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Weed Pressure Varies

Jul 05, 2013

Farmers have finished up on planting soybeans (the first time), replanting corn, replanting soybeans and herbicide applications. The attention is now turned to herbicide application in soybeans.

Weed pressure varies in the area soybean fields. Some of the target weeds are the lambsquarter and marestail that survived the spring tillage operations. Clarke McGrath has a good discussion on the management of those weeds in a June 26 CropWatch blog article.

Corn development is also a concern. The following are some of my observations of area corn development stage corn by planting date. The days and Growing Degree Days (GDDs) needed to reach the tassel stage is listed.

Plant date

stage 7/2

days to tassel

GDDs to tassel

April 30, May 15




May 24




June 20




Obviously the days and GDDs to tassel are estimates. The corn planted (actually replanted) on June 20 will tassel earlier than indicated above. But it does show that this replanted corn will need to have a decent amount of GDDs for it to mature before early October.

Expected GDDs for Spencer is about 660 for July and 600 for August. This makes the pollination date for the normal planted (April 30, May 15, May 24) corn late July and early August. That is behind normal and certainly well behind what we have been used to the past couple of years.

The average pollination date for northern Iowa is around July 25. The research and observations sometimes conflict regarding the effect of pollination date on corn grain yield.

There is some thought that pollination before July 25 leads to higher yield potential because the grain fill occurs during the cooler part of the summer. However, there is also research that would contradict that somewhat. Obviously August rainfall and temperatures will have a large impact on the final yield this year. However, any extremes in temperature or lack of rainfall in August could have a large impact on northern Iowa corn production this year.

Source : iowafarmertoday