Residuals 101: 5 Things Every Farmer. Should Expect from a Residual Herbicide

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1 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide

2 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide Introduction Across the country, residual herbicides have become the standard recommendation of leading researchers and a key component of sound farming practices. University research has proven that adding a residual to a herbicide program aids in keeping fields clean longer and free of yield-robbing weeds to improve overall profit and resistance management practices. Put simply: a residual herbicide is a smart and valuable investment for today s farmer. Yet with several products on the market today, it is important for farmers to know what to look for in a residual herbicide. Many researchers assess residuals based on one or more of the five areas of performance:. Length of Residual 2. Application Timing Flexibility 3. Broad Spectrum Weed Control. Resistance Management 5. Crop Rotational Flexibility

3 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide Length of Residual Experts agree residual control of tough weeds is a critical component of a good preemergence herbicide as well as a strong overall herbicide program. An effective, long-lasting residual product will mean less competition for the crop, higher yield and a better return on investment on a farmer s overall weed control program. Length of Days Residual Provided umber of days between PRE and POST applications ( 6 tall weeds) Valor XLT (3 oz) Gangster (.8 oz) Days: Valor (2 oz) Boundary (.5 pt) Authority Assist (5 oz) Authority MTZ ( oz) Prowl H2 (2 pt) The longer a residual material can hold off yield-robbing weeds, the greater value it will bring to a farmer s operation and, ultimately, bottom line. Additionally, a long-lasting residual keeps fields cleaner longer, giving farmers and crops a jump start. Yet some herbicides that are marketed as residuals may have limited residual control and may become ineffective as the season evolves and tough weed pressure increases. With products that range from a few days of residual control to as long as several months of control, it is important for farmers to know what time frame of control to expect from a preemergence herbicide. Source: K. Bradley, University of Missouri, 28. Length of residual varies by weed, soil texture, soil ph, organic matter present, rainfall and herbicide rate. University of Missouri Weed Scientist Dr. Kevin Bradley said, With residuals, the longer the control the better. I think two weeks of control is probably not enough out of any herbicide to really even justify spraying. Four weeks is a realistic amount of control to expect from a residual six weeks would be great. You should get at least a month of residual so that your program can include one preemerge herbicide and one postemerge spray and you re done. If you only get two weeks control, you are probably going to have to spray a postemerge twice. Dr. Christy Sprague, weed scientist at Michigan State University, agrees that a herbicide should ideally last at least four weeks to be deemed as a residual. 2

4 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide Percent Control 28 Days After Application Giant Foxtail Valor XLT 3 oz Scepter 2.8 oz Valor XLT 3 oz + Sencor oz Giant Ragweed Scepter 2.8 oz + Sencor oz Source: Ohio State University Trial Data, 28. Valor XLT 3 oz + Sencor 6 oz Researchers also note that tillage should not be performed after a residual is applied, as it will eliminate residual activity. Farmers should, therefore, not assume that all residuals are created equal in terms of length of control. Four weeks is a realistic amount of control to expect from a residual six weeks would be great. Dr. Kevin Bradley, University of Missouri 2Application Timing Flexibility Depending on geography, crop selection, weather trends or even personal preference, farmers may have a variety of timing needs for their herbicide program be it a fall/winter application or a spring burndown. Application flexibility lets farmers apply the product based on their seasonal timing needs. A highly flexible preemergence residual will allow a farmer to apply any time from post-harvest to preemergence. The most popular time to apply a preemergence herbicide is in the spring, several days or weeks before planting. Advocates of this practice argue this application timing allows for the longest period of residual weed-killing activity to last through the planting season. In recent years, however, many farmers have opted to apply a preemergence fall or winter application (October February, depending on the geography) to rid fields of nutrient-robbing winter weeds that may also harbor pests and diseases. Among a variety of winter annual weeds controlled by post-harvest-applied residuals, Purdue University Weed Scientist Dr. Bill Johnson said, Fall applications are a great idea for dandelions, chickweed, henbit and purple deadnettle. Another benefit of this clean spring approach is the ability to ensure that a preemergence herbicide is applied before poor springtime weather conditions occur. Many farmers experienced this situation firsthand during recent springs, when long periods of rain kept them out of fields well into what should have been the spring burndown and planting months. Conversely, farmers who had applied residuals in the fall already had a head start on fighting weeds and were able to plant as soon as fields were dry. 3

5 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide Farmers who rely exclusively on burndown applications may find themselves stuck if springtime conditions do not cooperate with targeted application timing. A flexible residual product allows a farmer to apply it at various points throughout the season, including fall and winter months, helping extend the window of possible control. Finally, many farmers see labor management advantages to applying herbicides during slower times of the season versus the busy springtime months. When choosing the timing of an application, a farmer must again consider the length of residual control a product can deliver. For example, if a product can only provide two solid weeks of residual control, that product may be limited to only immediate pre-planting applications. In summary, a residual product s ability to be applied at a variety of points throughout the season will allow for not only greater flexibility in a management program, but also overall value and return on investment from the residual material. 3Broad Spectrum Weed Control The primary reason for using any herbicide is to control weeds. Therefore, it is imperative that farmers look for a residual that will control the weeds that are problematic within their specific geographic location. It s important to focus on the weeds that certain residuals control better than others. Some weeds are more problematic in certain areas. For example, in Michigan you have common lambsquarters, which ends up being a continual issue that farmers are trying to control. Whatever the problem weed may be for the area, it is important to find a residual that is going to help control that issue, Sprague said. Bradley agreed that each farmer s weed issues should be analyzed to ensure that the farmer is choosing the herbicide that will control specific problematic weeds. Residual weed control really should be about what weed problems that person is facing whether it be resistant weeds, waterhemp or even giant ragweed, Bradley said. Additionally, using a residual that has broad spectrum weed control, and even offers performance on grasses, will ensure that more of the specific targeted weeds are controlled, rather than just one or two. Ultimately, it will be more economical and timely for the farmer to use a residual that is able to control several weed species, including grasses, with little to no breakthrough pressure. Resistance Management ot long ago, resistance was a threat most farmers assumed was happening in someone else s field. However, resistant or even tolerant weeds are becoming a major issue in weed control across most of the country. Many researchers suggest that controlling these weeds with a comprehensive herbicide program including a residual and other modes of action before they grow too large is the best fight against resistance. Johnson explained, In dry climates weeds can start robbing crops of yield when they reach about the six-inch height. Every day that we delay our postemerge weed management strategies due to weather, equipment failure or other circumstances can result in about a.2 bushel per acre per day yield loss in corn and one third of a bushel per acre per day yield loss in soybeans.

6 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide By applying a residual herbicide, we can extend the window for putting on a postemergence herbicide to reduce yield losses and also reduce the exposure of our worst weed problems to glyphosate. I think that s the key to resistance management simply not exposing weed species to the same mode of action numerous times. Residuals are our number one line of defense against glyphosate-resistant waterhemp in Missouri. We have more success at reducing the total population of waterhemp in a field with a preemerge herbicide, rather than attempting to treat a tremendous number of glyphosate-resistant waterhemp all at once with only a postemerge. With an effective preemerge foundation, there just won t be as many weeds to treat with a postemerge. The numbers are stacked more in your favor, Bradley said. Percent Weed Control with Residual Herbicide in Soybeans (Preemergence application listed) Authority Assist (5 oz/a)* Authority First (3 oz/a)* Authority MTZ ( oz/a)* By applying a residual herbicide, we can extend the window for putting on a postemerge herbicide to reduce yield losses and also reduce the exposure of our worst weed problems to glyphosate. Dr. Bill Johnson, Purdue University Boundary (.5 pt/a)* Gangster (2. oz/a)* Prefix (5.2 pt/a)* Valor XLT (3 oz/a)* Envive (2.5 oz/a)* *Postemergence application includes Touchdown Total, AMS Foxtail Lambsquarters Ragweed Pigweed Velvetleaf Wild Mustard Rating date: June 3, 28. Data obtained from Michigan State University Weed Science Research Program. 5

7 Residuals : 5 Things Every Farmer Should Expect from a Residual Herbicide 5Crop Rotational Flexibility Crop rotation is widely regarded as one of the best ways to keep fields healthy. There are many benefits to rotating crops, including pest control, disease prevention, soil nutrition availability and overall weed control. Therefore, a good residual must be designed to work well with a variety of possible crops a farmer may introduce into his or her crop rotation plan. However, many farmers are also finding that even the best-laid crop plans can change unexpectedly and at the last minute. Erratic springtime weather has caused numerous farmers to abandon one planned crop for another when spring planting (or in many cases, re-planting) was driven late into the season. Add to that uncertainty several seasons of wildly fluctuating market prices, and many farmers are shifting their crop plan even days prior to scheduled planting. As a result, many researchers agree that rotational flexibility is an increasingly key component to consider in a residual herbicide. It s important for you to make sure that the residual you choose will allow you to rotate to certain crops, Sprague said. Conclusion All residuals are not created equal. But by understanding the specific needs and weed pressure of an individual farm operation and by analyzing residuals based on a few key factors, farmers can make an educated decision on which residual herbicide to choose to maximize their profit and minimize risk. Researched and written by archer>malmo, Memphis, T. Contact for more information. Length of Residual Rotational Interval (months) Pursuit Valor XLT Gangster Valor Authority Canopy Optill Plus Scepter Sencor Sharpen Alfalfa Corn, Field 8.5 Cotton 8.5 Drybeans Peanuts L* Rice L* Spring 8 Sorghum Soybeans Wheat ph Restriction Y Y Y Please check the label for other crops. *ot labeled 6

8 Residual Control Worksheet When meeting with your local agricultural dealer, use this checklist to outline key attributes you find important when making your residual herbicide selection. Residual Control To fight tough weeds, I am looking for at least weeks residual control. *Reminder: Most university researchers recommend at a minimum weeks residual control. Recommended product: Proven length of control: Application Timing Flexibility I am interested in the following residual herbicide applications (check all that apply): fall or winter application spring burndown layby (cotton only) other Broad Spectrum Weed Control I have the greatest issues with the following weeds (check all that apply): annual grasses annual nightshades Carolina geranium chickweeds cocklebur common ragweed cressleaf groundsel cutleaf eveningprimrose dandelion field pennycress giant ragweed henbit kochia lambsquarters marestail morningglories Showing resistance?

9 Residual Control Worksheet Broad Spectrum Weed Control (cont.) I have the greatest issues with the following weeds (check all that apply): Palmer pigweed pigweed purple deadnettle Russian thistle shepherd s-purse smartweed sunflower teaweed velvetleaf waterhemp Showing resistance? Resistance Management I have suspected or confirmed resistance issues within my fields. Yes o I am interested in using a different mode of action, such as a PPO-inhibitor, in my herbicide program. Yes o Crop Rotation I will be planting or have the possibility of planting the following crops on my fields: soybeans corn cotton wheat sorghum peanuts rice drybeans alfalfa other