Herbicide injury during and after emergence in soybean

Pre-emergence and post-emergence herbicides can injure soybean plants. This year, soybean injury symptoms following pre-emergence applications have been relatively slight for May 13 and May 19 planting dates. In the herbicide evaluation program, soybean injury symptoms that we typically observe are stunting, drawstring (puckering), chlorosis (yellowing), and necrosis. However, it is important to keep in mind that injury symptoms may be due to weather, soil conditions, or disease.

To diagnose an injury problem at or during emergence, first check the root system of the plant. Seedling root growth inhibitors, ALS inhibitors, and growth regulators change the root architecture in different ways. Next step, if the roots appear normal, take a look at the leaves for yellowing (chlorosis), bleaching, or drawstring (puckering). To help with diagnosis, University of Wisconsin Extension has a two-page guide, available for download and an online diagnostic tool.

After emergence, PPO inhibitor injury tends to appear on the leaves that receive the application but younger leaves will not show any injury symptoms. Typical damage includes yellowing (chlorosis) and browning of the leaf surface in spots (necrosis) (Fig. 1A). Researchers at Purdue University have a five minute video discussing PPO inhibitor and fluopyram (ILeVO) seed treatment injury.

It is important to remember that despite the damage, in most cases yield is not affected. Also, PPO inhibitors add another site of action to your resistance management plan and effectively control a variety of broadleaf weed species. Growth regulators cause leaf cupping or epinasty (downward growth habit) (Fig. 1B). The leaves of soybean plants with ALS inhibitor injury show chlorosis and distinctive reddish leaf veins (Fig. 1C).

injury_figure

Injury symptoms typically appear seven to fourteen days after application and will gradually decrease through the season when the plants resume normal growth. Phytotoxicity data are available in the WCWS research reports. Each trial contains a summary section that will mention if any phytotoxicity symptons were observed. If the injury differed by treatment and exceeded five percent then a bar graph is included. Crop injury resulting from an application made according to the label instructions usually does not cause a reduction in yield. “Pest Management in Wisconsin Field Crops” shows the relative risk of soybean injury from different herbicides on pages 143 and 144, available at Cooperative Extension’s Learning Store.

Herbicide resistance management for giant and common ragweed

Weed scientists across the Midwest and Midsouth have identified eleven species of weeds that are of most concern for herbicide resistance because of their ability to compete with crops and to develop resistance to different herbicide sites of action (SOA). They are common waterhemp, Palmer amaranth, horseweed (marestail), giant ragweed, common ragweed, common lambsquarters, kochia, Italian ryegrass, barnyard grass, johnsongrass, and giant foxtail. All of the species have shown resistance to between two and nine herbicide sites of action.

Herbicides are typically classified in two ways by (1) mode of action or (2) site of action. The mode of action is generally how the herbicide inhibits plant growth and development. The site of action is specifically which biochemical pathway in the plant that the herbicide disrupts. Each site of action is associated with a number and the number is located on the first page of most herbicide labels. The TakeAction herbicide classification chart clearly displays the herbicides and premixes by sites of action. A successful resistance management plan will include multiple effective sites of action applied at the full rate to weeds less than four inches in height.

In 2011 and 2013, University of Wisconsin weed scientists identified two separate giant ragweed, Ambrosia trifida, populations resistant to either glyphosate (SOA 9) or ALS inhibitors (SOA 2). In 2013, a population of common ragweed, Ambrosia artemisiifolia, was confirmed resistant to ALS inhibitors. Not sure what a glyphosate resistant giant ragweed plant looks like, check out a time lapse video from Purdue University comparing susceptible and resistant biotypes of giant ragweed, two minutes fifteen seconds in length.

At this point in the season, the most important task for herbicide resistance management is to scout fields several times before and after an herbicide application. Scouting after pre-emergence applications, prior to a post-emergence timing, can ensure that the post application is on target for weed species and size. It is important to pay attention to any weed species that is becoming more abundant across the field and then to double-check that your planned herbicide program is effective at controlling that species. Also, factoring in current weed size with weather forecasts is important for scheduling that next application. After applying herbicides, the next task is to follow-up with scouting at 14 days after the post application to verify adequate control. For more information about effective scouting, please visit the TakeAction website.

Both ragweed species reduce crop yields because early season germination and growth interferes with crop establishment prior to canopy closure. Giant ragweed can be difficult to control with a one-pass herbicide program because seedlings can emerge from deeper soil depths where a pre-emergence herbicide may not reach and some populations tend to emerge over an extended period. For herbicide resistance management recommendations, please consult the TakeAction fact sheet. Giant ragweed tends to be more of a problem in conventional tillage systems whereas common ragweed infestations are common in reduced and no-till systems. Management recommendations for common ragweed infestations in corn and soybean are available on the WCWS website.

Post-emergence herbicides for corn and soybean

At this time of the year, integrated weed management programs focus on scouting and diversifying management practices including non-chemical methods and herbicide sites-of-action. For more information, please visit the United Soybean Board’s TakeAction website for field management guidelines and to learn more about herbicide sites of action. Michigan State University’s Weed Science website has detailed web pages on common weeds in annual crops with biological information and management recommendations. After each field season, the Herbicide Evaluation Program here at the university publishes efficacy data in a research report. Summary ratings for many weed species are located in “Pest Management in Wisconsin Field Crops” available as a free pdf or in print at Cooperative Extension’s Learning Store.

Herbicide Injury Diagnosis for Corn Seedlings at Emergence

Depending upon the herbicide, injury can occur after a pre-emergence application when corn is germinating in cool, wet soils. This year, if corn was planted in mid-April then you may observe some injury. However, it is important to remember that other environmental factors can mimic herbicide injury symptoms such as corn emerging in crusted or compacted soil. For this spring, WCWS has a re-designed online diagnostic tool, available at http://wcws.cals.wisc.edu/herbicide-injury-diagnostic-tool or from the main page, go to ‘Resources’ and then to ‘Tools’. The diagnostic tool asks three basic questions 1) When do injury symptoms appear? 2) Are both broadleaves and grasses affected or just one group? and 3) What are the symptoms and where do they occur? The original web-based tool was developed by Tim Trower and Chris Boerboom to accompany a handy two-page guide. The following changes were made to the new version:

  1. Each page shows your previous answers.
  2. A ‘Start over’ button is located at the bottom of each page.
  3. For each herbicide mode-of-action, an herbicide chart from the TakeAction Herbicide Classification poster or on the WCWS website under ‘Resources’, ‘Documents’(Fig. 1).
  4. Simplified guides to symptoms that mimic herbicide injury during and after emergence are included on each mode-of-action page (Fig. 2).
  5. Photo galleries for both corn and soybean injury symptoms are located on the same page (Fig. 3).

Figure 1. Herbicide site-of-action groups, chemical  families, active ingredients, and product examples for the seedling shoot growth inhibitor mode-of-action.  Specific sections of the larger TakeAction chart are on each mode-of-action page.

Figure 1. Herbicide site-of-action groups, chemical families, active ingredients, and product examples for the seedling shoot growth inhibitor mode-of-action. Specific sections of the larger TakeAction chart are on each mode-of-action page.


Figure 2. Mimics of herbicide injury to corn during or at emergence.

Figure 2. Mimics of herbicide injury to corn during or at emergence.


Figure 3. Example of a photo gallery for corn and soybean herbicide injury symptoms.

Figure 3. Example of a photo gallery for corn and soybean herbicide injury symptoms.

For pre-emergence applications in corn, the seedling shoot growth inhibitors, particularly the chloroacetamides, may injure seedlings when soils are cool and wet. Injury will not always be apparent aboveground. For example, corn plants with seedling root growth inhibitor damage will display clubbed root tips and grasses will be more affected than broadleaves. To get an idea of injury risk, check out the herbicide tables in “Pest Management in Wisconsin Field Crops” available in pdf and print formats at Cooperative Extension’s Learning Store.

Scout your fields for weed seedlings this spring

Figure 1. A) Common lambsquarters, Chenopodium album; a soil sampler, one inch diameter, is in the foreground B) Horseweed (marestail), Conyza canadensis; C) Giant ragweed, Ambrosia trifida, with seed capsule attached; D) Giant ragweed seedlings.

Figure 1. A) Common lambsquarters; a soil sampler, one inch diameter, is in the foreground B) Horseweed (marestail); C) Giant ragweed, with seed capsule attached; D) Giant ragweed seedlings.

The fields may look cold, wet, and dormant this week but weeds were germinating in some fields in Janesville and Arlington last week. On April 17 at Janesville, common lambsquarters, giant ragweed, and horseweed were emerging (Fig. 1A-D). At Arlington in a plowed area, velvetleaf was emerging (Fig. 2). If you are leasing new land this year or want to get a head start on weed management, then scouting for weeds at the seedling stage before tillage can be a good way to assess density, the number of weeds in a given area, and for which weed species will likely be an issue around planting time. The Weedometer, developed by University of Wisconsin, can predict when weed species will likely be emerging for your location at http://weedecology.wisc.edu/weedometer/ . A guide to identifying the “Common Weed Seedlings of the North Central States” is available in pdf and print formats at Cooperative Extension’s Learning Store, or on the WCWS Weed info page.

Figure 2. Velvetleaf seedling.

Figure 2. Velvetleaf, Abutilon theophrasti, seedling.

UW Cooperative Extension Cover Crop Workgroup Website

What are the economic costs of cover crops? What are the environmental and economic benefits? How do the nutrients from cover crops cycle through the soil? What is The New York Times saying about cover crops? All of this information and much more can be found on the UW Cooperative Extension Cover Crop Workgroup website, where UWEX personnel across Extension programs and disciplines provide resources regarding cover crops which will be frequently updated.

Farm Financial Management Workshops for Women Farmers

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University of Extension Rusk and Taylor counties will be hosting Annie’s Project Financial Management workshops on February 25 and March 4. For more information, read Sandy Stuttgen’s news release below.

February 2015
Contact: Sandy Stuttgen, 715-748-3327, sandy.stuttgen@ces.uwex.edu,

Annie’s Project Financial Management Workshop scheduled for February and March

Medford, Wis. – University of Wisconsin-Extension Rusk and Taylor Counties are hosting a two day Annie’s Project on Farm Financial Management. The workshop will be held on Wednesday, Feb. 25 and Wednesday, March 4 from 10 a.m. to 3 p.m. at the Jump River Community Center in Jump River, Wisconsin.

This workshop series is for farm women who are interested in learning or improving their farm financial management, which is part of the fabric of farm life. The series will be inter-active between speakers and participants with in-class exercises.

Topics include:

  • Introduction to Financial Management
  • Records and Recordkeeping Systems
  • Filing Important Family Papers
  • Management Reports including the Balance Sheet and Income Statement
  • Analysis and Interpretation of Financial Statements
  • Benchmarking of Financial Position and Performance
  • Decision Making Tools including Budgets

The cost of the program is $40 which includes materials and lunch both days. Brochures and registration information are available by contacting UW-Extension Taylor County office at 715-748-3327 or http://taylor.uwex.edu/ .

Annie’s project is an opportunity for farm women to learn about farm management skills by providing resources and information to improve farming operations. Class sizes are small which allows for opportunities to network with other farm women in similar situations.

Certified Crop Advisor Training Series

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Here is another resource brought to you by University of Wisconsin Extension! Free, online certified crop advisor training videos are available now. In addition to CCA training, they are great for adding to your general knowledge about integrated pest management, soil science, and field and forage crops.

Vince Davis has created a series of weed science videos that can be accessed directly from the videos page.

Resource: Wisconsin Farm Center

Wisconsin Farm Center, another resource from the state of Wisconsin and the Department of Agriculture, Trade and Consumer Protection, releases quarterly newsletters with a wide array of topics. If you are too busy during the growing season, winter may be a great time to catch up on Farm Center newsletters. Another great way to stay up-to-date is to subscribe to their email newsletter.

The Farm Center offers a variety of services to Wisconsin farmers.