Showing posts with the label herbicides

Post-Emergence Herbicides in Corn

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It is time for farmers to control weeds in their corn fields. However, the cool, wet start to the growing season makes it doubly important to read and follow herbicide labels.

The post-emergence herbicide labels they’ll be following usually allow applications to be made at various growth stages says University of Illinois Extension Weed Scientist Aaron Hager. He says it is really important to read the label, making sure to get the height, or the stage, maybe both, of the crop correct.

This is because most all of the products for corn have a growth stage listed on the label beyond which applications, at least broadcast applications, should not be made. It is usually either plant height - measured at the highest arch of the uppermost leaf at least 50% out of the whorl - or a leaf number. Hager says if both are listed, then it is important to use the more restrictive of the two, For example, because of some of the weather conditions we’ve had across a large part of the state this year we may have corn plants which are older than their height would suggest. Using the leaf collar method is typically a better way to stage the development of the corn plant. If you can do both the height and the counting, the leaf collar method is the better method to determine the stage of the corn plant."

Using the leaf collar method is typically a better way to stage the development of the corn plant. - Aaron Hager, University of Illinois

Corn plants under stress conditions may be more prone to injury from post-emergence herbicides. On that note, Hager says farmers should be sure to consult the product label when selecting spray additives. Many labels suggest changing from one type of additive to another when the corn crop is stressed. Also, trying to save a trip across the field by applying a post-emergence corn herbicide with liquid nitrogen as the carrier is not advisable. The U of I weed scientist says while applying high rates of UAN by itself can cause corn injury, adding a post-emergence herbicide can make it worse.

4 Step Weed Control Plan for Corn or Soybeans

Since the 1960’s farmers have been using herbicides to control weeds. Frankly, herbicide formulations haven’t changed that much and the weeds have managed to find ways to adapt. Todd Gleason has this four step plan from the Univesity of Illinois to control them in corn or soybeans.

Some weeds have become resistant to the herbicides farmers use to control them. Others have lengthened their germination period, emerging later in the season, avoiding early spring control methods. University of Illinois Extension Weed Scientist Aaron Hager has a four step plan farmers can use to maintain a competitive edge in corn or soybeans. It starts by planting into a weed free seedbed.

Quote Summary - It is easy to achieve a weed free seedbed by either replant tillage, burndown herbicide or a combination of those two. Given the challenges of weather and of resistant populations it is advisable not to plant into existing weed populations or any green vegetation without adequate control ahead of time.

Step two in the plan is to select an appropriate residual herbicide. Be sure it provides very good control of the most problematic weed species in a given field. Pay attention to the label, says Hager, and always apply the recommended rate for the spectrum of weeds in the field.

> Quote Summary - The third step is to make timely post emergence applications. Base those on just not the number of calendar days after planting, but rather base those post decision on adequate scouting. So, return to the fields about two weeks after crop emergence. Scout the fields and determine the weed size, crop development stage and make the decision on a timely application of a post herbicide.

The final and fourth step is to go back to the field seven to ten days later and evaluate how well the post emergence herbicide application worked. It may be that another germination of a weed species warrants a second application. This won’t be know without a return trip.

If we fail to go back and look at how well the product performed, or the level of crop injury we see soon after that application, we could have some very significant challenges later in the growing season.

The days of set-it-and-forget weed control have ended. Todays farmers must scout fields for competitive weeds before during and after the growing season.