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?
A: Based on a very limited number of trials, I have not seen the same increase in VOM in GER-affected corn plots that I have seen in head scab-affected wheat plots following treatment with strobilurin fungicides. In other words, I have not seen the same relationships between vomitoxin and strobilurin fungicides in corn, but again, I have looked at far fewer fungicide trials for vomitoxin in corn than I have for vomitoxin in wheat.
Q: Does spraying fungicide at full silking hurt pollination in corn.
A: I know of no studies showing negative effects of the application of fungicides at full silking (at and shortly after the R1 growth stage) on pollination, BUT it is an interesting question that needs to be investigated through research. Yields in my plots that were treated with drop nozzles (fungicide applied close to the silks) were very similar to yields from plots treated with a high clearance sprayer (fungicides applied over the top, near the tassels).
Q: How do fungicide applications affect the soil biology?
A: When applied at or after tasseling, most of the fungicide is captured on the leaves. I do not have data regarding fungicide effects on soil biology, but since several soilborne fungi are related to (or the same as) fungi that cause diseases, fungicides may have very similar effects of fungi in the soil and fungi on leaves, thus affecting the soil microbial community. However, this will all depend on the specific fungicide, the weather conditions, and the soil properties. However, I do not have my own data to support this.
Q: What role if any does fertility/plant nutrition play in disease? Can plants be healthy enough to fight off disease?
A: A healthy plant is better able to defend itself against some pests and diseases, so keeping plants healthy and well fertilized is a good place to start. However, fertility tends to affect diseases differently. For instance, high nitrogen may cause some diseases to increase and other diseases to decrease. The form of nitrogen also plays a role in disease development. So, while good nutrition will help to maintain the plant health, fertility alone will not control all diseases if the hybrid does not have the right genetics (resistance) to prevent or minimize infection, particularly if weather conditions are highly favorable for disease development.
Q: Observations of Physoderma in corn and treatment successes.
A: I do not see a lot of Physoderma in my trials. It is very rare and never reaches high levels of severity or impacts yield in Ohio. As a result, I have not been able to evaluate fungicide efficacy against this disease in any of my trials.
Q: Have you looked at Xyway from FMC In-Furrow Fungicide on corn? Do you have any comments?
A: Yes, I did test Xyway in-furrow treatment in two trials in 2020 and plan to do so again in 2021. So far in my trials, when used alone without a foliar fungicide application, I have not seen any benefits in terms of disease control or yield increase.