Seedling Diseases In Corn

May 25, 2016

By Nathan Kleczewski

Corn planting is underway. Persistent rain has increased the concern about potential seedling diseases and the need to replant. Corn seedlings in DE and most of MD can be affected by two main pathogen groups 1) Pythium spp; and 2) Fusarium spp. Pythium is an oomycete, whereas Fusarium is an ascomycete. Even though these organisms are very different, they can damage corn seedling in similar ways. All of these organisms produce recalcitrant (hearty, tough, long lasting) overwintering structures in soil and litter. When conditions in the soil are wet and the seedling is under stress these structures are able to easily colonize seedling tissues. If colonization is severe, the seedling may never reach the soil surface. This is called PRE-EMERGENT damping off. Other times the seedling emerges, but the pathogen then colonizes root tissues and causes a rapid root decay. This is called POST-EMERGENT damping off.

Both pre and post emergent damping off is facilitated by damp soil conditions. Typically seedling disease issues are not problematic in hot, dry planting seasons. Why does this tend to occur?

Many times saturation of the soil by water is the main cause of damping off and stand issues, with a lack of oxygen in the soil choking off the germinating seedling or newly germinated roots. The stressed, suffocating plant then is easily colonized by damping off organisms that may, under optimal conditions, be considered weakly pathogenic or even saprophytic (living off of decaying or dead plant tissues). The direct effects of stress and a lack of oxygen to germinating or newly-germinated seedlings is one reason that seed treatments may have limited utility for controlling seedling diseases in heavily saturated soils. A second reason for limited efficacy of seed treatments during periods of prolonged soil saturation is the zone of activity of the fungicide as well as the effective duration of control. Seed treatment fungicides may be contact fungicides, which typically only have activity on the seed coat and the immediate seed area. This means that they will not protect seedling roots once the plant has germinated and started to grow. Prolonged, wet periods serve to dilute these compounds in the soil, which may be locked up in organic matter in the soil, limiting their bioavailiblity. Other fungicide active ingredients may be taken up by the plant roots and move within the plant. This allows better overall activity of the fungicide; however, activity typically lasts 10-14 days, depending on the compound and environmental conditions. Other seed treatments, such as those containing biological controls (mostly bacteria) may interfere with pathogen activity by competing with the damping off pathogens for space on the roots, hiding signals that may stimulate germination of spores or preventing growth of the pathogen to the root. As with any biological product, activity is going to be highly variable, even within the field. Remember that these are living organisms and that, just like damping off pathogens, the environment needs to be just right for them to establish properly.

To minimize damping off issues consider the following practices:

Plant into well drained, warm soil
Avoid planting excessively early
Use high quality, fresh seed
Do not plant too deep
Consider a seed treatment, but realize it will only have a marginal effect in severely saturated soils

Source:udel.edu

Video: Why Your Food Future Could be Trapped in a Seed Morgue

In a world of PowerPoint overload, Rex Bernardo stands out. No bullet points. No charts. No jargon. Just stories and photographs. At this year’s National Association for Plant Breeding conference on the Big Island of Hawaii, he stood before a room of peers — all experts in the science of seeds — and did something radical: he showed them images. He told them stories. And he asked them to remember not what they saw, but how they felt.

Bernardo, recipient of the 2025 Lifetime Achievement Award, has spent his career searching for the genetic treasures tucked inside what plant breeders call exotic germplasm — ancient, often wild genetic lines that hold secrets to resilience, taste, and traits we've forgotten to value.

But Bernardo didn’t always think this way.

“I worked in private industry for nearly a decade,” he recalls. “I remember one breeder saying, ‘We’re making new hybrids, but they’re basically the same genetics.’ That stuck with me. Where is the new diversity going to come from?”

For Bernardo, part of the answer lies in the world’s gene banks — vast vaults of seed samples collected from every corner of the globe. Yet, he says, many of these vaults have quietly become “seed morgues.” “Something goes in, but it never comes out,” he explains. “We need to start treating these collections like living investments, not museums of dead potential.”

That potential — and the barriers to unlocking it — are deeply personal for Bernardo. He’s wrestled with international policies that prevent access to valuable lines (like North Korean corn) and with the slow, painstaking science of transferring useful traits from wild relatives into elite lines that farmers can actually grow. Sometimes it works. Sometimes it doesn’t. But he’s convinced that success starts not in the lab, but in the way we communicate.

“The fact sheet model isn’t cutting it anymore,” he says. “We hand out a paper about a new variety and think that’s enough. But stories? Plants you can see and touch? That’s what stays with people.”

Bernardo practices what he preaches. At the University of Minnesota, he helped launch a student-led breeding program that’s working to adapt leafy African vegetables for the Twin Cities’ African diaspora. The goal? Culturally relevant crops that mature in Minnesota’s shorter growing season — and can be regrown year after year.

“That’s real impact,” he says. “Helping people grow food that’s meaningful to them, not just what's commercially viable.”

He’s also brewed plant breeding into something more relatable — literally. Coffee and beer have become unexpected tools in his mission to make science accessible. His undergraduate course on coffee, for instance, connects the dots between genetics, geography, and culture. “Everyone drinks coffee,” he says. “It’s a conversation starter. It’s a gateway into plant science.”