2019 Ontario Grain Corn Ear Mould and Deoxynivalenol (DON) Mycotoxin Survey

OMAFRA field crop specialists in collaboration with Grain Farmers of Ontario (GFO) and members of the Ontario Agri-Business Association (OABA) have completed the annual Provincial corn ear mould and mycotoxin survey. Corn ear moulds such as Gibberella and their corresponding mycotoxins occur every year in Ontario. These mycotoxins, particularly deoxynivalenol (DON, or also referred to as vomitoxin) are produced primarily by Gibberella/Fusarium ear moulds can be disruptive when fed to livestock, especially hogs. The 2019 survey found 96% of samples tested low (<2.00 parts per million (ppm)) for DON which is considerably lower than 2018.  

 

 

From October 3 to 9, 2019, a total of 222 ear corn samples were collected from across the province. Five consecutive ears were collected from four random locations throughout a field and placed into high temperature driers as soon as possible after collection. Pictures were taken to document moulds (Fig. 1) and insect and bird feeding damage. Dry ears were shelled and the entire shelled sample was coarse ground and mixed for sub-sampling consistency. Sub samples were collected and finely ground for DON analysis by quantitative ELISA analysis at the University of Guelph Ridgetown Campus mycotoxin lab.

 

 

 

Results for the 2019 survey are presented in Table 1. Overall, visual mould symptoms and DON concentrations were much lower than 2018, and in the lower range of long-term survey results (Table 2). Most samples exhibited no visual ear mould symptoms. In samples where ear moulds were observed, it was most often associated with insect or bird feeding damage opening husks and damaging kernels.  Other mouldy samples with no apparent insect/bird ear damage were observed where weather and hybrid susceptibility were likely factors.

 

 

 

While 95% of 2019 samples tested below 2 ppm, it is important to remember that growers should remain vigilant and be aware of management options in those fields with higher ear mould and DON concentrations. Ear moulds and mycotoxins occur every year in Ontario and fields need to be assessed individually. Distribution of samples and their corresponding DON levels are presented in Figure 2.

 

 

 

Growing conditions may have been less conducive for ear moulds in 2019, but the corn crop is also less mature than it normally would be, which may partially explain low levels. The 2019 DON survey was delayed given that planting and crop development were delayed due to wet spring conditions, but despite this, samples still mostly ranged from half milkline to not quite black layer, while in most years samples would have largely been black layered. High grain moistures later in the growing season and slow dry down can be factors for ear mould development if ear moulds are established and environmental conditions are suitable, although cooler temperatures of November and December should also slow further mould development. For comparison, in the high-risk year of 2018 visual mould symptoms were already very apparent by the latter half-milk stage.

 

 

Ear feeding by pests, particularly western bean cutworm (WBC), or birds can open husks and damage kernels and present an opportunity for greater mould infection. Feeding damage can be a significant contributor towards elevated DON levels in survey samples. While generally low pest pressure overall,  feeding from WBC and corn earworm (CEW) was present in some samples but at levels typically observed in most DON surveys. Where pest feeding was present, ear damage did appear to elevate the risk for ear mould and DON. This was markedly different than 2018 where pest feeding was very minimal, and most ear moulds appeared to be silk-initiated infections. Late season corn earworm damage in some fields, particularly Southwestern and Eastern, Ontario could have contributed to increased ear mould incidence and DON production. Particularly in later planted fields that were most attractive to CEW.

 

 

The importance of collecting a representative sample cannot be emphasized enough, since 90% of the variability associated with mycotoxin testing comes from incorrect sample collection. While taking a sample from the top of a storage bin, truck or combine may be easy and convenient, mycotoxins are rarely distributed evenly in a load of corn.

 

If the sample is to come from a bin, truck, V-box, or other stationary load of corn, a sample probe is recommended. Although 10 probe samples are recommended for best results, 5 probe samples is the minimum necessary for accurate results. Mix the grouped sample. Because individual kernels can be highly variable and are still relatively coarse in size for subsampling, the whole sample should ideally be ground (at least coarsely) to improve mixing and ability to collect a representative sub sample for analysis. If you are dealing with a moving stream of grain, use a diverter or randomly collect cupfuls of grain. Regardless of how the sample is taken, it must be processed quickly. Ship or deliver the fresh sample promptly. The longer the sample sits around the greater potential for inaccurate results.

 

 

This survey does not fully capture all regions of the province, and results can vary locally from field to field depending on local weather, hybrid, planting date, insect feeding, rotation, residue levels, fungicide practices and moisture. These survey results may not fully capture what is occurring in your fields, and therefore monitoring is always recommended. Timely harvest is important. Leaving diseased grain in the field allows the ear rot fungi to keep growing, which will increase the risk of mouldy grain and mycotoxin contamination since most ear rot fungi continue to grow (and potentially produce mycotoxins) until the grain has less than 15 percent moisture. In severely infected fields or those under higher risk, growers should consider harvesting grain at higher moisture and then dry it to less than 15 percent to minimize further mycotoxin accumulation.

 

If a field contains a significant level of ear mould (10% or more ears with mould symptoms), collect a representative sample prior to harvest and have it tested for mycotoxins before storing the grain or feeding it to livestock. If necessary segregate the harvested grain from your other corn.  A lab test is often the only reliable way to definitively determine mycotoxin presence and levels.

 

When ear rots are present, the following harvest, storage and feeding precautions are advisable (Adapted from OMAFRA Pub 811, Agronomy Guide for Field Crops):

 

 

Preventing ear rots and mould can be difficult since weather conditions are critical to disease development. A few things to consider for 2020. Hybrid selection is important but remember although some tolerant hybrids are available, none have complete resistance. Growers are encouraged to discuss with their local seed supplier, what ear mould tolerant hybrids are best suited for their operation. New for 2019, the Ontario Corn Committee has initiated inoculated DON trials for evaluating differences in DON susceptibility across Ontario hybrids. This information is expected to be released this fall.  Crop rotation may help reduce the incidence of ear rots, while several foliar fungicides aimed at suppressing ear rots have also been registered. Cultural practices such as tillage have been shown to have limited success in preventing ear and kernel rots.