Corn growth and development occurs during a growing season with predictable stages. Understanding how the corn plant develops is key to interpreting the effects of the growing season on yield. The plant is the ultimate integrator of the environment in which it grows. The environment has much more impact than we have with management, but we need to provide basic inputs at the right time in order to increase our chances for successful yields.

Identifying corn growth stages is necessary for post-emergence application of pesticides or growth regulators, to monitor the progress of seasonal development, and to determine the effect on yield of a hail storm, insect feeding, disease, drought or early frost. Table 1 describes a summary for a corn development model in use in Wisconsin during the early 1990s. We will test this model in the planting date summary provided in a separate article every week through V12.

Numerous factors affect corn growth and development. Below are a few environmental and management practices that have been shown to influence development, especially emergence.

Conservation tillage: more than 75% residue, add 30-60 GDU (Swan et al., 1977; Imholte & Carter, 1987)
Soil texture: fine = add 30-60 GDU; coarse = subtract 30-60 GDU
Planting date: < April 25 = add 10-25 GDU; > May 15 subtract 50-70 GDU
Seed-zone soil moisture: below optimum, add 30 GDU (Schneider and Gupta, 1985)
Seed-bed condition: soil crusting or massive clods add 30 GDU (Schneider and Gupta, 1985)
Seeding depth: add 15 GDU for each inch below 2 inches (Hunter and Kannenberg, 1972)
Severe drought or heat stress
Hybrid differences for development

Table 1. Corn development stage, required GDUs, and average date of stage when planted on May 1 in south and south central Wisconsin.
Development stage, Required GDUs, and average date	Yield implications	Management options	Plant responses
VE 125 GDUs May 12	Potential number of ears per acre is determined at seeding. Plant attrition will occur as season progresses.	Numerous pests attack the corn seedling until it becomes established. Use seed treatments. If slow nutrient uptake is possible, band small amounts of fertilizer to the side for uptake by the seminal root system. Watch for crusting and weeds. Rotary hoe if necessary.	Cool temperatures at planting slow nutrient uptake and cause slow growth. The depth where the growing point is at emergence (1 to 1.5 inches), determines where nodal root growth begins. This is constant over different planting depths due to mesocotyl elongation. At later planting dates, soil temperature is adequate throughout planting depths. Usually have better soil moisture contact with deeper planting.
V3 300 GDUs May 26	Watch for early nutrient deficiencies at this time and correct if possible.	Good weed control reduces competition by weeds for light, water and nutrients. The use of chemicals, mechanical cultivation, and management practices such as higher plant densities or crop rotations, or combinations of these are effective weed control practices. Careful cultivation after V2 can occur.	The below ground growing point during the very early leaf stages is especially affected by soil temperatures. Cold soil temperatures may increase the time between leaf stages, increase the total number of leaves formed, delay tassel formation, and reduce nutrient availability. Often temporary nutrient deficiencies are observed. Root system is transitioning from seminal root to nodal root system
V6 475 GDUs June 7	All parts of plant "factory" are present.	Late frost can cause serious damage at this point because the growing point of the plant has moved above ground.	Early stages of tassel parts on apical meristem.
V9 645 GDUs June 17	Potential number of kernel rows around ear is determined.	Nodal root system is well distributed in the soil. Side dressing of nitrogen fertilizer may be performed. Avoid excess root pruning. Watch for insect damage such as leaf feeding by corn borers.	Tillers often appear on the plant at this time. If they appear, it is an indication that the plant density used for this field in this year was too low and should probably be increased slightly next year.
V12 815 GDUs June 26	Kernel numbers per row and ear size are determined.	Moisture or nutrient deficiencies at this time reduces the potential number of seeds and size of ears harvested.	Earlier maturing hybrids progress through these stages in a shorter time, and usually have smaller ears than later maturing hybrids. Higher plant densities are needed for early maturing hybrids to produce comparable seed yields.