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When rain is in the forecast, it can be tempting to rush corn planting to avoid delaying into the season. However, it may be better to wait if the forecast includes cold temperatures and precipitation. This is due to the physiological processes occurring in the first 24 to 48 hours after seed placement.
Many corn growers believe that cold temperature damage is not an issue because the growing point of corn is at or below the soil surface until the V6 growth stage. This rule of thumb is usually the case regarding air temperature, but not always true with respect to soil temperature. In fact, wet soils with a temperature below 50°F may cause chilling injury during germination. Imbibitional chilling injury happens when a dry corn seed takes in cold water from rain or melting snow. Corn kernels imbibe 30% of their weight in moisture before germination can begin.1 Imbibition of moisture begins within the first 24 to 48 hours after planting.2 Cold water can cause cell membranes to become rigid and rupture, which may result in aborted radicles, proliferation of seminal roots, and delayed seedling growth. Such damage may limit or cease nutrient uptake, restricting normal development of the mesocotyl and coleoptiles, as well as allow for soil disease and pest entry.
Figure 1. Chilling injury to a corn kernel.
Chilling injury symptoms can be caused by other factors and may be compounded by additional stresses during germination, which include herbicide injury, disease, or soil crusting.
A few typical symptoms include:
The diagnosis can be confused when looking at a combination of symptoms from a combination of causes. It is a good idea to evaluate fields largely affected by imbibitional chilling symptoms. If the coleoptile and mesocotyl are missing or broken off, damage is fatal. Seedlings with coleoptiles and mesocotyls intact may have new leaf development and normal growth may resume when temperatures warm and fields dry.
The following describes the processes corn plants go through from emergence (VE stage) to stand establishment (V9 stage):
VE Stage. Emergence is achieved when the coleoptile reaches and breaks through the soil surface. Normally corn seedlings require about 100 to 120 GDUs to emerge, which under favorable conditions can be 4 to 5 days after planting.3 If cool or dry conditions exist, emergence may be delayed several weeks. At the VE stage, growth is also taking place below the soil surface as the nodal root system begins to grow. At about 6 weeks, the nodal root system will replace the work of the lateral seminal roots in supplying the plant with water and nutrients.
V1 Stage. The V1 stage is reached when the first leaf has fully emerged and the leaf collar is visible. The V1 stage typically occurs 3 to 4 days after emergence. The first leaf to emerge will have a rounded tip, while all later-emerging leaves will have more pointed tips.
V2 Stage. The V2 stage occurs when two leaves are fully emerged with collars visible. The V2 stage occurs typically 7 to 10 days after emergence or around 200 GDUs.4
V3 Stage. The V3 stage marks the end of the seed being the main food source and the beginning of the photosynthetic process. The V3 stage is reached at 10 to 20 days after emergence or at around 350 GDUs.4 At the V3 stage, the plant begins to rely more on the nodal root system as these roots form root hairs and continue to increase in size. Growth of the seminal root system has ceased.
Figure 2. Corn seedlings at V1 to V3 growth stages.
V4-V6 Stage. During these stages the uppermost ear and tassel is initiated and kernel row numbers are determined. The growing point of the corn plant is near the surface. The V6 stage occurs at about 475 GDUs.4
V7-V9 Stage. These stages begin the rapid growth phase. If the corn plant is stressed, lower leaves may die. At about 610 GDUs, 8 leaves will have formed.4
Sources: 1Nielsen, R.L. 2000. Corn growth & development: What goes on from planting to harvest? Purdue University AGRY-97-07. 2Nielsen, R.L. 2012. Seeding depth considerations for corn. Purdue University. http://www.agry.purdue.edu. 3Abendroth, L.J., Elmore, R.W., Boyer, M.J., and Marlay, S.R. 2011. Corn Growth and Development. PMR 1009. Iowa State University Extension. 4Neild, R.E. and J.E. Newman. 1990. Growing season characteristics and requirements in the Corn Belt. National Corn Handbook, Purdue University, Cooperative Extension Service, West Lafayette, IN. Extension educational partnership of 74 universities in the United States, Corn Germination and Emergence. October 2, 2008. Iowa State University. Did the recent cold weather affect corn germination and seedling growth? Integrated Crop Management. May 1, 2006. Nielsen, R.L. 2006. Crappy stands of corn. Department of Agronomy. Purdue University. Web sources verified 4/6/2018. 180410052209