With cold temperatures lingering longer than many farmers prefer, you might wonder just how late a freeze could hit. Historically, the Corn Belt has seen some, but not many, freezes after June 1. Most late freezes occur in the May time frame. Take a look at the map below for your area. What to expect if late freezes hit corn and soybean seedlings. First and foremost, wait three to five days before checking corn and soybeans for freeze or frost injury. This gives the plants time to bounce back so you can determine the actual level of damage.
“At young developmental stages, a soybean plant is more susceptible than corn to aboveground damage by frost or lethal cold temperatures because its growing points are exposed above ground as soon as the crop emerges,” according to a report from Bob Nielsen and Ellsworth Christmas at Purdue University. “Frost or freeze damage extending below the cotyledons translates to complete death of the seedling.” When scouting soybeans look for water-soaked lesions on cotyledons, leaves or hypocotyl that will dry and turn brown in a few days, according to the University of Minnesota. Firm, white tissue, cotyledons and growing points indicate the plant is recovering properly. Note: if a significant portion of the population is dead, you might need to replant. The closer soybeans are to maturity, the less likely they are to suffer yield loss from frost or freeze, according to AgAnytime, by Monsanto. In very late frost situations narrow row spacing might trap heat and allow the plants to survive the cold better than wider rows. The growing point of corn is underground until leaf four or five—this gives the crop some protection from freezing temperatures and allows it to recover easily. However, if temperatures are below 28° F for more than just a few hours it can penetrate the soil and cause damage. If the corn plant is damaged, look for coleoptile and mesocotyl to be soft and brown—indicating dying or dead tissue, according to Corteva Pioneer. Even if leaves within the coleoptile survived, the likelihood of them emerging is low because the coleoptile won’t be able to protect them as they push to the surface. Corn plants might also leaf out underground, dig to see how often this occurred. If the growing point tissue is damaged plants won’t recover. If corn suffers some damage but lives through it, look for it to be more susceptible to herbicide, disease, bacterial and other damage. Damage is more likely in corn when the seedling isn’t emerged.