The presence of mold does not always have a strong correlation to mycotoxin development, but it does present the chance for incidence to occur.
A number of factors influence the prevalence of molds from year to year. Conducive weather conditions for mold and mycotoxin development are outside the control of management options. But hybrid characteristics and physical damage to the ears can be managed through the selection of hybrids and pest-resistance traits in the hybrids.
Western bean cutworm (WBC) is a pest of corn (as well as dry beans), and its territory has been expanding eastward over the last 10 to 15 years, with pockets of high populations now found in New York and Ontario, Canada. The moth emerges near the time of corn tasseling and lays its eggs near the ear leaf of a pollinating corn plant.
When the larvae hatch, they enter the corn ear, often opening a wound in the husk and feeding on kernels. Unlike other earworms, which are cannibalistic, you can find multiple WBC larvae feeding on one ear, increasing the chances for significant ear damage.
Where WBC populations are high, the corresponding ear damage from WBC feeding can leave wounded corn ears more susceptible to pathogen development, but a clear relationship between ear damage and mycotoxin development has not been documented. A number of mold species may develop on corn ears, though relatively few of these produce mycotoxins. Principal concern in New York is with the mycotoxins deoxynivalenol (DON or vomitoxin) and zearalenone (ZON), both produced by the fungus Fusarium graminearum. Infection by this fungus also occurs in roots and stalks and leads to Gibberella stalk rot and the accumulation of DON and ZON in stalk tissues. Much of the toxin loading in 2018 corn silage in New York was contributed by contaminated stalks as well as ear tissues.
While WBC damage to corn ears can be significant and may have detrimental effects on corn grain yield and quality, the economic impact on corn silage is less understood. For corn silage growers, understanding whether or not this pest significantly impacts the yield or quality of the forage is critical to their decision-making to manage this pest.
Since the Cry1F protein, which is most commonly used for protection against numerous corn insect pests, is ineffective against WBC, producers are left with limited management options. Currently, the Vip3A trait in select corn hybrids in combination with a scout and spray program is the best option for WBC management in areas where the pest is prevalent.
With the increased population of WBC in New York, the Commercial Corn Silage Hybrid Evaluation program conducted by Cornell University, in collaboration with the University of Vermont and the Northeast dairy industry, offers a good opportunity to evaluate numerous hybrids for ear damage from WBC and mycotoxins. This was done in 2017 and 2018 with financial support from the New York Corn Growers Association and the Northern New York Agricultural Development Program.
Each hybrid was planted (in triplicate) at two locations in New York and one location in Vermont, with hybrid planting location based on hybrid relative maturity (Table 1).
Mycotoxin screening was limited to the New York locations based on available funding. In 2017, composite whole-plant silage samples (three replicates combined) were taken for each hybrid at two locations: Madrid in northern New York and Aurora in central New York. In 2018, a slightly different strategy was used with individual replicate samples taken on a subset of hybrids at each location.
For both seasons, each plot was scouted prior to harvest to assess WBC feeding damage to the ears. At harvest a whole-plant silage sample was collected and submitted to the Dairy One forage laboratory for a mycotoxin screening package, which included aflatoxins B1, B2, G1, G2, vomitoxin, 3-acetyl DON, 15-acetyl DON, zearalenone and T2 toxin.
Through the New York State Integrated Pest Management (NYS IPM) WBC Pheromone Trapping Network, WBC populations were monitored at each location. It should be noted, because the traps only attract male moths, they help in understanding geographic differences in WBC population but may not be representative of the population of egg-laying females.
The results of the WBC and mycotoxin screening project revealed large differences in the pheromone trap counts and the number of plots damaged by WBC (Tables 2a and 2b).
There was also wide variation in the prevalence of samples testing positive for mycotoxins, particularly in 2018. However, there was a lack of correlation between WBC damage and incidence of mycotoxins in both years (Tables 2a and 2b).
Additionally, despite the damage to corn kernels inflicted by WBC, in plots with up to 60% of ears showing some level of WBC damage, the WBC feeding did not correlate to any negative impact on silage yield or forage starch content in this study.
The most prevalent species of mycotoxin-producing mold found in the screening was Fusarium graminearum. This fungal pathogen can also infect corn ears through the silk channels at the time of pollination during favorable weather conditions and result in contamination of the grain and silage with the mycotoxins DON, 3-ADON, 15-ADON or zearalenone. A review of the weather data from both years (despite very different overall weather patterns) showed wet conditions at silking conducive to this type of infection. As expected for New York, no aflatoxins were detected.
While there aren’t many in-field management options to reduce the chances of mycotoxin development (note that controlling plant diseases and mycotoxins are not the same thing), harvesting corn silage at the proper whole-plant dry matter is helpful. Based on numerous field observations, and notable at the 2018 Aurora location in this study, a whole-plant dry matter in the high 30s or above appears to increase the risk of mycotoxin development.
While there are numerous ways molds can establish themselves in forages, this study reflects a common challenge researchers face while attempting to document the conditions where mycotoxin development is likely. These results, over two growing seasons, provide no evidence WBC damage is an added risk factor for corn silage growers worried about deoxynivalenol and zearalenone in their silage.
In areas of the country where other toxins are more prevalent, the impact of WBC and other insect pests may differ. It is important to note these results do not reflect what may occur in corn harvested for grain because the time between silage harvest and grain harvest offers additional opportunities for infection and growth.
Growers should continue to scout for this pest and weigh the cost of control with the potential for damage. However, it does not appear that controlling WBC should be viewed as a significant management consideration to reduce risk of mycotoxin development in corn for silage. 
Gary Bergstrom is a Cornell professor and extension field crop pathologist. Jaime Cummings is a field crops and livestock IPM coordinator with NYS IPM. Elson Shields is a Cornell professor and Extension field crops entomologist. Ken Wise is a field crops and livestock IPM specialist with NYS IPM. Mike Hunter is a regional field crops specialist with the Cornell Cooperative Extension North Country Regional Ag Team.
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Joe Lawrence
- Dairy Forage Systems Specialist
- Cornell University
- Email Joe Lawrence
