University of Minnesota Extension
Menu Menu

Extension > Minnesota Crop News

Monday, May 4, 2015

Will soil-applied herbicides work in a dry year?

Tom Peters, Extension Sugarbeet Agronomist

Two questions are on farmers minds. First, how long will soil-applied herbicides ‘last’ in the soil if it doesn't rain and second, should a farmer consider using a rototiller or drag harrow to incorporate herbicides?

Volatility (evaporation), adsorption, and soil moisture effect soil-applied herbicides. Volatility is the change in herbicide physical state, from a liquid to a gas. Most soil-applied herbicides used by farmers have a medium or low vapor pressure meaning they generally will not volatilize during warm and dry conditions. However, understand that herbicides sprayed on soils will move with blowing soil and these effects may impact efficacy. Adsorption is the attachment of herbicides to soils. Herbicides must be bound to soils or they would easily leach away. Most herbicides are moderately or strongly bound to soils colloids and should not be impacted by our dry conditions.

Soil moisture (and rainfall) affects soil-applied herbicides in two ways. First, rainfall moves the herbicide from the soil surface and into soil. Second, rainfall contributes to the amount of herbicide available for absorption by weeds. While ‘half an inch’ is a good rule of thumb to activate herbicides, soil moisture conditions at or after the time of soil-applied herbicide application will influence herbicide activation. Rainfall must first wet the soil surface before water and the herbicide can move into the soil profile under dry conditions. Additionally, herbicides bind more tightly to soils and are less active for weed control in dry conditions. Thus, under our dry conditions, it might take more than 0.5 inch of .rainfall for satisfactory levels of activation and resultant weed control. But on the other hand, your herbicide should be ‘there’ and available for activation once we get rain...provided the soil does not blow.

Our soils are extremely mellow this year due to the dry conditions during tillage. Running a tractor and pulling an implement across fields may disturb too much soil and may break the ‘herbicide barrier’ and thus do more harm than good.

We recommend farmers continue to use soil-applied herbicides small seeded broadleaf weed control in row crops in freshly planted row crops even though it has been dry. Second, remember, farmers are using soil-applied herbicides primarily for control of waterhemp. We know that waterhemp will not germinate and emerge until mid to late May and we will eventually get rain to activate these products.

There might be weed escapes from deep germinating weeds like giant ragweed or wild oat that germinate and emerge from moisture and will need to be controlled with postemergence herbicides.

Thursday, April 30, 2015

Announcing the University of Minnesota's Institute for Ag Professional 2015 Summer Educational Programming

Dave Nicolai, Extension educator - crops

2015 Ag Professional Field School

July 29 & 30, 2015 – St. Paul, MN

UofM field school

A hands–on, in–field program emphasizing crop and pest management diagnostic skill building in field crops. The program is geared to the educational needs of new and recently employed ag professionals who are in a beginning to intermediate phase in their agronomy careers.

Wednesday, April 29, 2015

Windbreak and crop yield study

Gary Wyatt, Extension educator - agroforestry

Recent land values, farm innovations and management such as adoption of no-till, minimum till, use of wide farm equipment, and windbreak plantings that are just getting old, have led to many windbreaks being removed. In time, windbreaks need to be renovated to restore the multiple benefits they offer rural landscapes. There are cost share programs available to plant new windbreaks and renovate mature plantings through the Natural Resources Conservation Service (NRCS). In most areas where windbreaks were planted, there have been documented crop yield increases.

Thursday, April 23, 2015

Anhydrous Ammonia Applications

Fabian Fernandez, Nutrient management specialist

Anhydrous ammonia (AA) is one of the most widely used nitrogen (N) fertilizer source in Minnesota and the Midwest. Some of the reasons for its importance include the fact that this source is by far the most concentrated N fertilizer with 82% N (less weight of fertilizer per unit of N); it is readily available since AA is used in the manufacture of many commercial N fertilizers; it can be applied several weeks before planting with less N loss potential than other N sources; and most importantly AA normally represents a less expensive source of N. Some of the drawbacks of AA include the need for special facilities to store this gas as pressurized liquid, and special equipment to transport and applied this fertilizer; the application of AA can be slower than that of some other N sources; and because AA is released as a gas, it can pose a risk to human health if not handled properly. Every year as farmers start applying AA, invariably I get asked similar questions which I will try to address today.

New Irrigation Resources

The new Irrigation Extension website is up and running, and we have been able to add some new resources, and update some of the past resources.
Now that spring has sprung, one of the most powerful tools for maximizing irrigated yield is uniform application of irrigation water.  Testing uniformity every few years is a low cost way to make sure that your water is going where you want it. On a pivot with 15 foot nozzle spacing, one bad nozzle 1000 feet from the center can influence the yield on over 2 acres. That one bad nozzle (that costs about $5 to replace) could cost you over $600 in lost yield.
Below is a quick tutorial on irrigation uniformity testing.

A Quick Test to See Whether Your Small Grains Seed or Emerging Seedlings is Still Alive.

With air temperatures dropping down into the high teens overnight, I have fielded a number of calls already this morning with the question whether the earlier seeded wheat, barley, oats (or any crop for that matter) will make it, especially if the ground is frozen solid.

The fastest way to tell is to dig up some seed or seedlings and place them on a wetted-down paper towel at room temperature.  Within 24 hours you should see elongation of the coleoptile of the seedlings.  With seed that had not germinated yet, you may have to wait another day before you see a radicle and coleoptile appear.  If the seed and the germ are damaged by frost they will turn to mush within 24 hours at room temperature.  If the crop had already emerged, you can simply cut the above ground leaf material and place the seedling on the wetted-down paper towel and wait for new growth to elongate. 

PS) Ensure that the paper towel remains moist throughout the duration of the experiment.

Photo 1: Germinated wheat seed with adventitious roots pointing down and coleoptile pointing up. The radicle is hidden between the adventitious roots.

Tuesday, April 21, 2015

Forage Quarterly - Spring 2015

Dear Forage Producer,

The University of Minnesota Forage Team is proud to announce the third edition of the Forage Quarterly. Since spring is here, this issues focuses on establishment and early season management of forage production systems. In this edition we highlight seeding strategies, weed management, cover crops, insect control and identification.

We would like to take this time to highlight the contributors to this edition:

  • Bradley Heins, Ph.D. Assistant Professor. Expertise: Organic Dairy Production. Email:
  • Bruce Potter. Assistant Extension Professor. Expertise: Integrated Pest Mgt, crops, and forages. Email:
  • Craig Sheaffer, Ph.D. Professor. Expertise: Alfalfa, forage, and sustainable cropping systems. Email:
  • Deborah Samac, Ph.D. Research Plant Pathologist. USDA. Expertise: Disease resistance mechanisms in alfalfa.
  • Doug Holen. Regional Extension Educator. Expertise: Crops, small-grains, and forages. Email:
  • Jim Paulson. Regional Extension Educator. Expertise: Dairy nutrition,forages, grazing and organic production. Email:
  • M. Scott Wells, Ph.D. Assistant Professor. Expertise: Forages and cropping systems. Email:
  • Reagan Noland. Graduate Research Assistant. Expertise: forages, cropping systems, and precision agriculture. Email:
  • Roger Becker, Ph.D. Professor. Expertise: Agronomy and weed science. Email:

University of Minnesota Forage Team

In this issue
Alfalfa Assessment: Factors Leading to Winter Injury
Alfalfa Establishment: A Pathway to Increased Yield
Preparing for Successful Alfalfa/Grass Production
Using Herbicides to Establish Alfalfa
Aphanomyces Root Rot of Alfalfa Widespread Distribution of Race 2
Alfalfa Insects: What to Look for, How and When</a>

Click to read the Spring 2015 newsletter.

Click to read past issues of the Forage Quarterly.


University of Minnesota Extension Forage Team

  • Copyright 2014 Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy