season the lab is testing the pre-tassel model, which uses the number of hours that the temperature is between 68°F and 86°F and the 6-hour periods that relative humidity is greater than 80. These variables are used to create the forecast of the probability of contamination with DON. This year the lab is putting up twenty weather stations across the state and collecting weather data before silking to run the algorithm to inform the risk of DON contamination, then that is communicated to the farmer to assist with fungicide application decisions. The data from this year will be used to validate the model being used to predict the risk level of contamination and use as a tool to make fungicide decisions. The end goal is to create a phone app where the farmer and practitioners can just put in the date of silking and the field location to generate a risk level of DON for that field.

What’s happening in the field?
This week, the Western location received a good rain and the crops have been progressing well. The March 25^th planted corn is beginning grain fill with some of the hybrids reaching R3 but on average at R2 stage (Figure 3). As disease ratings continue for each planting date, minimal disease is being found. Gray leaf spot is the most common and the severity is at 1% on the ear leaf and incidence is less than 50%. Soybeans planted on March 25^th began flowering on May 28^th have been continually producing flowers and are currently at the R3 stage and has been at R3 for three weeks (Table 1). If you would like to see what is happening in the field, join us at the 2024 Western Agronomy Field Day on July 17.

The Northwest location also received rain this past week. The first planting date of soybeans reached R1, and the corn is still a week or more away from tasseling. Corn at this location is anywhere from V3 to V13. Soybeans are from VC to R1.

At the Wooster location, planting dates one, two, and three have reached reproductive stages in soybean. The third planting date began flowering this week and the first planting date of corn began tasseling and silking. At this location, the crops are not showing many symptoms of disease. There were minimal symptoms of gray leaf spot in corn.

Stay tuned for more updates in the coming weeks!