Cool temperatures send shivers up grower's backs

A recent cold snap with accompanying freezing rain and snow in some areas has Ohio and Indiana corn growers questioning the fate of their newly planted crop. But Ohio State and Purdue University agronomists say the crop is probably in better shape than it looks.

"In regards to the freezing event, I think that the chances for recovery for corn are pretty good," said Ohio State University Extension agronomist Peter Thomison. "The lethal effects of freezing temperatures are usually not a major issue for us. We've had similar conditions in past years and came out of those problems with little damage and pretty good yields."

Bob Nielsen, Purdue Extension corn specialist, said what crop damage there might be isn't likely to be fatal.

"My contention earlier this week that little crop injury resulted from the low temperatures on the morning of April 24 has been tempered by what appears to be minor injury to exposed corn leaves during the clear-sky early morning hours on April 25," Nielsen said.

"The leaf damage that occurred Monday (4/25) morning to emerged corn was not life threatening to the plants by itself, and I am confident that most affected fields could recover satisfactorily with good growing conditions. However, the continuing cool -- and often cloudy -- weather this week has slowed overall crop development, including leaf expansion from whorls, and has changed previously green plants to a putrid yellow-green color."

Agronomists generally downplay the impact of low-temperature injury in corn because the growing point is at or below the soil surface, thereby protecting it from air temperatures. Additionally, the plant's cell contents can act as an "antifreeze," protecting plant tissue from temperatures as low as 32 degrees Fahrenheit.

"Probably a greater concern to us is how long soils remain saturated," Thomison said. "If we get periods of cloudy conditions that prevent drying out and the soil remains saturated, then we are probably opening the doors to seedling blight problems."

Said Pat Lipps, an Ohio State plant pathologist with the Ohio Agricultural Research and Development Center, "Cold temperature injury can play a significant role in predisposing plants to root infection and blight. Under normal conditions plants can continue to grow and produce new roots, but when other injuries occur, new roots cannot develop rapidly and Pythium and other soil fungi can kill stressed plants."

Additionally, excessive rainy weather can cause problems to already damaged corn, Lipps said.

"Bacterial soft rots can destroy the corn growing point," he said. "If growing conditions are favorable, the plants typically outgrow bacterial damage. But if weather remains cold, wet and cloudy following the freezing event, the potential for bacterial damage increases."

Freeze-damaged corn plants may also suffer cosmetically from a twisted whorl condition. Thomison said that the freezing conditions prevent the leaf from unfurling normally, resulting in a tied leaf whorl.

"The damage resembles the tight leaf rolling often associated with herbicide injury," said Thomison. "But the plants tend to outgrow this condition when growing conditions improve."

Though it's too early to tell what damage, if any, has been caused from the cold temperatures, growers can evaluate the seedlings or the newly germinated plants to determine the extent of any damage. Thomison said that mushy seedlings or rotting growing points are a sign of potential seedling blight problems.

The solution to such a situation is replanting. Farmers should not be in a hurry to put new seed in the ground until they've adequately evaluated their crops, Nielsen said.

"Don't rush to replant these fields," Nielsen said. "The current cool weather will delay your ability to confidently assess recovery from leaf damage. Instead of waiting the usual 3-5 days to assess fields, it may take a week or longer. Furthermore, growers with corn acres yet to plant the first time around should concentrate on completing that task before replanting suspect fields."

"Growers have to plant when the growing conditions are favorable,” Thomison said. "Long-term historical data in Ohio shows that during the optimal planting time there is about one day out of three when field work can occur, and this varies depending on soil drainage. Because it's so wet during this time of year, growers took advantage of the favorable conditions to plant and now they may have to wait a couple of weeks to find out how the plants have responded to these most recent weather conditions."

For additional updates on crop conditions, log on to Ohio State University's Agronomic Crops Team Crop Observation and Recommendation Network (C.O.R.N.) newsletter at http://corn.osu.edu or Nielsen's "Chat 'n Chew Café" at http://www.agry.purdue.edu/ext/corn/cafe/ .

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