Corn Growth and Development Chad Lee Grain Crops Extension Specialist 859-257-3203 ● cdlee2@uky.edu www.uky.edu/Ag/GrainCrops/ This is an introduction into corn growth and development.

Corn Growth Stages Vegetative (V) Reproductive (R) How a Corn Plant Develops, Special Report No. 48 Iowa State University http://maize.agron.iastate.edu/corngrows.html Corn growth and development is divided into two major sections: vegetative and reproductive. There are several methods for determining vegetative stages, but we are going to focus on the leaf collar method or fully-extend leaf method. This method uses a defined, visible part of the plant to identify stages. The leaf collar is defined as the part of the leaf that connects the leaf to the sheath of the plant. The leaf collar resembles a an shirt collar with one button open around someone’s neck.

Corn Emergence (VE) Emergence occurs when the plant shoot pokes through the soil surface. The radicle emerges from the seed and starts the seminal root system. The seminal root system will be the major root system of the corn plant until the plant reaches about V3. The coleoptyle emerges upward from the seed and contains five leaves of the plant. The mesocotyl extends from the coleoptyle until the shoot reaches the soil surface. Once the shoot reaches the soil surface the mesocotyl stops growing and the leaves begin to emerge. Cool temperatures and/or severe compaction can prevent the mesocotyl from growing straight up toward the soil surface.

Corn Growth Stages: Vegetative 3 Collars V6 6 collars V12 12 collars V15 15 collars VT tassel The vegetative stages begin at emergence (VE) and end at tassling (VT). We are going to focus on a few of the vegetative stages. The numbers following the V stage represent the number of collars that are visible.

V3 V6 V12 Corn Growth Stages 3 Collars 6 collars 12 collars Nodal roots active. Growing point below ground V6 6 collars Growing point above ground. Tassel and ear development starting. V12 12 collars Ear size, kernel size and kernel number being determined. Limits on water and/or nutrients will reduce yields. V3 occurs when 3 leaf collars are visible on the stalk of the plant. V3 means that 3 nodes have fully developed in the plant. At this stage, roots have formed from the first node and these roots will become more important than the seminal root system at collecting water and nutrients and providing structural support to the plant. Nodal roots will eventually form at about the first six or seven nodes. The growing point is still below ground at the V3 stage, making the plant fairly tolerant of freezes. If all of the above-ground growth is removed and no damage is done to the growing point below ground, the plant will regrow a shoot and have minimal yield losses . . .as long as growing conditions are favorable. By V6, or six collars, the growing point is above ground and removal of all the above-ground growth will likely kill the entire plant. Tassel and ear development have started. Many post-emergence herbicides have restrictions against corn that is at the V6 growth stage. Applications of some herbicides directly on the corn plant at or after this stage of growth will damage the developing ears. At or shortly after V6, the corn stalk will expand and start to tear off older leaves and collars. The stalk of the corn plant may need to be split in two to identify the number of fully developed nodes. V12 has 12 fully developed nodes or collars. Ear size, kernel size and kernel number are being determined. Any limits on water or nutrients at this stage will reduce yields. The level of yield reduction depends on the intensity and duration of the stress. For example, a mild limit to water will hurt yields very little, but a severe drought will hurt yields by 10 to 15%, if growing conditions following this stage are favorable.

V15 VT Corn Growth Stages 15 collars tassel Rapid growth, about 10 to 12 days before silking. Most sensitive to stress. VT tassel Last tassel branch is visible but prior to silking. Complete leaf loss will cause nearly 100% yield loss. When the plant reaches V15

Corn Growth Stages Comparing visible collars to actual nodes. Tassel and ear development start early.

Corn Growth Stages: Reproductive Silking R2 Blister R4 Dough R5 Dent R6 Physiological Maturity

R1 R2 Silking Blister Corn Growth Stages N and P uptake are rapid. About 50% of total N is taken up after R1. K uptake is nearly complete. Water needed for pollination. Pollination occurs. R2 Blister Ear size nearly complete. Silks begin to dry out. A miniature corn plant is being formed in each fertilized kernel.

R4 R5 Dough Dent Corn Growth Stages Kernels have accumulated ½ of total dry weight. Five leaves have formed in the kernel. R5 Dent Most kernels have dented and are near 55% moisture at start. Starch layer has formed and progresses down the kernel.

R6 Corn Growth Stages Blacklayer has formed at bottom of kernel. Physiological Maturity Blacklayer has formed at bottom of kernel. Kernel is about 30 to 35% moisture.

Corn Growing Degree Days Each day has a slightly different average temperature. Temperature affects corn growth rate. Attempt to relate temperature to corn growth rate. Corn Growing Degree Day Base 50° F Max 86° F Min 50° F

Corn Growing Degree Days Base 50° F Max 86° F Min 50° F Example 1: 74° F average daily temperature 74 – 50 = 24 GDD Example 2: 90° F average daily temperature 86 – 50 = 36 GDD

Corn Growing Degree Days Corn Maturity (Days) GDD 85 to 100 2100 – 2400 101 to 130 2400 – 2800 131 to 145 2900 – 3200 GDD Requirements of a 2700 GDD Hybrid Growth Stage GDD V2 200 V6 475 V12 870 VT 1135 R1 1400 R6 2700 From NCH-40 Growing Season Characteristics and Requirements in the Corn Belt. National Corn Handbook.

Planting Date and GDD April 20 1155 --- May 3 1029 126 May 18 825 330 Hybrid: DKC67-91: 119 CRM 3000 GDD to Black Layer Planting Date GDD As of 06/26/05 Difference From First Planting April 20 1155 --- May 3 1029 126 May 18 825 330 May 31 596 559 June 15 281 874 From University of Kentucky Ag Weather Center: http://wwwagwx.ca.uky.edu/ Growing Degree Day calculator: http://wwwagwx.ca.uky.edu/cgi-bin/cropdd_www.pl

Planting Date and GDD April 20 1503 --- May 3 1377 126 May 18 1173 330 Hybrid: DKC67-91: 119 CRM 3000 GDD to Black Layer Planting Date GDD As of 07/11/05 Difference from First Planting April 20 1503 --- May 3 1377 126 May 18 1173 330 May 31 944 559 June 15 629 874 From University of Kentucky Ag Weather Center: http://wwwagwx.ca.uky.edu/ Growing Degree Day calculator: http://wwwagwx.ca.uky.edu/cgi-bin/cropdd_www.pl

Corn Ears: Good and Bad 1

Corn Ears: Good and Bad 1 2

Corn Ears: Good and Bad 1 3