By Ryan Miller
Corn diseases tend to be less of a yield limiting issue in Minnesota, but questions do arise about fungicides and fungicide efficacy. The Crop Protection Network (CPN), https://cropprotectionnetwork.org/, is an excellent online resource to help with these questions. Crop Protection Network is a collaboration between University Extension Plant Pathologists from the U.S. and Canada. CPN is a platform for multi-state extension pest management information, including publications, webinars, fungicide efficacy data, and tools.
Publications
The fungicide efficacy guides provide a non-biased assessment on how different fungicide products should work for managing various plant diseases. In order to build these efficacy guides, a collection of plant pathologists from land grant institutions review their state’s fungicide trials and work towards a consensus on ranking fungicide products into efficacy classes for each plant disease.
Other popular publications include those on managing white mold of soybean , conditions conducive for tar spot of corn, and how do agronomic choices affect tar spot severity.
Fungicide efficacy data
Not all fungicides are equal. Uniform fungicide trials are conducted across the U.S. and Canada and data have been analyzed for over a decade in corn. These trials are conducted in states across the U.S. and for the most part the trials were the same across locations. Occasionally a site might not have been able to obtain a product or choose not to include a product, so that product would not be represented in their trial location. These trials have been instrumental in better assessing fungicide efficacy. Stay tuned to the CPN for some exciting new data exploration tools that are set to be released in the coming months.
With the exception of the SE part of the state in the past few years since tar spot arrived, Minnesota typically has fewer problems with foliar fungal diseases than states to the south of us and we haven’t participated in the uniform trials recently that were discussed in the webinar. Results from other uniform trials that include data from Minnesota were published: https://doi.org/10.1094/PHYTO-03-11-009. In addition, here are some MN specific corn foliar fungicide results from other trials:
https://blog-crop-news.extension.umn.edu/2020/07/foliar-fungicide-decisions-for-corn-and.html
Tools
Corn yield response to fungicide and fungicide efficacy data is often split into high disease severity (severity > 5%) sites and low disease severity (severity < 5%) sites, and it's typical to see more of a response in high disease severity sites. The corn disease severity training tools could be particularly useful when trying to determine if a fungicide application was beneficial. The corn tar spot severity training tool will make you better prepared for making in-field assessment of disease severity.
Discussion from the webinar
Fungicide use in low foliar disease severity environments (i.e. disease severity below 5%) is less likely to impact yield and consequently return on investment. When conditions are conducive for foliar disease and severity levels reach over 5%, a positive return on investment is more likely, but not guaranteed. Yield response, the price of corn, and cost of fungicide and application will determine if an application is profitable.
What about applications of fungicides for physiological benefits or “plant health”? In some cases, foliar fungicides may induce physiological effects in corn that can be observed even in the absence of disease. These effects can include corn staying greener longer in the season, improved standability, or modest yield increases even without disease pressure. These effects can occur in certain situations but yield gains in the absence of disease can be inconsistent and not always profitable.
The uniform trials have not compared fungicide application methods, but individual researchers in states have looked at trials comparing ground or aerial methods, or ground vs. drone applications. Foliar disease pressure in corn has been low in recent years, so it is difficult to say if there are differences in fungicide efficacy with different application methods. That said, in Dr. Wise’s trials, all application methods appear to reduce disease when done correctly. She recommends talking to your applicator to ensure that they are using the adequate carrier volumes and are following other label instructions to maximize efficacy.
What about standability data? Standability data are not reported with uniform trial data, but many researchers, including Dr. Wise collect this data in their fungicide program trials. Dr. Wise’s observations are that hybrid and environment matter most when it comes to standability. A fungicide application will not improve standability if the hybrid has poor stalk strength to begin with. Foliar fungicide applications that occur at tasseling/silking(VT/R1) are most likely to have a positive effect on standability compared to later fungicide timings
In Dr. Wise’s trials, post-blister fungicide applications often increase final corn moisture, and harvested grain moisture can be 1-2 points higher than corn that did not receive a fungicide application. Depending on harvest timing and grain drying capacity, this can be a factor when planning harvest, and determining profitability of fungicide applications.
The benefits of foliar fungicides are often promoted, and they are an excellent tool for managing foliar diseases in corn. However, it is important to remember that foliar fungicide applications are not without risk, and repeated use of foliar fungicides over time can lead to fungicide resistance in fungal populations. When this occurs, foliar fungicides are less effective or not effective at managing these diseases. Consider using multiple disease management methods, including hybrid resistance, to reduce disease risk and apply foliar fungicides only when necessary to maximize profit and maintain chemistries for future use.
Source : umn.edu