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News Release

Northern Illinois Ag Report

February 13, 2012

FOR IMMEDIATE RELEASE from University of Illinois Extension Northern Illinois Agronomy Research Center

SHABBONA, Ill. - We are quickly approaching mid-February and the excitement is starting to build at the Northern Illinois Agronomy Research Center. Our last major educational event in Northern Illinois takes place on February 21st and 22nd at the Kishwaukee College in Malta. The Northern Illinois Crop Management Conference is a two day event that will cover topics ranging from cover crops, bioenergy crops, seed treatments and more.

As we near March we will be in a very similar mindset of other farmers in Northern Illinois. We will be designating different varieties to certain plots; we will be double checking intended planting populations and herbicide plans. We will also make sure that the required refuge acreage is in place. The planters will be pulled out of the sheds and scrutinized to insure that we will be ready to plant when field conditions permit us to do so.

Many producers have had the opportunity this winter to learn about real and impending weed resistance issues in Illinois. A weed that has emerged as potential issue in Illinois is Palmer amaranth. At the Corn Soy Classic Dr. Aaron Hager Extension Weeds specialist at the University of Illinois shared the following description of Palmer amaranth "Palmer amaranth is most common in the southern third of Illinois but, it may be expanding its range northward, The growth rate and competitive ability of this species exceed that of other Amaranthus species. Waterhemp can add close to one inch of new growth per day under good growing conditions, whereas Palmer amaranth can add multiple inches." While Palmer may not be an issue for northern Illinois producers yet, we still have Common waterhemp, Giant ragweed, Lambsquarters and Morning glory issues that are becoming more challenging to control in total post programs.

If you have decided to be proactive on the battle against weed resistance and have plans to include a preplant or preemergence herbicide in 2012 a reminder on how these products function may be in order. The following information was gleaned from a Bulletin article authored by Drs. Aaron Hager and Christy Sprague. For a soil-applied herbicide to be effective, the herbicide needs to be available for uptake by the weed seedling (usually before the seedling emerges, but some soil-applied herbicides can control small emerged weeds under certain conditions). Most soil-applied herbicides do not prevent weed seed germination; rather, they are first absorbed by the root or shoot of the seedling and then exert their phytotoxic effect. Generally, this happens before the seedling emerges from the soil. For a herbicide to be absorbed by weed seedlings, the herbicide must be in the soil solution or vapor phase (i.e., an available form).

How is this achieved? The most common methods for herbicides to become dissolved into the soil solution are by tillage or rainfall. Herbicide that remains on the soil surface following application will usually not provide much effective weed control and is subject to loss or degradation. Many weed species, in particular small-seeded species, germinate from fairly shallow soil depths. The top 1 to 2 inches of soil is the primary zone of weed-seed germination and should be the target area for herbicide placement. Shallow incorporation can be achieved by mechanical methods or by precipitation. Which of these two methods is more consistent? Rainfall provides for a fairly uniform incorporation, but mechanical incorporation reduces the absolute dependence on receiving timely precipitation. How much precipitation is needed and how soon after application the precipitation should be received for optimal herbicide performance depend on many factors, but generally 1/2 to 1 inch of precipitation within 7 to 10 days after application is sufficient.

In 2011 an independent study evaluated several herbicide chemistries for corn and soybean production. This study did not include all possible combinations and was a single year evaluation. The combinations were evaluated on their control of Giant ragweed, Velvetleaf, Pigweeds, Morning glory and grasses. If crop injury was evident as a result of the herbicide application it was noted as well.

Our take home message from this study was that effective control of the designated weed spectrum was achieved with a variety of chemistries but were most efficiently achieved with a two pass program of a pre emerge followed by a post application. Our two pass program also effectively utilized different modes of action to combat resistance issues in northern Illinois.

The complete 2011 University of Illinois Weed Science report is available on line at http://weeds.cropsci.illinois.edu/field%20reports/default.htm

Follow us through the growing season at the NIARC with future reports!

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Source: Russel Higgins, Extension Educator, Commercial Agriculture, rahiggin@illinois.edu