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Corn+Soybean Digest

Frost Damage to Corn

Much of the Upper Midwest experienced frost damage to crops over Mother’s Day weekend, which is causing concern among farmers in many areas. The main concern is with the corn that was planted in mid-April, and was fully emerged with two to four leaves. The leaves on the emerged corn were severely damaged by temperatures that dropped to 30° F or lower in many areas of southern and central Minnesota on the morning of May 9. The most severely affected cornfields, or portions of fields, are likely to be on sandier or peat-type soils, and in fields that were also planted to corn in 2009. Areas near road ditches, grass waterways or other non-tillable acres, as well as very dry soils, are more likely have more severe frost damage. Most of the region had adequate rainfall in recent weeks to fully moisten the topsoil, which may help alleviate some of the widespread frost damage.

Fortunately, the growing point on corn is below the soil surface until the corn is 8-10 in. tall, and should still be protected from serious frost damage. The corn plant should start to exhibit new surface growth in about five to seven days under normal conditions. Producers are encouraged to wait at least a week, or longer, to allow the corn to recover before making any replant decisions, and to rely on the assistance of a crop consultant or agronomist before finalizing replant decisions.

According to most university and seed company agronomists, yield reductions from replanting in mid-May will likely be greater than potential yield reductions from minor frost damage. Ideally, some warm, sunny days are needed for quick recovery of the frost damaged corn plants. If replanting is necessary, producers also need to consult their crop insurance agent before replanting the corn, as most crop insurance policies contain replant provisions. Producers will also want to be cautious regarding post-emergence herbicide applications to corn following frost-damage, in order to prevent further damage to the recovering corn.

Most planted soybeans will not likely have major impact from frost damage, as they had not yet emerged, or were just emerged in the early cotyledon stage. Soybeans become much more susceptible to frost damage after they begin to leaf out. Small grains may show leaf damage, but are not likely to be seriously damaged from the frost. Early planted sweet corn is also likely to show significant signs of frost damage, and may be somewhat more susceptible to frost damage than field corn. Small producers of farmers’ market vegetables and flowers may also have been impacted by the frost damage.

Planting Progress
Soybean planting progress varies widely across the region, from county to county and even within the same neighborhoods. Some growers planted all of their soybeans during late April and the first few days of May, some planted 50-75% of their soybeans, and others have planted 0-50% due to wet field conditions or concern over the cool temperatures. Overall, probably about 65-70% of the soybeans in south-central Minnesota were planted as of May 10. Thus far, growing conditions in early May have not been conducive to soybean germination, early plant development and emergence. Ideally 24-hour average soil temperatures should be around 60° F or higher for good germination and early growth of soybeans.

At the University of Minnesota Research and Outreach Center at Waseca, average soil temperatures in the first 10 days of May have tended toward the 54-57° range, after being near or above 60° for the last 10 days of April. At Waseca, 2010 was the second warmest April on record, with the air temperature averaging 8.8° above normal, and trailed only April 1915 as far as average monthly temperature. The combined March-April 24-hour average air temperature in 2010 at Waseca was also the second warmest on record, trailing only 1946.

Editor’s note: Kent Thiesse is a former University of Minnesota Extension educator and now is Vice President of MinnStar Bank, Lake Crystal, MN. You can contact him at 507-726-2137 or via e-mail at [email protected]

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