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Early Season Frost Damage to Corn

By Clifford Mcdonald,2014-02-10 01:53
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Early Season Frost Damage to Corn

    Early Season Frost Damage to Corn

    by Paul Carter, Research Coordinator

    and Daniel Wiersma, Field Sales Agronomist

Summary Freeze and Frost Defined

    ; Late spring freezes occur periodically, often causing While often used synonymously, the terms freeze and

    significant leaf tissue damage to corn fields. This damage frost are not completely interchangeable. A freeze is

    may or may not lead to plant death. defined as the occurrence of air temperatures below o32F or lower measured at five feet above the ground. A ; Field topography has a significant impact on frost damage frost occurs when the temperature of the earth’s surface potential. Cold, dense air flows to depressions and valleys, oor objects on the earth’s surface are 32F or lower. cooling these areas more than surrounding high points. (Griffiths and Driscoll, 1982). Given these definitions,

    it is possible for a frost to occur when a freeze does not. ; Several cultural practices such as tillage, crop residue

    level, weed control and soil moisture influence the Kunkel and Hollinger (1995) explain this phenomenon potential for frost damage in a field. as follows:

    ; Plant maturity is the most important factor in determining “Under certain weather conditions, the official corn recovery after frost. Young plants with their growing minimum air temperature can be several degrees point protected below ground are more likely to recover. higher than the minimum temperature of the earth’s

    surface. Under moderate to high winds, the ; Corn replant decisions following a frost should be consid-atmosphere near the ground is well mixed and the air ered only after careful examination of frost-damaged temperature is nearly equal to the surface plants and assessment of plant stand. temperature. However, under light winds and clear ; Clipping frost-damaged corn plants to remove dead tissue skies, the air near the ground cools due to infrared and allow plant regrowth is a management option studied radiation and the temperature of tender vegetation by researchers. Most often, no yield benefit was realized. near the surface can be several degrees cooler than the

    official five-foot temperature.”

    (Image 1). The potential for late spring freeze or frost damage to corn

    exists on an annual basis throughout much of North America. ; Plants turn brown When plant cells have been This Crop Insights examines microclimate differences destroyed, the damaged leaf portions will dry up and affecting frost occurrence, describes symptoms of frost begin to turn brown within a day after a frost. Some damage to corn, and reviews research and experience with lower plant parts (pseudo stem) may remain intact and factors that may kill frost-damaged plants. Assessing stay green (Image 2). recovery potential and determining post-frost management

    options are also discussed.

    Symptoms of Frost Damage in Corn

    Various symptoms help growers identify when low tempera-

    tures have produced frost damage to corn. These symptoms

    include the following:

    ; Darkening of leaves Within the first 24 hours after the frost, corn plants will take on a darkened, almost black

    appearance due to the destruction of cell membranes and Image 1. Plants show dark-Image 2. Later, damaged

    the release of cell contents from damaged corn leaves ened leaves within 24 hours leaf areas will wilt and turn

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    Soil moisture can also influence soil radiation potential, of the frost. brown.

    with increased heat capacity in wet compared to dry soil.

    This explains the decreased corn frost injury in fields or Microclimatic Effects on Frost Damage portions of fields recently irrigated compared to those that

    were not irrigated before a frost (Elmore and Doupnik, 1995). While general climatic systems can bring freezing

    The unique combinations of residue quantity, soil moisture, temperatures to a region, there are other microclimatic

    and soil structure determine corn damage occurrence within factors that may contribute to differences in the potential for

    specific fields when frost occurs within a region (Tollenaar, frost damage in a field. These factors include the following:

    personal communication). ; Topography / Elevation - In hilly areas, cold, dense air

    Dense weed patches within fields can have the same will flow to depressions and valleys causing these areas

    influence as previous crop residue on soil radiation. These to be cooler than the surrounding high points (Image 3).

    weedy areas reduce soil radiation and increase the incidence ; Soil radiation Soils radiate heat upward and warm the of frost damage. Likewise, vegetation growing in field edges air immediately above the soil surface. Crop can function as a “blanket” to restrict the ability of warm soil management practices that encourage soil warming help to heat the air above it. to prevent frost damage from occurring.

    Plant Maturity, Health Affect Frost Recovery

    When low temperatures occur in a region and the potential

    for frost or freeze exists, there are several factors that dictate

    the extent and severity of frost damage to the corn crop. One

    of the most important factors is plant maturity. Young corn

    plants are less susceptible to frost injury that leads to plant

    death since the growing point is below ground and protected

    from freezing temperatures. Older plants have more exposed

    leaves and may have growing points above the soil surface

    beginning at the six-leaf collar stage (about 12 inches tall).

    When the large leaves of these corn plants are frozen, they

    can form a tightly twisted whorl that is difficult for the

    emerging leaves to penetrate. Another factor that determines post-frost plant recovery Image 3. Cold air flows into low areas of hilly fields, result-potential is plant health just prior to frost. If plants have ing in differential crop damage within the field. been under stress due to cold temperatures, herbicide injury,

    excessive moisture or disease, they are less able to recover Practices that inhibit soil radiation can increase the from even minor frost damage. Likewise, when growing

    conditions following a frost event are not ideal, corn plants probability of frost damage. Tillage systems that leave heavy

    may be slow to recover and more susceptible to death. previous crop residue coverage in a field tend to intercept

    radiant heat from the soil. This prevents the moderation of

    nighttime temperatures that often occurs near the soil surface Diagnosing Frost Injury and Recovery Potential in fields with little or no residue. Without soil heat radiating

    upward, the young corn leaves are more susceptible to frost When freezing temperatures injure corn plants in a field, damage. some plants may survive and recover, while other plants will

    die. Corn plants die immediately when growing point tissue On the other hand, tillage tends to loosen the soil, which is frozen. Corn plants not killed immediately may still decreases soil heat conductance. Tilled soil cannot supply as succumb to various physical or biological factors that prevent much radiation heat energy to corn leaves as untilled soil recovery, including: (Bland, 1993). Tillage also tends to dry the soil, which

    results in lower soil heat capacity. Dry soil near the surface ; Plant starvation Leaf loss due to frost injury reduces insulates soil below it, which prevents warming of the air photosynthetic area available to produce carbohydrates for above the soil surface by soil radiation. These factors explain new plant growth and recovery.

    why fields that have been cultivated or had anhydrous ; Plant disease Injured plants have reduced levels of ammonia applied immediately before the frost often resistance to secondary pathogens invading damaged experience more frost damage than adjoining fields. tissues.

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One of the first steps in diagnosing frost injury is to check often will survive and develop into plants with high yield

    the health of the internal growing point. Plants can be split potential.

    vertically and the growing point region inspected visually for damage (Nielsen, 1999). This is typically manifested as mushy, discolored tissue at the top of the mesocotyl. If the growing point tissue is obviously damaged, plants will not recover.

    However, even if the growing point appears healthy immediately after the frost, plants still may die. Cool weather after the frost can delay visible deterioration of damaged tissue on plants. Those plants not directly killed by the frost can succumb to the other factors described above. Therefore, it is usually best to wait until three to five days after the frost or freeze damage occurred to make an assessment of recovery potential (Nielsen and Christmas, 2001). Crop damage can appear very severe immediately after the injury, but plants often recover if the growing point is not damaged. Nevertheless, each situation is different and decisions regarding whether to keep existing stands or replant often need to be made over a longer period of time on a field-by-field basis. The next sections describe observations from the extensive experience of Pioneer agronomists in assessing frost damaged corn.

    Assessing Recovery Potential Growing Point

    Below Ground

    Recovery from early season death of above ground tissue depends on:

    ; Stage of growth Potential for recovery is higher at VE-

    V2 than for V3-V4 stages because energy reserves still exist in the seed to support growth.

    ; Amount of green tissue remaining - The more green tissue for the plant to live on until there is enough re-growth for photosynthesis, the higher the potential for recovery, especially at V3-V4 stages when seed reserves are nearly depleted.

    ; Weather conditions during re-growth Dry, warm

    conditions are more favorable than cold and wet weather. ; Number of frost events Plants at this stage will often

    recover from one episode, but reserves can be depleted with multiple frosts while damaged seedlings are recovering. The probability that plants will not re-cover or that the stand will contain non-competitive “runts” is

    increased with repeated frost damage/recovery cycles. Experience has shown that seedlings with tissue damage within 0.5 inches or less of the growing point will most likely not recover. Even if plants survive, potential to produce competitive plants with acceptable yield potential is compromised. Seedlings less severely damaged, with more than 0.5 inches of healthy tissue above the growing point

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Image 4 (taken 24-48 hours after damage occurred) shows

    progression from most to least damage for corn seedlings

    affected by frost within a field when plants were at V1-V2

    stages.

    Image 5. Corn seedling damaged by frost at the V2 stage, two

    warm days after damage occurred.

Image 4. Corn seedlings with a range in damage from frost

    injury when plants were at V1-V2 stages.

The two seedlings on the left represent those that will likely

    not recover, even though the growing point was not damaged

    by the frost. Recovery and yield potential of the seedling in

    the middle is uncertain. For the seedling second from the

    right, recovery is likely but three to four days of warm

    temperatures are needed to verify this. The seedling on the

    far right has a very high probability of survival with little

    impact on yield potential. As mentioned previously, in most

    instances it is best to wait several days before making the

    final decision regardless of how hopeless or promising Image 6. Corn seedling from Image 5 dissected to show seedling damage appears soon after the injury. growing point. oAfter a few days with high temperatures near or above 70F, look for green tissue close to the soil surface. If evidence of

    progressive increases in green tissue are not observed in this Eight days after the frost, plants with this level of damage portion of the plants, the seedlings are unlikely to recover show significant growth but the two largest leaves are tied at and produce healthy plants. Fields with visible re-growth the tip (Image 7). A small leaf (not visible in the image) is should still be monitored for several more days for continued emerging from the whorl, free from the “knot”. This plant is

    progress. New green plant growth is an important first step, on the way to healthy recovery and should be counted in a but watch for developing leaves and nodal root growth. post-frost stand assessment. After seven or more days of

    post-frost warm weather have transpired, any plants that are Images 5 to 8 show plants damaged by a frost at the V2 stage, both smaller than this and still tightly knotted should not be which killed all above-ground leaf tissue to within 0.25 counted in a stand assessment. If conditions are cool after the inches of the soil surface. frost, more than seven consecutive days may be required to Two days after the frost, green tissue has emerged, but dead develop this level of re-growth.

    tissue is restricting the new growth. The growing point is a The plant to the left of the stake in image 8 is the same plant healthy white/yellow color and the mesocotyl is white as in image 7, 20 days after the frost. By this time, the plant (Images 5 and 6). has six visible green leaves.

     Because of the microclimate factors mentioned above, fields

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next to each other and plants within fields will respond 9). Amount of green tissue remaining, growing conditions

    during re-growth, and whether frost damage involved

    single

    Image 7. Corn seedling in same field and with similar level of damage as in Images 5 and 6, eight warm days after damage occurred.

    Image 8. Corn seedling to left of stake is same plant as in Image 7, 20 warm days after damage occurred.

    differently to both the damaging temperatures and the recovery process. When damage has been severe/repeated or if recovery conditions have not been favorable, diligent scouting and close observation for two to three weeks after frost events are often needed before assuming that an accurate, final assessment has been made.

    Assessing Recovery Potential Growing Point

    Above Ground

    Many of the considerations are the same as for earlier stages. It is important to evaluate the health of the growing point and not to assume that plants will recover, even if the growing point was not damaged directly by the frost (Image

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    60

    or repeated episodes are important factors that will influence 50recovery potential.

    40

    30

    y = 0.7x - 3.2202 = 0.92Yield Loss (%)R10

    0

    020406080100

    Percent Frost Damaged Leaves Figure 1. Yield loss for corn when frost damage occurs at Image 9. Growing points of dissected corn plants after the 7 to 10 leaf collar stage of maturity (Carter, 1995). frost at V5-V6 stage. Left: Growing point is brown

    indicating plant death. Middle: Growing point is plants to recover. Another option if still early in the growing discolored indicating probable death. Right: Growing season is to replant the field to corn or another crop. A final point is healthy. management choice is to clip corn plants after frost to

    remove the dead and decaying tissue found above the

    growing point (Images 10 and 11). This is usually only an Similar to earlier stages, the most reliable way to determine option when the plants are at the V5 toV6 or later stages frost impact is to wait until after three to five days with daily when the damage occurs. It will be difficult to clip smaller ohigh temperatures above 70F and check for evidence of new plants with field-sized clipping equipment. growth. Remove dead whorls and look for erect, lime green

    Clipping frozen corn plants to remove dead tissue has been leaf growth inside the corn plant. Another sign of active

    studied by several researchers. While results are somewhat growth is a “rippled” leaf effect within the whorl when the

    variable, the general conclusion is that clipping does not plant is cut lengthwise. The “rippled” leaves indicate that

    enhance yield in most situations, and often further reduces new growth occurring after the frost is backing up behind the

    yield compared to not clipping damaged plants. damaged, knotted whorl.

    Assessing Yield Potential

    After determining the viable stand that remains, growers need to compare yield expectations of the damaged stand versus a late replanted stand, and consider replant costs and pest management issues.

    Yield expectations of frost-damaged stands can be assessed by measuring stand loss when corn plants are at the six-leaf Image 10. Frost-damaged corn plants two weeks after frost. collar stage or less. Damage effects on yield are relatively Plants not clipped (L) and clipped 3 days after the frost (R). minor at these stages for plants that are making progressive recovery. When frost damage occurs to plants beyond the six-leaf collar stage, conservative corn yield loss estimates can be made using hail damage defoliation charts. However, a summary of several Wisconsin studies for corn with 7 to 10 leaf collars indicates that yield losses due to frost damage at these advanced stages can be substantially greater than that suggested in hail damage charts (Figure 1).

    Post-Frost Management Options

     When growers experience frost damage in a corn field, they are faced with several management options. They may choose to do nothing, leaving the field as it is and allowing

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    Elmore, R.W. and B. Doupnik. 1995. Corn recovery from Image 11. Clipped treatment left of red flag, unclipped early-season frost. J. Prod. Agric. 8:199-203. treatment at flag. Clipped plants appear less restricted two

    weeks after the clipping treatment (L). However, very little Griffiths, J.F., and D.M. Driscoll. 1982. Survey of difference between treatments is apparent one week later (R). climatology. p. 310. Charles E. Merrill, Columbus, OH.

    Kunkel, K.E. and S.E. Hollinger. 1995. Late spring freezes A Wisconsin study (Carter, 1995) showed that post-frost in the central USA: Climatological aspects. J. Prod. Agric. clipping reduced grain yield by 15 to 34% at three sites and 8:190-198.

    increased yield by 10% at one site. At two additional sites, Nielsen, R.L. 1999. Assessing frost damage to young corn. clipping had no effect, positive or negative, compared to Purdue Pest Management and Crop Production Newsletter. doing nothing. Purdue Univ., 27 May 1999.

    Similar results in Nebraska suggest that post-frost clipping is Nielsen, B. and E. Christmas. 2001. Frost and low an unreliable method of promoting recovery from early temperature injury to corn and soybean. Purdue Pest season frost (Elmore and Doupnik, 1995). Management and Crop Production Newsletter. Purdue Univ., Taken together, these studies indicate that there appears to 20 April, 2001.

    be little consistent advantage to clipping damaged corn, even Tollenaar, Thys. 1998. Personal communication. Crop when growers are careful to clip well above corn growing Science Dept., Univ. of Guelph, Ontario. points.

    References Acknowledgements

    Bland, B. 1993. Lessons from the 1992 Father’s Day frost: The field experiences, insights, and photographs of the Climate and microclimate. p. 126-128. In Proc. 1993 following Pioneer Field Sales Agronomists, Technical Infor-Wisconsin Fertilizer, Aglime and Pest Mngmt. Conf., mation Managers, and Scientists were essential in preparing Middleton, WI, 19-21 Jan., Soil Sci. Dep., Univ. of this Crop Insights: Brent Wilson, Imad Saab, Scott Wisconsin-Madison. Jungman , Greg Jones, Brad Van Kooten, Jason Kolln, Mike

    Dillon, Scott Dickey, Jim Lafrenz, Bill Long, and Mike Carter, P.R. 1995. Late spring frost and post-frost clipping Hellmer. effect on corn growth and yield. J. Prod. Agric. 8:203-209.

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