Source: Dr. Pierce Paul, OSU
Now is the time to take a closer look at your Wheat field … In between rain showers!
Wheat is now between Feekes 8 (flag leaf emergence) and Feekes 10 (boot) across the state. Feekes 8 marks the beginning of the period during which we recommend that you begin scouting fields to determine which disease is present and at what level. Septoria tritici leaf spot is usually one of the first to show up, and it has already been reported in some fields. So far, it is restricted to the lower leaves and severity is low in most of the affected fields. This disease is favored by cool (50-68F), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete.
Like many other foliar diseases, Septoria reduces grain fill and the size of the grain. It usually does not affect the number of spikelets per spike, an important yield component that is defined very early in the development of the plant. A fungicide application at this time will control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, protect the flag leaf, and minimize grain yield loss. If the weather conditions continue to be rainy and favorable for foliar disease develop, spores will continue to be produced or blown in from other areas, and new infections will occur, particularly if the variety is susceptible.
Results from previous studies have shown that the greatest benefits from foliar fungicide applications were seen when applications were made to a susceptible variety between Feekes 8 and 10. This is largely because most of our major foliar diseases usually develop and reach the flag leaf after Feekes 8-9. However, the residual effects of a Feekes 8-9 fungicide application will not adequately protect the head from late season diseases such as head scab and Stagonospora glume blotch or the flag leaf from rust and Stagonospora leaf blotch. In addition, some of the fungicide that effectively control foliar diseases are ineffective again, or are not recommended for control of, head scab.
There are several very effective fungicides available for use on wheat see the post above or (see resource chart). Carefully read labels before making an application.
On Feb 11, 2021, I gave a talk entitled “Management of Gibberella ear rot and Vomitoxin in Corn with Fungicides: Lessons Learned from Head Scab” as part of the 2021 Virtual Corn and Soybean School. I summarized years of fungicide efficacy research on head scab, a disease of wheat caused by the same fungus (Fusarium graminearum [Gibberella zeae]) that causes Gibberella ear rot (GER) in corn. Head scab and vomitoxin in wheat have been more widely studied than GER and vomitoxin in corn, as a result, a lot more is known about fungicide efficacy against scab/vomitoxin than against GER/vomitoxin. I therefore used lessons learned from head scab research, coupled with data from a limited number of GER fungicide efficacy studies to provide guideline on GER and vomitoxin management in corn. More than 220 people attended the 40-min-long program, asking questions covering various aspects of corn pathology. Below are more complete responses to several of these questions:
Q: How do you explain high vomitoxin levels in grain with no apparent ear rot observed? Can drought stress alone be a culprit?
A: Infection of the ear, development of visual symptoms (ear rot), and contamination of grain with vomitoxin all depend on weather conditions during the weeks after silk emergence. Once the fungus enters the ear via the silks (infection) and begins to colonize the developing grain, it produces vomitoxin, even if subsequent weather conditions are not favorable for mold and ear rot to develop on the outside of the ear. This is particularly true if infections occur late and conditions become relatively dry and unfavorable for visual symptoms to develop.
Q: It looks like the triazoles are doing the work on VOM, more than strobies, is this correct?
A: Pulling from my years of experience with head scab and a limited number of fungicide efficacy studies on Gibberella ear rot and vomitoxin in corn, I would be more inclined to recommend a triazole than a strobilurin fungicide for Gibberella ear rot and vomitoxin control in corn. Miravis Neo (a combination fungicide of a triazole, an SDHI, and a strobilurin) also looks promising.
Q: Is there any relationship between using a strobilurin for vomitoxins in corn compared to what is found in wheat?
The Agronomic Crops Team will host a virtual Corn College and Soybean School on February 11, 2021. Corn College is in the morning, from 9:00 – 12:00pm, with Soybean School in the afternoon from 1:00-4:00pm. Each program will feature updates from OSU Specialists. CCA CEUs are available. The schedule for the day is as follows:
Corn College, 9:00am-12:00pm
- Corn Management for 2021, Peter Thomison, 1.0 CM CCA CEUs
- Meeting Nutrient Needs in Corn, Steve Culman, 1.0 NM CCA CEUs
- Disease Management, Pierce Paul, 1.0 PM CCA CEUs
- Insect Management, Andy Michel, 1.0 PM CCA CEUs
Soybean School, 1:00-4:00pm
- Soybean Management for 2021, Laura Lindsey, 1.0 CM CCA CEUs
- Weed Management, Mark Loux, 1.0 PM CCA CEUs
- Disease Management, Anne Dorrance, 1.0 PM CCA CEUs
- Insect Management, Kelley Tilmon, 1.0 PM CCA CEUs
This program is free to attend. Register at www.go.osu.edu/agronomyschools.
The Ohio State Digital Ag Team’s Ag Tech Tuesday webinars are continuing this month! The online February series will cover results from several 2020 eFields trials and be held each Tuesday starting at 10:00 EST for 1 hour. There will be plenty of time for participants to ask questions. The following provides details for the 2021 Ag Tech Tuesday sessions.
2021 AG TECH TUESDAY: EFIELDS RESULTS
- February 2 – Improving Profitability in Corn Production
Weather and Climate Trends, Aaron Wilson
Irrigation, Amanda Douridas and Will Hamman
Corn Seeding Rates, Chris Zoller
SmartFirmer Seeding Rate, Elizabeth Hawkins
- February 9 – Pushing Soybean Productivity in Ohio
Boots on the Ground, Laura Lindsey
Local Boots on the Ground Results, Mary Griffith
Foliar Fertilizer, James Morris
Soybean Seeding Rates, Ken Ford
Sulfur on Soybeans, John Barker
- February 16 – Tech to Improve On-Farm Efficiency
Manure On-the-Go Sensing, Chris Shoup
Yield Monitor Data, Alysa Gauci
Virtual Reality and Field Demonstrations, Brooke Beam
Equipment Technology, Andrew Klopfenstein
- February 23 – eFields Small Grains, Forages, Soil Health, and Water Quality Results
Production Budgets and Custom Rates, Barry Ward
Winter Annual Forages, Jason Hartschuh
Barley Cohort, Eric Richer
Hemp, Lee Beers
Soil Health Testing, Boden Fisher
Source: Mark Badertscher, OSU Extension
Join OSU Extension for a virtual New Private Pesticide Applicator Training to help new pesticide applicators prepare for the Ohio Private Pesticide Applicator License scheduled for Tuesday, January 26 from 12:30-4:30 pm. The class will provide instruction in CORE, Grain, and Cereal Crops. For further study and to prepare for the test, books can be purchased from OSU Extension Publications online and shipped to your house at your expense.
Optional books for the online participants include:
Applying Pesticides Correctly (Core Manual)
Ohio Pesticide Applicator Training: Core Student Workbook
Ohio Pesticide Applicator Training: Field Crops Student Workbook
Register for this virtual event at https://go.osu.edu/virtualnewpesticideapplicatortraining-january26 and you will be sent a link for the class. There is no cost to participate and those who are unable to participate on the scheduled webinar date will be sent an email to watch the recording later if they register for the class. Following the class, participants can schedule an exam time at https://pested.osu.edu/PrivateApplicator/testing when they are ready to take the tests.
Adopted from: CPN-2012 Corn – Tar Spot, Crop Protection Network
Tar spot is a foliar disease of corn that commonly occurs throughout Mexico, Central America, South America, and the Caribbean. The disease was identified in the United States for the first time in 2015 in northern Illinois and Indiana. As of 2018, it has been confirmed in Iowa, Michigan, Wisconsin, Ohio, and Florida. During the 2018 growing season, the prevalence and severity of the disease increased dramatically, and in some areas tar spot caused substantial yield losses.
In the United States, tar spot of corn is caused by the fungus Phyllachora maydis. The fungus produces small (0.2-0.8 inch), round to semi-circular, raised black structures called stromata. In severe cases, stromata may also be observed on leaf sheaths and husks. Tar spot severity on ear leaves at growth stage R5 (dent stage) can exceed 50 percent in susceptible hybrids when conditions are favorable for the disease.
Corn at any developmental stage is susceptible to infection by the tar spot fungus when conditions are favorable. Disease symptoms have been observed as early as the third-leaf (V3) growth stage in the United States. P. maydis overwinters on infested corn residue on the soil surface, which serves as a source of inoculum for the subsequent growing season. It is not known if P. maydis overwinters on or infects any other plant hosts in the United States.
Conditions that Favor Disease In Latin America, cool temperatures (60-70°F) and high relative humidity (greater than 75 percent) favor tar spot development. In addition, disease incidence increases when there is at least seven hours of free moisture on the leaves due to rain, fog, or high relative humidity. However, it is not currently known what conditions favor the disease in the United States. In both 2015 and 2018, warm weather and periods of persistent rain and high humidity during the growing season likely favored the development and spread of the disease.
Continuous corn cultivation with minimum tillage practices, and high application rates of nitrogen fertilizer are also positively correlated with increased disease in Latin America. Although corn lines have been identified in Latin America that have resistance to tar spot complex, U.S. observations indicate that most hybrids grown in the North Central region are susceptible to P. maydis (although they differ in susceptibility).
Yield Losses and Impact Preliminary data from the Midwest indicate that severe tar spot outbreaks can reduce yield by more than 30 bushels per acre. Yield losses are a function of reduced ear weight, poor kernel fill, loose kernels, and vivipary (a condition in which the seed germinates while still on the cob). Observations also suggest that stalk rot and lodging are increased when tar spot severity is high. Severe tar spot also reduces forage quality.
Diagnosis You can diagnose corn tar spot in the field by examining corn leaves for the presence of black, tar-like spots. To date, tar spot has been observed most often during mid-to late grain fill (growth stages R3-R6) and usually on leaves below or near the ear leaf. You can observe stromata in green and senesced tissues. Occasionally, you may also observe necrotic brown tissue surrounding the black structures, which produces a fisheye appearance.
Management Most of what we know about tar spot has originated from Mexico and Central America. However, differences in the environments, fungal populations, hybrid genetics, and cropping systems may influence disease development in different areas. Our understanding of this disease in the United States is limited because of its very recent history.
However, several management practices may help reduce tar spot development and severity.
- Manage residue. Tilling fields buries infected residue and encourages it to decompose, which may help reduce the amount of overwintering tar spot inoculum.
- Rotate to other crops. This will allow residue to decompose and reduce the primary It is not yet known how many years it may take to sufficiently reduce inoculum.
- Avoid highly susceptible hybrids.
- Investigate fungicides. Some fungicides may reduce tar spot, however, we have little data about application timing that will provide an effective and economical response. Efforts are underway to understand the biology and epidemiology of this disease, which may help formulate fungicide application decisions in the future.
And next year’s crop may be at risk as well. The fungus that produces the toxin can survive the winter, particularly if stalks or other plant material from the 2018 corn crop are left on the surface of the soil, said Pierce Paul, an Ohio State University Extension specialist in corn and small grain diseases. OSU Extension is the outreach arm of the College of Food, Agricultural, and Environmental Sciences (CFAES).
The extent of vomitoxin across Ohio and the rest of the Corn Belt led some farmers to receive a lower price for their crop, Paul said.
High moisture levels spur the spread of vomitoxin, which can cause people and animals to get sick. The rainy summer and fall in the state and across the Midwest not only left more moisture in fields, but also delayed some farmers from harvesting.
And any corn left standing in wet fields becomes more susceptible to vomitoxin, Paul said.
Gibberella ear rot, a fungal disease that produces vomitoxin, also sucks nutrients out of corn, leading to smaller and lighter kernels, which can reduce yields and what farmers earn for the grain.
“I know there were farmers who had problems with price discounts, and some had their grain completely rejected,” Paul said.
Vomitoxin can cause animals, particularly pigs, to vomit or simply refuse to eat the tainted corn. If contaminated grain or grain products are consumed, this toxin can also make people ill, which is why the U.S. Food and Drug Administration has set strict limits on the amount of vomitoxin allowed in grain for human and animal consumption.
Moldy corn still can be used to produce ethanol. But the byproduct of ethanol production, typically a rich source of nutrients for animals, cannot be given to them because it will have a high concentration of vomitoxin, Paul said.
Vomitoxin can also contaminate wheat and barley. However, in Ohio, both of these crops were harvested by the first few weeks of July and were out of the fields before the persistent rains came, Paul said.
Not every cornfield had a problem with vomitoxin, because rainfall amounts are never uniform across the state.
The fields that were tainted with vomitoxin could still be a problem next season if the same or another susceptible hybrid is planted, Paul said.
Gibberella ear rot can survive in a field through winter and potentially harm the new crop if wet weather occurs, and “there’s nothing you can do after the fact” to control the disease, Paul said.
As a result, it’s important for farmers to choose corn seed that’s resistant to the fungus, he said. No corn hybrid is totally immune to Gibberella ear rot.
So, buying a hybrid that resists the disease is akin to people getting a flu shot. The hybrid does not guarantee that the crop will not get the disease, but it reduces the odds of that happening. If the crop does get infected, the damage is less extensive.
In a field contaminated with vomitoxin, burying the stalks and other plant material that remain will help reduce, but won’t eliminate, the spread of the fungus in next year’s crop, Paul said.
Symptoms of Gibberella ear rot include pinkish mold. But it can be easy to overlook if a growing crop has been tarnished by the fungus because the husk covers up where the damage occurs, on the ear of the corn.
“A lot of farmers are caught off guard,” Paul said. “After you harvest the grain or when you take it into the grain elevator, that’s when you start seeing weird stuff and realize you have a problem.”
For more information on vomitoxin, see go.osu.edu/vomitoxinfacts