Fusarium ear rot causing fumonisin contamination in corn

Introduction

Fusarium ear rot is a corn disease caused by the fungi Fusarium verticillioides, Fusarium proliferatum and Fusarium subglutanins. In all three species the disease symptoms are similar, but only F. verticillioides and F. proliferatum produce a group of mycotoxins called fumonisin which at high enough levels can be toxic to animals, livestock, and humans.¹ Fusarium ear rot can begin during or after flowering (R1 growth stage) and is most problematic when with hot and dry weather is followed by periods of high humidity. Rain before harvest may intensify the contamination of fumonisins in corn.

Due to health risks associated with fumonisin, grain must be tested to determine fumonisin levels. Management practices can be implemented to help reduce the risk of Fusarium in future corn crops.

Fusarium Identification

Infected kernels have a white-to-pink cottony mold which are scattered around the ear (Figure 1).

Infected kernels may have white streaks that are arranged in a starburst pattern (Figure 2). The mold can produce a mycotoxin called fumonisins.

Sampling and Testing Procedures

If Fusarium ear rot is suspected, scout fields at physiological maturity (R6 growth stage) to determine the severity.¹ If the ear rot is widespread, harvest as early as possible to reduce the level of fumonisin contamination and ear rot damage to kernels. At harvest grain must be tested to determine the level of fumonisin as toxin levels are not synonymous with visible ear rot symptomology. Fumonisin can be detected in a kernel that does not have any damage to the seed coat (pericarp). In order to know if a cornfield is impacted by mycotoxins, testing can be completed by an elevator with testing capabilities, grain exchanges, or an approved independent laboratory.

Fumonisin does not occur uniformly in bulk corn, and grain handlers should sample in several areas of a load or bin. Contact a toxicology laboratory for specific sampling, handling instructions and analysis. There are a variety of commercial laboratories and quick-test kits for mycotoxin analysis. Actlabs Agriculture (laboratory@actlabsag.com) and Agribrands Purina are two of many that do fumonisin testing.

A farmer with fumonisin contaminated grain has some options; however, discounted prices are likely if the milligrams per kilograms (mg/kg) levels reach a high level. If fumonisin contaminated grain is being used to make ethanol, the ethanol fermentation process increases the mycotoxin concentration levels in the distillers dried grain (DDG). Experiments have evaluated the mycotoxin concentrations in DDGs and have reported to be approximately three times as high as the level in the grain. Moulds can grow and mycotoxins can be produced in DDGs during transport, storage, and feeding at the farm which can further increase the fumonisin levels and danger when fed. ¹

According to a report by the Government of Canada, 2010-2011 Fumonisins in Corn Products, there are no Canadian maximum levels, tolerances, or standards for fumonisins in corn products .²

Corn Product Selection and Management

Corn product selection is an important step in managing fusarium outbreaks in corn. Products with insect resistance traits (above ground Bt protection), drought tolerance, and downward position ears at maturity can help reduce the potential production of mycotoxins. Corn products with insect resistant traits (Trecepta^® Technology) that protect the ear from corn earworms and Western bean cutworm may have lower levels of ear moulds as insect feeding can create additional pathways for the disease to infect the kernels. Fumonisin can be detected in a kernel that does not have any damage to the seed coat (pericarp). Other factors that may influence fumonisin contamination are environmental conditions during two periods of corn development. The tasseling growth stage (R1) and physiological maturity (R6), are critical growth stages for kernel contamination with fumonisin.¹ Contact your local agronomist to select the best locally adapted corn products with proven disease tolerance or resistance.

Fungicide seed treatments can help protect young plants and reduce the buildup of fusarium pathogens in the soil. Optimize soil fertility to aid in plant health and improve residue decomposition. Avoid high levels of nitrogen and low levels of potassium.

Management to Minimize Mycotoxin Contamination

Some management practices can help to minimize mycotoxin contamination. These include:

• Limiting bird and insect damage, because moulds tend to invade damaged kernels more easily than intact ones.
• Harvesting grain as soon as possible. Fusarium mould grows readily under warm, damp conditions.
• Adequate drying and storage of grain to prevent mould growth and mycotoxin production post-harvest. Once corn dries down to 17% moisture, ear rot caused by Fusarium should cease development. Store grain at cool temperatures 2 to 6.5 ⁰C (36 to 44 ⁰F). Stored grain should be checked periodically for temperature, wet spots, and insects.
• High moisture corn should be checked to ensure that ensiling conditions remain anaerobic to limit mould growth and mycotoxin contamination. Moulds cannot grow under truly anaerobic conditions.
• Using crop rotation to minimize the carry-over of moulds from one year to the next. Fusarium survives on crop residue. If corn-on-corn rotations are used, then crop residue should be completely buried so that pathogens will have the least chance of survival. Tillage operations that only partially bury residue, such as chopping, disking, or chiseling, are also beneficial for pathogen reduction.
• Avoiding planting crops that may be susceptible to mould infestation in adjacent fields where the disease may spread from one crop to the other.
• When contamination does occur, mould spores and mycotoxins are often concentrated in the fines and dust of grains. Use of masks to avoid inhalation and ingestion of dust by grain handlers is recommended.³

Steps for Dealing with Mycotoxins

If a corn field is suspected to have high levels of fumonisin, testing must be completed by elevators, grain exchange, or approved independent laboratory facilities.

Farmers that suspect fumonisin contamination should:

1. Inform crop insurance provider of suspected issue prior to harvest or storage.
2. Insurance adjuster must collect samples prior to grain entering storage.
3. Only Approved Insurance Provider (AIP) Testing Facilities can complete analysis of corn samples.

Farmers with questions regarding handling protocol should contact their insurance provider.