Plenty of corn acres have been planted in eastern and north central Kansas over the past couple weeks. Since that time, there have been a few freeze events and periods of below-normal temperatures that cooled soils in some areas of eastern and north central Kansas near 50 degrees F or below in the top 4 inches. Some of the freezes in late April had the potential to cause leaf burn and other kinds of damage to recently planted corn. Leaf burn is largely cosmetic, but other effects of the cold temperatures can be more significant and longer lasting even though temperatures have now warmed to more normal levels.
Cold temperatures can result in injury to the germinating seed as it is absorbing moisture – a problem called imbibitional chilling injury. When soil temperatures remain at or below 50 degrees F after planting, the damage to germinating seed can be particularly severe.
Soil temperatures at the 4-inch depth during the first 24‐72 hours after seeding, when the kernels imbibe water and begin the germination process, are critical. Kernels naturally swell when hydrating. If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process, resulting in “leaky” cells. Injury symptoms may include swollen kernels that fail to germinate or aborted growth of the radicle and/or coleoptile after germination has begun.
For example, at the North Central and Irrigation Experiment Field near Scandia going into the last week of April, corn planting was in full swing until rainfall over the weekend of April 29-30. Soil temperatures in the seed zone (two inches) were well below 50° F, and at the four-inch depth, minimums reached well down into the mid-40’s and lower.
|
|
2” Soil temperature |
4” Soil temperature |
||
|
Scandia |
Max (degrees F) |
Min (degrees F) |
Max (degrees F) |
Min (degrees F) |
|
April 24 |
65.6 |
47.8 |
66.3 |
53.5 |
|
April 25 |
54.9 |
46.3 |
59.7 |
52.6 |
|
April 26 |
54.0 |
42.8 |
57.6 |
49.4 |
|
April 27 |
55.5 |
37.4 |
58.1 |
45.3 |
|
April 28 |
44.9 |
39.7 |
51.9 |
47.4 |
|
April 29 |
39.7 |
36.8 |
47.4 |
44.7 |
|
April 30 |
39.0 |
34.6 |
45.6 |
42.4 |
|
May 1 |
51.1 |
32.9 |
55.1 |
41.2 |
Chilling injury can also occur following germination as the seedlings enter the emergence process, reducing plant metabolism and vigor, potentially causing stunting or death of the seminal roots, deformed elongation (“corkscrewing”) of the mesocotyl, and either delayed or complete failure of emergence, often leafing out underground. Chilled seedlings may also be more sensitive to herbicides and seedling blights.
Figure 1. Seedling corn plant starting to corkscrew in the wrong direction under the soil surface. Photo by Doug Shoup, K-State Research and Extension.
Figure 2. Leaf burn and brown lesion on the upper section of the mesocotyl from freeze damage early after corn emergence. Photo by Ignacio Ciampitti, K-State Research and Extension.
Figure 3. Brown lesions on the first developed leaves from freeze damage early after corn emergence. Photo by Doug Shoup, K-State Research and Extension.
Freeze damage and chilling injury to corn can vary with:
- Soil type (as related to water holding capacity) and soil moisture. Less freeze injury is expected with wetter soils than dry soils. Dry soils are more sensitive to changes in temperature.
- Residue: The effect of residue is not entirely straightforward. The more surface residue, the more the emerging seed and seedlings will be insulated and protected from temperature fluctuations. However, soils with less residue will warm up faster, resulting in less freeze injury when compared with no-till conditions where more residue is on surface.
- Duration and intensity of cold weather: More than 2 to 4 hours of soil temperatures in the mid-to-low 40’s could result in some injury. Shorter periods of more intense cold or periods of more than 4 hours of soil temperatures in the mid-40’s could be equally damaging.
- Field natural gradient: Low areas are most sensitive to freeze injury.
- Growth stage: On newly planted corn, the emergence process could be affected. On newly emerged plants (before V4-V6), the first leaves could be burned but plants can recover as long as the growing point remains below the soil surface.
Early planted corn has the risk of facing cold injury, reducing yield potential. However, if the corn emerged uniformly and had good early-season growth then a longer growing season could be expected from these early planting dates – and possibly higher yield potential.
Assuming the plant makes it through the initial cold and or freezing temperature problems, it is still not necessarily out of the woods for cold-related problems. Over the years, we have observed another type of chilling injury that occurs in the crown. It is often referred to as cold weather crown stress or cold weather crown rot.
This condition often develops when young corn plants are exposed to an extended period of cold soils combined with soil moisture levels near saturation. It is not clear if there is an exact stage of growth when the corn is most susceptible to this problem. When this type of chilling injury occurs, plants are usually stunted and may display nutrient deficiency symptoms including nitrogen, phosphorus, or especially potassium. Root development is usually normal, but the crown will have a dark brown or black discoloration in the crown area, which can be seen by splitting the stem (Figure 4).
The plants often survive, but they will be slow to grow and will typically produce a smaller ear. More importantly, if heat and drought stress occur during the later reproductive stages of development, these plants will be more likely to develop stalk rot and lodge. Hybrids that have been developed from “southern” germplasm appear to be more susceptible than those developed from “northern” germplasm.
Figure 4. Cold weather crown injury. Plant in center is healthy. Photo by Doug Jardine, K-State Research and Extension.
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
ciampitti@ksu.edu
Stu Duncan, Northeast Area Crops and Soils Specialist
sduncan@ksu.edu
Doug Shoup, Southeast Area Crops and Soils Specialist
dshoup@ksu.edu
Doug Jardine, Extension Row Crops Plant Pathologist
jardine@ksu.edu
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