Corn Agronomics

Growing Degree Days (GDD) are calculated for each 24 hour day and accumulated from the time the hybrid is planted until it reaches physiological maturity (about 35%) in the fall. The formula used to calculate GDDs is:

T. Max + T. Min. / 2 - 50 = GDD T.

Max. is the maximum temperature during the day and T. Min. is the minimum. Fifty degrees F is substituted for the minimum temperature when it falls below 50° F and 86° F is substituted for the maximum if the temperature goes above 86° F.

Maturity days assigned to hybrids registered and sold in the state of Minnesota.

The percentages given in this guide are recommended population levels relative to the current field/farm planting populations. To calculate planting rates, multiply the population percentage by your current field or farm average population.

The height a corn plant achieves is dependent on several factors, including: planting date, row width, maturity of hybrid for the area, growing conditions, and genetics. S = Short, M = Medium, and T = Tall.

The placement of the ear on the stalk of a corn plant is dependent on several factors including planting date, row width, growing conditions, and above all, genetics. L = low on the stalk, M = medium height on the stalk, H = high on the stalk.

F = Fixed, SF = Semi-Fixed, FL = Flex, SFL = Semi-Flex

R = Red, P = Pink, W = White

Y = Yes, N = No, WF = Acceptable with fungicide application

M = Moderate, H = High

Peak nitrogen uptake times differ from hybrid to hybrid. Hybrids that flower relatively early for their maturity require peak N earlier, hybrids that flower average for their maturity need N consistently throughout the growing season, and those that flower late for their maturity require peak N later in the growing season.

The following items are rated on a scale from Excellent to Not Recommended based on the following scale: E - Excellent VG - Very Good G - Good AV - Average NR - Not Recommended:

After the corn plant reaches physiological maturity, hybrids tend to give up moisture at varying rates compared to other hybrids in the same maturity.

This score reflects the ability of a hybrid’s root system to keep the plant erect, especially under wet conditions.

This score reflects a hybrid’s ability to stay upright at harvest time. Standability scores are assigned on the following basis: E = all stalks stand at harvest; G = 3 - 5% of stalks down; NR = 10% or more of stalks down.

Stress scores are are based upon a hybrid’s ability to perform adequately under adverse environmental conditions such as drought.

This test is done in seed laboratories to examine the vigor of different hybrids under cold field conditions. The higher the score, the better the ability of the hybrid to bring its coleoptile and first leaf above the soil surface under lower than ideal soil temperatures.

Corn test weight is affected by several factors, including genetic traits and weather conditions, particularly after flowering. The score given to each hybrid rates its ability to maintain adequate-to-above average test weights relative to varieties within its maturity.

The irrigation score is designed to reflect a hybrid’s response to irrigation systems.

Gray leaf spot is a foliar disease occurring in warm-to-hot humid areas, especially where minimum tillage is present. Lesions are long and narrow, parallel-sided, and tan-to-gray in color. The fungus overwinters in corn debris, on or near the soil surface.

Eye Spot is a foliar disease occurring in the northern United States during cool, wet weather. Numerous round-to-oval spots up to 1/2 inch in diameter are characteristic of this disease. Infected areas have tan-to-cream centers, and are surrounded by a yellowish halo. The upper leaves of the plant may wither and die prematurely, late in the season. The fungus overwinters in corn debris, on or near the soil surface.

This disease is prevalent in the northern half of the U.S. following warm, moist weather and heavy dews. Diseased areas have long, elliptical, tan lesions, and may be up to six inches long. Lower leaves show symptoms first. In severe cases, the plant may turn grayish green and die prematurely. This fungus also overwinters in corn debris.

This disease is most prevalent in the southern half of the U.S. following warm, moist weather. Leaf lesions are tan, with buff-to-brown borders, elongated between the veins, and up to one inch in length. Two races of the fungus exist - Race O and Race T.

A fungus with enlarging, oval-to-spindle shaped lesions that appear on leaves. Lesions are yellow-to-brown, with distinct borders. Leaf lesions occur mostly on the young plants, and frequently appear on the upper leaves after silking. Black streaks appear on the lower stalk late in the season, with the pith turning a dark brown color, and appearing shredded. The tops of infected plants may turn yellow or red prematurely. Also, upper or lower stalk may break over. The fungus survives in corn debris and on the seed.

A disease caused by the bacterium Pantoea stewartii. The bacteria is spread by the corn flea beetle, which is more severe following mild winters. Two stages include early seedling blight when, in severe cases, plant death may occur. Later in the season, bacteria reproduce in the leaf causing a scorched or strawlike color to develop. Yield is rarely affected but standability may be. Hybrids have differing levels of tolerance to this disease.