Every year, some farmers write down the date when each of their cornfields reach the silking stage. "Knowing the date when your corn silks is a valuable piece of information," says Roger Elmore, Iowa State University Extension corn agronomist. "Silking dates mark a milestone in growth and development of corn."

This year in particular, estimates of the date when your cornfields silk are of interest since they provide an idea on the timing of fungicide application as well as give you a look forward for conditions that might occur during this critical time for corn development.

Crop simulation models are useful tools to project silking dates based on season-to-date weather conditions. Models also provide estimates of yield potential.

With this in mind, Elmore used Hybrid-Maize, a University of Nebraska computer program, to predict silk dates for different areas of Iowa. In each area, the approximate date when half of the corn was planted in 2008 (based on USDA reports) was included in the model.

Here are estimated silking dates for Iowa

Here's the information and assumptions Elmore plugged into the program. Planting dates for the western third of the state were set at May 10; May 15 was used for the remainder of the state. Different hybrid maturities represented the different locations as well. Hybrid maturities were 105, 110, and 115 days in the northern, central and southern thirds of the state, respectively. Given those inputs and weather data up through July 7, 2008, the model estimated the silk dates. Silk date ranges are shown here:

Estimated corn silk date ranges based on Hybrid-Maize simulations. The simulations used weather data from automated stations through July 7, 2008.

To compare these estimated silk dates with those of previous years, Elmore again used Hybrid-Maize estimates for Ames with May 15 as the planting date with a 110 day hybrid. These comparisons are shown in the table below.

Silk dates for the different yield possibilities range from one to 12 days behind those of previous years. The least difference occurs in the years with the best yields. The largest difference in silk dates occurs in the worst-yielding years. Days to maturity (R6) are also shown. Best yields are associated with the latest maturity date, points out Elmore.

Silking dates will be delayed in 2008

Delayed silking dates will be the norm across Iowa in 2008, he notes. If fungicide applications are necessary, Elmore says you should schedule the applications based on crop growth stage rather than on calendar date. Although silking will be delayed this year, weather forecasts for the next month are for normal precipitation and below normal to normal temperatures. These are both promising forecasts for corn development.

Estimated silk dates and estimated yield potential for an array of years from Hybrid-Maize for Ames, Iowa. Compare these with days to silk estimated for all other years in the weather data base. Weather data included: January 1986 to 7 July 2008.

The computer model Elmore used to predict the silking dates also estimates maximum potential yields. Included in the table is an estimate of yield as a percent of the best possible yield estimated from May 15 plantings from 1986-2007.

"In the best of years, yield is only 4% less than maximum potential yield," he points out. "However, in the worst yielding year, yields are only 45% of maximum. We might expect an average yield of 77% of normal."

Crop model simulations provide an idea of crop development rates and yield potential, he says. But, remember, as the Hybrid-Maize developers state, "As with all simulation models, Hybrid-Maize still represents a simplification of the 'real-world' system and, as such, model predictions may differ from actual outcomes. Therefore, the results of model simulations should be considered approximations and not taken as fact."

Summing up, Elmore concludes:

• 2008 estimated silk dates could range up to 12 days later than in previous years.
• A longer growing season and a delayed frost may help maximize yield this year.
• Excellent yields are still possible.