On the Bookshelf: 2015 Pest Management in Wisconsin Field Crops

Don’t miss this year’s “Pest Management in Wisconsin Field Crops” from University of Wisconsin Extension. This is a comprehensive guide to insect, weed, and plant disease management in corn, soybean, forage, and stored grain crops.

To obtain a print copy of the guide, go here. For a free electronic copy in pdf format, go here for the download. For mobile access, go to University of Wisconsin Extension’s Pest Management Mobile.

Event- 2015 Wisconsin Crop Management Conference

The 2015 Wisconsin Crop Management conference will be held at the Alliant Energy Center in Madison, Wisconsin from January 13 until January 15. To save on advance registration, make sure to submit your form and payment by December 19, 2014.

To access the conference programming, go here for a complete list of events and the registration form. Also, online registration is available here.

Vince Davis, Thomas Butts, and Dan Smith will be presenting at this year’s conference. During the Weed Management section on Wednesday January 14, Vince will be talking about “Efficacy of “new” herbicides and program approaches for resistance management.” Tommy will be discussing his latest research results, “Herbicide-resistant pigweeds (Amaranthus spp.) are in Wisconsin, how serious is it?” Dan will be presenting his research on “Cover crop establishment following commonly applied corn and soybean herbicides in Wisconsin.”

More Winter Reading, the 2014 WCWS Research Report

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Yep, it is that time of year. Winter is setting in and the 2014 WCWS Research Report is here to chase away the winter blues. Print copies will be distributed at the Pest Management Update meetings and at the Wisconsin Crop Management conference. Check out our Documents page again in December for an updated report with yield data.

Hurry! Register for Pest Management Update Meetings

Hopefully, you will have finished or nearing the end of harvest by mid-November and will be ready to attend Extension’s Pest Management Update series. County Extension agents across Wisconsin will be hosting Pest Management Update Meetings during the second and third weeks in November. The purpose of each meeting is to review the past growing season and provide updates on research that can be applied to your farm. The speakers are Extension State Specialists including:

  • Bryan Jensen, Entomologist
  • Damon Smith, Field Crops Pathologist
  • Dan Heider, IPM Specialist
  • Mark Renz, Weed Scientist for Perennial Cropping Systems
  • Vince Davis, Weed Scientist for Annual Cropping Systems

Please register one week prior to the event. For a complete schedule of meetings including county agent contact information, please go here. Registration includes lunch, an information packet, and a copy of the 2015 Pest Management in Wisconsin Field Crops book. Four hours of CEU pest management credits will be available at each location. The registration fee is $40.

Winners Announced from the Biggest Weed Contest

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The Department of Agronomy’s Mark Renz announces this year’s winners of the Biggest Weed Contest at the Farm Technology Days, August 12-14, 2014.

2014 Contest Winner

This giant ragweed, submitted by Ken McGwin of Montello, was the Day 1 winner of the Biggest Weed contest at Wisconsin Farm Technology Days. Measuring 12’6” x 4’, its overall size wasn’t big enough though to beat the grand champion – another giant ragweed measuring over 10 feet tall and seven feet wide.

Here is Mark’s press release:

Contact: Mark Renz, UW-Extension weed specialist, 608-263-7437, mrenz@wisc.edu

Biggest Weed contest winners announced

Madison, Wis. – Despite the cool summer, plenty of weeds were entered in the ‘Biggest Weed’ contest sponsored by University of Wisconsin-Extension/Madison Weed Experts at the recent Wisconsin Farm Technology Days. Of the many samples brought in for identification, eight participants submitted nine weeds they felt deserved the title of Biggest Weed.

“While none of the samples topped the 13 foot mark like last year, several were quite wide, making up for the lack of height,” said Mark Renz, University of Wisconsin-Extension/Madison weed specialist. “Of the nine samples submitted, four were annuals, four biennials, and only one perennial plant – common milkweed.”

Typically the biennial and perennial plants take the prize, but this year a giant ragweed was the grand champion. Wayne Greeler from Neillsville, Wisconsin brought in this specimen that was over 10 feet tall and seven feet wide. The overall size of the plant is determined by multiplying the weed’s height by the maximum width when held in its normal growth form.

Renz said, “It is uncommon for a giant ragweed to get this wide but the extra girth allowed it to take the grand prize.”

Tuesday’s winner was another giant ragweed submitted by Ken McGwin from Montello. It was much taller than the grand champion, more than 12 feet, but only four feet wide. Wednesday’s winner Mary Jane Fry from Pittsville did bring in a massive bull thistle, but its dimensions couldn’t match the winners from Tuesday or Thursday.

“All submissions were found next to a barn, shed, fence, or tree,” Renz noted, “So apparently having a structure nearby helps. Remember this tip when we hold the event next year at Wisconsin Farm Technology Days in Dane County.”

All daily winners will receive a weed identification book, as thanks for hauling these winning specimens to Wisconsin Farm Technology Days. Anyone who has tried to bring in one of these plants can attest that it is no easy task.

For more information about identifying and controlling weeds in your field or yard, contact your local county Extension agent or visit the University of Wisconsin Weed Science website at http://fyi.uwex.edu/weedsci

 

To-Do List: Fall Dandelion Management

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It’s time to start planning ahead for fall dandelion management. The Weed Science website at the University of Wisconsin Extension has a thorough description of the dandelion’s life cycle and some suggestions for control. A group of researchers at the University of Wisconsin evaluated fall and spring herbicide applications for control of dandelion in 2011. Their key findings were:

  1. Herbicide applications in the fall were most effective for early-season dandelion control compared to applications at normal corn planting in the spring.
  2. Applications during the spring were ideal for late-season control when soybean planting occurs.

For specific information on herbicides, please see their slide presentation.

The flowering stage of dandelion is easily identified by most. However, identifying the seedling stage is helpful because management is best before dandelions enter the adult stage. The following plant characteristics will help with identifying seedling dandelions:

  • Seed leaves (cotyledons) are oval or spoon-shaped
  • First true leaf is ovular and 0.4 inches (1 cm) long. Leaf margins have a few very small teeth that point back toward the base of the leaf. The midvein is prominent on the underside of the leaf.
  • Later leaves are more elongated and will have the toothed margins and rosette arrangement typical of the mature plant.

Managing dandelions can either be done through the use of herbicide or physical removal in either the spring or fall. However, dandelions are more susceptible to herbicides applied in the fall. If physical removal is the management mode of choice, it must be done in the spring as well as the fall.

Management options for corn and soybean are listed below.

Corn

Chemical control options:

  • Fall application of 2,4-D or dicamba at 1 pint per acre applied alone or as a tank mix prior to the first killing frost. Another option is glyphosate but for optimal activity applications need to be made when the air temperature is above 50 degrees F and the plant is still actively growing.
  • Spring applications of 2,4-D ester at 1 pint per acre prior to corn emergence or a tank-mix of 2,4-D with glyphosate will provide some dandelion control. Also, post-emergence applications of growth regulator herbicides typically provide acceptable control.

Mechanical control options:

  • Moldboard or chisel plowing will weaken the plant by disturbing the taproot and may make chemical applications more effective.

Soybean

Chemical control options:

  • 2,4-D ester may be applied prior to soybean planting if a seven-day interval is observed between application and planting.
  • There are no good post-emergence options for dandelion control in soybeans.
  • If possible, control heavy infestations of dandelions in the fall if the field is to be planted to no-till soybeans.

References:

  1. http://www.extension.psu.edu/pests/weeds/weed-id/common-dandelion, site accessed July 27, 2014.
  2. http://www.umanitoba.ca/outreach/naturalagriculture/articles/dandelion.html, site accessed July 27, 2014.
  3. http://fyi.uwex.edu/weedsci/2002/11/12/dandelion/, site accessed July 27, 2014.

Authors:

Madeline Fischer and Liz Bosak

Madeline Fischer is an undergraduate research assistant working for WCWS at the Arlington Agricultural Research Station. In Fall 2014, Madeline will be a sophmore pursuing a degree in Life Science Communcations and Environmental Studies.

To-Do List: Late-Season Scouting

A critical component of herbicide resistance management and integrated pest management is scouting for pests. In this case, it is time to start thinking about scouting for late-season weed escapes. Late-season weed scouting will help to focus your weed management plans for next year- what worked, did not work, and which weed species may be a problem during the next growing season. If you suspect that you have found an herbicide-resistant weed, please contact your local county Extension agent or Vince Davis at vmdavis@wisc.edu

To learn more about late-season weed scouting in soybean, please watch Vince’s videos:


For more videos, please visit our video page, http://wcws.cals.wisc.edu/videos/

Preliminary data suggests glyphosate resistance of two Wisconsin common waterhemp (Amaranthus rudis) populations

Thomas R. Butts and Vince M. Davis

Department of Agronomy, University of Wisconsin-Madison

Common waterhemp (Amaranthus rudis) is a dioecious, small seeded, broadleaf weed species native to North America, specifically common in the Midwest region of the United States. This weed species has become increasingly problematic for corn and soybean growers due to its prolific growth characteristics and highly competitive ability. Among its fellow pigweed (Amaranthaceae) family members, common waterhemp is second only to Palmer amaranth (Amaranthus palmeri) in growth rate and size reaching heights of nearly ten feet 4. Furthermore, common waterhemp can produce over one million seeds per female plant under ideal growing conditions 8. This intensifies the likelihood and speed that herbicide-resistant biotypes can increase in a population and transfer from one location to another through seed dispersal. If common waterhemp is left unmanaged in corn and soybean, growers can see yield reductions of 74 and 56%, respectively2,7.

Control of common waterhemp has become increasingly difficult due to its ability of evolving resistance to numerous herbicide sites-of-action. To date, this weed species has been identified as resistant to six different sites-of-action, including an ALS-resistant biotype located in Wisconsin. Several common waterhemp populations have also evolved resistance to multiple herbicide sites-of-action, further complicating control methods1,5. Glyphosate-resistant common waterhemp biotypes have already been confirmed in fifteen other states including nearby Illinois, Indiana, Iowa, and Minnesota3. Our current research reported here suggests we will add Wisconsin to this list as data from our first greenhouse experiment indicates at least two Wisconsin common waterhemp populations are resistant to glyphosate out of 14 populations examined.

The two weed populations examined were collected from crop production fields in Eau Claire and Pierce counties. They were identified through the Late-Season Weed Escape Survey in Wisconsin Corn and Soybean Fields conducted in 2012 and 2013 by former graduate research assistant, Ross A. Recker. Plants that were collected in the field were likely to have survived a postemergence glyphosate application based on in-field observations of herbicide symptomology, plant locations, personal communication with growers, and other additional data documented during the survey. To confirm glyphosate resistance, seed was collected from 30 mature plants in the field, progeny were grown in the UW-Madison greenhouse, and 10 plants per glyphosate rate were sprayed with Roundup PowerMAX® plus ammonium sulfate at 17 lbs. per 100 gallons of spray solution when they reached three inches tall. Glyphosate rates used were 0, 0.22 (5.5), 0.43 (11), 0.87 (22), 1.74 (44), and 3.48 (88) kg ae ha-1 (fl. oz. ac-1). Plant dry biomass data were collected 28 days after application (DAA). Comparisons between our putative resistant and susceptible biotypes were determined by the effective glyphosate dose needed to reduce plant dry biomass 50% (ED50).

The ten Pierce County plants sprayed at the 0.87 kg ae ha-1 (22 fl. oz. ac-1) rate all survived and grew to an average of three times their spray date height (Figure 1). At the 1.74 kg ae ha-1 (44 fl. oz. ac-1) rate, nine of ten plants survived and grew to an average of two times their spray date height (Figure 2). The ED50 of glyphosate for the Pierce County and susceptible populations was 2.23 and 0.18 kg ae ha-1, respectively (Figure 3). This indicates the Pierce County population has a 12.5-fold level of resistance.

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The ten Eau Claire County plants sprayed at the 0.87 kg ae ha-1 (22 fl. oz. ac-1) rate all survived and grew to an average of five times greater than their spray date height (Figure 4). All ten plants also survived the 1.74 kg ae ha-1 (44 fl. oz. ac-1) rate and quadrupled in size from their spray date height (Figure 5). The Eau Claire County population was not able to be analyzed using the log logistic Dose Response Model in R due to inadequate high rates of glyphosate to reduce dry biomass at 28 DAA. Therefore, linear glyphosate response models were established for the Eau Claire County and susceptible populations and analyzed using ANOVA tables which indicated significant differences at all glyphosate rates (Figure 6) (Table 1).

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There are several key components to an effective control strategy for glyphosate-resistant common waterhemp. The use of alternative herbicide sites-of-action, such as PPO inhibitors, and tank-mixing multiple herbicide sites-of-action will improve glyphosate-resistant weed control. An early planting date will allow crops to gain a head-start and outcompete common waterhemp due to its late emergence timing6. Herbicide applications should be made at the correct timing when weeds are small and actively growing to ensure the greatest efficacy of the herbicide based on label recommendations. Furthermore, special care should be taken to clean tillage and harvest equipment thoroughly as they can quickly spread weed seed among fields. The focus of these best management practices is to diversify weed control measures, reduce weed seed additions to the soil seedbank, and utilize control measures in the most effective method possible.

This research experiment will be repeated to officially confirm glyphosate resistance in these common waterhemp populations. For updates on Wisconsin weeds please visit our Wisconsin Crop Weed Science website at http://wcws.cals.wisc.edu/. Further information on controlling common waterhemp or other glyphosate-resistant weeds can be found at: http://takeactiononweeds.com/. Finally, if you believe you may be facing glyphosate-resistant weeds in your fields, contact your local county extension agent and/or Dr. Vince Davis at vmdavis@wisc.edu or (608) 262-1392.

References:

  1. Bell MS, Hager AG, Tranel PJ (2013) Multiple Resistance to Herbicides from Four Site-of-Action Groups in Waterhemp (Amaranthus tuberculatus). Weed Science 61:460-468
  2. Bensch CN, Horak MJ, Peterson D (2003) Interference of redroot pigweed (Amaranthus retroflexus), Palmer amaranth (A. palmeri), and common waterhemp (A. rudis) in soybean. Weed Science 51:37-43
  3. Heap I (2013) The International Survey of Herbicide Resistant Weeds: Web page. http://www.weedscience.com/Summary/home.aspx. Accessed April 01, 2013
  4. Horak MJ, Loughin TM (2000) Growth Analysis of Four Amaranthus Species. Weed Science 48:347-355
  5. McMullan PM, Green JM (2011) Identification of a Tall Waterhemp (Amaranthus tuberculatus) Biotype Resistant to HPPD-Inhibiting Herbicides, Atrazine, and Thifensulfuron in Iowa. Weed Technology 25:514-518
  6. Sellers BA, Smeda RJ, Johnson WG, Kendig JA, Ellersieck MR (2003) Comparative Growth of Six Amaranthus Species in Missouri. Weed Science 51:329-333
  7. Steckel LE, Sprague CL (2004) Common waterhemp (Amaranthus rudis) interference in corn. Weed Science 52:359-364
  8. Steckel LE, Sprague CL, Hager AG, Simmons FW, Bollero GA (2003) Effects of shading on common waterhemp (Amaranthus rudis) growth and development. Weed Science 51:898-903

Late-season weed escape survey in Wisconsin identifies a second county with a glyphosate-resistant horseweed population

Ross Recker (Graduate Research Assistant), John Buol (Undergraduate Research Assistant), and Vince Davis (Assistant Professor) Department of Agronomy, UW-Madison

Glyphosate-resistant weeds continue to be a major threat to corn and soybean production across the Nation. A pro-active survey of late-season weed escapes in corn and soybean fields was conducted throughout Wisconsin in 2012 and 2013. One objective of the survey was to identify areas where populations of glyphosate-resistant weeds may exist.

In 2012, a population of horseweed (Conyza Canadensis) collected from Jefferson County, and glyphosate screening in the greenhouse confirmed it was glyphosate-resistant with a 6-fold tolerance compared to a susceptible population. This announcement and more information about horseweed biology and management were previously reported and can be read here.

During the 2013 late-season survey, another putative glyphosate-resistant horseweed population was collected from Columbia County. Again whole-plant dose response experiments were recently conducted in the greenhouse and results confirm this population is also nearly six-fold glyphosate-resistant (Figure 1).


Figure 1. Shoot dry biomass of Columbia County horseweed and susceptible horseweed following treatment with glyphosate at doses up to 3.48 kg ae ha-1 as estimated by a four-parameter log-logistic regression function.

Figure 1. Shoot dry biomass of Columbia County horseweed and susceptible horseweed following treatment with glyphosate at doses up to 3.48 kg ae ha-1 as estimated by a four-parameter log-logistic regression function.

The horseweed seeds were collected from mature plants in a soybean field with a history of no-till, corn/soybean rotation, and glyphosate use. These plants displayed symptomology at the time of collection including shortened internodes (Figure 2) and were scattered randomly at low densities in about a 2 to 3 acre patch. If you have horseweed or other weeds that survive postemergence applications, you should have concern about herbicide resistance. Contact your local county Ag Extension Agent who can help you further evaluate the situation and plan a pro-active resistant management program so you can take action against herbicide resistance.


Figure 2. Horseweed plant late in the 2013 growing season that was not controlled with a previous postemergence glyphosate application in a no-till soybean field in Columbia County, Wisconsin.

Figure 2. Horseweed plant late in the 2013 growing season that was not controlled with a previous postemergence glyphosate application in a no-till soybean field in Columbia County, Wisconsin.

Updated 2013 WCWS Research Report


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The 2013 WCWS Research Report is now updated with nine corn and seven soybean herbicide evaluation trials. Some highlights include:

  • Redroot pigweed and wild buckwheat efficacy data on pages 19 to 31.
  • Liberty Link system comparisons of PRE+EPOST, PRE+MPOST, and EPOST+MPOST programs on pages 81 to 91.
  • Dandelion control with preplant-incorporated herbicides on pages 1 to 6.
  • Comparisons of corn PRE only, PRE_POST, and POST only programs on pages 7 to 13 and 48 to 55.