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Don’t wait for weed resistance - Proactive practices to minimize the evolution of herbicide resistance in U.S. Pacific Northwest wheat fields


USA
May 20, 2014

Source: Syngenta

With the arrival of spring and the growing season now in full swing, growers are diligently scouting for yield-robbing weeds that can compete with crops for valuable water and nutrients and ultimately impact yield potential and crop quality.  Growers turn to herbicides as one method to minimize these threats and protect their wheat crop.  Many factors impact the effectiveness of a herbicide program – application timing, use of full labeled rates, proper use of adjuvants and effective spray application. Even when all label instructions and local agronomic recommendations have been followed, growers may still find weed escapes in their fields. This lack of control could potentially mean a larger issue is developing: herbicide resistance. 
 
Herbicide resistance is the inherited ability of a weed to survive the rate of herbicide which would normally give effective control. The development of herbicide resistance is dependent on a number of factors, including lack of chemical and cropping diversity, using below recommended herbicide labeled rates, genetic diversity in weed populations and spread of resistant weed seed through machinery, irrigation water and manure.
 
According to The International Survey of Herbicide Resistant Weeds, there are 13 herbicide-resistant broadleaf and grass weed species found in U.S. wheat crops today. Pacific Northwest wheat growers have observed widespread occurrence of herbicide-resistant kochia. Like other weeds, once kochia infests a field, it robs wheat of valuable sunlight, water and soil nutrients needed for robust development and strong yield. 
 
“Once resistance has been confirmed, it can remain in the population for decades. If growers wait until herbicide resistance is confirmed in their field, the ability to manage their weeds may become more difficult,” said Don Drader, agronomic service representative for Syngenta in Washington. “Implementing a proactive approach helps combat herbicide resistance before it has the chance to impact an entire farming system.”
 
To stay ahead of this issue and retain maximum yield potential, Syngenta recommends growers consider the following proactive management techniques.
Start early to manage the seed bank
Weeds are often prolific seed producers, meaning that when weeds emerge and mature, they can develop and contribute seeds back into the soil, creating a large seed bank. For example, kochia is capable of producing 14,000 seeds per plant. Depending on the weed species, seeds may be viable in the seed bank for many years and can emerge when least expected. In terms of herbicide-resistant weeds, these are the seeds that are capable of building a resistant population.
 
To minimize the evolution of herbicide resistance, manage weed escapes to prevent an increase in next year’s weed seed bank. Limiting resistance starts with anticipating or recognizing the issue in the field by evaluating the plants that survive a herbicide application.  Once growers understand the issue, they can try to limit weed production by implementing cultural and herbicide management practices, including:
 
·         Scout fields early and often to manage weed escapes, and identify weeds properly to select a product that addresses the weed spectrum in their fields.
·         Clean equipment as machinery can easily spread seed into other fields.
·         Alternate tillage practices at a reasonable interval to change the environment and destroy weeds that can contribute back to the soil seed bank.
·         Do not allow weeds to reproduce by seed or to proliferate vegetatively.
·         Manage weeds by applying an effective burndown herbicide like Touchdown® CT2 or Gramoxone® SL 2.0.  
 
Nilda Burgos, professor and researcher in the Department of Crop, Soil, and Environmental Sciences at the University of Arkansas, explains “Managing the seed bank is a year round activity.” As the season progresses and crops grow taller, growers may begin to let their guard down. Throughout the season, diligent record keeping is also critical for growers to know which herbicides were applied to which fields. Later in the season is still an important time to continue scouting fields, implementing agronomic practices and to consider an effective herbicide application.
 
Mind the label
Help prolong the effectiveness of available herbicides and delay the onset of resistance in wheat fields by changing herbicides with different modes of action often and using the full recommended rates. Full herbicide rates eliminate biotypes with a low level of natural resistance, whereas reduced or cut rates allow those biotypes to survive, build up resistance and increase the population of resistant weeds.
 
“Using full rates is important as some of the early stages of resistance will survive half rates of the chemicals. If growers allow the plants treated with half rates to produce seeds, those seeds will carry some of the resistant traits”, said Kirk Howatt, weed scientist at North Dakota State University.  “By keeping the rate of the chemical up to its fully labeled capacity, we are putting our best foot forward to fight resistance.”
 
Even injured low‐level resistant weeds still have the ability to reproduce, which can allow resistant weed populations to spread rapidly. When applying herbicides, ensure good spray coverage of target weeds is obtained for complete control. 
 
Diversify herbicide modes of action
Syngenta offers a robust portfolio of cereal herbicides that include multiple grass, broadleaf and cross‐spectrum options with varying modes of action (MOAs). The MOA is the way in which the herbicide controls susceptible plants. Over‐reliance on a single herbicide MOA places heavy selection pressure on a weed population and may eventually result in the evolution of resistant weeds. Over time, resistant weeds will multiply and become dominant in a field, resulting in herbicides that are no longer effective for weed control.
 
“Understanding which MOA is being utilized can help when planning a herbicide program,” Howatt said. “Changing the MOA will ensure the weed is attacked in different ways.”
 
SierraThis spring, Syngenta recommends applying an effective, post-emergence herbicide like Axial® XL (Group 1; ACCase inhibitor), (Group 2; ALS-inhibitor), Orion® (Group 2; ALS-inhibitor and Group 4; synthetic-auxin) and Axial Star (Group 1 and Group 4; ACCase Inhibitor and synthetic-auxin). Additionally, tank-mixing herbicides with multiple modes of action can help control the entire weed spectrum and minimize resistance in fields.
 
Reap the benefits of crop rotation
In addition to alternating herbicide MOAs, diversifying crop management practices by planting rotational crops can help minimize the development of herbicide resistance in wheat fields.  According to Gaylon Morgan, professor and extension specialist in the Department of Soil and Crop Sciences at Texas A&M, “Crop rotation is a key technique for mitigating the risk of herbicide resistant weeds from ever developing.” Different crops are prone to different weed infestations. One benefit of crop rotation is that it allows growers to change the weed population complex in their fields, and therefore change up the MOA used in a particular field.  This minimizes the pressure of different weed species that can develop or may already be present in fields.
 
Rotational crop options vary greatly based on geography and economics. Researchers suggest rotating wheat with a broadleaf crop to help minimize the pressure of typically resistant grass weeds in wheat fields. However, good and consistent crop rotation requires an investment. Each crop requires different equipment and a variety of management techniques, but the investment can pay off with healthy crops and effective weed control.
 
“Waiting for resistant weed populations to appear can cause herbicide resistance to spread faster across an entire field,” Drader said. “By practicing best management techniques early and continuing them throughout the season, growers can fight the onset of resistance and ensure productive wheat fields with high quality and yield potential at harvest.”
 
© 2014 Syngenta. Important: Always read and follow label instructions. Some crop protection products may not be registered for sale or use in all states or counties.  Please check with your local extension service to ensure registration status. Gramoxone SL 2.0 is a Restricted Use Pesticide. Axial®, Gramoxone®, Orion®, Sierra, Touchdown® and the Syngenta logo are trademarks of a Syngenta Group Company.


More solutions from:
    . Syngenta USA
    . Syngenta Crop Protection, Inc. (USA)


Website: http://www.syngenta-us.com

Published: May 20, 2014

 

 

 

 

 

 

 

 

 

 


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