The first frost of the season shouldn't affect the harvest, says an expert

Eastern Iowa will likely see its first frost of the season overnight, followed by the possibility of temperatures falling below freezing Tuesday night into Wednesday.

Brian Pierce, a meteorologist with the National Weather Service in Davenport, said the first frost in eastern Iowa typically occurs in the first 10 days of October, putting the Cedar Rapids area “about right on schedule.”

Cedar Rapids itself “is kind of on the verge of potentially seeing some frost,” he said.

The National Weather Service issued a freeze warning for eastern Iowa from 1 a.m. to 8 a.m. Tuesday, with temperatures ranging from 32 to 35 degrees. It has placed the area under a freeze Tuesday night into Wednesday morning, with lows in the upper 20s possible.

Because cool conditions could prevail over the next few mornings, Pierce said gardeners should take steps to protect sensitive plants, such as bringing them indoors.

Joshua Michel, an Iowa State University Extension and Outreach field agronomist for northeast Iowa, said there isn't too much concern that freezing conditions could affect the crop.

“As far as grain harvest for corn and soybeans is concerned, the harvest season is already so advanced that many fields in northeast (and) eastern Iowa have already been harvested or will be harvested soon,” Michel said.

Michel said the only threat of frost affecting crops would be for corn or soybeans that were planted late in the season and have not yet reached maturity.

“But there are very few,” said Michel. “If there are such fields, then a freeze event will essentially cause those facilities to shut down… wherever they are in growth and development. But fortunately that will be very, very limited.”

Michel said that as he surveyed northeast Iowa last week, he could count on one hand the number of times he saw corn and soybean crops “shut down” in fields.

How can frost affect other plant species?

Michel said he is more concerned about the frost affecting cover crops and forage in the northeast and eastern parts of the state.

Michel said cover crops like oats and beets could die from the frost. Cereal rye, on the other hand, has greater “cold hardiness” to withstand cooler temperatures.

In his opinion, another risk exists with fodder crops that are grown to feed livestock, especially sorghum varieties. Michel said when these plants are exposed to stress – such as that caused by colder temperatures – they can produce hydrogen cyanide, which can cause “acute toxicity” to livestock that eat them.

“Currently, production of these specific types of sorghum is fortunately quite limited throughout eastern Iowa, but there are some out there,” Michel said.

Michel said alfalfa and clover do not contain hydrogen cyanide and are not considered toxic, but when eaten by livestock after a frost there is a slightly higher risk of bloat.

“If a producer wants to allow their livestock to turn out to pasture, they should follow normal bloat prevention pasture management just to avoid potential problems,” Michel said.

Olivia Cohen covers energy and the environment for The Gazette and is a corps member with Report for America, a national service program that places journalists in local newsrooms to report on undercovered issues.

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