Risk of Freeze Damage in Early-Planted, Emerged Corn
Figure 1. Buggy-whipping, shown hear in the two plants on the left, is when dead leaf tissue traps new leaf tissue, is one symptom of frost-damaged early season corn. (Archive photo by Roger Elmore)
Risk of Freeze Damage in Early-Planted, Emerged Corn
Warmer than normal mid-April temperatures have allowed corn planting to jump ahead of the five-year average (11%) with 17% of acres planted and 1% emerged as of April 23. Since then farmers in some areas have completed or nearly completed planting. Early-planted corn has emerged in some parts of the state.
Warm mid-April temperatures were followed by freezing temperatures over large parts of the state on Wednesday, April 26 and Thursday, April 27. For details on low temperatures by location see Assessing Freeze Injury to Wheat in this week's CropWatch. Freezing temperatures are being followed by cool wet conditions that are expected to continue throughout the weekend. Such conditions can be favorable for plant pathogens that can reduce corn survival.
Al Dutcher, Nebraska Extension agricultural climatologist, indicates that average last freeze date over the last seven years ranges from April 28 in the eastern half of Nebraska to May 17 in the western Panhandle. (See Dutcher’s article in CropWatch.) With a recent frost and freeze advisory and cool temperatures in the forecast, it’s important to take note of the impacts these conditions might have on a germinating and emerging corn crop.
Impact of Freeze on Corn Seeds and Seedlings
The extent of freeze or frost damage to corn depends on
the low temperature,
duration of exposure at that low temperature,
corn development stage,
water status of the plant, and
the environmental conditions that follow the event.
Yield Impacts
Figure 2. On June 8, 2007 a freeze in the Panhandle caused damage in corn ranging from only top growth being killed to plant tissue death down to the growing point. (Photos by Gary Hergert)
Early-season freeze damage results in a range of potential yield impacts. Severe damage is often limited to low-lying areas within a field because cool air is heavier than warm air. As a result, frost damage to plants can range from slight to severe in a single field. Early season survival of corn plants is attributed to growing-point protection below the soil surface; however, a hard frost can penetrate the ground and kill plants. Regrowth of corn following freeze damage is often impeded by dead leaf tissue that can entrap new leaves; this leads to abnormal growth commonly known as “buggy whipping” (Figure 1). Plants significantly impacted by frost may experience delayed silking by 7 to 10 days (Arny and Upper 1973, Carter 1995). If conditions following the frost continue wet and cool – as forecasted, plants may die from bacterial soft rot infections reducing plant stands.
Management Options
Farmers have few management options after a major freeze event. Depending on the level of damage, they may decide to leave the crop, replant, or clip the dead plant tissue to prevent plants from becoming wrapped or tied. Replanting corn affected by frost will depend on numerous factors such as potential planting date, frequency of plant death, replanting cost, and seed availability.
Clipping frost-damaged plants has led to highly variable results. In one study clipping heights greater than 1 inch was found to increase grain yields by 40% compared to non-clipped plants (Carter 1990). In contrast, Carter (1995) found that post-frost clipping of corn plants reduced yields by 15-34% at three sites with two of these sites showing no differences with unclipped plants and one showing a 10% increase in yield for clipped plants.
Research conducted in south central Nebraska by Roger Elmore and Ben Doupnik (1995) evaluated three frost-damaged fields at V3-V4 growth stage with varying levels of defoliation (100%, 70%, and 55%) for replant, clipping, and no treatment. Replanted corn yielded 22%-90% greater than corn with 100% defoliation, no differences were observed with 70% defoliation, and a yield loss was observed when comparing replanting and a field with 55% defoliation. Clipping plants did not increase yields at any site, but did reduce yield and plant stands at the 100% defoliated site and reduced plant stands at the 70% defoliated field.
The variability of corn response to clipping could be due to numerous factors. Temperature during clipping can have a significant impact on corn plants. Johnson (1978) found that clipping corn plants under high temperatures (86-90°F) reduced stands by more than 90%. None of the previous studies noted temperature at time of cutting, but it is possible that this could influence the yield potential of cut plants. Elmore and Doupnik (1995) indicated that cool conditions following frost could lead to continued plant mortality as a result of Pseudomonas flourescens. This bacterial soft rot disease does not typically cause a problem in corn fields; however, several days of cool and humid weather following the frost event in 1995 allowed the bacteria to cause continued stand loss. Other pathogens such as bacterial stalk rot diseases also could cause continued losses in early-season frost damaged corn fields. In 2014 after widespread hail, corn in the early growth stages became infected with a bacterial stalk rot disease suspected to be Pectobacterium carotovorum. Clipping could provide a means of widespread dissemination of bacterial pathogens in the field leading to increased yield losses.
Replanting
The success of replanting corn depends on both the calendar date and prevailing environmental conditions. Nafziger (1994) found yield losses of 18% with replanting dates between May 9 and May 29 in central Illinois. Planting in mid-June caused yields to decline rapidly with losses as high as 50% (Nafziger 1994). In Wisconsin Lauer et al. (1999) found similar grain yield reductions for replanting after May 9: 0.5%-1.1% per day (0-2 weeks later), 1.3%-1.9% (2-4 weeks later), and 2.0%-2.8% per day (4-6 weeks later). Data from southern Iowa – perhaps similar to southeast Nebraska conditions – indicates planting dates from April 17 to May 8 likely will result in 98% yield potential; data from northwest and central Iowa – perhaps similar to northeast Nebraska conditions – indicates planting dates from April 15 to May 9 will likely result in 98% yield potential (Abendroth and Elmore, 2010).
Yield losses with later planting dates indicate the importance of properly evaluating the yield potential of the existing crop before replanting. These evaluations should only be made after the crop has had adequate time for regrowth following the frost/freeze event. Replant decisions should also consider weed competition, herbicide options, seed availability, field conditions, and the cost of equipment.
(This article is adapted from the first author’s Doctor of Plant Health2016 document, “A Vision for Extension: Case Studies on Managing Extreme Weather Challenges in Corn” and a 2016 CW story.)
