First Frost, Next Seedling Blight?

While corn planting progress is way ahead of the miserable 2019 planting season, Indiana’s corn crop has already experienced more than its fair share of misery. Most of April and the first half of May was cooler than normal across much of the state and, consequently, corn planted  early April through early May has germinated, emerged, and developed very slowly. Emergence in many of those fields was a 3+ week ordeal because sub-optimal soil temperatures. Corn planted the first week of April is today barely at the two-leaf collar stage (V2) of development!

The second blow came in the form of a combined frost and literal freeze event on 9 May across much of the state. Air temperatures that Saturday morning dropped to lethal mid to high 20s F as far south as Butlerville in Jennings County.  The bad news is that the combined frost / freeze event killed much, if not all, of the exposed above-ground plant tissue in many fields that had emerged before Saturday. The good news is that the potentially lethal temperatures did not penetrate the soil and so the all-important growing points of the young corn plants escaped mostly unscathed because they were still positioned below the soil surface.

The third blow, if you can call it that, came in the form of cooler than normal temperatures for the 3+ days following the frost / freeze event that slowed the visible recovery from the whorls of the damaged plants. Consequently, it was difficult to determine these past few days which plants or fields were truly “okay” and which were on “death’s bed” and might require replanting. A return to warmer weather beginning Wednesday will hasten that recovery and by this weekend, assessment of the recovery potential of damaged fields will be much easier.

The POTENTIAL fourth blow to this year’s corn crop MAY come in the form of the development of seedling diseases, partly because fungicidal seed treatments on corn that was planted 3 to 5 weeks ago have probably deteriorated by now and yet, because of the cooler than normal temperatures during those same 3 to 5 weeks, initial development of the plants and their permanent root system (the “nodal” roots) is not established well enough for the plants to have “weaned” themselves from reliance on the stored energy reserves in the kernels. Damage to kernels or the connecting mesocotyls in corn that is VE (emergence) to V3 (three leaf collars) is usually lethal to young corn plants.

Cool (or warm) and wet conditions will increase the risk of seedling disease and root rot in corn. A number of soilborne fungi can infect corn seed and seedlings, including Fusarium, Pythium, Diplodia, Penicillium, and Rhizoctonia. These may cause a damping-off or root rot. Fungicide seed treatments have been shown to help mitigate cold stress and protect against soilborne fungi. Initial symptoms of seed and seedling diseases include rotten seeds, dead or yellowed emerging seedlings, stunted or uneven growth, reduced vigor, and root rot. Root rot may also lead to poorly filled ears or wilting. Low-lying areas with poor drainage are most at risk. It is important to identify the underlying disease causes to make sure of appropriate selection of seed treatments in a field for following years. The diagnosis of seedling injuries can be difficult in the field as many abiotic (non-living) issues can mimic pathogen infection leading to similar symptoms. These include cold injury, flooding, crusting, herbicide injury and soil compaction. Plant samples can be sent to the Purdue Plant Pest Diagnostic lab (https://ag.purdue.edu/btny/ppdl/Pages/default.aspx) for determination if the underlying issue is a soilborne pathogen or abiotic issue.

Now is the time to scout fields to determine if you have any frost or seedling blight issues. If damage is severe and considerable stand loss has occurred in a field, replant considerations may need to be taken – but it is important to get out and dig up your plants to determine.

Related reading:

Anonymous. 2019. Root Rots of Corn. Crop Protection Network. https://cropprotectionnetwork.org/resources/articles/diseases/root-rots-of-corn [URL accessed May 2020].

Nielsen, R.L. (Bob). 2020. Assessing Frost / Cold Temperature Injury to Young Corn. Corny News Network, Purdue Agronomy Extension. http://www.kingcorn.org/news/timeless/FrostedCorn.html [URL accessed May 2020].

Nielsen, R.L. (Bob). 2020. Corn Replant Considerations. Corny News Network, Purdue Agronomy Extension. http://www.kingcorn.org/news/timeless/CornReplant.html [URL accessed May 2020].

Nielsen, R.L. (Bob). 2020. Root Development in Young Corn. Corny News Network, Purdue Agronomy Extension. http://www.kingcorn.org/news/timeless/Roots.html [URL accessed May 2020].

 

Seedling blight symptoms in corn. Note the shriveled, discolored mesocotyl and lower crown of the stunted (soon to be dead) V2 plant. (Photo Credit: Bob Nielsen)

Seedling blight symptoms in corn. Note the shriveled, discolored mesocotyl and lower crown of the stunted (soon to be dead) V2 plant. (Photo Credit: Bob Nielsen)

 

Figure 2. Cold injury on corn seedling. (Photo Credit: Darcy Telenko)

Figure 2. Cold injury on corn seedling. (Photo Credit: Darcy Telenko)

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