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Insight 13

FUSARIUM CONSIDERATIONS

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Fusarium ear rot is the most widespread disease of all corn kernel cob rots.

The spores typically infect the immature kernels through the silk channel at the tip of the ear.

Injury can also occur as a secondary function due to insect or bird attack.

Insects not only cause an open entry point for infection but can often act as the vector in moving fusarium spores from plant to plant and across fields.

Fusarium overwinters in crop residue and can be spread by wind, insects and splashing rain. A wide range of environmental conditions will trigger the release of spores which then infect senescing silks and grow down into the immature kernels.

The silks appear to be the most susceptible for the first five days after they appear. The fungi will infect intact or damaged kernels.

Fusarium over winters in crop residue and can be spread by wind, insects and splashing rain.

Weather

Cooler weather at flowering together with rainfall or overhead irrigation will increase the potential for infection.

Insects

Typically insects either carry the spores to the plants infecting them as they move thru the crop. Any insect that makes contact with the immature kernels has the potential to infect the cob.

Thrip activity has been associated with increased levels of fusarium infection. It has been suggested that the thrips will move the spores throughout the kernel thus making the infection significantly greater than in a lower insect environment.

Harvest practices

The harvest of an infected crop will produce a spore loading of the paddock to potentially infect next seasons planting. The fungi will also overwinter in a large range of dead or dying plant tissue but the corn plant residue is the main economic host.

 Key Features of Biology

Fusarium moniliforme

Corn seeds and plants showing no symptoms are commonly infected with F. moniliforme. Usually, most plants in a given field have symptomless infections of F. moniliforme. F. moniliforme can sometimes also be detected in crop debris on the soil surface.

Kernels may become infected in two general ways. One route is

1 – through systemic infection in which F. moniliforme internally colonizes plants grown from infected seed. As plants grow internal colonization continues in the stalk, the ear shank, the cob, and the kernels themselves.

2 – Another way kernels become infected is from airborne spores. Airborne spores of F. moniliforme can land on silks, germinate, and colonize corn silks. The fungus then can grow down the silk channel and among the developing kernels. From there, F. moniliforme may enter kernels through the silk scars or through cracks and breaks in the seed coat.

Researchers do not know which pathway—systemic colonization or infection via the silk channel—is the more common route of kernel infection.

Under certain conditions that are stressful for the corn plant, the fungus becomes pathogenic and causes disease of infected tissues. Infected seeds usually germinate normally and produce healthy seedlings, although F. moniliforme can cause damping off of seedlings under certain conditions, especially in supersweet corn hybrids.

Stalk rot, ear rot, and/or kernel rot can occur in infected tissues, although infected tissues often have no symptoms. There are no diagnostic symptoms of fusarium stalk rot, and it is not easily distinguished from Gibberella stalk rot. The pith of the lower internodes becomes spongy as the plant matures, taking on a whitish pink to salmon discoloration. Distinctive fungal structures in tissues are rare, and laboratory analysis is required for definitive diagnosis.

Where fusarium kernel or ear rots occur, symptoms often appear on individual kernels or groups of kernels scattered over the ear. Kernels often exhibit salmon-pink to reddish discoloration on the kernel cap, and the damage is sometimes associated with insect injury.

White streaks radiating down from the tops of kernels (“starbursting” – see picture above) are another symptom associated with F. moniliforme; however, other fungi can cause these symptoms, as well. Once symptoms develop, the pathogen may continue to spread on the ear and form a heavy cottony mycelia growth that can consume the entire ear. (See picture below).

fusarium2

Rots caused by F. moniliforme—and possibly contamination by fumonisins—appear to be favoured by drought stress before and during silking. Warm, wet weather during grain fill may further favour activity of F. moniliforme and fumonisin contamination. While infected intact kernels may be symptomless, rotting and fumonisin contamination can occur when the same kernels are damaged during maturation by birds or lepidopterous insects (corn earworms). Damaged, fusarium-rotted kernels often contain higher fumonisin levels than intact grain. This explains why corn screenings often are associated with animal toxicoses attributed to fumonisins.

The minimum moisture for growth of F. moniliforme in corn kernels is 18.4%. Thus, timely harvest, prompt drying, and moisture management in storage are all important to reduce the risk of fumonisin contamination.


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Revised: March 2017
Expires: March 2018