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Ontario Grain Farmer Magazine

Managing Fusarium and DON with new fungicides

Principal Investigator: Art Schaafsma and David Hooker

Research Institution: University of Guelph

Timeline: June 2018 – January 2022

Objectives:

  • Determine relative effectiveness of ADEPIDYN® Technology compared with current fungicides against Fusarium disease and mycotoxin reduction in corn and wheat.
  • Determine the overall agronomic fit of ADEPIDYN Technology in intensively-managed and high-yielding wheat and corn; validate the importance of any significant interactions uncovered first in the greenhouse (wheat only).
  • Determine impact of corn refuge genetics, population density, and delayed plant development on DON levels.
  • Determine the cause of blackened corn stalks.
  • Determine interactions of fungal strains (chemotypes), and the use of fungicides alone and in combination on the biosynthesis and profile of mycotoxins (various DON metabolites and masked mycotoxins) in liquid culture in the laboratory.

Impacts:

  • Independent public data will allow producers to make informed decisions on the most cost effective and sustainable strategy to manage Fusarium head blight (FHB) and Gibberella ear rot (GER) in wheat and corn, respectively.
  • These data will inform extension workers and crop advisors to give appropriate advice to wheat and corn producers in a broader context of variety selection, fungicide selection and desired market endpoints.
  • Understanding the relative fit of this new chemistry with its competitors will open opportunities for introducing fungal resistance management strategies for all the fungicides available for control of mycotoxins in wheat and corn.
  • Ensure that there are no surprises in how the fungicides interact with fungal chemotypes when applied alone or in combination.

Scientific Summary:

Fusarium head blight (FHB) in wheat and Gibberella ear rot (GER) in corn and the mycotoxins associated with these diseases are serious problems in Ontario grain production. Much attention has been given to the use of fungicides to manage these problems and currently there are four products used: Folicur, Prosaro, Proline and Caramba. Under the best conditions some of these provide a maximum of 70% reduction of mycotoxins and only up to 80-90% disease control. All of these belong to the same family of chemistry, the triazoles, and there are no alternatives, so the risk of the fungus responsible for these diseases developing resistance to this group of materials is relatively high. Alternatives with different modes of action are needed, and a new chemical called ADEPIDYN Technology is being developed by Syngenta (it is in a different class of chemistry with a new mode of action). There are recent important shifts to more virulent and potentially more toxic fungal strains predominating in North America accompanied by shifts in the mycotoxin profiles appearing in the grain, plus the occurrence of masked mycotoxin metabolites that are not easily detected. Not much is known about how these shifts interact with current fungicides or their new alternatives.

This project assessed ADEPIDYN Technology in the field, in corn and wheat, relative to its current competitors, alone and in combination, to provide public data on its performance, spectrum of control, and fit in the agronomic package relative to other inputs for high-yielding wheat and corn. These data will inform their ranking in the provincial recommendations through OMAFA Publication 812, Field Crop Protection Guide.

Further, this project informs the positioning of ADEPIDYN Technology in a resistance management plan. Finally, this project showed how the triazole fungicides and ADEPIDYN Technology interact with the new strains of fungi appearing in the lab and in the field and how they affect the profile of mycotoxins that these fungi produce both in corn and wheat.

Results:

1. To compare the relative effectiveness of ADEPIDYN Technology compared to standard fungicides on GER disease and mycotoxins in corn, with and without ear injury by Western bean cutworm (WBC; Striacosta albicosta):

ADEPIDYN Technology performed as well in the field and in controlled studies as its older competitors in managing GER disease and reducing mycotoxins associated with this disease. Disease control of up to 80% was achieved and mycotoxins were reduced by up to 70%. As noted, ADEPIDYN Technology belongs to a different class of chemistry (relative to the competitor fungicides) and has a different mode of action. Products containing ADEPIDYN Technology allow grain producers to rotate classes of chemistry for an effective resistance management program; this product has been in use on Canadian farms for two years as a result of this project. The WBC did not infest our experiments in any of the years of our study as we expected, plus we were not able to collect or rear enough eggs to artificially infest plots (after several attempts) so we could not make any conclusions regarding the integrated management of GER and WBC.

With regards to the optimum timing in which to apply products containing ADEPIDYN Technology for GER control in corn, the window of application was between early silk emergence and the onset of silk browning. The early part of this window allows farmers to apply a fungicide for GER control at the same time as an insecticide to manage WBC infestation, if warranted by scouting. This is a positive finding because only a single pass with a ground sprayer in very tall corn would be required. Ground application is preferred to aerial applications because both pests, GER and WBC, are better targeted and timed with ground application equipment and there is less environmental exposure.

2. Determine if insecticide has any effect on mycotoxins in the absence of insect damage and determine if there are different interactions of fungicides and insecticides on DON accumulation:

In 2018, in 2 out of 3 field experiments we saw significantly higher concentrations of DON in plots treated with a certain insecticide without fungicide. This insecticide was widely used in 2018 for WBC control and there was concern that its use could have contributed to the extremely high concentrations of DON detected in the crop. In 2019 and 2020 we set out experiments in farmers fields and in controlled experiments with inoculation and misting to see if this phenomenon could be duplicated. Thankfully, insecticides applied alone or in combination with fungicides did not result in elevated DON concentrations in any of the experiments in 2019 and 2020 and we are at a loss to explain the strange result obtained in 2018.

3. To determine the relative effectiveness of ADEPIDYN Technology for reducing FHB and DON in wheat in different wheat varieties under different N rates:

Varieties of wheat with the highest resistance to FHB and with the highest yield potential responded the best to application of products containing ADEPIDYN Technology. Those varieties that responded the best to increased rates of N application also responded better to applications of ADEPIDYN Technology. Yield increases of 15-20% were observed with integrated inputs of optimum variety, fungicide, and optimum N rate. Reductions of mycotoxins of 60 – 80% were observed. All important DON-related compounds were reduced by similar percentages in the harvested grain. ADEPIDYN Technology containing products presented a slight advantage in yield and mycotoxin reduction in wheat than its competitor products. However, the main benefit for having ADEPIDYN Technology in the toolbox is the new possibility to manage resistance of FHB to fungicides as the only class of chemistry previously available to growers were the triazoles.

The optimal timing to apply products containing ADEPIDYN Technology to reduce FHB and DON contamination was at early anthesis (when the anthers were extruding). We found that the fungicide could also be applied when heads were just fully emerged until the time when anthers began to dehisce, about a 5-to-7-day window. One could expect 50% control of FHB and reduction in DON at the two extremes of this window and about 70-80% when application was optimally timed. The other fungicides were more sensitive to optimal timing, presenting a narrower window of opportunity (3-5 days).

4. To determine the effect of corn refuge genetics on DON accumulation in four hybrids:

Corn hybrids are often sold with transgenic traits for insect control. To prevent resistance developing in the target insect, a refuge of non-traited corn is included in the bag. Seed providers are not required to declare what the genetics of this refuge are, and we thought that this refuge seed might be more or less susceptible to Fusarium. We purchased a bag of corn seed for several hybrids and sorted out the refuge seed (it is coloured differently). We planted non-refuge and refuge separately in controlled field experiments with misting and inoculation. There were differences in susceptibility between refuge and non-refuge hybrids from the same bag, but it varied from more susceptible to less susceptible between bags. We concluded that refuge seed was not a major contributor to the GER epidemic in 2018.

5. To determine the effect of the stress of high plant population density on DON accumulation:

We planted four hybrids at three plant populations during two seasons. There were no differences in DON concentration between the two lower populations. However, there was over 100% more DON produced in corn planted at the highest population, leading us to conclude that stress from crowding resulted in more disease and more mycotoxins. Two recommendations emerged: plants must be evenly spaced, and very high populations must be avoided.

6. To determine the effect of delayed plant development on silking date and DON accumulation in four hybrids:

We conducted two experiments in 2019 and 2020 under controlled and inoculated conditions. In these experiments we planted four hybrids, followed by delayed planting in the same row such that there were earlier and later developing plants in the same row. In all cases we observed significantly more GER disease and much higher concentrations of mycotoxin (up to 600% more DON) in delayed plants. We concluded that delayed plants are stressed by neighbouring, more-advanced plants leading to more disease and higher mycotoxin concentrations. In the bad GER epidemic in 2018, we recall that there were many cases of very uneven emergence, and the resulting stress in delayed plants could have been a main contributor to the extremely high concentrations of mycotoxin observed in the crop. We now recommend that growers attempt to achieve uniform emergence when planting.

7. To determine the cause of black stalks observed after harvest and their relationship to Fusarium inoculum:

We have been observing a dramatic new increase in the blackening of corn stalks in the weeks following harvest in the last number of years. To the naked eye it appeared that Fusarium perithecia were forming very quickly on cut stalks, which was unusually early. We though it had something to do with the “stay green” trait in newer corn hybrids which we believed had higher sugar and carbohydrate content. We sampled corn stalks from ten fields in the spring of 2020, separately isolating from blackened and clean stalks. Most of the samples were positive for Fusarium graminearum and there was no difference in its presence on blacked or clean stalks. We concluded that the black mold was not Fusarium and was probably another saprophytic fungus like Cladosporium.

8. To determine the baseline sensitivity (EC50 colony growth) of ADEPIDYN Technology (commercial formulation) on field collected strains of F. graminearum on culture media:

Ten single spore isolates from wheat heads, corn stalks and corn kernels, resulting in 30 isolates in total, were collected from several regions around southern Ontario. EC50’s were calculated using fungal colony growth on agar medium amended with a series of concentrations of the various fungicides. Wild cultures (fresh isolates, not from a culture collection) of F. graminearum were most sensitive to ADEPIDYN Technology with EC50 values for the 30 isolates of F. graminearum exposed ADEPIDYN Technology ranged from 0.01 to 0.10 ug/mL, with a mean of 0.05 ug/mL. The mean of EC50 of the subset of 10 isolates exposed to ADEPIDYN Technology, Miravis, Ace, Caramba, Prosaro 250 EC and Proline 480 SC were 0.06, 0.18, 0.13, 0.05, 0.30 and 3.75 ug/mL, respectively. These are the first data reported from our region and are important because now they can be used as a baseline to determine whether resistance to any of the fungicides is occurring. We recommend that samples of the wild population of F. graminearum should be taken periodically and EC50’s calculated for each fungicide to monitor for selection toward resistant populations of F. graminearum. These data could also be used as a reference in the event a fungicide fails and fresh samples of F. graminearum are collected and tested.

9. To determine if fungicides differ in mycotoxin profile outcomes when they interact with competing F. graminearum chemotypes in culture:

Originally, we planned to do this work in culture, but realized our error when it came to following the production of one of the important metabolites DON-3G. DON-3G is made by the plant in response to the occurrence of DON so we had to move to an in-plant system. We chose spring wheat. The two chemotypes we chose were the main ones found in Ontario. Small plots of spring wheat were set up in a 2x7x4 RCBD experiment with 4 replications. Factor one was chemotype: 15ADON, 3ANX (DAOMC 251911, 252201) and 15ADON (DAOMC 251904, 251954). Factor two was fungicide (ADEPIDYN Technology+ propiconazole, propiconazole, azoxystrobin, prothioconazole, metconazole, water). Factor three was sampling timing after inoculation: 1wk, 3wk, 4wk, 5 wk. All plots were misted and inoculated with F. graminearum. Heads of wheat were hand-harvested at designated timing and were prepared for mycotoxin analyses using LCmsms. The experiment was done in 2019 and 2020.

In 2019 we had dry weather in spring and very hot weather during flowering and the experiment was lost. In 2020 we did not achieve the concentrations of DON in our control plots as we normally expected with misting and inoculation, but some initial inferences could be made. DON and related compounds were reduced by 50-70% using fungicides and all the fungicides performed similarly. There were no interactions between chemotype and fungicide in mycotoxin production. The 15-ADON, 3 ANX chemotype produced 3 times more DON than 15 ADON chemotype. This finding is of concern because the 15ADON, 3 ANX chemotype is new to Ontario and its frequency is growing. An important future line of research would be to determine if this is confined to only the two strains we happened to select or if this is generally true for all 15-ADON, 3 ANX strains.

External Funding Partners:

We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).

Syngenta Canada

Project Related Publications

Eli, K., Limay-Rios, V., Hooker, D., Miller J.D., and Schaafsma, A. 2024. Trichothecence mycotoxin profiling of Fusarium graminearum isolates from wheat and maize, and the baseline sensitivity to pydiflumetofen and other fungicides. Canadian Journal of Plant Pathology. Online: 2024.