Temperatures must remain at-or-below freezing for at least a couple of hours to cause damage.
Frost damage indicators typically include a dark and/or water-soaked appearance, followed by a browning, necrotic appearance a few days later. - Corn and soybean plant survival can be gauged by new leaf growth or the presence of injury to the growing points.
- Allow plants time to recover from frost before making a final management decision.A late spring frost is a yearly concern for corn and soybean farmers in most growing areas. Crops planted earlier have a greater risk of frost injury due to earlier plant emergence. It is important to be able to diagnose early season frost symptoms, assess damage severity and determine if replanting would provide an economic return.
Assessing Symptoms
Freezing temperatures do not automatically cause crop injury. Temperatures of 28-30° F or lower are typically needed for damage to occur; however, there are multiple examples where 28° F may not cause significant damage or stand loss. Temperatures must remain at-or-below freezing for more than a couple of hours to impact the crop significantly. Microclimatic conditions, such as air movement (wind), cloud cover and topography, can also increase or decrease risk of frost injury.
Plants damaged by frost will appear darker in color within hours after freezing. With less severe damage, leaves may only appear water soaked. Severely damaged plants will start to turn brown and necrotic in appearance over the following days.
Determining Survival
Determining survival of frost-damaged corn is highly dependent on the growth stage at the time freezing occurred. During normal plant development, the growing point of corn will remain protected below the soil surface from fluctuating air temperature until reaching the V5-V6 growth stages, reducing risk of injury. Upper leaf area may still be damaged from freezing temperatures, but if the growing point is protected, plants will usually recover quickly with warmer growing conditions. Plant recovery potential can be gauged by digging up plants and cutting open stems to evaluate the growing point health. A dark yellow to brown growing point could indicate a damaged plant that is less likely to survive.
Soybeans can generally tolerate slightly cooler temperatures than corn. However, due to the positioning of soybean growing points on the uppermost part of the plant, they are susceptible to frost damage at any time after emerging. Each new node becomes the dominate growing point for soybeans. Taller soybeans experiencing frost damage still have a chance of surviving if lower nodes are insulated enough by upper canopy leaves to protect against freezing. Warm soils can provide additional insulation to lower nodes, usually resulting in regrowth from the uppermost surviving node.
Tips for Evaluating Frost-Damaged Crops
- Wait 2 or more days after frost occurrence to evaluate regrowth and growing point health to determine the number of surviving plants remaining.
- Flag frost-damaged plants and reinspect after a few days of good weather to determine the number of viable plants.
- Compare yield potential of reduced stands to the reduced yield potential with later planting dates.
- Factor additional costs of replanting, such as seed, fuel and labor expenses, as part of the decision.
- Refer to the Golden Harvest Replant Calculator as an online resource for corn decisions.
- Understand that final soybean stands near 100,000 plants per acre or greater likely will not need replanting.
Management: Clipping Plants to Speed Recovery
Many producers and researchers have experimented with cutting off frost-damaged tissue to allow regrowth to occur more easily and quickly. This method is usually only considered for corn at the V5 stage or later as a method to remove damaged tissue. Due to the growing point being above the soil line at this stage, caution should be taken to avoid further damage while clipping. University research has shown mixed results with this management practice and even observed grain yield loss because of clipping. Clipping plants should be reserved for severe cases where you are certain plants will not survive without action.
Reacting quickly after frost can often be the first response by farmers. Unfortunately, frost damage situations require patience and investigation to determine the impact. Getting a good idea of the number of surviving plants will be the most critical decision factor. Allow plants the chance to recover before making any final management decisions.
For more information on potential assessing spring frost risk, contact your local Golden Harvest Seed Advisor.
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