ISSUE 4 May 31, 2007
CORN GROWTH AND GROWTH STAGING
The warmer weather of early May favored rapid emergence in early-planted corn. However, with the cooler temperatures of the last couple of weeks corn growing degree day (GDD) accumulations for most of the state are now more in line with the long term average. Corn development is more closely related to the accumulation of GDDs than it is to calendar days. Corn GDDs are calculated using a base temperature of 50 degrees F and are, therefore, not the same as small grain growing degrees days which use a base of 32 degrees. GDDs for both corn and small grains for locations near your farm can be obtained using NDAWN (http://ndawn.ndsu.nodak.edu/corndd form.html). Corn requires about 120 GDDs to emerge and 85 GDDs to produce a new leaf through the 10 leaf stage (and only 50 GDDs after the 10 leaf stage). Corn planted on May 1st is now in the V-1 stage in NW ND (~200 GDDs) while corn in SE ND (320 GDDs) is approaching the V-3 stage.
Growth staging corn
Many management practices are growth stage dependent, therefore, being able to properly identify the growth stage of your corn crop will be important to ensuring that management practices are applied at the appropriate time. This is particularly true of the application of herbicides during early vegetative development.
The leaf collar method of growth staging is the method most often used in recommendations related to the timing of herbicides. When growth staging your crop you should begin by obtaining a representative sample of plants from the field or part of the field of interest. Ten plants should be selected at random. If emergence has been uniform, you can probably get by with fewer plants. Remove any soil attached to the plants so that you are able to observe the roots and crown. The number of leaves defines vegetative growth stages of corn (i.e. V1 equals the 1st leaf stage). Counting leaves in corn is straight forward as the process is not encumbered with tillers and leaves on tillers as is the case in small grains. However, care must be taken to ensure that the earliest leaves are included when counting leaf numbers. The first leaf is small and often dies and is torn from the plant during early plant development. The first leaf has a blunt tip. Look for sheath remnants at the crown of the plant if you suspect that the first leaf (or second for that matter) is missing. Count only those leaves that have a collar. Do not exclude leaves that have been damaged by hail or frost. The total number of leaves that a plant will develop is more or less fixed for a given hybrid; additional new leaves will not replace leaves that are stripped from the plant.
In order to determine the growth stage of older plants that have lost their lower leaves, uproot the plant and split the stem with a knife through the root ball. At the very base of the stem, identify the first visible internode. Internodes are the white area between the more yellow bands of the nodes. The first obviously visible internode should be about ½ to 3/4 inch in length. The node directly above this internode will be the fifth node, and the leaf arising from this node will be the 5th leaf. Find that leaf and continue counting leaves from that point.
A few corn management recommendations are based on the height of the plant, rather than growth stage. For example, certain herbicides can only be applied to corn less than 12 inches tall. The plant height in this case is measured from the base of the plant to where the upper most leaf reaches without stretching it out.
Extension Agronomist for Cereal Crops